Building Engineering and Systems Design_NoRestriction.docx

Building
Engineering
and
Systems
Design

Building
Engineering
and
Systems
Design
Second Edition
Frederick s. Merritt
Consulting Engineer, West Palm Beach, Florida
and
James Ambrose
University of Southern California
J VAN NOSTRAND REINHOLD
1_________________ New York

Copyright ©1990by Van NostrandReinhold
Softcover reprint of thehardcover 1st edition 1990
Library of Congress CatalogCardNumber 89-14641
ISBN 978-1-4757-0150-0 ISBN 978-1-4757-0148-7 (eBook)
DOI 10.1007/978-1-4757-0148-7
All rights reserved. Certainportions ofthis work ©1979by
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Library of Congress Cataloging-in-Publication Data
Merritt, Fredericks.
Building engineeringandsystems design / Frederick s. Merritt andJames Ambrose.—2nded.
p. cm.
Includes bibliographies andindex.
ISBN 978-1-4757-0150-0
1. Building. 2. Systems engineering. I. Ambrose, James E.
II. Title.
TH846.M47 1989
690—dc20 89-14641
CIP

V
Preface to Second Edition
This edition is basedupon a firmconviction ofthe authors thatthe purpose of,and the need forthe book,
as described in the Preface to the First Edition, are as critical today as they were when the first edition
was prepared. In fact, now, there is a greater need for applications of systems design to buildings. This
need occursbecause ofrisingconstructioncosts,greaterdemandformore and improved buildingservices,
and betterquality controlofconstruction.In brief,this bookexplains what needs to be designed,and the
issues to be addressed in the design process.
Revisions ofthefirst editionhave beenaimed at refining the text and developingnewtopics whichhave
emerged during the past decade.Increasedattention is given to the involvement ofarchitects in systems
design,andtotheinclusionofarchitecturalgoalsandobjectives in the value systems foroptimized design.
Traditionally, architects have been the only members of the building team whose formal training has
included some work in all the major areas of building design. College courses in structures, plumbing,
lighting, electrical power, mechanical systems, and building services in general, have, in the past, been
included in most architectural education curricula. What is new is the tendency for architects to work
directly and interactively with engineers, contractors, and other specialists during design development.
This is facilitated by the use of shared computer-stored data and interactive computer-aided design
processes.
While architects have traditionally been broadly educated for building design, engineers usually have
not been so rounded in their education. One of the most valuable uses for this book is as a general
educationin the building design andconstructionprocess forthosemembers ofthe building designteam
who did not experience comprehensive architectural training. This education is hard to obtain but of
increasing importance as interactive design becomes more common.
To make the bookmore suitable foruse in selfstudy,the bibliographies and studymaterials have been
arranged by chapter section, rather than by chapter, as in the first edition. Thus, study units are smaller
and easierto handle forpersonswith limited study time. Chapter summaries have also been provided.
Learning any technology requires familiarity with a large new vocabulary. Many technical terms are
defined and explained in this book,but a glossary would be too large forinclusion in the book.However
this edition contains compilations, at the ends of most chapter sections, of terms used in those sections.
The use of these lists will permit readers to develop a considerable technical vocabulary, by using the
book indexto find the definitions and explanations in the text. It would be advantageous, however, for
readers to obtain at least one dictionary of building terminology.
While both authors of this edition have diverse backgrounds in education, writing, and management,
ourmajor focus in this workis on the needsofthe building designer.That interest was the principalguide
in the developmentofthe text and in the generalselectionandemphasis oftopics.In total,what we want
to achieve are betterbuildings,and ourmajorintention is to assist those persons whoworkin this field to
accomplish that end.
FREDERICK s. MERRITT
JAMES AMBROSE

vii
Preface to First Edition
As a consequence of technological, economic and sociological changes throughout the civilized world,
new buildings are becoming ever more complex and costly; however, the public is demanding better
buildings at less cost. To meet this challenge, building designers and constructors must improve their
skills and develop better building methods. This book was written to help them.
Fundamentally,the bookis a compendiumofthe best ofthe current building-engineering practices.It
describes building materials, building components, types of construction, design procedures and
construction methods that have been recommended by experts, and it covers nearly all disciplines. It
presents the basics of building planning, structural engineering, fire safety, plumbing, air conditioning,
lighting, acoustics, electrical engineering, escalator and elevator installation and many other technical
skills needed in building design.
But if the challenge of constructing better buildings at less cost is to be met, future designers and
builders will need more than just technicalinformation.Theywill have to be more creative and ingenious
in applying this information. In addition, they will have to organize more efficiently for design and
construction and manage the designand constructionprocesses in a more expert manner.The bookalso
is intended to help meet these goals.
For the reasons cited above, a new concept of building design and construction is needed. Such a
concept is the main theme of the book.
The concept requires that designers treat buildings as systems and apply techniques of operations
research (more commonly known as systems design) to their design. Systems design employs the
scientific method to obtain an optimum, or best, systemand calls for an interdisciplinary approach to
design. The techniques involved have been successfully used in machine design, but it was necessary,
here,to adapt themto building design.However,the adaptation is accomplished in a way that will enable
professionals accustomed to traditionalproceduresto convert easily to the newtechniques and will also
permit students who learn systems design fromthis book to fit readily into traditional organizations, if
necessary for their employment.
The interdisciplinary approach to design advocated in the book requires that design be executed by a
team, the building team. It consists of consultants specializing in various aspects of design and
construction and also should include future users of the proposed building along with exp erienced
building operators or managers.
For the teamto function effectively,i.e.for intelligent participation in decision making,each member
of the team, in addition to contributing his or her own special knowledge, skills and experience to the
teameffort, should also be acquainted with the duties, responsibilities and output of the other members
ofthe team.In particular,the teamleadershould be more knowledgeable on allaspects ofbuilding design
and construction,to lead,guide and coordinate the team.An important objective ofthis book,therefore,
is to educate potential members of the building teamfor the roles they will have to play and to prepare
professionals for leadership of the team.
For practical reasons, the book is restricted to presentation only of pertinent topics that the

viii Preface to FirstEdition
authorconsidersbasic and important.The treatmentshould be sufficient to provide a foundation onwhich
the reader can build by additional reading and on-the-job experience. To assist toward this end, each
chapter in the book concludes with a list of books for supplementary reading.
The book has been designed for use in either of two ways:
1. as a textbook in an introductory course for architecture, building engineering or construction
management;
2. as a home-study bookforprofessionalbuilding designers and builders who wish tolearn howto use
systems design in their work.
The bookassumesthat,at theoutset,thereaderhas a knowledgeofbuildings,physics andmathematics
comparable to that of a high-school graduate. Based on this assumption, the book describes building
components, explains their functions and indicates how they are assembled to form a building. While
these introductory discussions will be familiar to building professionals, they should find the review
worthwhile as an introduction to the new design concept.
In preparation of this book, the author drew information and illustrative material from sources too
numerous to list. He is indeed grateful to all who contributed and, where feasible, has given credit
elsewhere in this book.
FREDERICK s. MERRITT

ix
Contents
Preface to Second Edition V
Preface to First Edition vii
CHAPTER 1. New Directions in Building Design 1
1.1. Change fromMaster Builders to Managers 2
1.2. Basic Traditional Building Procedure 8
1.3. Systems Design Approach to Building 14
1.4. Design by Building Team 19
CHAPTER 2. Basic Building Elements and Their Representation 24
2.1. Main Parts of Buildings 24
2.2. Floors and Ceilings 26
2.3. Roofs 28
2.4. Exterior Walls and Openings 29
2.5. Partitions, Doors, and Interior-Wall Finishes 32
2.6. Structural Framing and Foundations 34
2.7. Plumbing 37
2.8. Heating, Ventilating, and Air Conditioning (HVAC) Systems 38
2.9. Lighting 39
2.10. Acoustics 40
2.11. Electric Supply 40
2.12. Vertical-Circulation Elements 41
2.13. Why Drawings Are Necessary 43
2.14. Drawing Conventions 43
2.15. Types of Drawings 44
2.16. Specifications 45
2.17. Scales and Dimensions on Drawings 45
2.18. Elevation Views 46
2.19. Plan Views 47
2.20. Lines 48
2.21. Sections 49
2.22. Details 50
2.23. Survey and Plot Plans 52
CHAPTER 3. Systems Design Method 58
3.1. Models 58
3.2. Value Measures for Comparisons 64

X Contents
3.3. Comparisons of Systems 66
3.4. Return on Investment 67
3.5. Constraints Imposed by Building Codes 70
3.6. Zoning Codes 74
3.7. Other Constraining Regulations 76
3.8. Systems Design Steps 77
3.9. System Goals 83
3.10. SystemObjectives 85
3.11. SystemConstraints 86
3.12. Value Analysis 87
3.13. OptimumDesign of ComplexSystems 89
CHAPTER 4. Application of Systems Design to Buildings 97
4.1. Considerations in Adaptation of Systems Design 98
4.2. Role of Owner 101
4.3. Conceptual Phase of Systems Design 103
4.4. Design Development Phase of Systems Design 110
CHAPTER 5. Contract Documents and Construction Methods 115
5.1. Responsibilities Assigned by the Construction Contract 115
5.2. Components ofthe Contract Documents 118
5.3. Contract Drawings 121
5.4. Specifications 123
5.5. Bidding Requirements 128
5.6. Contractors Drawings 130
5.7. Construction and Occupancy Permits 130
5.8. Construction Procedures 131
CHAPTER 6. Life Safety Concerns 137
6.1. Windstorms 138
6.2. Earthquakes 145
63. Fire 148
6.4. Fire Extinguishment 150
6.5. Emergency Egress 152
6.6. Fire Protection 156
6.7. Security 160
6.8. Barrier-Free Environments 160
6.9. Toxic Materials 161
6.10. Construction Safety 162
CHAPTER 7. Building Sites and Foundations 165
7.1. Site Considerations 165
7.2. Site Surveys 168
7.3. Soil Considerations for Site and Foundation Design 169
7.4. Shallow Bearing Foundations 178
7.5. Deep Foundations 181
7.6. Lateral and Uplift Forces on Structures 186
7.7. Site Development Considerations 191

Contents xi
7.8. Cofferdams and Foundation Walls 193
7.9. Dewatering of Excavations 195
7.10. Investigation and Testing 196
7.11. Systems-Design Approach to Site Adaptation 200
CHAPTER 8. Structural Systems 205
8.1. Building Loads 205
8.2. Deformations of Structural Members 209
8.3. Unit Stresses and Strains 211
8.4. Idealization of Structural Materials 214
8.5. Structural Materials 217
8.6. Typical Major Constraints on Structural Systems 253
8.7. Tension Members 255
8.8. Columns 257
8.9. Trusses 261
8.10. Beams 265
8.11. Arches and Rigid Frames 285
8.12. Shells and Folded Plates 292
8.13. Cable-Supported Roofs 297
8.14. Pneumatic Structures 302
8.15. Horizontal Framing Systems 305
8.16. Vertical Structural Systems 313
8.17. Systems-Design Approach to Structural Systems 320
CHAPTER 9. Plumbing 331
9.1. Water Supply 331
9.2. Wastewater Disposal 336
9.3. Basic Principles of Plumbing 337
9.4. Water-Supply Systems 339
9.5. Sizing ofWater-Supply Pipes 349
9.6. Wastewater-Removal Systems 354
9.7. Sizing ofWastewater and Vent Pipes 363
9.8. Piping for Heating Gas 368
9.9. Systems Design of Plumbing 370
CHAPTER 10. Heating, Ventilation, and Air Conditioning 379
10.1. Design Considerations 379
10.2. Measurement of Heat 3 82
10.3. Heat Flow and Human Comfort 388
10.4. Thermal Insulation 395
10.5. Prevention of Damage fromCondensation 400
10.6. Ventilation 402
10.7. Heat Losses 412
10.8. Heat Gains 413
10.9. Methods of Heating Buildings 416
10.10. Methods of Cooling and Air Conditioning Buildings 426
10.11. Passive Design 435
10.12. Systems-Design Approach to HVAC 436
CHAPTER 11. Lighting 446
11.1. Accident Prevention 446
11.2. Quantity of Light 447
11.3. Quality of Light 448

xii Contents
11.4. Color 448
11.5. Lighting Strategies 449
11.6. Daylight 450
11.7. Lighting Equipment 451
11.8. Systems-Design Approach to Lighting 459
CHAPTER 12. Sound and Vibration Control 468
12.1. Nature of Sounds and Vibrations 468
12.2. Measurement of Sounds 470
12.3. Acoustic Properties of Materials 472
12.4. Sound and Vibration Design Criteria 477
12.5. Sound and Vibration Control 483
12.6. Systems-Design Approach to Sound and Vibration Control 486
CHAPTER 13. Electrical Systems 492
13.1. Characteristics of Direct Current 492
13.2. Characteristics ofAlternating Current 499
13.3. Electrical Loads 507
13.4. Electrical Conductors and Raceways 508
13.5. Power-Systems Apparatus 520
13.6. Electrical Distribution in Buildings 532
13.7. Communication Systems 537
13.8. Systems-Design Approach to Electrical Distribution 540
CHAPTER 14. Vertical Circulation 549
14.1. Ramps 550
14.2. Stairs 553
14.3. Escalators 557
14.4. Elevators 561
14.5. Dumbwaiters 581
14.6. Pneumatic Tubes and Vertical Conveyors 581
14.7. Systems-Design Approach to Vertical Circulation 582
CHAPTER 15. Systems for Enclosing Buildings 588
15.1. Roofs 588
15.2. Roofing 593
15.3. Exterior Walls 599
15.4. Single-Enclosure Systems 608
15.5. Windows 610
15.6. Doors in Exterior Walls 616
15.7. Systems-Design Approach to Building Enclosure 617
CHAPTER 16. Systems for Interior Construction 622
16.1. InteriorWalls and Partitions 623
16.2. Ordinary Doors 624
16.3. Special-Purpose Doors 632
16.4. Floor-Ceiling and Roof-Ceiling Systems 635
16.5. Interior Finishes 641
16.6. Systems-Design Approach to Interior Systems 648
CHAPTER 17. Building Systems 651
17.1. Mishaps and Corrective Measures 651

Contents xiii
17.2. Design of a Building System 652
17.3. Case-Study One: McMaster Health Sciences Center 655
17.4. Case-Study Two: XeroxInternational Center for Training and Management
Development 662
17.5. Case-Study Three: Suburban Office Building for AT & T 666
17.6. Case-Study Four: A Glass-Enclosed Office Tower 668
17.7. Case-Study Five: An Office Building on a Tight Site 670
17.8. Case-Study Six: Office Building for Prudential Insurance Company 673
17.9. Case-Study Seven: Rowes Wharf Harbor Redevelopment Project 676
Index 681

1
Chapter 1
New Directions in Building Design
Building constructionis essentialto the economy of
nations. If building construction declines, the
economy suffers.Buildings also are essentialto the
economic well-being of architects, engineers and
contractors who engage in building design and
construction.Ifpotentialclientsdonotwish tobuild,
these professionals do not work.Thus,there are both
personal and patriotic incentives for building
designers and constructors to encourage building
construction.
A potential client considers many things before
deciding to proceed with a building project. But
there are two conditions—costandtime— that when
violated are almost certain to preclude construction
of a project. If the proposed building will cost too
much, it will not get built; if the proposed building
will not be ready for occupancy when the owner
wants it, the project will be canceled. Building
designers and constructors know this and try to
produce buildingsthat willmeet the owners’budgets
and schedules. (Sponsors of building projects are
called owners in this book.)
Despite these efforts, many buildings that are
needed do not get built because they would costtoo
much. The cost of construction, maintenance and
operation exceeds what owners are willing to pay.
As a result, some families that need housing have
none. Some families have to live in substandard
housing because they cannot afford decent
accommodations. Schools may be inadequate and
hospitals may be unavailable.
In addition to preventing construction of needed
buildings, high building costs have other adverse
effects.The costsofexpensive buildingsare passed
along to users of the buildings or to purchasers of
products manufactured in the buildings, and
ultimately, as a consequence, the consumer pays
higher prices. Despite this undesirable situation,
building costs keep rising.
There are several reasons, beyond the control of
building designers,forthe continuous increase.One
is inflation, a steady decrease in the purchasing
powerofmoney.Another consists oflegaland social
pressure for pleasant, healthy and safe living and
working conditions in buildings.Still anotheris the
result oftechnologicalchanges that make it possible
to do things in and with buildings that could not be
done previously.Consider,forexample, the change
of status overtime—fromluxury, to occasionaluse,
then to frequent use,andfinally necessity—ofitems
such as indoorplumbing,telephones,hot water,and
air conditioning. All of these changes have made
buildings more complexand more costly.
Consequently, the traditional efforts of building
designers to control costs only for the purpose of
meeting a construction cost within the owner’s
budget are no longer adequate. Designers must go
further and bring down costs over the life of the
building, including costs for construction,
maintenance, and operation.
There is evidence,however,that traditionaldesign
methods have limited capability ofdecreasingcosts,
let alone any hope of halting their steady increase.
Designers must find newways ofreducing thecosts
of constructing and using buildings.
One technique that shows great promise is
systems design. It has been used successfully for
other types of design, such as machine design, and
can be adapted to building design. Systems design
consists ofa rationalorderly series ofsteps thatleads

2 Building Engineeringand Systems Design
to the best decision for a given set of conditions. It
is a generalmethod and therefore is applicable to all
sizes and types of buildings. When properly
executed,systems designenablesdesignersto obtain
a clear understanding of the requirements for a
proposed building and can help owners and
designers evaluate proposed designs and select the
best,oroptimum,design.In addition,systems design
provides a common basis of understanding and
promotes cooperation between the specialists in
various aspects of building design.
A major purpose of this book is to show how to
apply systems design to buildings. In this book,
systems design is treated as an integration of
operations research and value analysis, or value
engineering. In the adaptation of systems design to
buildings, the author has tried to retain as much of
traditional design and construction procedures as
possible.Departuresfromthe traditionalmethodsof
design,as described in this book,should not appear
radical to experienced designers, because they are
likely to have used some of the procedures before.
Nevertheless, the modifications, incorporated in an
orderly precise process, represent significant
improvements over traditional methods, which rely
heavily on intuitive conclusions.
Later in this chapter,the systems designapproach
to buildings is discussed. Also, this chapter
examines the changing role of building designers
with increasing complexity of buildings and
indicates how they should organize for effective
execution of systems design.
1.1. CHANGE FROM MASTER BUILDERS TO
MANAGERS
The conceptsofbuilding design have changed with
time, as have the roles of building designers and
constructors along with the methods employed by
them. These changesare still occurring,as building
design moves in new directions.
Buildings that have survived through the ages
testify to the ability of the ancients to construct
beautifuland well-built structures.What they knew
about building they learned fromexperience, which
can be an excellent teacher.
Art and Empiricism
Until the 19th Century, buildings were simple
structures.Nearly allofthemmight be consideredto
be merely shells compartmentalized into rooms,
with decorations. Buildings primarily provided
shelter from the weather and preferably were also
required to be visually pleasing.Exteriorwalls were
provided with openings or windows for light and
ventilation. Candles or oil lamps were used for
artificial illumination. Fireplaces for burning wood
or coal were provided in rooms for heating.
Generally, there was no indoor plumbing. Since
stairs or ramps were the only available means of
traveling fromlevelto level, buildings generally did
not exceed five stories in height. Floor and roof
spans were short; that is, floors and roofs had to be
supported at close intervals.
Design ofsuch simple structures could be andwas
mastered by individuals. In fact, it was not unusual
for designers also to be experts on constructionand
to do the building.Thesedesigners-builders came to
be known as master builders.
To assistthem,the masterbuilders soughtoutand
hired men skilled in handling wood andlaying brick
and stone in mortar.Thesecraftsmen establishedthe
foundation on which the later subdivision of labor
into trades was based.
Building design, as practiced by master builders,
was principally an art. Wherever feasible, they
duplicated parts of buildings they knew from
experience would be strong enough. When they
were required to go beyond their past experience,
they used theirjudgment.If the advance succeeded,
they would use the same dimensions under similar
circumstances in the future. If a part failed, they
would rebuild it with larger dimensions.
Early Specialization
By the 19th Century, however, buildings had
become more sophisticated. Soaring costs of

New Directions in Building Design 3
land in city centersbroughtabouteconomic pressure
for taller buildings. Factories and public buildings,
such as railroad terminals, created a demand for
large open spaces, which required longer floor and
roof spans. More became known about building
materials,and scientific methodscouldbe applied in
building design. Owners then found it expedient to
separate the building processinto twoparts—design
and construction—each executed by a specialist.
Building design wasassigned toan architect.This
professionalwas said to practice architecture,the art
and science of building design. Construction was
assigned to a contractor, who took full charge of
transforming the architect’s ideas into the desired
building. The contractor hired craftsmen and
supplied the necessary equipment and materials for
constructing the whole building.
Basic Principles of Architecture
Basically, however, architecture has not changed
greatly from ancient times. The Roman, Vitruvius,
about 2,000 years earlier, had indicated that
architecture was based on three factors:
“convenience, strength and beauty.” In the 17th
Century the English writer, Sir Henry Wotton,
referred to these as “commoditie, firmeness and
delight.” Thus:
1. A building must be constructed to serve a
purpose.
2. The building must be capable of withstanding
the elements andnormalusage fora reasonable
period of time.
3. The building, inside and out, must be visually
pleasing.
Advent of the Skyscraper
In the middle of the 19th Century, a technological
innovationmarked the beginningofa radicalchange
in architecture. Traveling from level to level in
buildings by means of stairs had limited building
heights, despite the economic pressures for taller
buildings. Some buildings used hoists for moving
goods from level to level, but they were not
considered safe enough for people; if the hoisting
ropes were to break,the platformcarryingthepeople
would fall to the bottomofthe hoistway.The fearof
falling, however, was largely alleviated after E. G.
Otis demonstrated in 1853 a safety brake he had in-
vented. Within three years, a building with a
passenger elevator equipped with the brake was
constructed in New York City. Considerable
improvements in elevator design followed; use of
elevators spread.Undereconomic pressure to make
more profitable use of central city land, buildings
became taller and taller.
At this stage, however, building heights began to
run up against structural limitations. In most
buildings, floors and roof were supported on the
walls, a type ofconstruction knownas bearing-wall
construction.Withthis type,the tallera building,the
thicker the walls had to be made (see Fig. 1.1). The
walls of some high- rise buildings became so thick
at the base that
Roof
12
Fig. 1.1. Required thicknesses
for brick bearing walls for a
12-story building. Building
Code of the City of Chicago, 1928.

architects considered it impractical to make
buildings any taller.
Then, another technological innovation eased the
structural limitation on building height and
permitted the radical change in architecture to
continue.In 1885, architect w. L. Jenney tookthe
first major step toward skeleton framingforhigh-rise
buildings. (In skeleton framing, floors and roof are
supported at relatively large intervals on strong,
slender vertical members, called columns, rather
than at short intervalson thick,wide masonry piers.)
In the 10-story Home Insurance Building in
Chicago, Jenney set cast iron columns, or posts, in
the load-bearing masonry piers to support wrought-
iron beams that carried the floors.(Also,in thatyear,
anotherrelevant event occurred.The first structural
steelbeams were rolled.) Two years later,architects
Holabird &Roche tookanothersteptoward skeleton
framing. By supporting floorbeams on cast-iron
columns along the two street frontages of the 12-
story Tacoma Building in Chicago, the architects
eliminated masonry bearing walls on those two
sides.
Cast-iron columns, however, have relatively low
strength. Their continued use would have
substantially limited building heights.Steelcolumns
proved to be a stronger, more economical
alternative. In 1889, the 10-story Rand McNally
Building, designed by Burnham & Root, was
constructed in Chicago with steel columns
throughout. This set the stage for the final step to
complete skeleton framing, with floors and roof
carried on steel beams, in turn resting on steel
columns (see Fig. 1.2). Thick walls were no longer
necessary.
The full possibilities of skeleton framing was
demonstrated in 1892 when it was used for the 21-
story, 273-ft-high Masonic Temple in Chicago.
Skeleton framing was thenadoptedin NewYorkand
other cities.
Meanwhile,developmentofreinforcedconcrete,a
competitor of structural steel began. In 1893,
construction ofa concrete-framed museumbuilding
at Stanford University, Palo Alto, Calif.,
demonstrated the practicability of monolithic
concrete construction. Ten years later, the first
skyscraper with concrete framing, the
Fig. 1.2. Structural steel skeleton framing for a multistory building.

16-story Ingalls Building in Cincinnati, was
completed.
Effects of Skyscrapers on Architecture
The trend to theskyscraper,which acceleratedin the
20th Century, had several marked effects on
architecture and its practice. For one thing, the
externalappearanceofbuildingsunderwent a radical
change. Large expanses of masonry with small
openings for windows (see Fig. 1.3) gave way to
large glass windows with relatively small amounts
of wall between them(see Fig. 1.4). Another effect
was that use of skeleton framing developed a need
for specialists capable of designing framing for
safety and economy. Architects hired structural
engineers for this purpose or retained consulting
engineering firms. Still another effect was that
indoor plumbing became essential. Pipes and
fixtures had to be provided for water supply, waste
disposal and gas for heating, cooking and
illumination. In addition,centralheating,with warm
air, hot water or steam distributed throughout a
building from a furnace in the basement, became a
necessity. A need for specialists capable of
designing plumbing and heating systems and
elevators developed. To meet this need, architects
hired mechanical engineers or retained consulting
engineering firms. Thus, building engineering was
incorporated in architecture.
At the same time, construction became more
complex. In addition to masons, bricklayers and
carpenters, contractors now needed to hire
ironworkers, plumbers, window installers and
Fig. 1.3. Late 19th Century building, still expressing the basic forms of load-bearing wall construction, although
its basic structure is steel framed. Auditorium Hotel, Chicago, by Adler and Sullivan. 80 years later, the worlds
tallest steel frame structure, the Sears Tower, looms over it, clearly expressing the frame structure.

Fig. 1.4. Sears Tower (1974), Chicago, rises 110stories,
1454 ft. Steel skeleton frame with bundled tube system
for lateral load resistance.
elevatorinstallers.Soon,companieswere formed to
offer such services to contractors. Thus, a building
owner contracted construction of a building to a
general contractor, who then subcontracted
specialty work to subcontractors.
Humanization of Architecture
Advances in technology usually do not occur
without mishaps.Floors,roofs and walls sometimes
collapsed because of poor materials or
workmanship, or sometimes because floor spans or
wall heights were extended beyond the capabilities
at the time. Also, many lives were lost in building
fires. To prevent such mishaps, municipal
authorities promulgated building codes, which
establishedby lawminimum design standards.Such
codes contained provisions for minimum loads for
structural design, minimum strength for materials,
minimum thickness of walls, fire protection of
structural components and emergency exits in case
of fire. In the interests of health, regulations were
incorporated governing plumbing installations and
ventilation.
When electricity came into widespread use in
buildings during the 20th Century, building codes
incorporated provisions governing electrical
installations.Specialists were neededto designsuch
installations,so architects hired electricalengineers
or retained consulting engineering firms. Similarly,
generalcontractors subcontractedelectricalwork to
electrical subcontractors.
During the 19th and 20th Centuries, industry
developed rapidly. More and more factories were
built, and more and more people were hired for
manufacturing.Concern forthe health and safety of
these people led to establishment of government
Labor Departments, which established regulations
for employee conditions, many of which affected
building design.
Concern for welfare, as well as health and safety,
of people was demonstrated in the early part of the
20th Century, when municipal authorities
promulgated zoning codes. These were intended to
limit congestion in cities andpreventconstructionof
buildings that would infringe unreasonably on the
rights ofoccupants ofneighboringbuildings tolight
and air. Regulations in these codes had decided
effects on architecture. Provisions indicated how
much of a lot a building could occupy and,to some
extent, where a building could be placed on a lot.
Some codes placed specific limits on building
heights, whereas others required the face of the
building to be set back as it was made higher. In
some cases,this requirement led architects to design
buildings with facades sloping away from the
adjoining street.
In addition,zoning codes generally indicated what
type of building—residence, office building,
shopping center, factory, etc.-and what type of
construction—combustible or noncombustible-
could be constructed in various city districts.
Concern for welfare of building occupants also
was demonstrated by city Health Department
regulations forheating ofbuildings in cold weather;
however, by the middle of the 20th Century,
commercial establishments began voluntarily to
provide cooling in hot weather. To attract patrons,

owners oftheatersand retailstores installed cooling
equipment,and sodid ownersofoffice buildings,to
provide more efficient working conditions for
employees. A convenient method of supplying the
required cooling wasby airconditioning,which also
provided humidity control, and this method was
widely adopted. Its use spread to residences, most
public buildings and factories.
There was an effect on architecture but it was not
very visible. Mechanicalengineers tookon the task
ofdesigning coolinginstallations,incorporatingit in
a general category HVAC (heating, ventilation and
air conditioning). Heating subcontractors became
HVAC subcontractors. Architects endeavored to
make HVAC installations inconspicuous. They
placed equipment in basements and other areas
where it would not be noticeable, or they disguised
equipment spaces with decorative treatment. The
designers also hid ventilation ducts, when it was
expedient, in enclosed shafts or between floors and
ceilings.
During the last half of the 20th Century, concern
forthe effects ofbuildingsonpeople became deeper.
More stringent regulations for fire safety were
promulgated.Otherrules set minimumillumination
and maximum sound levels in work areas.
Requirements were established that prevented
construction ofa buildinguntilits fullenvironmental
impact could be assessed. And the need for energy
conservation in building operation to conserve
natural resources became apparent. These
requirements placed additional constraints on
building design. Both design and construction
became even more complex.
New Twist in Construction Management
While complex buildings demanded by owners
made design more difficult than before,ownersnow
encounteredproblemseven more difficult than in the
past, from the start of a project to its completion.
Few owners were sophisticated enough to cope
successfully with these problems. Consequently,
projects often were completed late and construction
costs exceeded expectations. Some owners
consequently sought new ways to control costs.
With respect tocostcontrol,the subdivisionofthe
building process into design and construction by
separate specialists was proving to be
counterproductive. By specializing in design,
architects and their design consultants gave up
control of construction methods and equipment,
exerted little influence on construction scheduling
and lost intimate contact with actual construction
costs. Hence, orthodox building designers could
provide little help to owners in controlling
construction costs and time.
There was onealternative.Masterbuilders hadnot
become extinct. Often, though, they had become
transformed froman individualdesigner-buildertoa
corporation consisting of architects, engineers and
construction management personnel. Under a
turnkey contract,such companies would designand
build a project for a stipulated sumofmoney.Some
owners liked this arrangement because they knew
what theirmaximum cost would be almost fromthe
start of the project. Others disliked it because they
were uncertain that they were getting the best
possible design or the lowest possible cost.
Seeking a better alternative, some owners
continued to engage architects and engineers for
design only,in the hope of getting the best possible
design for their money, but sought different means
of controlling construction costs and time. Public
agencies, for example, awarded prime contracts to
former major subcontractors, such as HVAC,
plumbing and electrical, as well as to a general
contractor. This was done in the expectation that
open competitivebidding onmajorcostitems would
result in lower totalcost.However,there neverwas
any certainty that theexpectation wouldbe realized.
Experienced owners often found that awarding a
construction contract to the lowest bidder gave
undesirable results—shoddy materials and
workmanship, construction delays and cost
overruns. Some owners therefore found it
worthwhile to select a reputable contractor and pay
a fee overactualcosts forconstruction.Owners were
uncertain, though, as to actual costs and especially
as to whether costs could have been lowered.
To meet the challenge,a newbreed of contractor
evolved in the second half of the 20th Century.
Called a construction manager, this contractor
usually did not do any building. Instead, for a fee,
the manager engaged a general contractor,
supervised selection of subcontractors and
controlled construction costs andtime.Engagement
ofa construction manageralso offeredthe advantage
that his knowledge of costs could be tapped by the
building designers during the design phase. Many
large and complex projects have been successfully
built under the control of construction managers.
Nevertheless, whether construction managers,

reputable general contractors or multiple prime
contractorsare used,goodconstructionmanagement
has demonstrated capability forkeeping costswithin
estimates; however, such management is generally
restricted primarily to the task of transforming the
conceptsofbuilding designersintoa structure.With
the design function in the hands of others,
constructors are limited in opportunities for
lowering construction costs. If costs are to be
lowered, designers probably will have to show the
way. For that, they will need new methods.
References
s. Gideon, Space, Time, and Architecture, Harvard Univ.
Press, 1954.
H. Gardner, Art Through the Ages, Eighth Ed. Harcourt,
Brace, New York, 1986.
w. Jordy and w. Pierson, American Buildings and Their
Architects, Doubleday, New York, 1970.
s. Timoshenko, History of Strength of Materials, McGraw-
Hill, New York, 1953.
Wordsand Terms
Architect
Building code Building engineeringConstructionmanager
Electrical engineerHVAC
Master builder
Mechanical engineerStructural engineerZoningcodes
Significant Relations, Functions, and Issues
Change in building design and construction processes over
time.
Roles of the architect, contractor, subcontractors, consulting
engineers, construction manager.
Effects of theemergenceof buildingcodes andzoningcodes.
1.2. BASIC TRADITIONAL BUILDING
PROCEDURE
Before any new approaches to building design can
be explored,a knowledge ofcurrentdesignpractices
is essential.Furthermore,the systems designmethod
proposed in this book is a modification of current
practices. Therefore, current practices are reviewed
in this section. For this purpose, a commonly
followed procedure is described.It is called thebasic
traditional building procedure. While other
procedures are often used, they can readily be
adapted to systems design in much the same way as
the basic traditional procedure.
What Designers Do
Generally, an owner starts the design process by
engaging an architect. In selecting the architect,
owners do not always act in their own best interest.
They shouldchoosean architect whohas established
a reputation for both good design and low
construction costs. Instead, some owners shop
around for the architect with the lowest fee. Yet, a
good designer can provide a high-quality building
and,at the same time, save the ownerseveraltimes
the design fee in lower construction costs.
The architect usually selects the consulting
engineers andotherconsultants whowillassist in the
design.A good architect selects engineers who have
established a reputation for both good design and
low construction costs.
Building design may be considered divided into
two steps, planning and engineering, which
necessarily overlap.
Planning consists generally of determining:
1. What internal and external spaces the owner
needs
2. The sizes of these spaces
3. Their relative location
4. Their interconnection
5. Internal and external flow, or circulation, of
people and supplies
6. Degree of internal environmental control
7. Other facilities required
8. Enhancement ofappearance insideandoutside
(aesthetics)
9. How to maximize beneficial environmental
impact and minimize adverse environmental
impact of project.
In some cases,planning alsoincludes locating,or
layout,ofmachinery andotherequipment tomeet an
owner’s objectives.
Engineering consists generally of the following
processes:
1. Determining the enclosures for the desired
spaces
2. Determining the means of supporting and
bracing these enclosures
3. Providing the enclosures and their supports
and bracing with suitable characteristics, such
as high strength, stiffness, durability, water
resistance,fire resistance,heat-flowresistance
and low sound transmission.
4. Determining the means ofattainingthedesired

environmentalcontrol(HVAC,lighting,noise)
5. Determining the means ofattainingthedesired
horizontal and vertical circulation of people
and supplies
6. Providing forwatersupply and waste removal
7. Determining the power supply needed for the
building and the means of distributing the
required powerto the placeswhere it is needed
in the building
8. Providing for safety of occupants in emer-
gency conditions, such as fire.
Legally, the architect acts as an agent of the
owner. Thus, at the completion of design, the
architect awards a construction contract to a general
contractor and later inspects construction on behalf
of the owner,who is obligated to pay the contractor
for work done.
What Contractors Do
In effect, the owner selects the general contractor.
The architect provides advice and assists the owner
in reaching a decision. The owner may pick a
contractor on the basis of price alone (bidding) or
may negotiate a price with a contractor chosen on
the basis of reputation.
The general contractor selects the various sub-
contractors who will be needed. Selection is
generally based on the lowest price obtained
(bidding)from reputable companieswith whomthe
contractor believes it will be easy to work. The
contractor compensates the subcontractors for the
work performed.
Construction consists of the processes of
assembling desired enclosures and their supports
and bracing to form the building specified by the
architect. Construction also includes related
activities, such as obtaining legal permission to
proceed with the work, securing legal certification
that the completed building complies with the law
and may be occupied, supplying needed materials,
installing specified equipment, providing for the
safety of construction employees and the general
public during construction, and furnishing power,
excavation and erection equipment, hoists,
scaffolding and other things essential to the work.
Programming
The basic traditional building design procedure is a
multistep process.It startswith thecollection ofdata
indicating the owner’s needs and desires and
terminates with award of the construction contract
(see Fig. 1.5).
The procedure starts with preparation of a
buildingprogram. The programconsists mainly ofa
compilation of the owner’s requirements. The
programalso contains descriptions ofconditionsthat
will affect the building process andthatwill exist at
the start of construction, such as conditions at the
building site.It is the duty ofthe architectto convert
the programinto spaces,which thenare combinedto
form a building. Hence, before planning of a
building can start,a programis needed.The architect
prepares the programfrominformation supplied by
the owner, owner representatives, or a building
committee.
In collecting data for the program, it is important
for the architect to learn as soon as possible how
much the owner is willing to pay for the building
(the budget)and if there is a specific date on which
the building must be ready for

should not proceed.Ifhe does andtheownersuffers
economic injury, the architect may not receive
compensation for work performed on the project.
The data supplied by the owner should indicate
clearly what his objectives are,so that thefunctions,
or purposes, of the building are evident. The
architect should also ascertain how the owner
expects to attain those objectives— the activities to
be performed in the building, approximate space
needed for each activity, number of employees per
activity, relationship between activities or work
flow, equipment that will be installed for the
activities, desired environmental conditions
(HVAC, lighting and sound control) and other
requirements that will be needed for design of the
building.
Information also will be needed on the site on
which the building will be erected.This information
should cover subsurface conditions as well as
surface conditions. If the owner has already
purchaseda buildinglot before the programhasbeen
prepared, the architect will have to adapt the
building to the site.A much more desirable situation
is one in which a site has not yet been bought,
because thearchitect willthen have greaterplanning
flexibility; the architect can assist the owner in
deciding on a site.
The owner is responsible for providing infor-
mation on the site necessary for design and con-
struction of the building. The architect, however,
acting as the owner’s agent,generally engagesa land
surveyor to make a site survey, and foundation
consultants for subsurface investigations.
The architect should then submit the completed
programto the owner for approval. If there are any
omissions or misconceptions of the requirements,
they should be rectified before planning starts, to
save time and money.Approvalofthe ownershould
be obtained in writing.
Conceptual Phase
During data collection, the architect may have
formulated some concepts of the building, but on
completion of the program, he formalizes the
concepts—translates requirements into spaces,
relates the spaces andmakes sketches illustratinghis
ideas. To see how other designers have met similar
requirements for build-
occupancy.Ifeitherthe budget orconstructiontime
are unrealistic, the owner should be informed
immediately, in writing. If realistic figures cannot
be negotiated, the architect
Fig. 1.5. Steps in the basic traditional building pro-
cedure.

ing design, the architect may visit other buildings.
Then,by a combination ofintuition,judgmentbased
on past experience and skill, he decides on a
promising solution to the requirements of the
program.
Cost estimators then prepare an estimate of the
construction cost for the selected solution. Since at
this stage, practically no details of the building
design have beendecided,the result is called a rough
cost estimate. If the estimate is within the owner’s
budget, the solution can be prepared for submission
to the owner for approval. Otherwise, the scheme
must be modified,usually by making thelayout more
efficient or by reducing allotted floor areas or
building volume.
Efficiency oflayout is sometimes measuredby the
tare, or ratio of useful floor area to the gross floor
area (totalfloor area enclosed within the outerfaces
of the exterior walls). Efficiency for some types of
buildings alsomay be measured bythefloorarea per
occupant or unit of production.
The proposed solution is submitted to the owner
mainly as sketches, known as schematic drawings,
along with the rough cost estimate (see Fig. 1.5).
Though lacking in detail, the schematics show the
ownerwhat the building will be like. They include a
site plan indicating the orientation of the building
and its location onthesite,aswellas the accesstobe
provided to thesite andthe building.The schematics
should also include major floor plans, showing the
location of rooms and corridors and floor areas
allotted. In addition, exterior views, or elevations,
should beprovidedto illustratethe proposed finished
appearance of the building exterior. The plans and
elevations should indicate the basic materials that
have been selected. Besides the schematics, the
architect may submit to the owner perspective
drawings or a model to give a better indication of
how the building will look.
The ownermay suggest modificationsoftheplans
or may reject the entire scheme. In the latter case, a
new concept must be developed. Because of this
possibility, time and money are saved in the
conceptual stage by developing no more detail than
necessary to present a possible solution to the
programrequirements.
The conceptual phase is further discussed in Sec.
4.3.
Design Development
After the architect receives, in writing, the owner’s
approval of the schematic drawings and rough cost
estimate, the design is developed in detail (see Fig.
1.5). In this phase, the designers concentrate on
technology.The objective ofthis phase is tobringthe
building into clearer focus and to a higher level of
resolution. The phase culminates in completion of
preliminary construction drawings, outline
specifications and preliminary cost estimate.
In the conceptual phase, the architect’s aesthetic
concerns were mainly with function,mass andspace.
During design development,the architectpays more
attention to surface and detail.
The structural engineer prepares drawings
showing the framing and sizes of components. The
mechanical engineer shows the layout of pipes, air
ducts, fixtures and HVAC equipment and provides
data on escalators and elevators. The electrical
engineerindicates in drawings the locationand type
of lighting fixtures and layout ofelectric wiring and
control equipment, such as switches and circuit
breakers.
The designers also prepare outline specifications
to record,forreview,the basic decisions onmaterials
and methods that will later be incorporated in the
contract documents.Thesespecifications neednot be
as precisely worded as the final specifications; they
may be brief, in the formof notes.
When the preliminary drawings and outline
specifications have been completed, cost estimators
can prepare a more accurate estimate of the
construction cost for the building. If the refined
estimate is not within the owner’s budget, changes
are made to reduce costs.It should not,however,be
necessary to revise the basic concepts approved in
the conceptual phase, but it may be necessary to
modify the structuralframing,switch windowtypes,
change the exterior facing, specify less expensive
heating orcooling equipment,pickdifferent lighting
fixtures, or even omit some features desired by the
owner but not really essential.
When construction cost estimates are brought to
the desired level, the preliminary drawings, outline
specifications and estimated cost are submittedto the
owner for approval. Revisions are made, as
necessary, to obtain the owner’s written approval.
Design development is further discussed in Sec.
4.4.
Contract Documents Phase
The ultimate objective of the design effort is
production of information and instructions to
constructors to insure that a building will be
produced in complete accordance with the design

agreed on by the owner and the architect. The
information and instructions are provided to the
builder in the form of working, or construction,
drawings and specifications(see Fig.1.5). These are
incorporatedin the construction contractbetweenthe
owner and the builder and therefore become legal
documents. As such, they must be prepared with
extreme care to be certain that they are precise and
their intent is clear.
In the contract documents phase of design, the
designers’efforts are concentrated mostly on details
and refinements, inasmuch as the main features of
the building were worked out in design development
and approved by the owner. If changes have to be
made in the design at this stage,theyare likely to be
much more costly than ifthey had been made in ear-
lier phases. The architect,.with the advice of legal
counsel, also prepares the construction contract.
With finaldetails ofthe designworked out,a more
accurate estimate of construction cost can now be
made. If this estimate exceeds the owner’s budget,
the designers have to revise drawings or
specifications to bring costs down. When they have
done this, the contract documents are submitted to
the owner for approval. Again, revisions are made,
as necessary,to obtainwritten approval; butwith the
high cost of changes at this stage, a sophisticated
ownerwould restrict requestsformodificationsonly
to corrections of mistakes.
Contract documentsare furtherdiscussed in Chap.
5.
Contract Award
After the contract documents have been approved,
the architect assiststhe ownerin obtainingbidsfrom
contractors or in negotiating a contract with a
qualified contractor(see Fig.1.5). The architect also
aids in evaluatingproposalssubmittedbycontractors
and in awarding the contract.
For private work, for example construction not
performed for a public agency, the owner usually
awards a single contract to a generalcontractor.The
contractor then awards subcontracts to specialists
who performmost or all ofthe work.The ownermay
negotiate a contract with a general contractor with
whomthe ownerhas had previousexperienceorwho
has been recommended by the architect or other
advisers.Orthe ownermay select a contractoron the
basis of bids for the work.
For public work, such as a city or state project,
there may be a legal requirement that bids be taken
and separate construction contracts be awarded for
the major specialties, such as the mechanical and
electricaltrades.In addition,a separatecontract must
be awarded to a general contractor, who is assigned
responsibility for coordinating the trades and
execution ofallof the work.Usually,bidding is open
to anyone wishing to bid, and the contracts must be
awarded to the lowest responsible bidders.
Bidding requirements and contract awards are
further discussed in Sec. 5.5.
General Critique
The basic traditional building process described in
this chapter and extended to the construction phase
in Chap. 5 evolved into its present formover many
years, and is widely used. Clients, designers and
contractors are familiar with it and generally produce
good buildings with it.
The basic traditional building procedure usually
yields buildings that meet functional requirements
well, are aesthetic,with safe structure,good lighting,
adequate heating and cooling, and good horizontal
and verticalcirculation.In addition,the procedureis
geared to submissionofbids forconstructionthat are
within the owner’s budget. The architect submits
cost estimates to the owner for approval at the start
of the conceptual phase, at the conclusion of the
conceptual phase, at the end of design development
and with the contractdocuments.At any stage,ifthe
estimate is too high, the design is revised to reduce
estimated costs. Also, if contractors’ bids or
negotiated prices are too high,changes in the design
are made to bring prices down.
If the procedure produces goodbuildings at prices
owners are willing to pay, why then should the
procedure be changed?
Should it be changed because the charge can be
made that the ownermay be paying too much forthe
building provided, though he is willing to pay the
price? This may be true,but it also is probably true of
almost every conceivable designprocedure.Enough
research and study can always produce a better
design.But the cost ofsuch research and study may
not warrant these efforts. Furthermore, the time
available for design and construction may not be
sufficient. Consequently, changes in the basic
traditional procedure must be justified by more
specific defects.
One drawback is the frequent occurrence of
construction costs that exceed bid or negotiated
prices. Such situations generally occur because the
owner orders design changes while the building is

under construction. Such changes almost never
reduce construction costs and almost always are
costly.
These situations may occur partly because of the
type of construction contract used. For example,
when a contractortakes a job for a fixed price, there
is a profit incentive to encourage change orders.
Design changes during construction usually yield
higher profits to the contractor. To low bidders,
change orders often mean the difference between
profit and loss for a project. Nevertheless, as
reputable contractors can point out, change orders
often are necessary because of design mistakes or
omissions. (Occasionally, changed conditions
affecting the owner’s requirements for the building
may compel issuance of change orders.) Modifica-
tions of the design procedure therefore could have
the objective ofreducingthenumberofmistakes and
omissions in design.
Anotherdefect arises because ofthe separationof
design and construction into different specialties. If
designers do not build, they do not have firsthand
knowledge of construction costs and consequently
often cannot prepare cost estimates with needed
accuracy.
In addition, construction costs usually depend on
the construction methods used by the contractor.
Since the contractor generally is free to choose
construction methods, designers can only base their
cost estimates on the probable choice of methods.
This can introduce further inaccuracies in the
estimates.
Also,knowledge ofthe construction market at the
time when and the place where the building will be
constructed is necessary. This requires familiarity
with availability of subcontractors, construction
workers,constructionequipment,building materials,
and equipment to be installed when needed for
construction. Contractors take such conditions into
account in establishing construction costs; designers
rarely do. Thus, further inaccuracies may be
introduced into their cost estimates.
The result often is that the owner pays too much
for the building provided, though the price may be
within his budget. Modifications of the design
procedure therefore could have the objective of
bringing constructionexpertsintothe designprocess.
Still another drawback is that construction costs
are kept within the budgetbypermitting maintenance
and operatingcoststo rise.Cheap building materials
and equipment are specified to cut initial costs, but
they proveexpensive in the longrun.Sometimes this
condition is made necessarybecausean ownercould
otherwise not afford to build and is willing to risk
high maintenance and replacement costs.He is will-
ing to pay the higher maintenance and operating
costs untilhe becomes affluent enough toreplace the
costly materials and equipment. Often, however,
owners are not aware of excessive life-cycle costs
untilafterthey occupy thebuilding. (Life-cycle costs
are the sum of initial installation costs and
maintenance and operating costs over a long period
of time, usually at least ten years for buildings.)
Changes in the designprocedure consequently could
have the objective of placing relevant emphasis on
construction and life-cycle costs.
Anothercommon defect is the lackofcoordination
of the work of the various design specialists. The
architect develops building forms and roomlayouts
with little advice from engineering consultants. The
latter, in turn, practice their specialties with little
concern for each other’s products, except when the
architect discovers that two different building
components are scheduled to occupythesame space.
Usually,then,one ofthe consultants is compelled to
move an overlapping component.
Often, there is no effort to integrate components
designed by different specialists into a single
multipurpose component,with consequentreduction
in construction costs. Hence, the objective of
revamping the design procedure could be production
and installation in buildings of more multipurpose
building components.
Furthermore,the whole philosophy ofdesign with
respect to the basic traditional procedure may be
questioned. Under existing economic pressures and
time schedules, each designer proposes one scheme
for his specialty, based on intuition judgment or
experience. This design may or may not be the
optimum for the cost or the least costly ; but the
decision may not be questioned,especially when bid
or negotiated prices fall within the owner’s budget.
Thus, there is no pressure for further reduction of
construction costs. Consequently, an important
reason forchanging the designprocedure is the need
for reducing construction costs without increasing
life-cycle costs.
Other variations of the basic traditional design
procedure often used include engagement of a
consulting engineer or an architect-engineer firm
instead of an architect. These variations generally
have about the same disadvantages as the traditional
procedure. All need to be changed to reduce
construction costs while maintaining high-quality

design.
References
Architect’s Handbook of Professional Practice (Volumes
1, 2, and 3), American Institute of Architects.
Guide for Supplementary Conditions (Publ. No.A511), AIA.
General Conditions of the Contract for Construction (Publ.
No. A201), AIA.
Standard Form of Agreement Between Owner and Architect
(Publ. No. B141), AIA.
J. Sweet, Legal Aspects of Architecture,Engineering, andthe
Construction Process, West Publishing Co., 1970.
c. Dunham, etal., Contracts, Specifications, and Law for
Engineers, 3rd ed., McGraw-Hill, New York, 1979.
Words and Terms
Bidding
Building Program
Design Phases: programming, conceptual, development,
construction documents, bidding
Engineering
Life-cycle costs
Planning
Tare
Two steps of buildingdesign: planningandengineering.
Sequential phases of design—from programmingtocon-
struction.
Functions of thearchitect as agent of theowner.
Building construction contract awarding process.
Cost control forconstructionrelatedto the owner/contrac-tor
contractural agreement.
Separate effects of cost control measures on design, con-
struction, maintenance, and operation costs.
1.3 SYSTEMS DESIGN
APPROACH TO BUILDING
The General Critique of Sec. 1.2 indicates that the
basic traditional building procedure could be
improved by
1. More questioning of the cost effectiveness of
proposed building components and greater
efforts to obtain better alternatives.
2. Coordinating the work of various design and
construction specialists to achieve more cost-
effective designs; for example, use of
multipurpose building componentsin which the
products of two or more specialties are
integrated.
3. Placing relevant emphasison both construction
and life-cycle costs.
4. Having construction experts contribute their
knowledge of construction and costs to the
design process.
5. Use of techniques that will reduce the number
ofmistakes and omissions in design thatare not
discovered until after construction starts.
The systems design approach described briefly in
this section and in more detail in following chapters
offers opportunities for such improvements.
Operations Research
Development of the technique known as operations
research orsystems analysis began early in the 20th
Century but became more intense after 1940. Many
attempts have been made to defineit,but noneofthe
definitions appears to be completely satisfactory.
They either are so broad as to encompass other
procedures or they consist merely of a listing of the
tools used in operations research. Consider, for
example, the definition proposed by the Committee
on Operations Research of the National Research
Council:
Operations research is the application of the
scientific method to the study of the operations of
large complex organizations or activities.
The scientific method comprises the following
steps:
1. Collection of data, observations of natural
phenomena
2. Formulation of an hypothesis capable of
predicting future observations
3. Testing thehypothesis to verify the accuracy of
its predictions and abandonment or
improvement of the hypothesis if it is
inaccurate
Operations researchdoes satisfy the definition;but
architects and engineers also can justifiably claim
that the design procedures they have been using are
also covered by the definition. A major difference,
however,between traditionaldesign procedures and
operations research, or systems analysis, is that the
traditional design steps are vague. As a result, there
usually is only a fortuitous connection between the
statement ofrequirements,orprogram,and the final
design. Systems analysis instead marks a precise
path that guides creativitytoward thebest decisions.
Definition of a System
Before the systems design method can be explained
in full, a knowledge of terms used is necessary.

Similarly, before the method can be applied to
building design, a knowledge of basic building
components is essential. Following are some basic
definitions:
A system is an assemblage of components formed
to serve specific functions or to meet specific
objectivesandsubject to constraints,orrestrictions.
Thus, a systemcomprises two or more essential,
compatible and interrelated components. Each
component contributes to the performance of the
systemin serving the specified functionsormeeting
the specified objectives. Usually, operation, or even
the mere existence, ofone componentaffectsin some
way the performance of other components. In
addition,the required performance ofthesystemas a
whole, as well as constraints on the system, impose
restrictions on each component.
A building satisfies the preceding definition and
descriptionofa system.Even a simple building,with
only floor, roof, walls, doors and windows, is a
system. The components can be assembled to
provide the essential functions:
1. Surface on which activities can take place and
furnishings or materials can be stored.
2. Shelter fromthe weather
3. Access to and fromthe shelter
4. Light within the shelter
5. Ventilation within the shelter
The components are essential, compatible and
interrelated. The combination of floor, roof and
walls, for example, meets the requirement of shelter
from the weather, because these components fully
enclose the spaces within the building. Floor, roof
and walls also must be compatible, because they
must fit tightly together to exclude precipitation. In
addition, they are interrelated, because they
interconnect,and sometimesthewalls are required to
support the roof. Similar comments can be made
about walls, doors and windows.
Systems Analysis
In systems analysis,a systemis first resolvedinto its
basic components. Then, it is investigated to
determine the nature,interactionandperformance of
the components and of the systemas a whole.
Components also may be grouped into smaller
assemblages that meet the definition of a system.
Such assemblages are called subsy5- terns. Systems
analysis also may be applied to subsystems.
A complexsystemcan be resolved intomany sizes
and types of subsystems. For example, it may not
only be possible to separate subsystems into
subsubsystems but also to recombine parts taken
from each subsubsystem into a new subsystem.
Hence, a systemcan be analyzed in many different
ways.
Consider, for instance, a building wall. In some
buildings, a wall can be composed of a basic
component.In otherbuildings,a wall may consistof
several components: exterior surfacing, water-
resistant sheathing, wood studs, insulation and
interior paneling. In the latter case, the wall may be
considered a subsystem. In such buildings, power
may be supplied by electricity, in which case the
electricalequipment and wiring may be considered a
subsystem. Suppose now that the wiring is incorpo-
rated in the wall, between the wood studs.Then,the
wiring and otherwallcomponents may be considered
a subsystem.
Systems Design
Systems design is the application of the scientific
method to selection and assembly of components or
subsystems to form the optimum system to attain
specified goals andobjectives while subjectto given
constraints, or restrictions.
Applied to buildings,systems designmust provide
answers to the following questions:
1. What precisely should the building ac-
complish?
2. What conditions exist, or will exist after
construction, that are beyond the designers’
control?
3. What requirements for the building or
conditions affecting systemperformance does
design control?
4. What performance requirements and time and
cost criteria can be used toevaluate thebuilding
design?
Value Analysis
An additional step, aimed at reduction of lifecycle
costs ofbuildings,was introduced intothetraditional
building procedure about the middle of the 20th
Century.This newsteprequired a study,generally by
separate cost estimators and engineers, of ways to
reduce cost, in addition to normal design considera-
tions ofcostandfunction.The technique usedin such
studies became known as value analysis, or value

engineering.
When used,value analysis oftenwas permitted or
required by a clausein the construction contract.This
clause gave the generalcontractoran opportunity to
suggest changes in the working drawings and
specifications. As an incentive for so doing, the
contractorwas givena share ofthe resultingsavings,
if the owner accepted the suggestions. Thus, the
design changes were made during the construction
phase,afterthe designershad completed theirwork,
and the construction contract had to be amended ac-
cordingly. Despite the late application of value
analysis in the building procedure, the technique
generally yielded appreciable savings to owners.
Nevertheless, the technique is applicable in the
other phases of the building process. Furthermore,
experience has shown that cost-reductionefforts are
more effective in the earlier phases of design.
Consequently, it is logical to start value analysis in
the conceptualphase and continue it rightthroughthe
contract documents phase.
As practiced,value analysisis an orderly sequence
of stepswith the goaloflowering lifecycle costsofa
proposed system. In the search for cost reductions,
the analysts question the choice of systems and
components and propose alternatives that are more
cost effective. Based on observations of current
value-analysis practice,the following definitionsare
proposed:
Value isa measure of benefitsanticipated froma
system or from the contribution of a component to
system performance. This measure must be capable
ofserving asa guide ina choice between alternatives
in system evaluation.
Value analysis is an investigation of the rela-
tionship between life-cycle costs and values of a
system,itscomponentsandalternativestothese.The
objective is attainment of the lowest life-cycle cost
for acceptable system performance.
Note that the first definition permits value to be
negative;forexample,an increasein costto anowner
because of a component characteristic, such as
strength or thickness.
Note also that the second definition setsthe goalof
value analysisas the least costforacceptable system
performance. This differs from the goal of systems
design, as previously defined, which is to produce
the optimum solution. Thus, systems design may
seek either the least cost, as does value analysis, or
the best performance fora given cost.Since there is
a common goal, it appears well worthwhile to
integrate value analysis into the overall design
process.
Sometimes, value can be expressed in terms of
money; for example, profit resulting froma system
change. If this measure is used, value analysis is
facilitated, because life-cycle cost and value, or
benefit,can be directly comparedin monetary terms.
Often,however,in value analysis ofbuildings,value
is based on a subjective decision of the owner. He
must, for example, decide how much more he is
willing to pay for an increase in attractiveness ofthe
building exterior, or conversely,whetherthe savings
in constructioncost froma decreasein attractiveness
is worthwhile.Thus,value analysis must be capable
of evaluating satisfaction, prestige, acceptability,
morale, gloom, glare, draftiness, noise, etc.
Value analysis is furtherdiscussed in Chap.3,Sec.
3.12.
Systems Design Procedure
In accordance with the definition of systems design
and the description of the scientific method, the
systems design procedure has three essential parts:
analysis, synthesis and appraisal. These may be
carried out in sequence or simultaneously.
Analysis is the process ofgiving the designers and
value engineers an understanding ofwhat the system
should accomplish. Analysis includes collection of
data,identification ofthe objectives and constraints,
and establishment of performance criteria and
relationships between variables.
Synthesis is the process ofselecting components to
form a systemthatmeets thedesign objectives while
subject to the constraints.
Appraisal is the process of evaluating system
performance. Value analysis is part of the appraisal
phase, to insure cost effectiveness of components.
Data obtained in the appraisal are used to effect
improvements in the system, through feedback of
information to analysis and synthesis.
Thus, the procedure is repetitive, or cyclical.
Information feedback should insure that the system
producedin each cycle is betterthanits predecessor.
Consequently, the design should converge on the
optimum system. Whether that systemcan actually
be attained, however, depends on the skills of the
designers and the value engineers. Each cycle
consumes time; costs mount with time, and in
addition,the designmustbecompleted by a deadline.
Hence,design may have to be terminated before the
optimumsystemhas been achieved.

Optimization
For complex systems,suchas buildings,it usually is
impractical to optimize a complete system by
simultaneous synthesis of optimum components. It
may be necessary to design some components or
subsystems in sequence, while, to save time, other
parts are designed simultaneously. In practice,
therefore, synthesis of a system can develop by
combination of components or subsystems that can
be realistically optimized rather than by direct
optimization of the complete system. Nevertheless,
to obtain the best system by this procedure, the
effects of each component or subsystem on other
components must be taken into account.
Thus, in building design, floor plans and exterior
views of the building are produced first. Then,
structural framing, heating and cooling subsystems
and electrical subsystems usually are synthesized
simultaneously. The effects of the various
subsystems on each other may result in changes in
each subsystem. Also, value analysis may suggest
improvements to reduce life-cycle costs. At some
stage in the design, however, the system can be
studied as a whole with optimization of the total
systemas the goal.
That optimization ofa building’s subsystems does
not necessarily lead to optimization of the building
can be demonstrated by a simple example. Assume
that a tennis court is to be enclosed in a building.
Suppose that initially a design is proposed with four
verticalwalls and a flat horizontalroof(seeFig.1.6a)
and with other appurtenances essential for a tennis
court.Suppose alsothatthe building is resolvedinto
three subsystems: the walls, the roof and the other
appurtenances.Then,each subsystemis designedfor
the lowest possible cost.Forthat condition,the cost
determined for the building is the sum of the
subsystem costs. There may now be possible,
however, a lower-cost building achieving the same
results.Forexample, a curved,cylindricalenclosure
may be constructed between the sides of the court,
with vertical walls at the two ends (see Fig. 1.6b}.
The curved enclosure may be lesscostly thanthetwo
walls and the roof it replaces.Hence,the alternative
building (see Fig.1.6Ồ) would cost lessthanthe one
with four walls and roof.
Fig. 1.6. Two possible building shapes for enclosing a
tennis court, (a) Building with four walls and a roof; (b)
building with cylindrical enclosure and two end walls.
Adaptation of the Traditional Procedure to Systems
Design
In the application ofthe systems-designprocedureto
buildings,it is desirable toretain as muchofthe basic
traditionalbuilding procedure as is feasible,because
of its advantages. In fact, with some revision of the
procedures in the various phases, the steps of the
traditional procedure indicated in Fig. 1.5 can be
retained in systems design ofbuildings.In brief, the
changes are as follows:
To have the greatest impact on design efficiency,
systems design application should commence at the
very earliest stages of the building process.
Programming should be done in anticipation of the
use ofvalue analysis as a design tool; value analysis
challenges should be made of proposals in the
conceptualstage,where design changes can be made
with little or no cost involved in effecting the
changes.
Systems design procedures should continue
through the design development phase, in which
major features of the design are synthesized. In that
phase also there is little cost for making design
changes.
During the contract documents phase, however,
major systemdesignchanges become costlyin terms
of time lost and redesign work required.
Consequently, complete application of the systems

design procedure may not be desirable.But forwork
that originates in this phase, such as that involving
detailed design and writing of specifications, value
analysis may be profitably applied.
During the construction phase, changes are very
expensive and should preferably be limited to
corrections of mistakes or adjustments for
unanticipated situations. If changes are proposed by
the contractor, they should be subjected to value
analysis to assure their fit with the original design
objectives.
General Critique
The systems design procedure, as outlined in this
section, has nearly all the advantages of the basic
traditional building procedure. Systems design, in
addition, offers the five desired improvements that
were described at the beginning of this section.
Two of the improvements are readily discerned.
Incorporation of value analysis in the procedure
provides the desired questioning ofdesign proposals.
Though aimed primarily at cost reduction, value
analysis, as a part of systems design, will also
encourage innovation,because use ofnewmaterials,
equipment ormethods is one means to reduce costs.
Systemdesignalsoprovides forthe desired inclusion
oflife-cycle costsin evaluationsofdesign proposals.
To the extent that data are available, maintenance
and operating costs can be incorporated in cost
estimates and value analyses.
Systems design does offer the other three im-
provements (coordination of design specialists,
contributions of construction experts, and reduction
of eưors), although how it does may not be evident
at this time. Those improvements come about as a
consequence of the organization of personnel
required for effective execution of systems design.
This is discussed in Sec. 1.4.
Systems design, however, does have disadvan-
tages. It takes more time and effort than the
traditionalprocedure.Consequently,designcostsare
higher. To offset the higher costs, the owner should
pay a higher design fee. It may be difficult, though,
to persuade an owner to do this, since some design
firms providing less desirable design services may
offer to do the design for less money.
Several difficulties are likely to be encounteredin
application of systems design:
Needed data may not be available.
Information supplied by the ownerforcompilation
of the building programmay be incomplete initially
or misunderstood by the designers.
Requirements,as statedby the owner,may not be
the actual requirements. Knowledge of existing
conditions;forexample, subsurface conditions at the
building site, may be erroneous.
Many of these difficulties, however, are also
experienced with the traditionalprocedure.Theyare
mentioned here to preclude the impression that
systems design is a cure-all for the problems of
building design.
In addition,the appraisalprocess is more difficult
and may be inaccurate in systems design.As with the
traditional procedure, the means used in cost
estimating may be faulty, but also in some cases, in
value analysis,the means usedin determining values
may be erroneous.
In summary, the systems design approach to
buildings is superiorto the traditionalprocedure.But
higher design fees are required to offset higher
design costs.
References
F. Merritt, Building Design and Construction Handbook, 4th
ed., McGraw-Hill, New York, 1982.
A. Mudge, Value Engineering, Society of American Value
Engineers, 1981.
D. Meredith et al., Design and Planning of Engineering
Systems, 2nd ed., Prentice-Hall, Englewood Cliffs, NJ,
1985.
Words and Terms
Analysis Synthesis
Appraisal System
Component Systems Design
Operations research Subsystem
Optimization Value
Scientific method Value analysis
Significant Relations, Functions and Issues
Steps in systems design procedure: analysis, synthesis, and
appraisal.
Composition and resolution of systems into subunits: sub-
systems and components.
Suboptimization: the perfecting of parts that does not nec-
essarily improve the whole system.
1.4. DESIGN BY BUILDING TEAM
Systems design of buildings requires, as does
traditional design, the skills of diverse specialists.

These may be the same specialistsas those required
for traditionaldesign.In addition,forthe purposesof
systems design, additional specialists, such as value
engineers, cost estimators, construction experts and
custodians or plant engineers, are needed. But for
systems design to be effective, the specialists must
operate differently fromthe independent manner in
which they did for traditional design.
In systems design, account must be taken of the
interaction ofbuilding componentsand the effectsof
each component on the performance of the system.
For better performance of the systemand for cost
effectiveness, unnecessary components should be
eliminated and, where possible, two or more
components should be combined. For these tasks to
be accomplished with facility when the components
are the responsibility of different specialists, those
concerned should be in direct and immediate com-
munication. They should work together as a team.
Thus, it is highly desirable that those responsible
for design and construction of a building form a
building team, to contribute their skills jointly.
Working together, the various specialists provide a
diversity of approach to synthesis, a multitude of
paths to creative design. The diversity of skills
available foranalysesinsuresthatallramifications of
a decision will be considered. With several
experienced designers with broad backgrounds
reviewing the designoutput,mistakesandomissions
become less likely.
The Team Leader
Just as for athletic teams, a building team needs a
leaderto direct the teameffort and to insure that the
owner’s objectives are met at minimum life-cycle
cost and in the least time.
The team leader should be a generalist, familiar
with all aspectsofbuilding designand construction,
cost estimating and value analysis. This person
should not only have leadership abilities but also
architectural or engineering training, artistic talents,
business expertise, public relations capabilities,
management skills and a professional attitude. As a
professional, the leader must abide by the highest
standardsofconduct and provide faithfulservicesto
clients and thepublic,just asdoctors and lawyersare
required to do. Though acting legally as an agent of
the owner,the professionalmust befairand objective
in dealing with contractors, especially when called
on for interpretations of provisions of construction
contract documents or approval of payments. In
addition,the leader should be skillful in maintaining
good relations with public officials, including
representatives of local building departments and
zoning commissions.
By educationandexperience,the teamleadermay
be an architect, a structural, mechanical, electrical,
value or industrial engineer, or a construction
manager or other professional with the required
capabilities. Under state laws established for
protection of the public, however, the leader should
be registered as either an architect or a professional
engineer.In eithercase,state registration is achieved
after completing architectural or engineering
courses, years of architecture or engineering
experience and passing a written examination given
by the state.
The leaderand the othermembers ofthe teammay
be employees of a single firm or representatives of
different firms participating in a joint venture for
design ofa project.The leadermay also be the prime
contractorwith the ownerand engage consultants to
serve on the team.
The leader provides liaison between the owner,
members of the team and contractors. With
responsibility for all design activities, the leader
coordinates and expedites the work, motivates the
team to the highest level of performance and
communicates clearly and accurately all necessary
information to all concerned with the project.
Other Team Members
Preferably, all team members should have the same
characteristics required of a team leader. Such
characteristics are needed to execute subsystem
design efficiently andto discharge responsibilities to
clients and the public. In particular, architects and
engineers should be licensed to practice their
professions.Following is a brief description of each
of the specialists usually included on the building
team:
An architect is a professional with a broad
background in building design. This background
should be sufficient to permit design of a simple
building, such as a one-family house, without the
help of specialists. The architect
should be trainedto analyze the needs anddesires of
clients and to transform those requirements into
buildings. The training should also include study of
the human factors involved in building use and
operation. In addition, the architect should be

familiar with the influence on buildings and their
occupants of natural factors, such as geography,
climate, material resources, site and orientation; the
influence of economic, technological and
sociological factors; and the influence of allied arts.
Furthermore, this professional should have artistic
talents,appropriate to making buildings attractive in
appearance, inside and outside.
Thus,as part ofa building team,the architect may
be delegated responsibility for any or all of the
following plus any other design tasks for which he
may have capabilities:
1. Preparation of the program
2. Arrangement and location of the building on
the site
3. Controloftraffic and accessto the siteandthe
building
4. Use of natural features of the site
5. Climate considerations in building design
6. Proper relationship between the building, its
neighbors and the community
7. Aesthetics
8. Compliance of the building and the site with
health, safety and zoning ordinances and
building codes
9. Determination ofthe size andshape ofinterior
spaces for human needs and the relationship
of such spaces to each other
10. Interior and exterior surface finishes, doors,
windows, stairs, ramps, building hardware
and, if required, interior decoration
11. Inspection of construction
A structural engineer is a specialist trained in the
application ofscientific principles to design ofload-
bearing walls,floors,roofs,foundationsandskeleton
framing needed for the support of buildings and
building components. As part of the building team,
this engineer may be delegated responsibility for
structuraldesignrequired forthe building projectand
inspection of structural members and connections
during construction.
A mechanicalengineer is a specialist trained in the
application of scientific principles to design of
plumbing and plumbing fixtures; heating,ventilation
and airconditioning;elevators;escalators;horizontal
walkways; dumbwaiters and conveyors. This
engineer also may have capabilities for designing
machines and planning their location for such
buildings as factories and hospitals. As part of the
building team, the mechanical engineer may be
delegated theresponsibility fordesign and inspection
of the installation of the aforementioned elements.
An electricalengineer is a specialisttrained in the
application of scientific principles to design of
electric circuits,electric controls and safety devices,
electric motors and generators, electric lighting and
other electric equipment. As part of the building
team, the electrical engineer may be delegated
responsibility for design and inspection of the
installation of the aforementioned elements.
A construction manager is a specialist with
considerable experience in building construction.
This expert may be a generalcontractor,ora former
project manager for a general contractor, or an
architect or engineer with practical knowledge of
construction management.The constructionmanager
should have the knowledge, experience and skill to
direct construction ofa complexbuilding,thoughhe
may not be engaged for erection of the building the
team is to design. He must be familiar with all
commonly used construction methods.He must be a
good judge of contractor and subcontractor
capabilities. He must be a good negotiator and
expediter. He must be capable of preparing or
supervising the preparation of accurate cost
estimates during the various design phases.He must
know howto schedule the construction workso that
the project will be completed at the required date.
During construction, he must insure that costs are
controlled and that the project is kept on schedule.
As part of the building team, the construction
managermay be assigned anyorallof the following
tasks:
1. Advisingon thecosts ofbuildingcomponents
2. Providing cost estimates, when needed, for
the whole building
3. Indicating the effects ofselected components
on construction methods and costs
4. Recommending cost-reducing measures
5. Assistingin selection ofcontractors and
subcontractors
6. Negotiating construction contracts with
contractors and subcontractors
7. Scheduling construction
8. Cost controlduring construction
9. Expediting deliveries of materials and
equipment and keeping the project on
schedule
10. Inspection ofthe workas it proceeds
A value engineer is a specialist trained in value

analysis. As part of the building team, the value
engineermay head a groupofvalue analysts,each of
whommay be a specialist,forexample, in structural
systems, plumbing systems, electrical systems, or
cost estimating.The value engineerprovidesliaison
between the building team and the value analysis
group.
The building teammay also include architectural
consultants, such as architects who specialize in
hospital or school design; landscape architects;
acoustics consultants and other specialists,
depending on the type of building to be designed.
Design, in the sense used in the preceding
descriptions, means analysis, synthesis and ap-
praisal; preparation of schematic, preliminary and
working drawings; and development of outline and
final specifications.
References
Architect's Handbook of Professional Practice, American
Institute of Architects, Washington, DC.
w, Caudill, Architecture by Team, Van NostrandReinhold,
New York (out ofprint).
Wordsand Terms
Architect Construction manager Electrical engineer
Mechanical engineer Structural engineer Value engineer
Needfor communication andcoordinationin the design team.
Responsibilities and skills of the design team leader.
Functions of thedesign team members: constructionmanager
andstructural, electrical,mechanical,andvalue engineers.
General References and Sources for
Additional Study
These are books that deal comprehensively with
several topics covered in this chapter. Topicspecific
references relating to individualchaptersectionsare
listed at the ends of the sections.
Architects Handbook of Professional Practice, (Publ. No.
A511), AmericanInstitute of Architects.(Volumes 1, 2,and
3).
D. Merdith et al., Design and Planning of Engineering
1985.
s. Andriole, Interactive Computer Based Systems Design and
Development, Van Nostrand Reinhold, New York, 1983.
A. Gheorghe, Applied Systems Engineering, Wiley, NewYork,
1982.
p. O’Connor, Practical Reliability Engineering, Wiley, New
York, 1985.
A. Dell’Isola, Value Engineering in the ConstructionIndustry,
Van Nostrand Reinhold, New York, 1983.
L. Zimmerman and G. Hart, Value Engineering: A Practical
Approach for Owners, Designers, and Contractors, Van
Nostrand Reinhold, New York, 1981.
EXERCISES
The following questions and problems are provided
for reviewof the individualsections and chapteras a
whole.
Section 1.1
1. What events made skyscrapers desirable and
practical?
2. What do general contractors do in the building
process?
3. What are the purposes of:
(a) building codes?
(b) zoning codes?
4. What do constructionmanagers do in the
building process?
Section 1.2
5. Describe two major ways of selecting a general
contractor.
6. Name the major steps in the traditionalbuilding
procedure.
7. What documents are produced by the building
designers to form a part of the construction
contract.
8. Describe some ofthe disadvantages ofthe basic
traditional building procedure.
Section 1.3
9. What is accomplishedby:
(a) systems analysis?
(b) systems design?
10. What is the purpose of value analysis?
11. Describe the three essential parts of systems
design.

Section 1.4
12. Who is best qualified to be the leader of the
design team for implementation of systems
design? Why?
13. What responsibilities andtasksmay be assigned
to the construction manager?
General
14. What are the disadvantages of awarding a
contract to lowest bidder for:
(a) design of a building?
(b) construction of a building?
15. What provision is made in systems design to
insure that eachdesigncycle is an improvement
over the preceding one?
16. Compare the objectives of analysis, synthesis,
and appraisal.

23
Chapter 2
Basic Building Elements and Their
Representation
Overall optimization of the building systemis the
goalof systems design.Buildings,however,usually
are too complex for immediate, direct optimization
of the total system. Instead, it is first necessary to
synthesize subsystems that, when combined, form
the building system.Afternormaldesign studiesand
value analysis of these subsystems, they may be
replaced partly orentirely by bettersubsystems.This
cycle may be repeated severaltimes.Then,the final
subsystems may be optimized to yield the optimum
building system.
The subsystems usually are composed of basic
elements common to most buildings. For the
preceding processto be carried out,a knowledge of
these basic elements and of some of the simpler,
commonly used subsystems in which they are
incorporated is essential. This information is
provided in this chapter.
This chapteralso describesthe means by which
designers’ concepts of buildings, building elements
to be used and the manner in which they are to be
assembled are communicated to others,in particular
to owners, contractors and building department
officials. Subsystem design is discussed in later
chapters.
To simplify terminology,a building as a whole is
called a building systemin this book, or simply a
building. Major subsystems of buildings are called
systems; for example, floor systems, roof systems,
plumbing systems,etc.Two ormore componentsof
such systems may forma subsystem.
2.1. MAIN PARTS OF BUILDINGS
Nearly all buildings are constructed ofcertain basic
elements. For illustrative purposes, several of these
are indicated on the cross section of a simple, one-
story building, with basement, shown in Fig. 2.1.
Structure
To provide a flat, horizontal surface on which
desired human activities can take place,allbuildings
contain at least one floor.In primitive buildings,the
ground may be used as the floor.In betterbuildings,
the floor may be a deck laid on the ground or
supportedabove groundon structuralmembers,such
as the joist indicated in Fig. 2.1.
To shelter the uppermost floor, buildings are
topped with a roof, usually waterproofed to exclude
precipitation.Often it is necessary tosupporttheroof
overthe top flooron structuralmembers,suchas the
rafter shown in Fig. 2.1. For further protection
against wind, rain, snow and extreme temperatures,
the outerperimeterofthe floors are enclosedwith an
exterior wall extendingfromgroundtoroof(seeFig.
2.1). If the building extends below the ground sur-
face, for example, to provide a basement as

does the structure in Fig. 2.1, foundationwalls must
be furnished to carry the exterior walls and to keep
the earth outside fromcollapsing into the basement.
Unless the foundation walls can be seated on strong
rock, some sort ofsupport mustbe furnishedto keep
them from sinking into the soil. For this purpose,
spread footings,suchas those shown in Fig. 2.1, are
often used.These distribute the loadofthe walls over
a large enough area that settlement ofthe soilunder
the walls is inconsequential.
In most buildings,spacesforvarious activities are
enclosed,to separate themfrom each other,to form
rooms. The enclosures are called interior walls or
partitions.
Circulation
At least one partition or wall around a roomhas an
opening to permit entry or to exit from the room.
Such openings usually are equipped with a door, a
panel that can be moved to fill the opening, to bar
passage,orto clear the opening.Exterior walls also
have openings equipped with doors, to permit entry
to and exit fromthe building interior.
In multistory buildings,because there is one floor
above another, stairs are provided, for normal or
emergency use,to permit movement from one floor
to the next.Sometimes,stairways with movingsteps,
driven by electric power, called escalators, are
installed to move people from floor to floor. In
buildings with many floors, elevators, powered
lifting devices, are provided for vertical
transportation. In some buildings, such as parking
garages and stadiums, sloping floors, or ramps, are
used for movement between floors.
Environmental Control
To admit daylight to thebuildinginteriorand togive
occupants a view of the outdoors,the exterior walls
usually contain openings in which windows glazed
with a transparent material are inserted. The
windows, like the exterior walls in which they are
placed, must exclude wind, rain, snow and extreme
temperatures.Also,the windows often are openable
so that they can be used to ventilate the building
interior.
For maintenance ofdesirable indoortemperatures,
equipment usually must be installed for heating or
cooling, or both. Often, this equipment is
supplementedby ducts orpipes that conduct warmed
or chilled air or liquid to various rooms in the
building.In addition, chimneys are provided to vent
to the outdoors smoke andgases produced in burning
fuel for heating.

Basic Building Elements andTheir Representation 25
Plumbing
In most buildings, certain pipes referred to as
plumbing,must be installed.Some ofthese pipesare
necessary for bringing water into the building and
distributing it to points where needed. Other pipes
are essential for collecting wastewater, roof
rainwater drainage and sometimes other wastes and
conducting those substances out of the building, to
an external sewage disposal system. Still other
plumbing may be used to bring heating gas into a
building and distributeit to pointswhere needed;and
other plumbing is needed for venting air or gases
from some of the pipes, when necessary, to the
outdoors.
Also considered as part of the plumbing system
are associated valves, traps and other controls and
fixtures. The plumbing fixtures include sinks,
lavatories, bathtubs, water closets, urinals and
bidets.
Electrical Systems
In most buildings, electric equipmentandwiringare
provided to bring electric powerinto theinteriorand
distribute the power where needed, for lighting,
heating, operating motors, control systems and
electronic equipment. Lighting fixtures also are
consideredpart oftheelectricalsystem.Otherwiring
also is installed forcommunicationpurposes,suchas
telephone, paging and signal and alarm systems.
2.2. FLOORS AND CEILINGS
As mentioned in Sec. 2.1, floors provide the flat,
horizontal surfaces on which desired human
activities take place in a building. Primarily then, a
floor is a deckon which people walk, vehicles ride,
furniture is supported,equipmentrestsand materials
are stored.
Floor-Ceiling Systems
Often, for aesthetic reasons, for foot comfort, for
noise controlortoprotectthe deckfromwear,a floor
covering is placed atop the deck. In such cases, the
deck is called a subfloor.
When a flooris not placed directly on the ground;
for example, when a floor extends above a room
below,some means must be providedforsupporting
the deckin place. Forthis purpose,the deckmay be
propped up on such supports as walls, partitions or
columns (posts).Ifthe deckis made strong and stiff
enough, it can span unassisted between those
supports. Usually, however, supports are placed far
apart so as not to interfere with the roomlayout be-
low. As a result ofsuchspacing,thedeckwould have
to be too thick and too heavy to be self supporting.
In such cases, horizontal structural members, called
beams,have to beprovidedto carry theweight ofthe
deck and the loads on it to the vertical supports.
Figure 2.2 illustrates two of many types of floor
construction in use.Figure 2.2a shows a floorsystem
often used in houses. The plywood subfloor is
covered with carpeting. On the underside, the
subfloor is supported on
Fig. 2.2. Floor construction, (a) Plywood subfloor on
wood joists, (b} Concrete deck on steel beams.
wood structural members, called joists. (Joist is a
term generally applied to very light, closely spaced,
floor-beams.)Because theplywood is thin,thejoists
are closely spaced, usually 16 or 24 in. center to
center, to provide adequate support. Figure 2.2b
shows a floor sometimes used in office buildings.
The subfloor is strong and thick, often made of
concrete. It may be covered with linoleum, asphalt
or vinyltile, or carpeting.Beams forsupportingthis
floor may be placed relatively far apart and have to
be strong and stiff. They may be steel beams, as
shown in Fig. 2.2b, or concrete or timber beams.
The underside of the floor, including the
floorbeams, and decorative treatment that may be

applied to that side is called a ceiling.Alternatively,
a ceiling may be a separate element, or membrane,
placed below the subfloor and beams and usually
supportedby them.Figure 2.2 showsflat,horizontal
ceilings.
The plenum, or space, between deck and ceiling
belowin Fig. 2.2 need not be wasted.It can be putto
use for housing recessed lighting fixtures and as a
passageway for ducts, pipes and wiring. Otherwise,
space forthese elements,exceptthe lightingfixtures,
might have to be provided above the floor, where
space is much more valuable.
Fire Protection
Beams,whetherheavymembers orjoists,are critical
members. If they should be damaged, they might
bend excessively or break, causing collapse of the
floor and serious injury to building occupants.
Damage to beams might be caused by overloading
the floor, cutting holesin improperplaces in a beam
for passage ofpipesorducts,orby fire or high heat.
Overloading, however, usually is very unlikely.
Structuralengineersdesign beams formuch heavier
loads thanthose likely to be imposed.Holes,though,
sometimes are cut in the wrong places by ignorant,
improperly trained or careless construction
personnel. Proper supervision and inspection can
prevent this or at least institute corrective measures
before an accident results. Fire damage, like
overloading,can become a rare occurrence by good
building design.
Beams usually are made of concrete, wood, or
steel.These materials havedifferent fire resistances.
Concrete, if thick enough, can withstand fire for
hours. But wood structural members are slow
burning at best and combustible at worst. Steel
structural members, though incombustible, can be
damaged by fire, if the fire is hot enough and lasts
long enough.
Both wood and steel members, however, can be
protectedfromfire. A common method is to enclose
such members with a suitable thickness of an
insulating, incombustible material, such as concrete
or plaster. As an alternative, wood members can be
impregnated with fire- retardant chemicals.
Tests have been made to determine forhowlong a
time specific thicknesses of various materials can
protect structural components froma rapid buildup
of heat, called a standard fire. Based on the tests,
these thicknesses and components have been
assigned fire ratings. The ratings give the time, in
hours, that the various types of construction so
protected can withstand a standard fire. Building
codes,in turn,indicatethe minimumfire ratings that
building components should possess, depending on
type of building and how the building is used.
Concrete is an incombustible material with good
resistance to heat flow. When concrete floors are
constructedwith the thickness required forstructural
purposes, the floors usually are assigned a high-
enough fire rating to protect wood or steel beams
below from a fire above the floors. In such cases,
however,fire protection stillmay be required forthe
bottomand sides ofthe beams.Forsteelbeams,this
protectionmay be furnishedby complete embedding
of the beams in concrete, with a minimum cover of
1 or 2 in.; but this type ofconstruction is heavyand
therefore often undesirable. When this is the case,
the sides and,if necessary,the bottomofthe beams
can be sprayed with a lightweight, protective
material to a thickness of about 1 or 2 in. (see Fig.
2.3ứ), or the fire protectioncan be boxed out with 1-
or 2-in .-thick plaster or concrete (see Fig. 23b).
In many buildings,however,foraesthetic reasons
as well as for fire protection, the beambottoms and
sides are protected with a continu-
Conerata Floor or Roof
Plaatar
(a) (b)
Fig. 2.3. Fire protection for beams supporting a concrete
floor or roof, (a) With a sprayed-on insulating material,
(b} With boxing-in by insulating construction.
OUS ceiling, as shown in Fig. 2.2. Gypsum plaster,
gypsumboard, or insulating, acoustic tiles often are
used for such fire protection.
Thus, a floor-ceiling systemoften may consist of
a floor covering, subfloor, beams, fire protection,
plenumand ceiling.Floor-ceiling systems are further
discussed in Chap. 16.
2.3. ROOFS
The purpose of a roof, as indicated in Sec. 2.1, is
mainly to shelter the uppermost floor of a building.

Thus, the roof must exclude wind, rain and snow.
Generally, it is desirable also that the roof resist
passage of heat, to keep out solar heat in warm
weatherand to prevent heat fromescaping fromthe
building in cold weather. In addition, the roof must
be strong and stiff enough to support anticipated
loads,including wind,pondedrainwater,collections
of snow and weight of repairmen.
Roof construction resembles floor construction.
Usually,a roof, like a floor, has a top covering.For
a roof, however, the covering generally is wind
resistant and waterproof, and unless intended to
serve also as a promenade or a patio, the roof
covering is not so wearresistant as a floorcovering.
Called roofing,this waterprooflayerusually is thin.
Therefore, it is laid on a roof deck, which is similar
to the subfloorin a floor system.Also,as in a floor,
beams often have to be furnished to support the roof
deck, which has to span over the interior spaces of
the building. In addition, a ceiling may be placed
under and supported from the roof and beams.
Unlike a floor, however,a roofoften incorporatesa
layerof thermal insulation to resist passage ofheat.
Figure 2.4 illustrates two of many types of roof
construction in use. Figure 2.4a shows a cross
section througha slopingroofoftenused forhouses.
A deckis needed to support the roofing,which may
be roofing paper or felt covered by protective
shingles,tile orsimilar, relatively small,overlapping
elements.Theseare usually also part ofthe aesthetic
treatment of the building, because a sloping roof is
visible from the ground. In Fig. 2.4a, the deck is
shown supported on wood rafters, which are laid
along the slope of the roof and rest on the exterior
walls of the building. (Rafter is a term generally
applied to a light roof beam.) The rafters are closely
spaced, usually 16 or 24 in. on centers. Because of
the close spacing, a thin deck can be used; for
example, plywood. A deck this thin often is called
sheathing, as indicated in Fig. 2.4a, to denote its
primary role as an enclosure.
Fig. 2.4/? shows a flat roof, often used for
industrialoroffice buildings.The roofdeckis strong
and thick, frequently made of concrete.It usually is
covered with a continuous, bituminous,
waterproofing membrane. Structural members,
called purlins, for supporting this deck may be
placed relatively far apart and may be steel beams,
as shown in Fig.2.4/?, orconcrete ortimber beams.
(b)
Fig. 2.4. Roof construction, (a) Plywood sheathing on
sloping rafters, (b) Flat concrete deck on steel beams.
Just as is done for floorbeams, protection against
injury must be provided for roof beams. Fire
protection, in particular, can be furnished for roof
beams in the same way as for floorbeams, as
indicated in Sec. 2.2. Building codes indicate the
minimum fire ratings that roof construction should
possess,depending on type ofbuilding and howthe
building is to be used.
Thus, a roof-ceiling system often consists of
roofing, roof deck, beams, thermal insulation, fire
protection, plenum and ceiling. Roof systems are
further discussed in Chap. 15.
2.4. EXTERIOR WALLS AND OPENINGS
For many reasons, buildings are enclosed by walls
along theirperimeters.The most important reasonis
to shelterthe buildinginteriorfromwind,rain, snow
and extreme temperatures.
An exterior wall may be a single element orit may
consist of several elements. In the latter case, a
typical wall may be built with an exterior facing, a
backing, insulation and an interior facing.
In general,a wall, interiororexterior, may be built
in one of the following ways:
Unit Masonry. One basic way is to assemble a wall
with small units,such as clay brick, concrete block,
glass block, or clay tile, held together by a cement,
such as mortar.Figure 2.5shows a wallconsisting of
two vertical layers, or wythes, of clay brick.

Fig. 2.6. Concrete panel wall.
Panel Wall. A second basic way is to form a wall
with large units.A panel,for example, may be large
enough to extend from floor to ceiling and to
incorporate at least one window. Figure 2.6
illustrates sucha panel.Sometimes,however,a panel
need be only deep enough to extend froma floor to
a window above or below.
Framed Wall. A third basic way is to construct a
wall with thin,closely spacedstructuralmembers to
which interior and exterior facings are attached and
between which insulation may be placed.Figure 2.7
is an example ofa woodframed exteriorwall, viewed
from the inside, often used for small houses. The
vertical structural members, called studs, are tied
togetherat top andbottomwith horizontalmembers,
called plates. A continuous bracing member, called
sheathing, which may be plywood or a gypsum
panel,is attachedto theouterface ofthe studs.Ifthe
sheathing is notwaterproof,a waterproofingsheetis
fastened to its outer surface. Then, the exterior is
covered by a facing, which may be brick, wood
siding, asbestos-cement shingles or other finish
desired by the architect and the owner. Thermal
insulation may be installed between the studs. An
interior finish, such as gypsum plaster or
gypsumboard,usually is attached to theinteriorface
of the studs, to complete the wall.
Combination Walls. Because metals, brick,
concrete and clay tile are strong, durable and water
and fire resistant, one of these materials

often is usedasanouterfacing.To reducewallcosts,
a less-expensive material may be used as a backup.
Often,forexample, unit masonry may be usedas the
exterior facing with wood framing, or unit masonry
may be the backup with a panel facing.
Curtain Walls
An exterior wall may serve primarily as an en-
closure. Such a wall is known as a nonloadbearing,
orcurtain,wall. The wall in Fig. 2.6 is a curtain wall.
Supported by the floors above and below, the wall
need be strong enough to carry only its own weight
and wind pressure on its exterior face.
Load-bearing Walls
An exterior wall also may be used to transmit to the
foundations loads fromother building components,
such as other walls, beams, floors and roof. Such a
wall is known as a loadbearing wall, or, for short,a
bearing wall. Figure 2.5 shows a brick-bearing wall,
while Fig. 2.7 illustrates a wood-framed bearing
wall.
Openings
In Sec. 2.1, the necessityofdoors forentranceto and
exit from a building and the desirability ofwindows
are indicated. Openings must be provided for these
in the exterior walls.
Where such openings occur, structural support
must be provided over each opening to carry the
weight of the wall above as well as any other loads
on that portion of the wall. In the past, such loads
were often supported on masonry arches.Currently,
the practice is tocarry the loadonstraight,horizontal
beams.Formasonry walls,the beams,oftensteelan-
Fig. 2.7. Load-bearing wood-framed wall.

Fig. 2.9. Windows in an exterior wall.
Fig. 2.8. Lintels support the wall aboveopenings.
gles orrectangularconcretebeams,are called lintels
(see Fig. 2.8). In wood-framed walls, the beams are
called top headers.
Windows
In exterior walls, openings equipped with windows
substitute a transparent material for the opaque
walls. Such openings offer occupants a view of the
outside (see Fig. 2.9) or, for retail stores, provide
passersby a view of merchandise on display inside.
The transparent materialusually is glass,butplastics
also may be used.In eithercase,the material, called
glazing, generally is held in place by light framing,
known as sash.The combination ofsashandglass is
usually referred to as a window.
An important functionofwindows is transmission
of daylight for illuminating the adjacent building
interior. When windows are openable, the opening
may also be used to provide interior ventilation.
Many types of windows are available.
Supports, called a window frame, usually are
provided around the perimeter of the opening and
secured to the wall (see Fig. 2.8). For sliding
windows,the frame carries guides in which the sash
slides. For swinging windows, the frame contains
stops against which the window closes.
In addition,hardware must be provided to enable
the window to function as required. The hardware
includes locks,grips formoving the window,hinges
for swinging windows, and sash balances and
pulleys for vertically sliding windows.

Exterior-Wall System
As indicated in the preceding, an exterior wall may
have many components. It is not unusual for a wall
system to include interior and exterior facings,
backup, thermal insulation, windows, doors, and
lintels and otherframing around openings.Exterior-
wall systems are further discussed in Chap. 15.
2.5. PARTITIONS, DOORS, AND INTERIOR-
WALL FINISHES
As indicated in Sec. 2.1, interior walls or partitions
are used to separate spaces in the interior of
buildings. The terminterior walls often is reserved
for load-bearing walls, whereas the term partitions
generally is applied to nonloadbearing walls.
Neither interior walls nor partitions are subjected
to such strenuous conditions as exterior walls. For
example, they usually do not have to withstand
outside weather or solar heat, but they do have two
surfaces thatmust meet the same requirementsasthe
interior faces of exterior walls, as described later.
Because load conditions generally are not severe,
partitions may be constructed of such brittle
materials as glass (seeFig.2.10a), weak materials as
gypsum(see Fig. 2.102) and c), or thin materials as
sheet metal (see Fig. 2.10a). Some light framing,
however, may be necessary to hold these materials
in place.
Some partitions may be permanently fixed in
place. Others may be movable, easily shifted.
Still others may be foldable, like a horizontally
sliding door.
Load-bearing walls must be strong enough to
transmit vertical loads imposed on themto supports
below. Such interior walls may extend vertically
from roofto foundations (see Figs. 2.10J and 2.12).
Often,interior walls and partitions are required to
be fire resistant as wellas capable oflimiting passage
of sound between adjoining spaces or both.
Doors
Exterior walls are provided with openings for
permitting entrance to and exit from buildings (see
Fig. 2.8). These openings are equipped with doors
that open to allow entry or exit and close to bar
passage.Similarly, openings are provided in interior
walls and partitions to permit movement of people
and equipment between interior spaces. These
openings also are usually equipped with doors to
control passage and also for privacy.
Many types of doors are available for these
purposes. They may be hinged on top or sides, to
swing open or shut. They may slide horizontally or
vertically.Or they may revolve about a verticalaxis
in the center of the opening.
A lintel is required to support the portion of the
wall above the door. Additional framing, called a
door frame, also is needed for supporting the door
and the stops againstwhich it closes (see Fig. 2.11).
(b)
Fig. 2.10. Partitions, (a) Nonload-bearing. (Z>) Gypsumboard on metal studs, (c) Gypsumboard face panels
laminated to gypsum core panel. (Ờ) Load-bearing concrete interior wall.

Hardware
Builders’ hardware is a general term covering a
wide variety of fastenings and devices, such as
locks, hinges and pulleys. It includes finishing and
rough hardware.
Finishing hardware consists of items that are
made in attractive shapes and finishes and are
usually visible as an integral part of the completed
building. Door and exposed window hardware are
examples of finishing hardware.
Rough hardware applies to utility items that are
not usually finished for attractive appearance.
Rough hardware includes nails, screws, bolts, and
window sash balances and pulleys.
In addition,hardware must be furnished to enable
the door to function as required. For example, a
swinging doormust be provided hingeson which to
swing.Also,a lockorlatch usually is neededto hold
the door in the closed position. A knob or pull is
desirable for opening and closing the door and
controlling its movement.
Fig. 2.12. Load-bearing concrete wallsupports concrete
floors in a multistory building. Floors and walls were
prefabricated away from the building site. (Courtesy
Formigli Corp.)
Interior-Wall Finishes
The inside faces of exterior walls and faces of
interiorwalls and partitions that are exposed toview
in rooms, work areas or corridors should usually
satisfy such requirements as attractive appearance,
easy to clean, durable under indoor conditions and
inexpensive maintenance. Preferably, the facings
should be fire and water resistant and also should
have acoustic properties appropriate to the space
enclosed.
A wide variety of finishes are used for interior
walls. In residential and commercial construction,
plaster and gypsumboard, with paint or wallpaper
decorative treatment,are often used because ofgood
fire resistance. Sometimes, however, plywood,
fiberboards or plastics are chosen for aesthetic
reasons. For factories or schools, where harder or
perhaps chemicalresistant finishes are desired,unit-
masonry or tile surfaces often are left exposed or
given a tough,decorative coating.In restaurants and
theaters,in contrast,acoustic requirements are given
high priority, though fire resistance and aesthetics
also are important.
Interior-Wall System
As indicated in the preceding, an interior wall or
partition may have several components. Often, an
interior-wall systemmay include a facing on one or
two sides, a backup, means of attachment to floors
and ceilings, doors and lintels or other framing
around openings.Interiorwallsystems anddoors are
further discussed in Chap. 16.
FOR SECTIONS 2.1 THROUGH 2.5
Fig. 2.11. Door and frame.

References
c. Ramsey and H. Sleeper, Architectural Graphic Standards,
8th ed., Wiley, New York, 1988.
Wordsand Terms
Beam Plenum
Ceiling Purlin
Curtain wall Rafter
Deck Roofing
Ducts Sash
Fire rating Sheathing
Glazing Spreadfooting
Joist Stud
Lintel Subfloor
Masonry Thermal insulation
Partition Vents
Piping Wiring
Plate Wythe
Significant Relations, Functionsand Issues
Components of building elements: structure, surfacing
(structural decks, sheathing), finishes (roofing, flooring,
etc.), enhancements (thermal insulation, weather seals, fire
protection, etc.).
Floor functions andfeatures: horizontal surface, facilitation of
activities, support of suspended items (ceiling, equipment,
etc.), creation of plenum, fire separation.
Roof functions: drainable surface, exclusion of precipitation,
insulation of buildingexterior, support ofsuspendeditems,
facilitation of openings (chimneys, vents, ducts, skylights,
etc.).
Exterior wall functions: insulationof buildingexterior, major
exterior building appearance, facilitation of openings for
windows and doors.
Interior wall functions: interior space andcirculationcontrol,
separation for fire, acoustics and security, ease of
rearrangement if nonstructural.
Circulation elements: doors, stairs, elevators, escalators and
ramps.
2.6. STRUCTURAL
FRAMING AND FOUNDATIONS
Sections 2.2 and 2.3 indicate that floors and roofs
must be strong and stiff enough to span alone over
spaces below or else beams must be provided to
support them.In eithercase,decksorbeams mustbe
propped in place. For this purpose, additional
structural members must be provided.
Sometimes, load-bearing walls can be used, as
pointed out in Secs.2.4 and 2.5 (see also Fig. 2.12).
In other cases, especially when beams support the
floors or roof, strong, slender, vertical members,
called columns,are used.If,however,columns were
used under every beam, the building interior might
become objectionably cluttered with them. So,
instead, the beams often are supported on strong
cross beams,called girders,whichthen are seatedon
the columns (see Fig. 2.13). This type of
construction is called skeleton framing.
Foundations
The vertical supports forfloors and roof must carry
all loads to foundations situated at orbelowground
level. The ground is the ultimate support for the
building.
Foundations are the structural members that
transmit building loads directly to the ground.
Usually, foundations are built of concrete, because
this material is strong and durable.
When a building has a basement,it is enclosed in
continuous foundation walls, to exclude the
surrounding earth. In that case, perimeter, or
exterior, walls and columns ofthe upperpart of the
building (superstructure) may be seated on the
foundation walls.
When there is no basement, foundations should
extend into the ground at least to the frost line, the
depth belowwhich the groundis not likely to freeze
in cold weather.Freezing and thawing ofthe soilcan
cause undesirable movements offoundations seated
on that soil.
Ordinarily, soilwill settle excessively ifcalled on
to support a column or wall directly, so walls are
spread out at the base to distribute the loads they
carry over large enough areas that settlement is
inconsequential. The spreadout base under a wall
is known as a continuous spread footing (see Fig.
2.14tf). Similarly, if column loads are to be
distributed directly to the ground, each column is
seated on a broad, thick pad, called an individual
spread footing (see Fig. 2.14/?). Sometimes,
however, soil is

SO weak that the spread footings for columns
become so large that it becomesmore economicalto
provide one huge spread footing for the whole
building. Such a footing is called a raft, or mat,
footing and occasionally a floating foundation.
When the soil is very weak, spread footings may
be impractical. .In such cases,it may be necessaryto
support the columns and walls on piles. These are
structural members very much
(b)
Fig. 2.14. Spread footings, (a) Continuous footing for
wall. (b) Individual footing for column.
like columns, except that piles are driven into the
ground.Usually,severalpiles are requiredto support
a column ora wall. Consequently,a thick cap,orpile
footing, of concrete is placed across the top of the
group ofpiles to distribute theload fromthe column
or wall to the piles (see Fig. 2.15).
Fig. 2.15. Pile footing for column.
Fig. 2.13. Skeleton framing of structural steel for a multistory building. Inclined columns are used to increase
spacing of exterior columns in the lower part of the building. (Courtesy United States Steel Corp.)

Lateral Stability
Walls and columns by themselves have good
capability for supporting the weight of a building
and its contents (gravity loads). Not all building
loads are vertical, though.Wind orearthquakes,for
example, may impose horizontal forces on the
building. Walls or columns alone may not be
adequate to withstand these lateral loads, which, if
not resisted, could destroy the building in either of
two ways: Horizontal loads may overturn the
building or they might collapse it like a house of
cards. If adequate precautions are not taken, the
horizontal loads might rack rectangular beam-
column or beam-wall framing into a flattened
parallelepiped.
To prevent overturning, height-width and height-
thickness ratios of buildings must be kept within
reasonable limits. Also, column bases must be
anchored to prevent uplift.
To prevent a rackingfailure,the structuralframing
must be designedto transmit the horizontalforcesto
the ground. Several means are available for doing
this.
One way is to provide diagonal members, called
bracing. These work with beams and columns or
other structural members in transmitting horizontal
forces to the foundations and from them to the
ground (see Fig. 2.16ứ).
Anotherway is tomake rigid connections between
beams and columns, to restrict rotation of these
joints (see Fig. 2.16Z?). Then, the lateral loads
cannot distort the rectangular beamcolumn framing
into a parallelepiped.
Still another way is to provide long walls, called
shear walls,in two perpendiculardirections (see Fig.
2.16c). Because a wallby itselfhas lowresistanceto
horizontal forces acting perpendicular to its faces
although it has high resistance to such forces acting
parallelto its faces,one wallalone cannotresistwind
or earthquake forces that may come from any di-
rection. But no matter in what direction the forces
may act, two perpendicular walls can resist them.
Fire Protection
Sections 2.2 and 2.3 point out that fire protection
may be required forfloors and roofs,and especially
for beams, and describe how such protection
generally is provided.Similarly, fire protectionmay
be required for columns and bracing.
Bracing in buildings where fire protection is
required often is encased in floors,roof or walls. In
such cases, the encasement usually provides
adequate fire protection.
Columns also may be encased in walls that
provide adequate fire protection. Otherwise,
columns may be encased in concrete or enclosed in
boxed-out fireproofing, much like the beamin Fig.
2.3b.
Structural System
From an overall view, the structuralsystemmay be
consideredto consist ofload-bearingwalls,skeleton
framing (beams and columns), bracing, shear walls
and foundations. Because foundation design has
become a specialty, the structural system is
sometimes partitioned into two systems:
foundations,orsubstructure,andsuperstructure,the
Fig. 2.16. Lateral bracing of buildings to resist horizontal loads, (a) X bracing, (Ô) Rigid-frame construction, (c)
Shear walls.

walls and framing above the foundations.Structural
systems are further discussed in Chap. 8.
FOR SECTION 2.6
References
M. Salvador!, Structure in Architecture: The Building of
Buildings, 3rd ed., Prentice-Hall, Englewood Cliffs, NJ,
1986.
J. Ambrose, Building Structures, Wiley, New York, 1988. F.
Merritt, BuildingDesign and ConstructionHandbook,4thed.,
McGraw-Hill, New York, 1982.
Wordsand Terms
Beam Rigid connections
Bracing Shear walls
Column Skeleton framing
Frost line Spreadfootings: continuous,
Foundations individual
Girders Substructure
Lateral stability Superstructure
Piles
Nature of structural system: skeleton framing versus bearing
wall.
Foundation issues: depth below grade (to bottom of con-
struction, to good soil, below frost line), type (spread
footingor deep—pile orcaissons), size for loadmagnitude.
Lateral stabilityissues: type ofbracing, critical load—windor
seismic, three-dimensional stability.
Relation of superstructure to substructure.
2.7 PLUMBING
The main functions ofplumbing are twofold:
1. To bring waterand also heating gas,ifdesired,
fromsourcesoutsidea building toplacesinside
where they are needed
2. To collect wastewaterandstormwaterat points
inside the building,oron the roof,orelsewhere
on the site and todeliverthesewastestosewers
outside the building
Execution of these functions of plumbing
primarily requires water, air, gas and pipes. Also
needed, however, are the following:
1. Fixtures for utilizing water,such as lavatories,
drinking fountains, bathtubs and showers
2. Fixtures for receiving waste water and
stormwater, such as water closets, urinals and
drains
3. Control and safety devices, such as valves,
faucets and traps
4. Storage tanks and pumps
5. Vents for removal of gases generated in the
wastewater systemor by combustion
6. Fire fighting devices, such as detection
devices, alarms, sprinklers, hoses and hose
valves
Water
Availability of good waterin adequate quantity is a
prime consideration in locating, designing and
constructing any building. Usually, there must be a
potable supply ample to meet the needs of all who
will reside,work or visit in the building.In addition
to this basic domestic need,there must be waterfor
heating, air conditioning, fire protection and
wastewater disposal. Also, for industrial buildings,
there are numerous process uses plus a vast
equipmentcooling job forwater.It is the function of
the plumbing systemto transport the needed water
from points of entry into the building to points of
use.
Heating Gas
This is an optionalfuel often selectedforbuildings.
Because the gas can formexplosive mixtures when
air is present,gas pipingmust be absolutely airtight,
not only to prevent gas from escaping but also to
prevent air fromentering.
Wastewater Disposal
The ability to get rid of wastes is as important a
consideration in building design as water supply.
Even for a small house with the normal small flow
of domestic sewage, early determination is
necessaryas towhethersewers are available and can
be connected to easily; or if not, whether local
regulations or physical conditions permit other
economic means of disposal, such as cesspools or
septic tanks. For big industrial buildings requiring
large quantities of water for cooling and processes,
site selection may well hinge on available and
allowable means ofwastewaterdisposal.The cost of
bringing water into a building may prove small
compared to the cost of discharging the water after
use in a conditionacceptable to thoseresponsible for

preventing pollution of the environment. When
wastewater cannot be discharged untreated into a
public sewer, the alternative usually is provision by
the building owner of sewage treatment facilities.
The responsibility of a building’s plumbing
systemfor wastewaterremovalextends frompoints
of reception inside the building to a public seweror
other main sewer outside.
Plumbing Code
Because improperfunctioningofany plumbing in a
building can impairthe health orsafetyofoccupants
and possibly others in the community, state and
municipal regulations have been established to
govern plumbing design and installation. These
regulations often incorporate or are based on the
“National Plumbing Code,” which has been
promulgated by the American National Standards
Institute as a standard,designated A40.8.This code
gives basic goals in environmentalsanitation andis
a useful aid in designing and installing plumbing
systems in all classes of buildings.
Plumbing systems are further discussed in Chap.
9.
2.8. HEATING, VENTILATING, AND AIR
CONDITIONING (HVAC) SYSTEMS
Two issues regarding the building interior are
usually combined for design purposes. The first is
the need for fresh, clean air, described as the need
for ventilation, and the second is the need for
thermal control. Systems design to achieve control
of these two conditionsare often combined,but it is
also possible to do the two tasks separately.
Ventilation is needed in the interior of a building
to supply clean air for breathing and to remove
odors, tobacco smoke, carbon dioxide and other
undesirable gases. Ventilation, however, also is
useful for drawing warmor cool air into a building
from outdoors to make the interior more
comfortable. For this purpose, large quantities of
outdoorair often are needed,whereasmuch smaller
quantities of fresh air usually are essential for the
prime objective of ventilation.
If an interiorspacehaswindowsthat are openable,
the simplest way to ventilate it is to open the
windows. This method, however, often is
impractical or cannot be used (see Sec. 10.6).
When natural ventilation cannot be used, me-
chanical ventilation is necessary.In suchcases,fans
are used to draw fresh air into the building and to
distribute the air to interior spaces. Often, the air is
filtered to remove particles in it before it is
distributedwithin the building.Whenit is necessary
to ventilate remote orwin-do wless spaces,fresh air
can be distributed throughconduits orducts to those
spaces.
In many cases,freshaircan be introduced directly
into interior spaces only in mild weather. In cold
weather, the air must first be heated, and in hot
weather,the airmust first be cooledorthe occupants
will be made uncomfortable.
General conditioning of ventilating air may
involve many concerns, depending on the nature of
building activities andthat ofthe climate andgeneral
environment outside the building.In warmclimates,
where cooling is generally the more critical
problem—instead ofheating—it is usualto combine
ventilation and general thermal conditioning in a
single operation. In very cold climates, however,
adequate heating of large masses of cold air is usu-
ally not practical.Hence only the minimum volume
of air required for ventilation is heated. General
building heating in cold climates is mostly achieved
by other means. In many cases, in fact, unless the
building exterioris very tightly sealed,ventilationin
very cold weather is assumed to be adequately
achieved by the leaking of air into the interior
throughcracks around doors andwindows andother
construction joints. In the latter case, however,
interior spaces at some distance from the exterior
walls may still need some form of mechanical
ventilation.
HVAC Systems
A wide variety ofsystems are available for heating,
ventilation and airconditioning (HVAC). Basically,
they may be divided into two classes: central plant
and unit.
A central-plant system concentrates heating or
cooling sources in one area to serve a substantial
portion of a building or one or more buildings.
A unit systemhas two ormore heating orcooling
sources throughout a building.
For example, a house with a furnace in the
basement has a central-plant system, whereas one
heated by a fireplace or stove in each of several

rooms has a unit system. An industrial building
heated with steamfroma boilerin a boilerroomhas
a central-plant system,whereasa building heatedby
direct-fired heaters in strategic locationsthroughout
production and storage areas has a unit system.
The two classes differ not only in sizes and
capacities ofequipmentrequired but alsoin methods
of delivering heating and cooling to points where
needed. Central-plant systems generally require
conduits,pipesorductsfordistributionofheating or
cooling media.Unit systems,in contrast,usually can
supply heating and cooling directly to the spaces
requiring them. Often, however, central-plant
systems give better distribution and are more
economical to operate, though initial costs may be
higher.
Humidity
An important factor affecting human comfort or, in
some cases, a desirable industrial environment is
humidity. Building air almost always contains
humidity, some water in vapor form. The relative
amount of this vapor influences the comfort of
building occupants, depending on the temperature.
In some cases, humidity is necessary for
manufacturing processes and in other cases, it is
undesirable,for example, for some storage spaces.
When a building is heated, the relative humidity
decreases unless moisture is added to the air. If the
air becomes too dry, occupants will become
uncomfortable. Hence, it is often necessary to add
moisture to building airduring the heating season.
In hot weather,highhumidity willmake occupants
of a building uncomfortable.In such cases,removal
of moisture fromthe air is desirable.
Consequently, a HVAC system should not only
provide appropriate temperatures within a building
but also control the humidity.
HVAC is discussed in more detail in Chap. 10.
2.9. LIGHTING
Illumination is a necessity in a building. Without
light, humans cannot see and are unable to perform
many essential activities. Furthermore, moving
about would be hazardouswithina building,because
of potentialcollisions with unseen objects,the peril
of tripping and the danger of falling down stairs.
Good lighting, for a specific building function,
requires an adequate quantity of light, good quality
of illumination and proper colors. These
characteristics are interrelated; each affects the
others. In addition, effects of lighting are
significantly influenced by the colors, textures and
reflectivities of objects illuminated.
Illumination of a building interior may be
accomplished by natural or artificial means.
Natural illumination is provided by daylight. It is
broughtinto a building throughfenestration,suchas
windows in the exterior walls or monitors or
skylights on the roof.
Artificial illumination usually is accomplished by
consumption of electric power in incandescent,
fluorescent, electroluminescent or other electric
lamps and occasionally by burningofcandles,oroil
or gas lamps. For artificial lighting, a light source
usually is enclosed in a housing, called a luminaire
or lighting fixture, which may also contain devices
for directing and controlling the light output.
Electric poweris conductedto the light sources by
wires. Manual switches for permitting or
interrupting the flow of electric current or dimmers
for varying the electric voltage to light sources are
incorporated in the wiring and installed at
convenient locations for operation by building
occupants.
Luminaires are mounted onorin ceilings,walls or
on furniture.The fixtures may be constructedto aim
light directly on tasks to be performed or objects to
be illuminated or to distribute light by reflection off
walls, ceilings, floors or objects in a room. Electric
wiring to the fixtures may be concealed in spaces in
walls or floors or between ceilings and floors orex-
tended exposed from electric outlets in walls or
floors.
Thus, a lighting system consists of fenestration
(windows, monitors, skylights, etc.), artificial light
sources, luminaires, mounting equipment for the
lighting fixtures, electric wiring, ceilings, walls,
floors and control devices, such as switches,
dimmers, reflectors, diffusers and refractors.
Lighting systems are furtherdiscussed in Chap. 11.
2.10. ACOUSTICS
Acoustics is the science of sound, its production,
transmission and effects. (Sound and vibrations are

closely related.) Acoustic properties of an enclosed
space are qualities that affect distinct hearing.
One objective of the application of acoustics to
buildings is reduction or elimination of noise from
building interiors. Noise is unwanted sound.
Acousticalcomfort requiresprimarily the absence of
noise. In some cases, noise can be a health hazard;
for example, when sound intensity is so high that it
impairs hearing.If production ofnoise in a building
is unavoidable,transmissionofthe noise frompoint
oforigin to otherparts ofthebuildingshould be pre-
vented. Accomplishment of this is one of the
purposes of acoustics design.
Another objective of acoustics applications is
provision of an environment that enhances
communication, whether in the form of speech or
music. Such an environment generally requires a
degree of quiet that depends on the purpose of the
space.Forexample, the degree ofquiet required in a
theater may be much different fromthat acceptable
in a factory.
In many building interior situations a major
concern is for the establishment of some degree of
acoustic privacy. This may relate to keeping
conversations from being overhead by persons
outside some private space,orto a need forfreedom
fromthe intrusionofsounds—thelatterbeing a form
of noise control. Separations between adjacent
apartments, hotel rooms, classrooms, and private
offices commonly presentconcern forthese matters.
Installations in a building for sound control may
be considered parts of an acoustical system. But it
generally will be more efficient if acoustical
installations and measures are integrated in other
major building systems orsubsystems.Forexample,
design of partitions, walls, ceilings and floors
should,fromthe start,havethe objective ofmeeting
acoustical requirements. Tacking on acoustical
corrections after design or construction has been
completed can be costly and notnearly as effective.
Acoustical design is discussed in more detail in
Chap. 12.
2.11. ELECTRIC SUPPLY
Electric power for buildings usually is purchased
froma utility company,publicly orprivately owned.
Sometimes, however,batteriesora generating plant
are provided for a building to supply power for
emergency use. Occasionally, a generating plant is
installed for normal operation. This may be
necessary for buildings in remote locations or for
industrial buildings with large or special needs for
power that make generation in their own plants
economical or essential.
In a building,electric powerfinds a wide range of
uses,includingspace heating; cooking;operationof
motors, pumps, compressors and other electric
equipment and controls; operation of electronic
devices, including computers; transmission of
communication signals; and provision of artificial
illumination and otherradiation,such as ultraviolet,
infrared and X ray.
Electric poweris broughtfroma generating source
throughcables toan entrance controlpointandoften
to a meter in a building. From there, electricity is
distributed throughout the building by means of
additional conductors. Where needed, means are
furnished for withdrawing electric power from the
system for operation of electric equipment. Also,
controls forpermitting flowofelectricity orshutting
it off, and devices for adjusting voltages, are pro-
vided at points in the distribution system. In
addition, provision must be made to prevent
undesirable flow of electricity fromthe system.
Accident Prevention
Even a relatively low-powersystemsuch as that for
a small house can deliver devastating amounts of
power. Hence, extraordinary measures must be
taken to insure personal safety in use of electricity.
Power systems must be designed and installed with
protection of human life as a prime consideration.
Also,should electricity be unleashed in unwanted
places, perhaps as the result of electrical
breakdowns, not only may electric components be
destroyed but, in addition, other severe property
damage may result, including fire damage. In
industrial plants, production equipment may be put
out of commission. As a result, replacement and
related delays may be costly.In some cases,merely
shutting down and restarting operations because of
an electrical breakdown may be expensive.
Consequently, safety features must be incorporated
in the power systemfor protection of property.
For safety reasons,therefore,state and municipal
regulations have been established to govern system
design and installation. These regulations often
incorporate orare based on the “NationalElectrical
Code,” sponsored by the National Fire Protection
Association. This code, as well as the legal

regulations, however, contain only minimum
requirements for safety. Strict application will not
insure satisfactory performance of an electrical
system.More thanminimumspecificationsoftenare
needed.
Electrical Systems
Generally, buildings may be considered to in-
corporate two interrelated electrical systems. One
system handles communications, including
telephone, video monitoring, background music,
paging, signal and alarm subsystems. The other
systemmeets the remaining electrical power needs
of the building and its occupants.
Both systems have as major elements conductors
for distribution ofelectricity,outlets fortappingthe
conductors forelectricity and controlsforturningon
or shutting offthe flow of electricity to any point in
the systems. The conductors and outlets may be
considered parts of an electrical subsystem; but it
generally will be more efficient if these subsystems
are integrated in other major building subsystems.
Forexample, design ofpartitions,walls,ceilings and
floors should,fromthe start,considertheseelements
as potentialconduits forthe electric conductorsand
possible housing for outlets.
Electrical systems are further discussed in Chap.
13.
2.12. VERTICAL-CIRCULATION ELEMENTS
Very important components ofmultistory buildings
are those that provide a means for movement of
people, supplies and equipment between levels.
Ramps
A sloping floor, or ramp, is used for movement of
people and vehicles in some buildings, such as
garages and stadiums. A ramp also is useful to
accommodate personsin wheelchairs in othertypes
of buildings.
Usually, however, a ramp occupies more space
than stairs, which can be set on a steeper slope.
People can move vertically along a much steeper
slope on stairs than on ramps. Stairs, then, are
generally provided,forboth normal and emergency
use.
Stairways
A stair comprises a set of treads, or horizontal
platforms,and theirsupports.Each tread is placed a
convenient distance horizontally fromand vertically
above a precedingtread to permit people to walkon
a slope fromone floorof a building to a floor above
(see Fig. 2.17). Often, a vertical enclosure, called a
riser, is placed between adjacent treads.A riserand
the tread

Basic Building Elements andTheir Representation
41
electric motors, may be provided for convenience
and rapid movement. Called escalators,these stairs
consist basically of a conveyor belt with steps
attached,motor,controls and structural supports.
Elevators
For speedier vertical transportation, especially in
tall buildings, or for movement of supplies and
equipment between levels, elevators usually are
installed. They operate in a fire-resistant, vertical
shaft.The shaft has openings,protected bydoors,at
each floorserved.Transportationis furnished byan
enclosed car suspended on and moved by cables
(see Fig.2.18a) orsupportedatop a pistonmovedby
hydraulic pressure (see Fig. 2.18b). The cable-type
elevator, driven by electric motors, is suitable for
much taller buildings than is the hydraulic type.
above often are referred to as a step. The steps of a
stairway can be made self supporting but generally
are supported on structural members. Stairs are
usually provided with railings along the sides, for
safety reasons.
Where two floors are connected by stairs, an
opening at least as wide as the stairs must be
provided in the upperfloor overthe stairs to permit
passage to that level. The opening must extend far
enough fromthe top of the stairs out over the steps
to preventpersonsusing the stairs frominjuring their
heads through collision with the ceiling, floor or
structural members at or near the edges of the
opening. For this purpose, adequate clearance, or
headroom, must be provided between every tread
and construction above.
Structural framing usually is required around the
perimeter of the opening to support the edgesofthe
floor. Also, railings or an enclosure must be
provided to prevent people or things from falling
through the opening (see Fig. 2.17). The enclosure
also may be required for fire protection.
Escalators
In buildings in which there is very heavy pedestrian
traffic between floors, for example, department
stores, moving stairs, powered by
Movement of Goods
When elevators are available, they may be used to
move freight to the various levels of multistory
buildings. For movement of small items, small
cable-suspended elevators,called dumbwaiters,may
be installed. For handling a large flow of light
supplies,suchas paperwork, vertical conveyors may
be provided. Belt convey-
Fig. 2.18. Elevators,(a) Cable type, (b) Hydraulic.
ors often are used in factories and storage buildings
for moving goods both horizontally and vertically.
Vertical circulation elements are discussed in
more detail in Chap. 14.
Third
Floor
Fig. 2.17. Stairs and floor openings.

References
B. Stein et aL, Mechanical and Electrical Equipment for
Buildings, 7th ed., Wiley, New York, 1986.
J. Flynn andw. Segil, Architectural Interior Systems: Lighting,
Air Conditioning, Acoustics, 2nd ed., Van Nostrand
Reinhold, New York, 1987.
Words and Terms
Acoustics Luminaire
Elevator Plumbing
Escalator Ramp
HVAC Stair
Illumination: natural, Ventilation: natural,
artificial mechanical
Functions of plumbing: supply and waste removal.
Functions of HVAC systems: air change andquality, thermal
control.
Aspects of lighting: visual tasks, natural illumination (day-
light), artificial illumination (electrical), components of
lighting systems (power, wiring, fixtures, controls).
Concerns for acoustics: hearing, privacy, noise control,
acoustic isolation, and separation of interior spaces.
Aspects of electrical systems: power source, distribution,
power level control,general flowcontrol (switches, circuit-
breakers, etc.), delivery devices, usage, communication
systems, signaling.
Vertical circulation components: ramps, stairs, elevators,
escalators, devices for movement of goods.
2.13. WHY DRAWINGS ARE NECESSARY
An architect or engineer designing a building may
have a fairly complete picture of the required
structure in his mind, but a mental picture at best
cannot be entirely accurate norabsolutely complete.
Too many items are involved,and thereare toomany
details that are impossible to design and correlate
with mental pictures alone. Consequently, the
designers’ mental pictures must be converted to
drawings on paper,filmorcloth,where conceptscan
be developed and completed.
Even if architects and engineers were able to
visualize accurately and completely in theirminds a
picture of the required building, they would find it
impossible to transmit exactly the same mental
picture to the building owner, consultants,
contractors, financiers and others interested in the
building. The concepts must be conveyed fromthe
designers to others concerned through construction
drawings, which make clear exactly what the
designers have in mind for the building.
Construction drawings (also called contract
drawings or working drawings) are picture-like
representations thatshowhowa building that is tobe
constructed will appear. They are also called plans
or prints.The lattertermrefers to reproductions that
are used for study, review, fabrication and
construction, to preserve the original drawings.
The drawings must show the builders what to do
in every phase of construction. In effect, they
constitutegraphic instructions to the builders.Every
detailof constructionfromfoundations to roofmust
be indicated, to show what has to be placed where
and how attached. This must be done in such a
manner as to avoid any confusion or
misunderstanding.
2.14. DRAWING CONVENTIONS
Construction drawings have to be made in a size for
convenient handling by thosewho haveto use them.
Hence, elements depicted are usually shown much
smaller than actual size. Also, to give an accurate
depiction of elements and their positioning in the
building,the drawings nearly always are prepared to
scale.
Each dimensionofan elementon a drawing bears
the same ratio totheactual dimension oftheelement
as does every other dimension shown to the
corresponding actual dimension.
Drawings, therefore, are miniature as well as
picture-like representations ofthe building,an exact
reproduction ofthe building ona smallscale.(Scales
are discussed further in Sec. 2.17.)
Because of the relatively small size of drawings,
however, many building components cannot be
shown on some drawings exactly as

they will look when installed in the building.
Consequently, designers have to use a special kind
of graphic language to indicate the many items that
they cannot actually picture.This language employs
symbols to represent materials and components that
cannot be reproduced exactly. Note, for example,
howwindows and doors are indicated in Fig. 2.19.
2.15. TYPES OF DRAWINGS
Several different types of drawings are required to
show all the information needed for construction of
a building. They form a set of construction plans.
Following are some of the types that might be
included:
Perspective drawings looklike pictures and often
are drawn to showa building ownera picture of the
building before construction begins.
Elevation views show what the exterior of a
building will look like. Usually,foursuch views are
required for an ordinary building. Elevation views
are discussed further in Sec. 2.18.
Plan views show what a building or its horizontal
components,suchas floors androofs,looklike when
viewed from above. A typical architectural plan
view shows the building interiorand indicates sizes,
shapes,and arrangementofrooms and otherspaces,
doors, windows, toilet fixtures, kitchen equipment,
and other needed information. A structural framing
plan indicates the location,orientation,andsizes and
gives other pertinent information for floor or roof
structural members, such as beams, girders, and
columns.An air-conditioning plangives similardata
for equipment, pipes, and ducts. An electrical plan
provides information on wiring, power-using
equipment,controls,and outlets that supply electric
power.Plan views are furtherdiscussedin Sec.2.19.
Section views are used to show the interior
construction ofvarious building parts.Sectionviews
are discussed in Sec. 2.21.
Detail views are used to provide required in-
formation about structural assembly, trim, and
various special equipment. Such views often are
given to supply information thatcannotbe shown in
the elevation,plan,orsectionviews.Detailviews are
discussed in Sec. 2.22.
.16’=8"
T
28'-4"
y3'-0"
12’-7” ---------Ị-*--------------- 12’-7”
Fig. 2.19. Arrows are used to give dimensions of drawings, (a) Floor plan for a one-room building, (b) Elevation
view of a door, (c) Alternate ways of showing dimensions, (d) The way to show the extent of a dimension line.
Dimension Line
1"
Extension Line
(d)

Survey plans supply information concerning the
site on which a building is to be constructed.Survey
plans are discussed in Sec. 2.23.
Plot plans show where a building is to be placed
on a site,howit is to be oriented in that location,and
howthe ground around the building is to be graded.
Plot plans are discussed in Sec. 2.23.
Originals and Prints
The single set of working drawings prepared by
designersis called an original.This one set could not
normally serve the purposesofallpersonsconcerned
with construction ofthe building.It is not practical,
however, for the designers to draw several sets of
identical plans. Hence, to provide the many sets of
plans needed, the original set is reproduced by a
duplicating process. The reproductions are referred
to as prints.(In yearspast,reproductionswere called
blueprints,because theywere made with white lines
on a blue background.Now,prints usually are made
with blackor brown lines on a white background.)
2.16. SPECIFICATIONS
It usually is impossible to provide on drawings all
the information necessary for construction of a
building. Some types of information, such as the
type ofbrick to be used to face a wall or the type of
windows to be incorporated in the wall, are best
provided in written form; but if such data were to be
written in notes on the construction drawings, they
would become so cluttered and confusing that
building construction would be hindered.
As a result, construction drawings are almost
always accompanied by separate written in-
structions, called specifications. These provide all
information concerning materials, methods of
construction, standards of construction, and the
mannerof conducting the workthat is not furnished
on the drawings.Thus,specificationssupplement the
drawings.Both are equally important toconstruction
of the building.
Specifications are discussed in Chap. 5, Sec.
5.4
2.17. SCALES AND DIMENSIONS
ON DRAWINGS
The process of drawing the parts of a building to a
proportionate size that can be contained on
convenient-size sheets ofpaperis called drawing to
scale. The drawings must be in exact proportion to
the actual dimensions of the components they
represent.Forexample, for most buildings,thescale
used makes the drawings the actual size. Thus,
instead ofdrawing a windowopening 3ft wide, the
designerdraws it 43 of 3 ft (36 in.), or|-in. long.As
a result, the drawing looks like the full-size
component but is only the size.
Selection ofa scale fora drawing depends bothon
the size of the sheet ofpaperto be usedand the size
of the building or components to be drawn. For an
ordinary building, elevations and plans often are
prepared to a scale of I" = l'-0". (One-quarter inch
equals one foot. On construction drawings, prime
marks are used to indicate feet, and double-prime
marks to indicate inches.) For detail drawings on
which types ofconstructionandmaterials are shown,
ị" = I’-O” or I" = l'-O" may be used; but if detail
parts are very small, and an easy-to-read drawing is
desired,3" =I'-O" may be chosen.Very smallscales,
such as I" = l'-O" and ĩ^" = l'-0", are generally used
for exceptionally large elevation views or for plot
and survey plans, to keep the overall size of draw-
ings within reasonable limits.
Title Block
Each of the several drawings comprising a set of
construction plans is provided with a title block. It
usually is placed at the lower right-hand corner of
the sheet. The title block shows the name of the
building, names of designers, type of drawing and
name ofcomponentshown.The title blockalsogives
other information, such as scale used, revisions and
date revisions were made.Forexample, a title block
might indicate in large letters that the drawingshows
the First-Floor Plan. If a single scale were used for
that drawing,that scale might be indicatedunderthe
type ofdrawing;forexample,underFirst-FloorPlan.
If a drawing contains parts drawn to differentscales,
each part should have a title given in large letters
directly under it, and the scale should be indicated
undereach title.Title blocks are furtherdiscussed in
Chap. 5.

Dimensions
Construction drawings would not permit con-
struction of the building intended by the building
ownerand the designersifthe drawingswere merely
a drawn-to-scale picture ofthe structure.Theymust
also show the dimensions of the building and its
parts.Everyone concerned wantstoknowthe length,
width and ceiling height ofeach room.Builders want
to know the wall thicknesses, foundation depth and
thickness, sizes and locations of window and door
openings,andnumerousothersize stipulations.Cost
estimators also need to know sizes because most of
the costs they calculate involve sizes of various
materials.
Size or space stipulationson drawings usually are
indicated by a systemoflines,arrows,and numbers,
called dimensions.
Despite the scale used for the drawing, di-
mensions give actual or full sizes or distances.
Figure 2.19a shows a plan view of a space en-
closed by four walls. The walls contain four
windows and a door. The drawing was made to a
scale ofI" = l'-0". (Reproductionofa drawing in this
book is done for illustrative purposes by a
photographic process and is unlikely to be to the
scale indicated.)The drawing showsthat the overall
dimensions of the enclosure are 30 ft by 28 ft 4 in.
(Feet are denoted by prime marks, and inches by
double prime marks.) Arrows indicate that the wall
is 12 in. thick. Windows are 4 ft wide and the door,
3 ft wide.
The limits of each dimension are indicated by a
pair of arrows. An arrow is called a dimension line
(see Fig. 2.19c). Each arrow terminates at an
extension line (see Fig. 2.19d). Thus, a pair of
extension lines shows where each dimension,
indicated by a setofarrows,ends.Numbers between
each pair of arrows give the actual size or distance
between the extension lines.
Figure 2.19b shows an elevation view that might
be used as a picture-like representation of a door.
This method ofshowing dimensions ofthe doorand
its parts is typicalfordoorsandotheritems forwhich
specialmillwork is required.Thus,ifa doororother
item of other than stock (standard) size is required,
the designer prepares a detail like the one in Fig.
2.19Z?, to show exactly what he has in mind. The
size ofeach part ofthe doorcan be determined from
the horizontal and vertical rows of dimensions.
Sometimes, different variations are used for
indicating dimensions. For example, when a single
dimension line with an arrowhead ateachendis used
to give a dimension,the numbergivingthe size may
be shown above oralongside the line.In some cases,
arrowheads may be replaced by dots.
2.18. ELEVATION VIEWS
An elevation view of an object is the projection of
the object on a vertical plane. Thus, an elevation
view shows what a vertical side of the object looks
like when viewed by someone facing that side.
To visualize an elevation of a building, imagine
that you can stand outside it so as to face squarely
one side ofit.The face will appearto lie in a vertical
plane. The image, to scale, of the building in the
verticalplane is an elevation.Because a rectangular
building has fourfaces,it also has four elevations.
Figure 2.20a is a perspective drawing of a one-
story house, on which the four directions in which
the walls face are indicated as north,south,east and
west. Thus, the house will have four elevations
correspondingly named,as shown in Fig. 2.20Z? to
e.
West Elevation
Imagine that you are standing at a distance fromthe
building and facing its west side squarely.You will
then see the west elevation (see Fig.2.20Z?). It was
drawn by projecting

the west sides of the building on a vertical north-
south plane.
The roofareas marked 6and 8on the elevation are
the same areas shown in the perspective marked 6
and 8. The chimney area,labeled 7 on the elevation,
is the same as the chimney side marked 7 in the
perspective.Similarly, the roofpoints marked e and
f are identicalin both perspective and westelevation.
The doors and windowslabeled 1,2,4 and 5 also are
the same in perspective and elevation. Points a and
c, at groundlevel,appear closetogetherin the eleva-
tion,though theyare shown relativelyfarapart in the
perspective.
The wall marked 14 in the perspective andshown
in the north elevation (see Fig. 2.20e) does not
appear as an area in the west elevation, because the
wall is perpendicular to the plane of projection.
Instead,wall14, when viewed fromthe west,is seen
as a vertical line and thus is indicated by a vertical
line above a on the west elevation.
East, North and South Elevations
The east elevation is obtained much like the west
elevation,by projectingtheeast sidesofthe building
on a vertical north-south plane. But the view is
drawn as seen fromthe east (Fig. 2.20J).
Similarly, the northandsouthelevations are drawn
by projecting thenorth and southsides,respectively,
on a verticaleast-westplane.Forthe northelevation,
the north sides are viewed fromthe north (see Fig.
2.20e). For the south elevation, the south sides are
viewed fromthe south (see Fig. 2.20c).
Note that no dimensions are shown in any of the
elevations in Fig. 2.20. In an actual construction
drawing, dimensions of the walls and openings in
themwould have been given.
2.19. PLAN VIEWS
A plan view shows what the interior of a building
looks like when viewed from above. While an
elevation view is actually a projection on a vertical
plane, a plan view is a projection on a horizontal
plane.For a floor plan,the view is usually obtained
by making an imaginary horizontal cut through the
building and then projecting the exposed parts on a
horizontal plane. For a roof plan, however,
visualizing a hori
(a) Isometric (b) Uest Elevation
(c) South Elevation (d) East Elavation (e) North Elevation
Fig. 2.20. Isometric and four elevations of a one-story house.

zontal cut is generally unnecessary, because roofs
are exposed to view fromabove.
Several types ofplan are used forconstructionof
a building. When a plan is drawn to show the size,
shape andlocationofrooms,it is called a floor plan.
When a plan showsthe structuralframing supporting
the floor, the view is called a floor framing plan.
Similarly, otherplan views may showductworkfor
HVAC, electric equipment and wiring, and other
information.
To visualize a plan view,imagine that the building
is cut horizontally and the top is removedsothat you
can look straight down at the cut surfaces. These
surfaces and the floor below will appear to lie in a
horizontal plane. The image, to scale, of the lower
part of the building is a plan view. (In some cases,
the view may be drawn as seen from below; for
example, for a ceiling plan,to showlighting fixtures
and air-conditioning outlets.)
Figure 2.21a is a perspective ofa one-story office
building, containing a reception room, office and
toilet (water closet,W.C.).Imagine the structure cut
throughhorizontally,as indicatedby thedashed line
from X to y, as if by a large saw. Imagine also that
the top part can be lifted so that you can lookdown
squarely at the surfaces cut along the lines abcdef
(see Fig. 2.2lb). The cut surfaces, shown in heavy
black, and the floor between them, shown in white,
constitute the plan view of the ground (first) floor
(see Fig.2.21c). Doors,windows and rooms,as well
as partitions and exterior walls, are all shown.
Note that no dimensions are given for the floor
plan in Fig. 2.21. In an actualconstruction drawing,
dimensions of walls, openings in the walls and
rooms would have been given.
For a multistory building, a plan view would be
drawn foreach floor,including basement,ifpresent,
and roof.
Cut surfaces are not always represented by heavy
black lines. Often, it is desirable to show the
boundaries,in detail,of a cut object.In those cases,
the cut surfaces may be indicated by a symbol.One
commonly used symbol is cross hatching, closely
spaced light lines, generally drawn at a 45° angle
with a main boundary. Sometimes, the symbol
selected represents a specific material, such as brick
or concrete.
2.20. LINES
Designers use different types of lines on drawings.
Each type ofline is applicable to a specific purpose.
Solid lines usually represent edges of objects.
Short dashes are used to indicate invisible edges,
boundaries covered by a part shown in the view
being drawn.Forexample, in the perspectivein Fig.
2.22a, which shows the exterior of a building, a
dashed line indicates the location of the ceiling,
because, in that view, it is hidden by the exterior
wall.
Dash-and-dot lines, made up of alternating long
and short dashes,generally are used as a centerline.
This is a line drawn to mark the middle of a building
or a component.A centerline,in addition,is labeled
with an inter
Fig. 2.21. Guide to visualization of a plan view, (a) Making a horizontal cut through a building, {b} Removing the
part above the cut. (c) Floor plan of the building.

Fig. 2.22. Guide to visualization of a vertical section. (a)
Making a vertical cut through a building, {b} Vertical
section of the building.
secting c and L. This representation is used for the
centerline of the construction, called a truss, in Fig.
2.23.
A heavy line,made upoflongdashes,oftenis used
to indicate where a building is to be imagined cut to
obtain a view, called a section. (The plan views
discussed in Sec. 2.19 are horizontal sections.)
Arrows are drawn at the ends of a section line to
indicate the direction in which to look to obtain the
view. Note that section linesneednotbe continuous,
straight lines but may have abrupt changesto show,
in one view, different cuts or levels.
Broken solid lines,with a wavy breakat intervals,
are used to indicate thatpartsofa drawinghave been
omitted or that the full length of some part has not
been shown.Such lines are usedalong the right side
of the truss in Fig.
2.23 to show that almost half the truss has been
omitted fromthe drawing.
2.21. SECTIONS
Seldom do elevation and plan views alone show
sufficient information to enable a builder to
determine exactly howthe various parts ofa building
are to be assembled and connected.Forexample, an
elevation view in Fig. 2.20 shows at what height
above ground a window is to be set, while the
corresponding floor plan would show how far the
window is to be placed from one end of the wall.
Also, the specifications for the building would
define the materials and their quality to be used for
the window. There are, however, many good ways
of constructing such a wall and window, and some
undesirable ways. Unless the builder is shown
exactly what the designerhas in mind,a type ofwall
may be built that will not please the designer. To
preclude such an event,designers provide additional
drawings, called sections.
A section shows theinteriorconstruction ofa part
of the building. This type of drawing indicates how
various structural components are to be assembled
and connected. Usually, sections are drawn to a
larger scale than plan and elevation views, because
sections are intended to show more detail.
In the explanation ofhowto visualize a plan view,
you were asked to imagine a building to be cut
through horizontally. A plan view actually is one
type of section. In general, however, to obtain a
section needed for specific illustrative purposes, a
designer may imagine the building cut through at
any angle. Usually, however, sections are taken
horizontally, vertically or sometimes perpendicular
to an inclined surface.This is convenientfordrawing
purposes,because building parts,such as floors and
walls are horizontal and vertical, respectively, and
structuralparts used in inclined surfaces,suchas the
framing in sloping roofs,generally are perpendicular
to each other.
To visualize a vertical section, for example,
imagine a building or one of its parts cut through
vertically and one part removedso that youcan look
squarely at thecut surfaces ofthe remaining portion.
The image, to scale, of the remaining portion is a
section view; that is,a verticalsection is a projection
on a verticalplane ofthe parts exposed by a vertical
cut.
Figure 2.22a shows a perspective ofa small, one-
story building.Imagine that the structure can be cut
through vertically along the lines between X and y.

The dashed line fg shows the path ofthe cut,which
goes through an opening for a door. Imagine now
that the part ofthe building labeled mis moved away
so that you can look squarely at the cut surfaces of
the n part. Figure 2.22b shows the resulting section
view.
The door is not shown in this view, because it is
imagined not installed at the time ofcutting.The cut
surfaces in this drawing are shown in black, but the
doorway is left white, because no surfaceswere cut.
In section views, including plans, cut surfaces
usually are indicated by some symbol.In Figs. 2.21
c and 2.22b, the cut surfaces are shown in solid
black.Sometimes,however,use is made ofa symbol
that represents the material that has been cut. For
example, concrete generally is represented by small
triangles in a matrix ofdots; plasterby dots;brickby
closely spaced lines at a 45° angle with the
horizontallines ofa drawing; and othermaterials by
similar conventional symbols.
If the designer does not intend to indicate a
specific material, he may use crosshatching,closely
spacedlines at a 45°angle.Fordifferent but adjacent
parts,crosshatchingis slopedin opposite directions,
to distinguish the parts.
Symbol lines are drawn much lighter than lines
representing edges.
The vertical section in Fig. 2.22b does not give
any dimensions. In an actual construction drawing,
dimensions would be shown for all the parts in the
section.
2.22. DETAILS
A detail view supplies information about structural
assembly, trim, and various special equipment that
cannot be givenin elevations,plans,orfull-building
sections. This has largely to do with the scale of
drawings. For example, elevations, plans, and full-
building sections are usually drawn at 4 in. equals
one ft (1:48) or smaller, so that they will fit on a
reasonably sized sheet whenprintedforuse.Details,
on the other hand, especially when drawn of very
small portions of the whole building, can be drawn
as large as full size—although scales of 1:4 (3 in.
equals one ft), 1:8 (1.5 in. equals one ft), or 1:16
(0.75 in. equals one ft) are more often used.
Many details are drawn as vertical sections,
although any formof drawing can be made large in
size for explanation of particular details of the
assemblage orthe formof individualparts.In some
cases, where ordinary orthographic projection (x-y-
z, right angle views, such as plans, elevations and
verticalsections)does notfully suffice toexplain the
assemblage, isometric or even perspective views
may be required for clarity.
Details views may generally be classified as
placement or assembly types. Placement details are
used to show the desired arrangement of objects in
the finished construction.Plans andelevations are of
this class,anddetailplans orelevations may be used
to explain objects in greater detail, such as the
arrangement offixtures in a bathroomorthe details
of a single window. Assembly details are used to
explain individual components (such as parts of the
structuralsystemorthe piping system).Figure 2.23a
is an example of an assembly detail,illustrating how
a wood truss forthe roofframing of a house is to be
assembled.The drawingshows a partialelevationof
the truss. As the truss is symmetrical, it is not
necessary to show the whole truss for the purposes
of the detail assembly drawing.
Fordetaildrawings it is common to showonly just
as much of the whole part as is necessary to clarify
the desired detailinformation.Specifications would
establish the type of wood and other detailed
information on materials, construction tolerances,
and so on. Notation on the detail view should be
limited to the identifications and dimensions thatare
specifically required to clarify the work. General
building dimensions should be indicated on plans,
elevations or full-building sections, and detailed
material information should be given in the

specifications.Repetitionof such informationallows
forthe possibility ofconfusionandconflict whenthe
information does notagreein different locationsdue
to error.
The exploded isometric view of Joint E, shown in
Fig. 2.23/?, more clearly indicates the form of the
parts and the assembly ofthe joint; for example, the
fact that there are gussetson both sides ofthe joint.
The note on the drawing actually calls for this, but
the isometric view drives the idea home.
Some of the most important drawings forbuilding
construction are the detail sections of the form
shown in Fig. 2.23c. These show the complete
construction assemblage, with arrangement of parts
and the identities oftheindividualmaterials made as
clear as possible. For persons trained to read such
drawings, they are very informative. Standardized
graphic symbols are used to indicate materials and
the notation uses terms carefully chosen to agree
Fig. 2.23. Construction detail drawings, (a) Elevation of a truss, {bi Exploded view of a truss joint—joint E in the
truss in (a), (c) Comprehensive architectural detail section, incorporating joint E of the truss.

with those used elsewhere on the construction
drawings or in the specifications.
While the comprehensive detail section in Fig.
2.23c is most useful for understanding the total
nature of the construction, the forms of individual
parts are often obscured by the complexity of such
views. Thus, to explain the truss assemblage—
although the truss appears in partial view in Fig.
2.23c—it is really necessary toremove the trussand
show it alone in the views in Figures 2.23a and b.
For the workers who perform the single task of
making the trusses,this is usefuland sufficient.For
this reason, the full set of building construction
contract drawings normally contains both fully
detailed architectural drawings and separate
drawings showingonly the structure,orthe electrical
components, or the plumbing, and so on.
2.23. SURVEY AND PLOT PLANS
Before land is purchased,the purchaser should have
a land surveyor survey the lot, for several reasons.
One reason is that the survey will indicate the exact
boundaries of the lot. Another reason is that most
municipalities require a survey plan of a lot for
establishment of ownership. Such a plan also is
required by a bankbefore it will make a loan forland
purchase or building construction. In addition, a
survey planis neededbyarchitectsand engineersfor
analysis of the property, to determine location of
buildings, access roads, walks, parking lots and
equipment.
A survey plan shows how a building site looks
when viewed from above. The plan should show
boundaries andexact dimensionsandgive elevations
(heights)ofthe land.Also,the drawingshould show
boundary streets and highways; utilities available,
such as water, gas and electricity; directions of the
compass; and topographic features, such as trees,
brooks and lakes.Survey plansare usually drawn to
a scale of 0.1"= 1.0'.
Figure 2.24 shows a surveyplan fora city lot.The
drawing indicates that the northern borderofthe lot
is an avenue in which there are a watermain and two
sewers. The drawing also shows that the lot is
rectangular,98X 158 ft in size, and containsseveral
trees.
The proposed building is not shown on a survey
plan but instead is drawn on a separate drawing,
called a plot plan. Developed fromthe survey plan,
the plot plan also is a view of the building site from
above; but the plot plan is used to showthe location
and orientation ofthe proposed buildings on the lot.
This plan should also indicate how the grounds
around the buildings are to be graded and where
walks, parking lots and storage areas are to be
located. In addition, it should provide other
information that builders need before they canstake
out the buildings and excavate forfoundations.Plot
plans are often drawn to a scale of jL" = l'-0".
Figure 2.25 shows a plot plandevelopedfromFig.
2.24 to show the location of a house to be built on
the lot. The area covered by cross hatching (closely
spaced 45°lines)represents the house.The drawing
indicates that the finished floorlevelofthe building
must be at Elevation 277. The front of the house is
to be 20 ft from the northern boundary. The
driveway is to be 18 ft wide, and the sidewalk
between porch and street, 4 ft 9 in. wide. Steps are
shown between porch and sidewalk.
Lines
On survey and plot plans,boundaries are represented
by a line consisting of a repeated set of a long dash
and two short dashes.Land elevations are indicated
by curved lines, called contours, drawn somewhat
lighterthan boundarylines.Utilities,such as sewers
and water mains, are represented by dashed lines.
Solid lines are used to indicate internal boundaries,
such as those of buildings and walls. Various
symbols are used to represent topographic features,
such as trees, swamps and waterways.
Elevations
Heights of points on a building site are determined
relative to a datum,orreference level,establishedby
the municipality or otherlegal authority.The datum
is assigneda specific elevation, such as 0 or 100 ft.

Fig. 2.24. Surveyplan prepared after a surveyof a city lot. Section and quarter lines shown are legal reference
lines for locating property boundaries.
Lincoln
Avenue
276 273.6
10' _______ 0 5' 10' 20' 30' 40' 50'
Scale
Fig. 2.25. Plot plan prepared from the surveyplan in Fig. 2.24, showing the location of the building and
regrading with fill to the dashed-line contour.

For convenience in surveying, other points of
known elevation, relative to the datum, may be
establishedin the region.These are knownas bench
marks. A bench mark 20 ft above a datum of 100
would be assignedan elevation of 100 + 20, or 120
ft. A bench mark 10 ft below this datumwould be
given an elevation of 100 — 10, or 90 ft. From
bench marks, surveyors determine with their
instruments the elevations of various points on a
building site.These pointsare usedto plotcontours.
A contouris a curved line thatconnectsallpoints
of the same level. For convenience, a contour may
be imagined as the waterline that would be formed
on the shore if a lake were to be created at the site
with water up to the level assigned to the contour.
For example, with the datumassigned an elevation
of 100 ft, a contourmarked 100 connects allpoints
on the site that are at the same elevation as the
datum. A contour marked 150 connects all points
that are 50 ft above the datum.
The closercontoursare,thesteeperis theslope of
the land. Note that contours can meet only at a
vertical cliff.
In Figures 2.24 and 2.25, elevations are shown
relative to a datumof100.Thus,thecontourmarked
276 is 176 ft above the city datum. Contours are
drawn for1-ft intervals ofelevation.(Ifthe property
were to be flooded by a lake to the 276-ft level, the
276 contourwould represent the waterline along the
shore throughout the site. Each time the lake were
to be lowered 1 ft, the waterline would lie along
another contour.) Between contours, elevations are
given in tenths of a foot to indicate the heights of
topographic features, such as trees.
The plot plan in Fig. 2.25 indicates that a fill is
required on the south side of the house. The
boundary ofthe fillis representedby the dashedline
28 ft from the terrace.
References
c. Ramsey andH. Sleeper, Architectural Graphic Standards,
T. French and c. Vierck, Engineering Drawing and Graphic
Technology, 13th ed., McGraw-Hill, New York, 1986.
R. Liebing and M. Paul, Architectural Working Drawings,
2nd ed., Wiley, New York, 1983.
F. Ching, Architectural Graphics, 2nd ed., Van Nostrand
Words and Terms
Bench mark
Constructiondrawings Contour lineDatum
Elevationdrawing
Perspective drawing
Plan drawing
Significant
Relations,
Functions, and
Issues
Purposes of drawings: communication of design information,
relation to specifications.
Relation of scale to level of detail possible in drawings.
Need to use conventional drawing techniques and symbols
and notation with terms that are compatible with speci-
fications, for clarity of communications.
GENERAL REFERENCES AND SOURCES
FOR ADDITIONAL STUDY
severaltopics coveredin this chapter.Topicspecific
references relatingto individualchaptersectionsare
F. Merritt,BuildingDesignandConstruction Handbook, 4th
J. Ambrose, Building Structures, Wiley, New York, 1988.
B. Stein et aL, Mechanical and Electrical Equipment for
Buildings, 7th ed., Wiley, New York, 1986.
F. Ching, Architectural Graphics, 2nd ed., Van Nostrand
EXERCISES, CHAP. 2
The following questions andproblems are provided
for review ofthe individualsections ofthe chapter:
Section 2.1
1. Name the following basic building elements:
(a) A horizontal structural member that
supports a deck above ground.
(b) A vertical wall that prevents earth from
coming into a basement.
(c) A horizontal element that keeps a
foundation wall from sinking into the
ground.
Plot plan
Scale
Section drawing
Specifications
Survey plan
Symbols

2. What are the purposesofthefollowing building
elements?
(a) Roof
(b) Windows
(c) Partitions
(d) Doors
(e) Chimney
(f) Plumbing
3. Describe two different ways of providing light
inside a building.
Section 2.2
(a) floor covering?
(b) ceilings?
5. Where are joists used and for what purpose?
6. The weight of a subfloor, floor covering, and
ceiling as well as loads from people and
furnishings are supported on a set of beams.
What may be used to support the beams?
7. From what source of information should you
obtain the fire rating required for an interior
wall of a building?
8. A floor systemhas been tested and assigned a
fire rating of 2 hr. What does this signify?
9. How is the fire rating of a building component
determined?
10. How can a wood beambe made fire resistant?
11. Describe two methods for protecting a steel
beamfromfire.
Sections 2.3 and 2.4
12. Describe the purposes of :
(a) A roof
(b) Roofing
(c) Thermal insulation incorporated in a roof
system
(d) Rafters
13. What is the main purpose of an exterior wall?
14. Why are exterior walls usually a combination
of different materials?
15. What is the primary difference between a
curtain wall and a bearing wall?
16. How does unit masonry construction differ
from:
(a) Panel construction?
(b) Framed construction?
17. Where is a lintel used?
18. Describe three important functions of a
window.
19. What provision is made in a wall opening to
receive a window?
Section 2.5
20. What are the major purposes ofinteriorwalls?
21. What prevents a doorthat is being closedfrom
swinging past the wall opening?
22. Builder’s hardware is classified either as
finishing or as rough. Which type are the
following?
(a) Doorknob
(b) Locks
(c) Nails
(d) Hinges
(e) Windows sash balances
23. What are the usual means of directly sup-
porting a door?
Section 2.6
24. What types of members are used in skeleton
framing?
25. What is the purpose of the following?
(a) Column
(b) Girder
(c) Bracing
(d) Rigid connection
(e) Foundation
26. Why is it desirable that footings be placed
below the frost line?
27. What must be done for safety reasons besides
just transmitting buildingloads to the ground?
28. For what soil conditions are the following
suitable?
(a) Spread footings
(b) Mat
(c) Piles
29. Describe some methods of protecting beams
from fire.
Section 2.7
30. What is the purpose ofwatersupply plumbing?
31. Why must gas plumbing be a sealed system?
32. What is the purpose ofwastewater plumbing?
33. Why is the presence of both water-supply
plumbing and wastewater plumbing in a
building a potential health hazard?

34. What consideration should be given to water-
supply and wastewaterdisposalin selection of
a site for a building?
Section 2.8
35. Why is ventilation necessary?
36. Why is mechanicalventilation used?
37. What effect on relative humidity does heating
of air have?
38. Why is it desirable to add humidity to a
building when it is heated in cold weather?
39. What effect does humidity have on building
occupants in hot weather?
40. Describe briefly the two types of HVAC
systems.
Section 2.9
41. What are the three factors that determine good
lighting?
42. Why should color of emitted light be con-
sidered in selection of a light source?
43. What are thetwo methodsusedforillumination
of the interior of a building?
44. Explain why walls, floors and ceilings should
be treated as parts of the lighting system.
Section 2.10
45. When doessoundbecome noise?
46. Which requiresgreatersoundcontrol:an office
building or a factory? Why?
47. Why should acoustics be considered in design
of ceilings, walls and floors?
Section 2.11
48. How is electricity distributed in a building?
49. Why is placement of electrical conductors
within walls, floors or ceilings desirable?
50. What should controls do in an electrical
distribution system?
51. Why is safety a prime consideration in design
of an electrical system?
Section 2.12
52. Define a ramp.
53. What advantages do:
(a) Stairs have over ramps?
(b) Elevators have over escalators?
54. What effect on the slope of stairs does the
following have?
(a) Decreasing the width ofthe treads with no
change in risers.
(b) Decreasing the height of risers with no
change in the treads.
55. What is the purpose of headroom?
56. Describe two commonly used methods for
propelling elevator cars.
57. What is the purpose of a dumbwaiter?
Sections 2.13 to 2.15
58. What is the purpose of construction drawings?
Of specifications?
59. Give two reasons why drawings are drawn to
scale.
60. Why are symbols necessary for construction
drawings?
61. How does a perspective drawing of a building
differ from an elevation view of the same
building?
62. What does a floor plan show?
63. What does a section view show?
64. In what views in construction drawings would
you find information on each ofthe following?
(a) Height of windows above a floor
(b) Arrangement of rooms
(c) Location of doors in partitions
(d) Arrangement offloorbeams for the second
floor of a building
(e) Construction of window framing
65. Howdoes a survey plandifferprimarily froma
plot plan?
66. What information do specifications provide?
67. Why are specifications necessary?
68. How can you tell what scale was used for a
drawing?
69. What distance is represented by a line 2-in.
long when the scale is:
(a) I in. = 1 ft?
(b) I in. = 1 ft?
(c) 3 in. = 1 ft?

Section 2.18
70. How is the elevation view of the side of a
building facing northeast obtained?
71. In Fig. 2.20, in what elevation would you look
to find:
(a) The number of windows in wall 14?
(b) The location of garage door 1?
(c) Material used for the outer facing of wall
16?
Section 2.19
72. How is a floor plan of a building obtained?
73. How is a ceiling lighting plan obtained?
74. In Fig. 2.21, what information is given by the
floor plan that is not given by the isometric or
any of the elevations?
Section 2.20
75. What type of line should be used in an el-
evation to represent an opening for a window
in a wall?
76. What type of line should be used to represent
in a floor plan the opening in a partition for a
door?
77. What type of line should be used in an el-
evation to showwhere a cut is to be made fora
ceiling plan?
78. What are the edges of the foundations in Fig.
2.22a represented by dashed lines?
79. How is a vertical section obtained?
80. How is a horizontal section obtained?
81. In Fig. 2.22, what information is given by the
vertical section that is not provided by the
isometric or the elevations?
82. Why is a detail usually drawn to a large scale?
Section 2.23
83. Can contourlines cross?Explain youranswer.
84. In Fig. 2.24:
(a) What utilities are available close tothe lot?
(b) What is the frontage along the avenue of
the lot?
(c) What part of the lot is steepest?
(d) Is the northern partofthe lot flat orsteeply
sloped?
(e) How far is the stormsewerfrom the north
property line?
85. In Fig. 2.25:
(a) How far is the west side ofthe house from
the west boundary line?
(b) What is the elevationofthe garage floor?
(c) How far above the ground is the finished
floor at the northeast and northwest
comers of the building?

57
Chapter 3
Systems Design Method
Building design, being as much an art as a science,
requires creativity,imaginationandjudgment.These
talents can be inspired and assisted by systems
design to produce better and less costly buildings.
The big advantage ofsystemsdesignovertraditional
building design is that systems designmarks clearly
the precise path forproduction of optimumresults.
In Sec. 1.3, systems design is defined as the
application ofthe scientific method to selectionand
assembly of components or subsystems to formthe
optimum system to attain specified goals and
objectives while subject to constraints or
restrictions. The scientific method requires
observationandcollectionofdata,formulation ofan
hypothesis and testing of the hypothesis.
Section 1.3 also pointsout that the systems design
procedure requires three essential steps: analysis,
synthesisandappraisal.The purpose ofanalysis is to
indicate what the systemis to accomplish.Synthesis
is the formulation of a systemthat meets objectives
and constraints. Appraisal evaluates systems
performance and costs.To insure cost effectiveness
of components,value analysis is included in the ap-
praisal phase. Value analysis investigates the
relationship between life-cycle costs and the values
ofa system,its componentsandalternativestothese,
to obtain the lowest life-cycle cost for acceptable
system performance. In practice, these steps may
overlap.
In this chapter, the systems design method is
explored in detail. Chapter 4 discusses the practical
application of the method to building design.
As proposed in this chapter, systems design is
applicable to the whole buildingas a system,to each
of its systems and subsystems, and to component
systems. The method requires that, at the start, the
characteristics required of the systembe described.
Then, a system with these characteristics is
developed. Various methods may be used to refine
the system,to attain acceptable performance at least
life-cycle cost, or the best performance for a given
cost, or some intermediate performance and cost.
Next, value analysis is applied to see ifcosts can be
reduced. Alternative systems are investigated in a
similar manner. Finally, all systems are compared
and the optimumsystemis chosen.
Execution of the method is expedited by the use
of models. These are discussed in Sec. 3.1.
3.1. MODELS
As used in systems analysis, a model is a repre-
sentation of an actual system for the purposes of
optimization and appraisal. A prime requisite for a
model is that it be able to predict the behaviorofthe
systemwithin the range of concern.
For each condition imposed on the system and
each reaction of the system to that condition, there
must be a known correspondingconditionthat,when
imposed on the model, evokes a determinable
response that corresponds to the system reaction.
The correlation need not be perfect but should be
close enough to serve the purposes for which the
model is to be used.
For practical reasons, the model should be a
simple one, consistent with the role for which it is
chosen. In addition, the cost of formulating and

using a model should be negligible compared with
the cost ofassembling andtesting theactualsystem.
A model may be formulated from among a wide
range of possibilities. A systemor a typical portion
of it, for instance, may serve as its own model. For
example, a few piles for supportinga foundation are
sometimes driven fulldepthintotheground and then
tested in place with gradually increasing loads t.0
determine theirsafe load-carryingcapacity.Thedata
obtained in the test are used to establish the safe
loads for other piles to be driven nearby under the
same soil conditions.
Sometimes, a model may be essentially a replica
of a systemto a small scale. For example, a model
sometimes is constructedaboutorless the size ofan
actual building for tests in a wind tunnel to
determine the effects of wind on the building or of
the building on air movements.
But many other models are possible and can be
used in systems analysis.Amodel,forexample,may
be a set ofmathematicalrelationships,graphs,tables
or words.Regardless ofform, however,a model, to
be useful, must behave like the real system.
Consequently, a model should be tested
continuously during its formulation for correlation
with the real system.
Types of Models
Despite the variety of models that may be used in
systems analysis,modelsmay be classified as one of
only three types: iconic, symbolic or analog.
Iconic models bear a physical resemblance to the
real system.They differfromthe realsystemin scale
and often are simpler. The previously mentioned
models of buildings used in wind tunnel tests are
iconic.
Symbolic models represent by symbols the
conditions imposed on the real system and the
reactions of the systemto those conditions. With
such models, the relationships between imposed
conditions and reactions, or performance, can be
generally, and yet compactly, represented. For
example, the maximum safe load on a steel hanger
can be representedby p= AFylk,where p is theload,
kips (thousands of pounds); A is the cross-sectional
area of the hanger, sqin.; Fy is the yield strength of
the steel,ksi(kips per sq in.); and A:is a load factor
that provides a safety margin. Symbolic models
generally are preferred for systems analysis when
they can be used, because they take less time to
formulate,are less costlyto developanduse,andare
easy to manipulate.
Analog models are realsystems but with physical
properties different fromthose ofthe actualsystem.
If mathematical formulas could be written to
representthe behaviorofa systemand its analog,the
formulas would be identical in form, although the
symbols used might be different. For example, a
slide rule is an analog model for representing
numbers by distances.When lengths on a slide rule
are made proportional to logarithms of numbers,
addition of lengths on a slide rule is equivalent to
multiplication of the corresponding numbers.
Similarly, electric current can be used to determine
heat flow through a metal plate; a soap membrane
can be used to determine torsional stress in a shaft;
and light can be used to determine bending stresses
in a beam.
It sometimes may be necessary to represent a
systemby more than onemodel.The models in such
cases may be used in combination, much like a set
of simultaneous linear algebraic equations; or they
may be used in sequence, the output of one model
serving as the input of another.
Regardless of the type of model, systems and
models must meet the following conditions:
1. It must be possible toconstructthemodelfrom
a knowledge of the known characteristics of
the system. Only those known characteristics
that are essential, however, need be
considered. Many properties of a model or
systemmay be irrelevant.
2. It must be possible to predict the response of
the systemfrom a knowledge of the response
of the model.
3. Accuracy of the response of the system
obtained by use ofthe modelmust be assured,
through tests of the model, to be within
acceptable tolerances. The tests may be made
physically or by mathematical computations,
or both.
Elements of a Model
A model relates imposed conditions, which usually
can be expressed numerically and hence can be

Systems DesignMethod59
represented by variables, and corresponding
responses, which also usually can be expressed
numerically and can be represented by variables.
Sometimes, the variables are known within
reasonable accuracy with certainty; that is, they are
deterministic.Often,however,only a probable value
of each variable can be assumed; that is, the
variables are random. The variables of concern in
building designandtheirrelationships,however,are
usually so intricate that it is impracticalto treat them
as random, with probabilistic orstatisticalmethods.
Hence, variables usually are treated as if they were
deterministic, sometimes assigned a mean value,
sometimes an extreme value and often what is
considered, by consensus, an acceptable value.
Variables representing imposed conditions and
properties of the systemusually may be considered
independent variables. These are of two types:
1. Variables over which the designer has com-
plete control: Xi ,x2 ,x3,. ..
2. Variables over which the designer has no
control: ^1,^2 ,y3, • • •
Variables representing the response or per-
formance of the system may be considered de-
pendentvariables. Z1,Z2,Z3.. . . They are functions
of the independent variables.
These functions also contain parameters, such as
coefficients,constants and exponents.When a form
of modelis selected,theseparametershave to be set
to match the response ofthe realsystem; that is,the
model must be calibrated.
As an example, consider a symbolic model
representing the cost of operating a heating system
for a building.Assume thattheshapeofthe building
and the material in the exterior walls have been
determined. Then, the cost can be shown to be a
function of wall thickness and difference between
interior and outdoor temperatures:
C=f(t,TbT0) (3.1)
where
c = cost of heating
t = wall thickness
Tị = indoor temperature
To = outdoor temperature
c is the dependent variable, the response of the
system that the designers are interested in
determining.Tị in this case is a parameter, a design
value established for the comfort of building
occupants. To, although actually a randomvariable,
may be taken as the expected value for the location
of the building, date and time of day. In any event,
To is an uncontrollable variable. In contrast, t is a
value that can be chosen by the designer and
therefore is a controllable variable.
In Sec. 3.8, where the various steps of systems
design are discussed,one step is given succinctly as
“Modelthe systemand apply the model.” This step,
however,requires severalactions,illustrated in Fig.
3.1:
1. Formulation of a model and its calibration,
setting of values for the parameters.
2. Values have to be estimated for the uncon-
trollable variables.
3. Values have to be determined for the con-
trollable variables from constraints and
conditions for optimization.
4. Finally, the sought-afterresponseofthe system
can be found, from the relationship of the
variables, through use of the model.
Cost Models
Costs are suchan overriding considerationin design
and constructionofmany buildings that costmodels
deserve specialattention.They are discussedbriefly
in the following paragraphs and other parts of the
book.

Fig. 3.1. Steps in "Model the system and apply the
model." See Fig. 3.4.
As indicatedin Chap.1,during the variousdesign
phases,conceptsare generated,changed,developed
and then worked out in detail. In the early design
stages, systems and some components may be
selected tentatively, and systems and subsystems
may be specified only in general form. With the
considerable uncertainty that exists in those stages,
reliability of cost estimates is not likely to be good.
Cost models used in those stages,therefore,may be
very simple. For example, at a very early stage,cost
c of the whole building may be represented by
C = Ap (3.2)
where
A = floor area,sq ft, provided in the building p =
unit cost,dollars persq ft
The unit cost may be based on past experience with
similar buildings.
Equation (3.2) may be interpreted differently for
specific buildings.Forexample, fora school, A may
be taken as the number of pupils and p as cost per
pupil.Fora hospital, A may be chosenasthe number
of beds and p as cost per bed. Similarly, for an
apartment building, A may be selectedas the number
of apartments and p as cost per apartment.
As design advances, more information becomes
available for cost estimating. The reliability of cost
estimates can then be improved. At some design
stage,forexample, building cost c can be expressed
as the sumof the cost of its systems:
C = AiPỵ +A2p2 + ■ ■ • +Anpn = SA,Pi (3.3) where
Aị = convenient unit for the i-th system
Pi = cost per unit for the z-th system
As designdevelops further,stillmore information
becomes available. Even greater reliability is
feasible for the cost estimate. Building costs may
still be expressed as the sum of the costs of the
systems, but those costs should then be given with
greateraccuracythanobtainedwith the terms in Eq.
(3.3). For example, systemcosts may be expressed
as the sumofsubsystemcosts,with those costs in the
general formof Eq. (3.2). In that case,
C=^AịPị (3.4)
where
Aj = convenient unit for the /-th subsystem
Pj = cost per unit for the /-th subsystem
Eventually, enough information becomes
available that costs may be estimated in detail, as a
contractor would do in preparing a bid. The cost of
systems may then be obtained as the sum of the
purchase price of components delivered to the site,
wages for construction workers, handling and
construction equipment costs, and contractor’s
overhead and profit.
Similar cost models may be formulated for
maintenance and operating costs for a building.
Optimization
Optimummeans best.Optimization,therefore,is the
act of producing the best.
In systems design, the objective is to find the
single bestsystem.Ifthere is only one criterion,such
as least cost,forjudgingwhich systemis best,it may
be feasible to generate a systemthat is clearly better
than all others, but if there are more than one
criterion, for example, least

cost andbestperformance,thenanoptimumsolution
may or may not exist. Hence, in establishment of
objectives for a system, if optimization is desired,
preferably only onecriterion forselectionofthe best
systemshould be chosen.
This criterion may be expressed in the form:
optimize =/r(xi,x2, • • J1,^2 • • •) (3.5) where
zr = dependent variable to be optimized (max-
imized or minimized)
X = controllable variable,identified bya subscript
y = uncontrollable variable, identified by a
subscript
fr = the objective function.
The system, however, generally is subject to one
or more constraints; for example, a building code
may specify a minimum thicknessora minimumfire
rating,orbuilding geometrymay require a minimum
clearance, thus imposing limits on system
dimensions. These constraints may be expressed in
the form
fl(Xi,X2, ■ • -^1,72, • • )>0
f2(xiyx2, ■ ■ -yt,y2, • ■ )>0
fn(xi,x2, • • J1,^2, • • )>0 (3.6) Thus,
Eqs. (3.5) and (3.6) must be solved simultaneously
to producethe optimumsolution.The solutionyields
values ofthe controllable variablesXas functionsof
the uncontrollable variables y, which, when
substituted in Eq.
(3.5) , optimizes zr.
Many techniques are available for finding a
solution. Sometimes, calculus can be used. When
Eqs. (3.5) and (3.6) are linear, linear programming
can be used. When time is a variable, dynamic
programming may be applicable.In such cases,use
of a high-speed electronic computer usually is
necessary for practical computation.
For a building as a whole, its systems and larger
subsystems, direct application of Eqs.
(3.5) and (3.6) is impractical, because ofthe large
numberofvariables and constraints.The difficulties
that may be encountered are perhaps bestillustrated
by an example.
Considera building with skeleton framing.In such
a building,columns are usually spaced alongrows in
two perpendicular directions. The quadrangle, such
asABCD in Fig. 3.2tf, formed by four columns, is
called a bay. The area of the bay is a controllable
variable that may affect construction and operating
costs ofseveralsystems.Bay area,in particular,has
a considerable effect on structural costs and on
production,oractivity,costs.Thelattermay be mea-
sured by the loss ofrevenueto the ownerbecauseof
the effect on production, or activity, of making the
bay area smaller or larger than desired for efficient
operation, flexibility and future expansion.
Because ofthe large numberofvariables involved
in optimization of bay area, an exact solution
generally is impractical.Any ofseveralstrategies for
choosing bay size consequently may be adopted.
Minimum
Bay Area
Fig. 3.2. (a) Plan view of building showing location of columns, (b} Curves showing variation with bayarea of
structural and activitycosts and of the sum of those costs.

These include selection of:the efficient,or activity-
preferred,area,making the loss ofrevenue zero; the
minimum area consideredessential; thearea making
the sumof structuraland activity costs a minimum;
or some arbitrary area chosen by the owner.
Logic appears tofavorthe minimum-cost strategy.
The influence of bay area on structural and activity
costs is very large compared with its effect on other
system costs. The strategy, for example, may be
carried out as illustratedin Fig. 3.2b.Structuralcosts
would be computed and plottedforgradualincreases
in bay area from the minimum consideredessential.
Similarly, the increase in activity cost would be
computed and plotted for gradual changes in bay
area from the activity-preferred size.Then,the sum
of the costs would be plotted. The bay area
correspondingto thelowpoint ofthe resultingcurve
would be the bay area to specify.
Optimization of the sumof structuraland activity
costs, however, also involves many variables and
may be impracticalfor severalotherreasons.It may,
for example, be impracticable for the owner to
predict the loss in future revenue because of
variations in bay area. In some cases, activity cost
may not be calculable; forexample, for a residence.
Structural costs are affected by bay area through
its influence on column spacing. This influence is
not easytopredict.Forexample,column spacingcan
determine choice of structuralmaterials and type of
framing. For a specific decision on these,increasing
column spacing may increase floor-framing costs
but, in some cases, decrease foundation costs. Con-
sequently, many alternative structural systems may
have to be investigatedto determine the bayarea for
minimum cost.
Even if an optimumbay area is not determinable,
such studies are well worthwhile because they
indicate the generalrangeofcosts with variationsin
bay size. Sometimes, owners demand much larger
bays than are essential to meet objectives but then
either accept smaller bays or drop the project when
confronted with the difference in estimated
structural costs.
Suboptimization. In some cases, it may be
practicable to optimize a systemby a process called
suboptimization, in which smaller, simpler
componentsare optimized in sequence.The process
is discussed in Sec. 3.13.
Simulation. Systems subject to change may
sometimes be optimized by a process called
simulation, which may also involve trial and error.
For the purpose, the actual systemor a model may
be used. In the latter case, highspeed electronic
computers may be very useful. The actual system
may be used when it is readily accessible and the
changes to be made do not affect othersystems and
have little or no effect on cost of the systemafter
installation. For example, a HVAC duct system,
after completion, may be operated for a variety of
conditions to determine the optimumdamper posi-
tion for each condition.
References
F. Jelen and J. Black, Cost and Optimization Engineering,
2nded., McGraw-Hill, New York, 1982.
R. Stark and R. Nicholls, Mathematical Foundation for
Design, McGraw-Hill, New York, 1972.
Wordsand Terms
Model: iconic, symbolic, analog Objective function
Optimization Simulation
Suboptimization Variables: dependent,independent
Significant Relations, Functions, and
Issues
Elements ofa model: variables, responses, measurement,
evaluation.
Methods of modelingortypes of models: iconic, symbolic,
analog.
Relation of optimizationtoobjectives.
Optimizationthrough observation ofsuccessive simulations.
3.2 VALUE MEASURES FOR COMPARISONS
Forthe purposes ofcomparingsystems andselecting
the best one, some criteria or values must be
established as a guide in making the decision.Each
must correspond to a measurable system
characteristic orto a response(output)to an imposed
condition (input). This requirement implies that
characteristics orresponses must be distinguishable.
Thus, it must be feasible to assign different
identification marks or numbers to those criteria or
values that are different.
It is desirable, but not essential, that criteria and
values be quantifiable; that is, that it be possible to
arrange assigned numbers in an order that is
significant in a comparison. Selection of the best

systemis easierwhen comparisonsare made on the
basis ofquantifiable criteria orvalues,such ascosts
and revenue.
Any one offourtypesofmeasurementscalesmay
be used for criteria and values in systems design:
ratio, interval, ordinal or nominal.
Ratio Scales
Engineers generally prefer to use measures that are
well defined,suchascosts,distancesandweights.If
a value of $6 is assigned to system A and of $3 to
system B, it can be accepted that A costs twice as
much as B. If A weighs 12 lb and B 3 lb, it can be
accepted that A weighs four times as much as B.
Such scales are called ratio scales.
A ratio scale has the property that, if any
characteristic ofa systemis assigneda value number
k,any characteristic that is n times as large must be
assigned a value number nk. The absence of the
characteristics is denoted by zero.
Interval Scales
For some characteristics, a well-defined measure
may not be available; however,it may be possible to
use a scale that would at least give a numerical
measure of differences in characteristics. The
Celsius scale for measuring temperatures is an
example. Temperature is a measure ofthe heat in an
object.On the Celsius scale,zero is arbitrarily set at
the temperature at which water freezes but does not
indicate the absence of heat. Consequently, 80°C
does notindicate the presenceoftwice as much heat
in an object as would be present at 40°C, although
80 is twice 40. Relative measurements,however,are
still possible. The scale may indicate, for example,
that four times as much heat is required to raise the
temperature of the object from 40°C to 80°C, an
increase of 40°C, as would be needed to raise the
temperature from40°C to 50°C, an increase of10°C.
An interval scale has the property that equal
intervals between assigned value numbers represent
equal differences in the characteristic being
measured. Zero on the scale is established
arbitrarily.
Interval scales are often used in making com-
parisons of systems that are the same except for a
few characteristics or responses. Calculations for
selection ofthe best systemin such casesneedonly
take into accountthe characteristics orresponses that
are different. Also, only the differences need be
compared.
Ordinal Scales
For some characteristics,the measure may be based
on a purely subjective decision or the characteristic
to be measured may not beprecisely defined.Beauty
is an example. While aesthetics may be a prime
consideration in the design of some buildings, how
much more beautiful is one building than another?
Generally, if a decision can be reached in a
comparison oftwo objects,it can at best be thatone
is more, orless,beautifulthanthe other.If,then,one
of these objects is compared with a third object, a
decision might be reached thateitheris more,orless,
beautifulthan the other.By sucha process,it may be
possible to assign numbers ranking the objects in
orderofbeauty.But thenumbers would notmeasure
howmuch the objects differin beauty.The numbers
would forman ordinal scale.
An ordinal scale has the property that the
magnitude of value numbers assigned to a char-
acteristic indicate whether an object has more, or
less, of the characteristic than another object

or is the same with respect to that characteristic.
Ordinal scales are useful in comparisons of
systems where criteria cannot be expressed in
strictly economic measures, such as costs or
revenuesin dollars.Forexample,an ownermay seek
a low-cost building but also want it to be
aesthetically appealing. He may also require low
maintenance.With severalobjectivesand criteria to
be met, it may be necessary to tradeoff higher
construction costs for more attractive and more
durable materials than a leastcost building would
permit. Selection of the best systemto meet these
objectivesmay have to be basedon an ordinalscale.
To illustrate how an ordinal scale may be set up
for comparison of systems with several objectives
when only some values are quantifiable, the
following example presents a scale that has been
used for value analysis. In the example, the scale is
applied to a comparison of two partitions, one all
metal, the other, glass and metal. Calculations are
shown in Table 3.1.
The characteristics of concern in the comparison
are listed in the first column. These characteristics
are assigned a weight, in accordance with the
relative importance of the design objectives, as
judged by the analysts.The weight assigned to each
characteristic may range from 1 for low priority to
10 for highest priority and is shown in the second
column.
Next, a relative value is assigned each alternative
partition for each characteristic. For example, for
construction cost, the all-metal partition is given a
value of 10 in Table 3.1 and the glass- and-metal
partition a value of 8, because the allmetal partition
costs somewhat less. Also, the glass-and-metal
partition is assigned a value of 9 for appearance,
because the analysts considered it to be slightly more
attractive thantheother,which is given a value of7.
For each characteristic, then, the weights and
values are multiplied and the products are enteredin
the table as weightedvalues.Finally,the ratio ofthe
sum of the weighted values to the partition cost is
computed for each alternative. The all-metal
partition would be recommended because its ratio is
larger.
Nominal Scales
For some characteristics, the measure may be
capable of doing no more than indicating that two
characteristics are different. No value, however, is
assigned tothe difference.Sucha measurementscale
is called a nominal scale.
The measures of such a scale, for example, may
indicate the presence or absence of a characteristic.
The measure, for instance, might be that a fan is or
is not needed; or space is or is not available for
electric wiring; or all components are or are not
Characteristics
Relative
importance
Alternatives
1
All metal
2
Glass and metal
Relative value Weighted value Relative value
Weighted
value
Construction cost 8 10 80 8 64
Appearance 9 7 63 9 81
Sound transmission 5 5 25 4 20
Privacy 3 10 30 2 6
Visibility 10 0 0 8 80
Movability 2 8 16 8 16
Power outlets 4 0 0 0 0
Durability 10 9 90 9 90
Low maintenance 8 7 56 5 40
Total weighted values Cost
Ratio of values to cost
360 $12,000
0.0300
397
$15,000
0.0265
Table 3.1. Comparison of Alternative Partitions

factory assembled.
3.3 COMPARISONS OF SYSTEMS
The discussion ofordinalscalesmakes an important
point: In evaluation of systems where many factors
in addition to cost have to be considered, analysts
have to determine the relative importance of design
objectives to the owner, building users and the
public and the weight to be assigned to values.How
important is initial cost? Aesthetics? Maintenance?
Flexibility?
While the owner would like to optimize all of the
values,optimization ofmore than onevaluemay not
be possible. Consequently, systems analysts may
have to determine the psychological value to the
owner of system characteristics or responses, the
intensity of his feeling for them. Such values then
can be used in systemcomparisons. Psychological
measurement, however, is crude compared with
economic measurement. Nevertheless, in some
cases, it may form the only basis for making a
decision.
Economic comparisons are preferred for several
reasons: When properly and accurately made, they
are much more reliable than comparisons based on
subjective values. Also, comparisons expressed in
monetary units are likely to be more easily
understood by owners. In addition, comparisons
may be facilitated by use of money units, because
the many different system characteristics to be
evaluated in a choice between alternatives may be
made commensurable by transformation into
money.Consequently,where possible,selectionofa
systemshould be based on aneconomic comparison.
Basis for Decisions
In the choice between alternative systems, only the
differences between system values are significant
and need be compared.
For example, suppose an exteriorwall considered
for a building is initially planned to contain 4 in. of
insulation.Suppose alsothat studiesindicatethat the
insulation would save $200 annually in HVAC
costs. Why not then for economy use 5 in. of
insulation? The question should be answered by
subtracting the additional equivalent annual cost of
1 in. of insulation fromthe corresponding decrease
in annualHVACcosts.(The effectsofa thickerwall
on reductionofinteriorspace and oninterfacingwith
otherbuilding components shouldalso be takeninto
account if relevant.) If the difference is positive, 5
in. of insulation would be better than 4 in. If the
difference is negative,the added insulation is not an
improvement. It is the difference in savings that
should control the decision.
Maximization of Profit
Costs are very important in building design because
they usually are incorporated in criteria, or
measures, that determine whether a building meets
the owner’s objectives. Generally, for example, an
owner would like to recover his investment and
maximize the profit, or return, on his investment in
the building. Return is the difference between
revenue fromuse ofthe building andtotalcosts.The
last is the sumofinitialinvestment,maintenanceand
operating costs. With the objective of maximum
return,therefore,it is the difference between revenue
and costs that should be maximized.
Sometimes, instead, costs are minimized. This
could lead to an erroneous decision in choosing
between alternatives. Minimum cost yields a
maximum return only ifrevenue is unaffectedby the
choice ofsystems ordoes not decreaseas rapidly as
cost.Similarly, maximizing revenue could lead to a
poor decision unless costs are unaffected by the
decision or do not increase as rapidly as revenue.
Also, sometimes, only initial investment, or
construction,cost is minimized.This,too,couldlead
to a bad decision,even though revenue would notbe
adversely affected.Lifecycle costs should beusedin
computing profit, not just initial investment cost.
Life-cycle costs include maintenance and operating
costs. Sometimes also, depreciation and taxes may
be important.
Maximum profit, however, may not be sufficient
to meet an owner’s objectives in some cases. The
owner may want profit to be com

mensurate with the risk involved in making the
investment and with the return available from other
investment opportunities. Thus, he might require
that the rate of return, the ratio of return to
investment, be larger than all of the following:
Interest rate forborrowed money Rate for
government bondsornotesRate forhighly rated
corporate bondsRate ofreturn expected froma
businessConsequently,the decisionwhetherto
proceed with construction ofa building may well
hinge on whethera maximum return can be realized
that is large enough to make the rate ofreturn
appealing to the client.
Time Value of Money
The preceding discussion should make evident the
importance ofthe time value of money in economic
comparisons.Allcostsrepresentmoneythatmustbe
borrowed or that could otherwise be invested at a
current interest rate, depending on the risk
considered acceptable. Consequently, in economic
comparisons,interestratesshould be usedtoconvert
costs of different types, such as initial investment
and annual costs, to a common base. For example,
initial investment may be changed to an equivalent
annual cost, or annual cost may be converted to
present worth. Use of interest rates for these
purposes is discussed in Sec. 3.4.
3.4. RETURN ON INVESTMENT
A typical economic comparison of alternative
systems involves evaluations of initial capital
investments, salvage values after several years,
annual disbursements and annual revenues. For the
comparison, it is necessary to make these different
types ofcosts andrevenuescommensurable.This is
usually done in either of two ways:
1. Conversion of all costs and income to
equivalent uniformannual costs and income.
2. Conversion ofallcosts andincome to pressent
worth as of time zero for the annual series of
disbursements and income.
Present worth is the amount of money that,
invested at time zero at a specified rate of return,
would yield annually the required series of
disbursements and income.
The conversions should assume a rate of return
that is attractive to the owner. It should be at least
equal to the interest rate that would have to be paid
if the amount ofthe investmenthad to be borrowed.
Consequently, the desired rate of return usually is
referred to in conversion calculations as the interest
rate.
The conversions should alsobebased on the actual
time periods involved, or reasonable estimates of
them. For example, salvage values should be
specified as the expected return on sale of an item
after a specific number of years that the item has
been in service.To simplify calculations,interest is
computed for the end of each year.
Compound interest formulas should be used for
the conversions.Thus,a suminvestedincreasesover
a specific number of years to
S = P(1+O" (3.7)
where
s = future amount ofmoney,equivalentto p,at the
end of n periods with interest i
i = interest rate per interest period
n = number of interest periods
p = present sum of money = present worth of
investment at time zero
Present worth of a future sum of money can be
obtained by solving Eq. (3.7) for P:
P = S(1 +/•)■" (3.8)
A capitalinvestmentp can be recovered in n years
with interest i through a series of annual payments
R. The amount of the annual payment for capital
recovery is given by
Ĩ .
—-——— +ị
(1 + 0" -1 J
(3.9)
The present worth of an
annual series of payments R
can be obtained by solving
Eq. (3.9)
R-P
i
_1 - (1 + iỴn
forP;
'1 - (1+0'"'
(3.10)

The present worth of an annual series of payments
continued indefinitely then is
„ R
When equipment has salvage value V after n
years, capital recovery can be computed by sub-
traction of the present worth of the salvage value
from the capital investment:
Example 3.1. Annual Cost Comparison
Alternatives: Two heating units are being con-
sidered foran office building.Estimatesforthe units
are as follows:
The annual costs include operation, maintenance,
property taxes and insurance. Which unit would be
more economical if the rate of return is chosen at
8%?
Comparison: Annual costs are computed as
follows:
UNIT>1
Conclusion:Unit Bis more economicalbecause its
annual cost is lower.
Example 3.2. Present Worth Comparison
Compare Units A and B of Example 3.1 by use of
present worths.
Comparison: Whereas the alternatives have
different service lives, conversion of all costs and
income to present worthmustbe basedona common
service life. A convenient simple assumption for
doing this is that replacement assets will repeat the
investment and annualcosts predictedforthe initial
asset. In accord with this assumption, a common
service life to be used in the comparison of present
worths must beselected.Sometimes,it is convenient
to choose for the common service life the least
common multiple of the lives of the alternatives.In
other cases, annual costs may be assumed to be
perpetual. The present worths of such annual costs
are known as capitalized costs.
Forthis example, assume a common service life of
20 years.Hence,Unit A willpresumably be replaced
at the end of 10 years by a similar unit at a cost of
$30,000, less the salvage value.The newunit willbe
assumed tohave a salvage value of$5,000 at the end
of 20 years.
By Eq. (3.12),
R = [$30,000
- 35.000(1.08)-! L(i o8)lO1
AnnualcostsTotalannualcost
Initial investment = $30,000
Present worth ofreplacement cost
in 10 years [Eq.(3.8)]
= ($30,000 - $5,000)(1.08)”10
= 11,580
Present worth ofannualcosts for
20 years [Eq.(3.10)]
Initial cost $30,000 $50,000
Life, years 10 20
Salvage value $5,000 $10,000
Annualcosts $3,000 $2,000
UNIT A UNIT B
(311)
(3.12)
UNIT?1
0-08
+ 0.08
= $4,125
= 3,000
= $7,125
UNIT B
By Eq. (3.12),
_ 1 - (1.O8)"20
= $3,000 —— 0-08
Present worth of all costs
= 29,454
= $71,034
R = [$50,000
- $10,000(1.08)’20
]
008 —7 + 0.08
L(1.O8)20
- 1
Annualcosts
Totalannualcost
= $4,874
= 2,000
= $6,874
Income:
Present worth ofsalvage value after
20 years [Eq.(3.8)]
= $5,000(1.08)”20
= 1,073
Present worth ofnet costs for
20 years =$69,961

UN IT-Ổ
Initial investment
Present worth of annual costs for 20
years [Eq. 3.10)]
' 1 - (1.O8)"20
'
= $2,000 ------7--;
[ 0.08 J
Present worth of all costs
Income:
Present worth of salvage value after
20 years [Eq. (3.8)]
= $ 10,000( 1.O8)"20
= 2,145
Present worth of net cost for
20 years =$67,491
Conclusion:Unit B is more economicalbecause it
will cost less.
Benefit-Cost Comparisons
As indicated previously, the objective of an eco-
nomic comparison may be selection of a system
yielding the maximum return; i.e., the largest
difference between revenues and costs. In the
preceding examples, however, least cost is the
criterion for selection of a system rather than
maximum return, because revenue is assumed to be
unaffectedby the decision,except forsalvage values
of the equipment. In other cases, revenue may be
affected by the decision and should be taken into
account.
Revenue,though,may be thought ofas more than
monetary income. Revenue may also include
intangible gains or prevention of losses. For
example, the decision whether to waterproof a
basement should take into account the damage that
would result were the basement to be flooded.
Nonoccurrence of such losses would be a financial
benefit accruing from waterproofing. Another
example is the decision to enclose acoustically a
noisy machine. The benefits would be worker
comfort, improved worker efficiency and possibly
also the ability to obtain workers at lower wages.
Benefits may be a bettertermto use thanrevenuesin
such cases.
Consequently, in economic comparisons, the
objective may be tomaximize the difference between
benefits and costs.
Example 3.3. Benefit-Cost Comparison
A step in a manufacturing process requires impact
forming of a product. The noise produced by the
impact, while not likely to impair the hearing of
workers,is unpleasantandwillcause a loss ofworker
efficiency. Three alternatives are under
consideration.
Alternatives:
Plan 1. Select Machine A and normal operation.
Plan 2. Select Machine A and isolate it with an
acoustical enclosure, thus improving worker
efficiency.
Plan 3. Select quieter Machine B, which costs
considerably more, but thus free workers from the
restrictions of the enclosure.
Estimates for the plans are as follows:
PLAN 1 PLAN 2 PLAN 3
Initial machine
cost $10,000 $10,000 $20,000
Life, years 5 5 7
Salvage value 0 0 0
Annualcosts
for machine
operation $ 2,000 $ 2,000 $ 1,500
Acoustical
protection cost 0 $ 2,000 0
Annualvalue
of improved
efficiency 0 $ 800 $ 1,000
Which plan would be the most economical for the
assumption of a 10% rate of return?
Comparison: The following annual costs are
computed:
PLAN 1 PLAN 2 PLAN 3
Capital recovery of machine cost [see Eq.
(3.12)] $ 2,638 $ 2,638 $ 4,108
Capital recovery
of acoustical
protection 0 528 0
Annualcosts
for machine
operation 2,000 2,000 1,500
Totalannual
cost $ 4,638 $ 5,166 $ 5,608
Benefits:
Annual value
of improved
efficiency _________0 800 1,000
= $50,000
= 19,636
= $69,636

Net annual
cost $ 4,638 $ 4,366 $ 4,608
Benefit-cost
ratio 0 0.155 0.178
Conclusion:Plan 2is the most economicalbecause
its annual cost is lowest.
Benefit-Cost Ratios
Note that in Example 3.3, Plan 3 has a higherratio of
annual benefit to annual cost than Plan
2. Yet, Plan 2 is more economical. Benefitcost
ratios, the example indicates, are not a reliable
measure of the relative economy of alternative
systems—at least not when the ratios are based on
total costs.
Reliable results can be obtained, however, if the
ratios are taken as that ofincrement in benefit to the
increment in cost that goes to produce the benefit.
Alternatives may then be compared in pairs in the
order of increasing costs. The incremental benefit-
cost ratio ofthe systemselected should exceed unity.
Forexample, in the comparisonofPlan 2with Plan
1, Plan 2 costs $528 more than Plan 1, has a benefit
increment of $800, and therefore has a benefit-cost
ratio of800/528 = 1.51. In the comparison ofPlan 3
with Plan 2, Plan 3 costs $442 more, has a benefit
increment of$1,000 - $800 = $200, and thereforehas
a benefit-cost ratio of0.452. Consequently,the extra
cost of Plan 3 is not warranted because the
incremental benefit-cost ratio is less than unity.
For Sections 3.2-3.4
References
c. Churchman, Prediction and Optimal Decision: Philo-
sophical Issues of a Science of Values, Greenwood, 1982.
E. Grant et aL, Principles of Engineering Economy, 7th ed.,
Wiley, New York, 1985.
w. Fabrycky and G. Thuesen, Engineering Economy, 6th ed.,
Prentice-Hall, Englewood Cliffs, NJ, 1984.
Words and Terms
Alternatives
Benefit-cost comparison Investment
Measurement scales: ratio, interval, ordinal, nominal Present
worth
Profit Return
Process of use andestablishingof values: definingobjectives,
measurement systems, comparisons, conclusions. Time value
of money.
3.5. CONSTRAINTS IMPOSED BY BUILDING
CODES
States and communities establish regulations
governing building construction under the police
powers ofthe state,toprotect the health,welfare and
safety ofthe community.These regulations comprise
a building code, which applies a multitude of
constraints on building design.
Building codes are administered by a building
department. In many communities, the building
department not only enforces the building code but
also the zoning code, subdivision regulations and
other laws affecting buildings.
If a state has a buildingcode,its provisions usually
take precedence over municipal codes if the state
regulations are more stringent.
The requirements of building codes generally are
the minimum needed toprotect the public.Architects
and engineers therefore must use judgment in
applying codes, to protect fully the interests of both
clients and the public. Often, more than minimum
criteria must be satisfied if a building is to serve
efficiently and ifpersonalinjuries are tobe prevented
in use of the building.
Sometimes,code requirements are notadequateto
protect the interests ofeitherthe client orthe public.
For example, a building code may specify a
minimum thickness ofconcrete floor,which may be
adequate for the client’s immediate needs. But the
client’s needs may changeorhe may sellthe building
to a new owner with different needs, in either case
making the floorthickness unsafe withoutexpensive
alterations. As another example, code requirements
for fire resistance may not be enough for public
safety. An oven is completely fire resistant but
unsafe for humans when the heat is on. Past fires
have demonstrated that fireresistant buildings may
actually be huge ovens! When the owner’s interests
conflict with the public interest, the public interest
must prevail.
Code Enforcement
The building department enforces regulations under
its purview by checking building plans before
construction starts and then inspecting the work
during construction. If the department approves the

plans, it issues a building permit authorizing
construction to start. If, while work is under way, a
building inspector finds a violation of a regulation,
he issues an order for removal of the violation.
Failure to correct a violation subjectsa contractoror
ownerto fines and even to imprisonment.Decisions
of the building department, however, may be
appealed to a Board of Appeals or to the courts,
whether design or construction is concerned. When
the building has been completed andapprovedby an
inspector, a certificate permitting occupancy is
issued.
Building codes, in general, apply only to work
within lot boundaries.(Exceptions include relatively
short overhangs,bridgesbetweenadjacent buildings,
or under-sidewalk vaults.) Construction affecting
sidewalks orstreets,curb elimination for driveways,
water and sewer connections, and other types of
work on public property usually are controlled by
regulations under the jurisdiction of other
departments, such as a department of highways and
sewers ora waterdepartment.Contractorsoften have
to obtain permits fromsuch departments.
Types of Codes
Attempts have been made in the past to classify
building codes as specification type or performance
type.
A specification-type code specifies specific
materials for specific uses. It gives minimum or
maximum thickness, height, or length, or com-
binations of these. For example, this type of code
may specify that an exterior wall must be made of
brick or concrete. It may also require that one-story
walls must be at least 8 in. thick.
In contrast,a performance-type code specifies the
performance requirements of buildings and their
components. It leaves materials, methods, and
dimensions to the option of the designer so long as
the performance requirements are satisfied. For
example, this type of code specifies that an exterior
wall must be:
1. Strong enough to resist all loads that may be
imposed on it
2. Stiff enough that loads will not cause per-
manent deformations or cracking
3. Durable
4. Capable of achieving a stipulated fire rating
5. Resistant to passage ofheat,sound,andwater.
The code may apply quantitative values, like the
fire rating,to many of these desired characteristics.
Performance-type codes have many supporters,
because this type gives designers more freedom in
selecting materials and methods,readily permits use
of newmaterials and methods,and does not become
obsolete as quickly. With specification-type codes,
new legislation often is required before new
materials or methods may be used.Even when such
action is not necessary, building officials may be
slowin approvingnewthings,to be certain that their
use is safe. In practice, however, performance-type
codes have not shown the advantages over spec-
ification-type codes that have been expected. The
principalreason is that as materials are demonstrated
to meet performance requirements theyare placed on
a list of approved materials.If materials planned for
a project are not on the list, extensive investigations
maybe necessary to obtain approval of those
materials. By the time the investigations are
completed, it may be too late to use those materials
on the project for which they were proposed.
Actually, performance-type codes are an
idealization. A purely performance-type code has
never been written. Sufficient information for the
purpose is not available.Consequently,allcodes are
partly performance type and partly specifications
type.Whethera building code is considered to be of
either type depends on the degree to which it relies
on performance requirements.
Forms of Codes
Building codes often vary in form with locality. In
general,however,theyconsist oftwo parts,ofwhich,
One part deals with administration and en-
forcement, including:
1. Licenses, permits, fees, certificates of oc-
cupancy
2. Safety
3. Projections beyond street lines
4. Alterations
5. Maintenance
6. Applications, approval of plans, stopwork
orders
7. Posting ofbuildings toindicate permissible live
loads and occupant loads
The second part contains the regulations directly
affecting building design andconstruction,andis,in
turn, subdivided to deal separately with:

1. Occupancy and construction-type classifi-
cations, limitations on these classes, fire
protection, and means of egress
2. Structural requirements
3. Lighting and heating, ventilating, air con-
ditioning, and refrigeration (HVAC) regu-
lations
4. Plumbing and gas piping
5. Elevators and conveyors
6. Electrical code
7. Safety of public and property during con-
struction operations
The form of subdivision depends on the mu-
nicipality.
Adoption of Standards
Building codes generally consist of a mixture of
good practices andminimumstandardsofadequacy.
To obtain building regulations suitable to local
conditions, a community may develop a completely
new building code for its own use and adopt it by
legislative action. By similar action, the community
may adopt the latest version ofa modelcode,such as
those promulgated by associations of building
officials or the American InsuranceAssociation,ora
state code,orany ofthese codeswith modifications.
The legislation need simply indicate that a specific
code ofgivendateis adopted,exceptforcertain listed
modifications. This action is called adoption by
reference.
It is common practice also for building codes to
adopt by reference existing standards of various
types. For example, a building code may, in this
manner, incorporate the latest version of ANSI
A40.8, “The National Plumbing Code,’’ American
NationalStandardsInstitute; ora code may adoptby
reference any ofthe manystandardspecificationsfor
materials or methods ofASTM;ora code may adopt
by reference thestandard building coderequirements
for structural design and construction promulgated
by the American Institute of Steel Construction,
American Institute of Timber Construction, and the
American Concrete Institute.
Code Constraints on Design
Many of the architectural and structural constraints
imposed by building codes depend on various
classifications of buildings defined in the codes. In
general, a building may be classified according to:
Fire zone in which it is located
Occupancygroup,depending on buildinguse Type
of construction, as a measure of fire protection
offered
Fire zones usually are shown on a community’s
fire-district zoning map. The building code indicates
what types ofconstruction and occupancy groups are
permitted or prohibited in each zone.
Occupancy group is determined by the building
official in accordance with the use or character of
occupancy of the building. Typical classifications
include:
Places ofassembly,such as theaters,concert halls,
auditoriums, and stadiums
Schools
Hospitals and nursing homes
Industrial buildings with hazardous contents
Buildings in which combustible materials may be
stored
Industrialbuildings with noncombustible contents
Hotels, apartment buildings, dormitories,
convents, monasteries
One- and two-story dwellings
Type of construction is determinedby the building
official in accordance with the degree of public
safety and resistance to fire offered by the building
and its components. These characteristics are
measured by the fire ratings assigned to building
walls and partitions, structural frame, shaft
enclosures, floors, roofs, doors and windows. Fire
ratings ofvarious constructions used in buildings are
determined by a standard test (usually ASTM El 19,
“Standard Methods of Fire Tests of Building
Construction andMaterial,” promulgated by ASTM,
formerly the American Society for Testing and
Materials), and measured in hours.
Some building codes give fire-resistance re-
quirements, in addition, for exterior walls and
protection of wall openings in accordance with
location of a building on a site and distances to
property lines and other buildings. The objective is
to prevent or delay spread of fire from one building
to another.
To prevent ordelay spread offire over very large
areas on any level of a building, codes usually
specify the maximum allowable floor area enclosed
within walls of appropriate fire resistance on any

level. The areas permitted depend on occupancy
group and type of construction.
Maximum building height and number of stories
also are specified in building codes for fire safety.
These limits, too, depend on occupancy group and
type of construction.
Similarly, occupant load, or number of persons
permitted in a building or room, is specified. The
objective is to enable rapid and orderly egress in
emergencies, such as fire, smoke, gases, earthquake
or any event that might cause panic. Occupant load
for any use is determined by dividing the floor area
assigned to that use by a specified numberofsquare
feet per occupant. Building codes list permitted
occupant loadsin accordance with the type ofuseof
the area or the building.Associated with these loads
is a specified number of exits of adequate capacity
and fire protection that must be provided.
The structuralsubdivision ofa building code lists
the minimum loads for which a building or its
components must be designed.The subdivisionmay
also indicate the minimum structural capacities
required, allowable unit stresses or maximum
permitted deflections. Sometimes, in addition,
minimum thicknesses of materials are specified, as
well as maximum spacing of bracing.
In a similar manner, building codes apply con-
straints to mechanical, electrical and other com-
ponents of buildings. Also, the codes contain rules
governing constructionofbuildingsincludinguseof
equipment, such as cranes.
References
Architect’s Handbook of Professional Practice, American
Institute of Architects.
Uniform BuildingCode, International Conference of Building
Officials.
The BOCA Basic National Building Code, Building Officials
and Code Administrators International.
Standard Building Code, Southern Building Code Congress
International.
Words and Terms
Adoptionof standards
Building code
Fire zone
Occupancy group
Occupant load
Performance-type code
Specification-type code
Type of construction (code classification)
Administration of building code: granting of permits for
construction, inspections.
Types of codes: performance, specification.
Adoption of documented standards by reference.
Code constraints on design work.

3.6. ZONING CODES
Buildings in a community may be regulated under
the police powers of the state, to protect the health,
welfare and safety of the community. The
regulations promulgated for this purpose generally
comprise a zoning code, which applies numerous
constraints on building design.
Zoning codes are usually administered by a
planning commission or by a building department.
The commission also may establish related
subdivision regulations, to control subdivision of
large parcels of land by developers. Subdivision
regulations alsoact as constraints on designers,who
are not completely free, as a result, to maximize
economic or aesthetic effects of a building, because
design must comply with the regulations.
Zoning is an important planning tool in guiding
growth and otherchangesin a community orregion.
Planning goals include better living conditions,
safety,sanitation,quiet andprovision forgrowthand
populationincreases.In endeavoringtoachieve these
goals, zoning may restrict the right of a property
owner to use his property as he sees fit. But at the
same time, zoning protects the property ownerfrom
being injured by improper use of nearby property.
Zoning attempts toachievetheplanningobjectives
through control of land use, building height, lot or
building area and population density. For the
purpose, the planning commission divides the
community into a numberofdistricts,in which limits
are placed on the features to be controlled.
Land-Use Regulations
These determine the type ofoccupancy permitted in
each district, such as industrial, commercial or
residential (single- or two-family dwellings or
apartment buildings, for example).
Building-Height Regulations
Height may be controlled practically in any of
several ways. One way is to place a limit on the
numberofstories orthe height,in feet,fromstreet to
roof (see Fig. 3.3a). Anotherway is to require that a
building lie within specified sloping planes defined
with respect to lot lines (see Fig. 3.3b). These
envelopes are known as skyexposure planes. Such a
regulation notonly places a practicallimit on overall
Maximum
Height
12 Stories or
150'
Fig. 3.3. Illustrations of limitations placed by zoning on building height, (a) Height limitations for building
constructed up to lot lines, {b} Setback required bya 3:1 skyexposure plane. A tower with floor area at anylevel
not exceeding 40% of the lot area may project above that plane, but the floor-area ratio of the building may not
exceed 15. (c) A sheer tower maybe allowed a floor-area ratio of 15 if the floor area at any level is 55%or less of
the lot area or a floor-area ratio of 18 if floor area is 40% of the lot area.

building height, for economic reasons, because a
building gets smalleras it gets higher,but the planes
also set a limit on height ofportions ofthe building,
because they must fit within the specified enveloping
planes. Shape of building (appearance),
consequently,is considerably influencedbythistype
of zoning regulation.
Still another way to control building height in a
zoning regulationis to specify a maximumfloor-area
ratio, the ratio of the maximum floor area permitted
within a building to the area of the lot. This type of
regulation controls bulk and trades off additional
floor area in a building for additional unused space
on the lot. For instance, for a floor-area ratio of 10,
each square foot by which a lot is expanded permits
an addition of10 sq ft of floor area within the build-
ing to be constructed on the lot. The effect of floor-
area ratio, for practical reasons, is also to limit the
overall height of a building and portions of it,
because, in congested city districts, lots are very
expensive.Land cost increasesrapidly with lot area.
Figure 33c illustrates a case where a considerable
portion of a lot is devoted to a plaza for public use.
A building without setbacks, a sheer tower, may be
erected to a considerable height in accordance with
local floor-area-ratio zoning regulations. For
example, one city assigns a floor-area ratio of 15 if
the cross-sectionalarea ofthe towerdoes not exceed
55% of the lot area or a ratio of 18 if the tower area
does not exceed 40% of the lot area. Consequently,
on a 10,000-sq ft lot, with a tower area of 40% of
10,000, or4,000 sq ft,a building would be permitted
a total of 18 X 10,000 = 180,000 sq ft. Thus, the
towercould be built 180,000/4,000 = 45 stories high.
Area Regulations
One type of regulation on lot area specifies the
minimum distancesthat must be providedbetweena
building exterior and the nearest lot line on all sides.
Also,the regulation specifies the minimum frontage
the lot must have along a street.
Anothertype establishesminimum area of lots for
single-family houses and minimum lot areas per
family for apartment buildings.The objective ofthis
type of regulation is to control population density.
An alternative is to specify the maximum numberof
families permitted per acre and allow the developer
the option of selecting the types of buildings he
prefers for satisfying that criterion.
Zoning Map
Current land-use controls are usually indicated on a
drawing called a zoning map.It is primarily based on
existing land use when it was prepared,modified by
granting of variances by the planning commission
and changed by rezoning legislation.
Master Plan
In addition to the zoning map, the planning
commission usually prepares a masterplanas a guide
to the growth of the community. An important part
of the master plan is a future landuse plan. The
objective is to steerchanges in the zoning map in the
direction of the future land-use plan.
Other Types of Zoning
The following legal regulations also may constrain
building design. Aimed at accomplishing specific
purposes, they are superimposed on the standard
zoning patterns.
Airport zoning is oneexample.Its objectives are to
maintain obstruction-free approach zones and to
provide noise-attenuating distances around an
airport. The approach zones are maintained by
establishment of limits on building heights. These
limits vary with distance fromand orientation with
respect to the airport.
Fire zones are another example. They prohibit
certain types ofconstruction that otherwisemight be
permissible.The restrictions dependoncongestion in
each zone, population density and proximity and
height of buildings.
Land subdivision regulations are still another
example. The local zoning ordinance specifies
minimum lot area and minimum frontage a lot may
have along a street. Subdivision regulations, in
contrast, specify the level of improvements to be
installed in new land-development projects. These
regulations contain criteria forlocation,grade,width
and pavement of streets, length of blocks, open
spaces to be provided and right of way for utilities.
References
J. Sweet, Legal Aspects of Architecture, Engineering,andthe

Construction Process, West PublishingCo., 1970.
Wordsand Terms
Area regulations
Building height regulations Fire zones
Landsubdivision Land-use regulations Master plan Zoning
Zoningcode Zoningmap
Zoningas a communityplanningtool.
3.7. OTHER CONSTRAINING REGULATIONS
In addition to building and zoning codes, there are
other legal requirements affecting building design
and construction. Local departments of highways,
streets, sewers and water have regulations with
which building construction must comply. Also,
local utility companies have standards that must be
met if a building is to be serviced. Designers and
construction contractors must be alert to the
possibility ofthese and otherconstraintsand toapply
them if they are applicable. In particular, buildings
are likely to be subject to requirements of the
following agencies.
Health
State or local health departments may have
jurisdiction over conditions in buildings that could
affect the health of occupants or visitors. Food-
handling establishments, hospitals and nursing
homes are especially likely to be subject to health
department regulation. But health departments may
also have the responsibility for enforcing such
regulations as those requiring maintenance of
suitable indoor temperatures in cold weather.
Labor
For industrial and office buildings and retail stores,
there may be laws for employee safety and health
established by the state department of labor.
Designers must insure that buildings they design
provide conditions that are in accordance with the
law. The law may require that building plans be
submitted to the department of labor for review
before construction starts. Failure to comply with
these laws will subject an owner to fines. During
construction ofa building,contractors,asemployers,
also must comply with the labor laws.
Occupational Safety and Health Administration
For occupational safety and health, the U.S.
Congress passed in 1970 the Occupational Safety
and Health Act (OSHA). This act contains reg-
ulations governing conditions under which em-
ployees work.In particular,OSHA contains detailed
standards for construction. Contractors and
subcontractors must comply with these regulations
Designers must insure that buildings they design
provide conditions that are acceptable underOSHA.
There is no provision in the law, however, for
reviewing plans before construction starts.
Inspections usually are made by the administrating
agency only after complaints have been received.
Consequently, owners and their design and
construction agents should be thoroughly familiar
with the law and interpretations of it and should
insure compliance.
Housing
For residential buildings for which government-
insured mortgages are tobe secured,theStandards of
the Federal Housing Administration orthe Veterans
Administration apply. In particular, housing must
comply with FHA “Minimum Property Standards.”
Military
Materials used in military construction must conform
with Federal Specifications. Each military
department may have regulations affecting
construction performed for it.
3.8. SYSTEMS DESIGN STEPS
The preceding sections provide much of the
background information needed for systems design
of buildings. In this section, the steps required for
execution of systems design are outlined.
The procedure proposed has nine basic steps (see
Fig. 3.4). These are generally taken in sequence; but
Steps 3 through 8, synthesizing, analyzing and
appraising alternative systems, may be repeated as
many times as costs anddeadlines permit oruntilthe
designers and analysts are unable to generate new
alternatives worth considering.
In showing thesteps in sequence,Fig.3.4 has been
simplified for the purposes of illustrating and
explaining the design procedure.
Though not shown in Fig.3.4, severalalternatives

may be acted on concurrently in actual practice,
rather than in sequence. This would make possible
comparisons of a group of alternatives
simultaneously.
Also, though not shown in Fig. 3.4, some steps
may start before earlier ones have been completed.
In addition, though not indicated in Fig. 3.4, there
may be feedback of information fromsome steps to
earlier ones. These possible feedbacks would create
loops—returnto an earlierstep,revisions,andrepeat
of a sequence of steps.
Implied but not shown in Fig. 3.4 is a very
important action—data collection. To show this
would complicate the flow diagram. Data collection
is likely to be almost continuous from the start in
systems design. Information is needed to prepare
objectives and constraints, develop criteria, select
and calibrate models,andevaluate alternatives.Early
in design, much of the information that will be
needed may not be available or the need may not be
recognized. Hence, data may have to be collected
throughout most of the design process.
In brief, system design comprises these stages:
data collection and problemformulation, synthesis,
analysis,value analysis,appraisaland decision.The
steps of these stages are as follows:
Step 1. Define briefly what is needed. Indicate
what the system is to accomplish. Describe the
effects the environmentorothersystemswillhave on
the performance of the required system. Also,
indicate the effects the system will have on its
surroundings.
Step 2. In viewof what is needed and the expected
interaction of proposed systems with the
environment and other systems, develop a set of
objectives that must be met. Also, compile a set of
constraintsindicating the range within which values
of controllable variables must lie.
Step 3. Conceive a systemthat potentially could
meet all the objectives and constraints of Step 2.
Step 4. Model the systemand apply the model.
This requires the actions indicated in Fig. 3.1 and
explained in Sec. 3.1.
Step 5. Evaluate the system.Determine if it meets
all objectives and constraints satisfactorily. In
particular, see if construction costs lie within the
owner’s budget.
Step 6. Apply value analysis. If potential im-
provements are possible, eliminate components that
are not essential, make simplifying or costsaving
changes, or integrate components so that one
component can do the work of several.
Step 7. Because the changes made in Step 6 result
in a new or modified system, model the systemand
apply the model,as in Step4.This may require a new
model, recalibration of the former model or just
substitutionin the formermodelofnewvalues ofthe
controllable variables.

Step 8. Evaluate the new or modified system.
Compare it with any other alternative systems that
have been evaluated. If the new system is more
expensive than any of the others, see if additional
changes can reduce costs. If they can, make the
changes(in effect,return to Step 6) and repeat Steps
7 and 8. Next, try to generate an alternative system
that will cost less or will perform better. If this can
be done, model the improved systemand apply the
model (in effect,return to Step 4); then,repeat Steps
5 through 8with the improved system.If a betteror
less costly systemdoes not appearfeasible,proceed
Data Collection and
Problem Formulation
Synthesis
and Analysis
Value Analysis
Appraisal
Decision
Fig. 3.4. Steps in Systems Design.

to Step 9.
Step 9. Select and specify the best systemfrom
among the alternatives investigated.
The following example is presented to illustrate
the systems design procedure. The conditions
described and the proposed solution have been
simplified, perhapsover-simplified,forthe purposes
of the example.
Example 3.4. Selection ofShape andSize ofan Office
Building
At the start of the conceptual phase of design of an
office building, the following information is
provided:
The owner is a federal government agency,
exempt from zoning-code requirements. The owner
wants to build an office building for the sole use of
the agency. A total of 350,000 sq ft of office floor
area is needed. But preliminary studies of office
layout indicate that no floorshould provide lessthan
13,000 sq ft of office area. Also, studies show that
the service core, containing stairs, elevators, toilets
and service rooms,is likely to require about2,500sq
ft of floor area per story. Budget: $41,500,000,
exclusive of land cost.
The owner wants the building erected on a
23,000-sq-ft lot owned by the agency. Located in a
congested, central business district of a big city, the
lot has a frontage on the south of 200 ft along an
avenue (see Fig. 3.5). On the east, the lot has a
frontage of130ft along a street.Andonthe west,the
lot has a frontage of100 ft along anotherstreet.The
lot may be considered,forconvenience,to consistof
two rectangularareas:Area 1 with 20,000 sq ft, and
Area 2 with 3,000 sq ft.
Adjacent to the lot,on thenorthwest,is a museum,
famous as a landmark. This building is about 40 ft
high. Other buildings nearby, however, are
skyscrapers, mostly about 400 ft tall, or higher.
Along the avenue, buildings usually are set back
from the property line, to permit wider- than-usual
sidewalks or to provide plazas for public use. In
contrast, along the streets, buildings usually are
constructed along the property line.
The owner, being a government agency, wants
Fig. 3.5. Building site for Example 3.4.
to set a good example for other builders. Con-
sequently, the owner would like the building to be
constructed to enhance the community,to provide a
public service,ifpossible.Thoughexempt fromlocal
building ordinances, the owner, for the preceding
purpose, requests that the building be designed and
constructedin accordancewith thecity building code
and zoning ordinance.
Step 1. Goal Provide, on a lot owned by a federal
government agency, a building for the agency with
at least 350,000 sq ft of office area at a cost not
exceeding $41,500,000. The building should be an
asset to the community.
Step 2. Objectives and Constraints Objectives:
1. Design a building forthe23,000-sq ft lot shown
in Fig. 3.5. Area 1 is 100 X 200 ft, and Area 2,
30 X 100 ft.
2. Provide a totaloffice floorarea of350,000 sq ft
minimum.
3. Provide, on each level of the building, office
floor area of at least 13,000 sq ft, plus service-
core area of about 2,500 sq ft.
4. As a public service, provide as much open
space at street level for public use as possible,
consistent with the preceding objectives.
5. Relate the building to and harmonize it in
appearance and position on the lot with
neighboring office buildings, many of which
rise 400 ft ormore above street level.Hence,if
possible, align the building with those on the
avenue thatare set backfromthe property line.
6. As a public service,provide open space around
the landmark museum.
7. For the public good,abide by the city building
and zoning codes.

Constraints:
1. Construction costofbuilding must not exceeding
$41,500,000. Cost estimates at this stage of
design may be based on a construction cost of
$100 per sq ft of gross floor area, the average
reported forrecently constructed office buildings
in the central business district.
2. Maximum possible floorarea perstory =lot area
= 23,000 sq ft; minimum required floor area per
story = 13,000 + 2,500 = 15,500 sq ft.
3. Zoning regulations (Note: Floor-area ratio is the
ratio of total gross floor area to the lot area.)
(1) Buildings constructed up to property lines
along streetsoravenuesmay rise 85 ft above
street level without a setback. Parts of
buildings more than85ft high mustlie within
a sky exposure plane starting at the 85-ft
level at the property line and with an upward
slope of 3:1 away from the street (see Fig.
3.3Z?), until the floor area in any story does
not exceed 40% of the lot area. Maximum
permissible floor-area ratio =15.
(2) Buildings set back fromthe property line to
provide a wider sidewalk or a plaza are
permitted a sky exposure plane as in
regulation (1) but with a slope of 4:1.
Maximum permissible floor-area ratio = 18.
(3) Sheer towers set back from the property
line to provide a wider sidewalkor a plaza
(see Fig. 3.3c) and with a gross floor area
perstory not exceeding50% ofthe lot area
are permitted a floor-area ratio =17.
Step 3. Alternative 1 A building satisfying zoning
regulation (1) would provide no open space at street
level. Such a building, therefore, would not meet
objectives 4 to 6. It cannot be considered an
acceptable system.
Instead, for Alternative 1, consider a building
satisfying zoning regulation (2). The building then
would consist ofa towerrising from a broaderbase.
The base, in turn, being set back fromthe property
lines along the streets,would be smaller than the lot
(see Fig. 3.6). The service core would be placed in
Area 2 of the lot.
Step 4. Alternative 1 Model For a floor-area ratio of
18, the totalgross floorarea permittedis 18X23,000
= 414,000 sq ft.
For a sky exposure plane with slope 4:1, the
setback fromthe property line and height of base H
to provide a base with maximum floor area can be
determined mathematically. On the assumption of a
25-ft-high first story and 12-ft- high stories above,
use of differential calculus indicates that the base
should be 12 stories (157 ft) high (see Fig. 3.6a).
Set back from the property line 18 ft, the service
cọre in the base would be 30 X (100—18) ft, thus
Fig. 3.6. (a) Elevation of building for Example 3.4, Alternative1. (bi Section through base, (c) Section through
tower.

providing a floorarea of2,460sq ft.Office floorarea
in the base would be 13,450 sq ft perstory,ora total
in the 12 stories of
161.400 sq ft. Total service-core floor area in the
base would be 29, 500 sq ft. Consequently,the base
would provide a total floor area of 190,900 sqft.
The towerthen would have to provideoffice areas
totaling at least 350,000-161,400 = 188,600 sq ft.
Floor area per story in the tower, however, may not
exceed 40% of the lot area, or 0.40 X 23,000 = 9,200
sq ft.Because some elevatorsandperhapsalsosome
stairs need not be extended above thebase,a smaller
service-core floorarea than 2,500 sq ft, say 2,000 sq
ft, may be assumed for the tower. In that case, the
maximum office area per story that can be provided
in the tower is 9,2002,000 = 7,200 sq ft. To furnish
the total office area required, the tower therefore
would have to extend above the base 188,600/7,200
= 26 stories.
The building would have a totalheight of 12 + 26
= 38 stories. The base would provide a gross floor
area of 190,900 sq ft and the tower, 26X 9,200, or
239,200 sq ft.The building would thenfurnish a total
floor area of
430.400 sq ft.
Construction cost of the building would be
430,400 X $100 = $43,040,000.
Step 5. Evaluation of Alternative 1 The estimated
cost exceedsthe $41,500,000 budget.Thegrossfloor
area exceeds the 414,000 sq ft permitted for a floor-
area ratio of 18. Furthermore,the floorarea perstory
in the toweris much less thanthe13,000sq ft desired
by the ownerand therefore is too small to be useful.
Alternative 1 consequently is unsatisfactory and
cannot be improved by value analysis.Loop backto
Step 3.
orfica Service Core
Fig. 3.7. Sheer tower for Example 3.4, Alternative 2.
Step 3. Alternative 2 Consider a sheer tower
satisfyingzoning regulation(3)(see Fig.3.7). As for
Alternative 1, the service core would be placed in
Area 2 of the lot.
Step 4. Alternative 2 Model Fora floor-area ratio of
17, the totalgross floorarea permittedis 17X23,000
= 391,000 sqft.
Underzoning regulation(3),the toweris permitted
an area of only 50% of the lot area, or 0.50 X 23,000
= 11,500 sq ft. This would require a building
391,000/11,500 = 34 stories high. With a service-
core floorarea of2,500 sq ft,the floorarea available
in each story for offices is 11,500 - 2,500 = 9,000 sq
ft.
Step 5. Evaluation of Alternative 2 The floor area
per story in the sheer tower, being much less than
13,000 sq ft, is too small to be useful. The system
cannot be improved by value analysis. Therefore,
loop back to Step 3.
Step 3. Alternative 3 It appears to be impossible to
meet the owner’s objectives of a total office floor
area ofat least 350,000 sq ft and office floorarea per
story of at least 13,000 sq ft and also satisfy the
zoning code.Therefore,the owner’s objectives must
be changedorthe projectwill have to be abandoned.
The requirements that the presently owned lot be

used and for minimum floor areas appear to be
essential. The owner, however, need not abide
completely by the zoning code. Since the owner is
exempt from the city code requirements,objective7
(see Step 2) could be relaxed. A more general
objective would be:
7. Abide by the localbuilding code andrespect the
intent of the zoning code.
This change in objective would make possible a
trade-off of additional space in the building and
greaterbuilding bulkfor more open space forpublic
use at street level. As a result also, objectives 5 and
6 could be more readily met.
To provide a large open area to serve as a plaza at
street level for public use, consider a sheer tower
with a major portion ofit raised up abovestreetlevel
on stilts, substantial columns (see Fig. 3.8). The
service core would extend from the ground to the
roof. The office floors would
Office Tower SerulcB CorB
Nuseum
Fig. 3.8. Shear tower on stilts for Example 3.4, Al-
ternative 3.
Start at a level,say about100ft above the street,that
would be sufficiently high above the landmark
museumnot to cut off light and air movements and
to give the plaza a feeling of openness.
Step 4. Alternative 3 Model The floorarea perstory
in the tower can be selected in several ways, since
the constraints ofthe zoningcode ontowerarea have
been relaxed. For example, the area can be chosen
mathematically by equating the product of the unit
cost,$100 per sq ft,numberof stories and floorarea
perstory totheowner’s budget,$41,500,000. But the
resulting structure might be bulkier than necessary.
So instead,select the minimum floor area consistent
with objective 3.
Thus,eachtowerfloorwould beassignedan office
area of 13,000 sq ft. The service core would have an
area of 2,500 sq ft, as for the other alternatives
considered.In addition,a floor area of about 700 sq
ft would be provided to connect the service core to
the office area.Totalfloor area per story would then
be 16,200 sq ft.
To furnish a total office area of 350,000 sqft, the
number of stories required is 350,000/ 13,000 = 27.
Construction cost of the building is estimated at
$100 X 27 X 16,200 = $43,740,000.
Step 5. Evaluation of Alternative 3 The sheertower
provides the minimumtotaloffice area of350,000 sq
ft, with at least 13,000 sq ft of office per story. But
the $41,500,000 budget would be exceeded.
Step 6. Value Analysis To bring the construction
cost within the budget, the floor area must be
reduced.
Alternative 3A. Floor-area requirements foroffices
can be decreased by treating the 700-sq ft area
connecting the service core to the office portion as
office space. The former rectangular office area can
then be reduced to12,300sq ft and the totalfloorarea
per story to 15,500 sq ft. The building then would
have a total area of 27 X 15,500 = 418,500 sq ft.
Alternative 3B. Floor-area requirements for the
service core can be decreased by reducing the
numberofstories in the building.If,forexample, the
700 sq ft were added to,ratherthan subtracted from
the 13,000 sq ft,the numberofstories required would
be 350,000/ 13,700 = 25.5, say 25. More accurately
then, a 25-story tower would provide 350,000/25 =
14,000 sq ft of office area per story.Totalfloorarea
per story would be 16,500 sq ft, and the total floor
area in the building would be 16,500 X 25 =412,500
sq ft.

Step 7. Recalibration of Model
Alternative 3A. Constructioncostwould be$100X
418,500 = $41,850,000.
Alternative 3B. Constructioncostwould be$100X
412,500 = $41,250,000.
Step 8. Evaluation of Alternatives Alternatives3A
and 3Bprovide both the required totaloffice area and
the required office area per story. Both alternatives
provide a plaza at street levelwith an area of nearly
20,000 sq ft, less the space required for the stilts.
With the office floors starting100ft above theplaza,
Alternative 3A would be about 420-ft high and
Alternative 3B about 400-ft high. These heights
would be about the same as those of neighboring
office buildings.Also,bothalternativeswould be set
backfrom the joint property lines with the museum.
Thus, the alternatives meet the first six objectives
listed in Step 1.
Estimated constructioncostsofthe alternativesare
close to the $41,500,000 limit. While the estimated
cost of Alternative 3A slightly exceeds the budget,
the excess is small and acceptable at this early stage
of design.
The alternatives differ principally in bulk and
height. The relationship between these factors and
the zoning code must be taken into account in
evaluation of the alternatives.
Alternative 3A hasa ratio of floorarea perstoryto
lot area of about 67%. Floor-area ratio is
418,500/23,000= 18.
Alternative 3Bhas a ratio offloorarea perstory to
lot area of about 72%. Floor-area ratio is
412,500/23,000= 18. The principal difference in the
alternatives then is that Alternative 3Bis two stories
lower but occupies 5% more of the lot.
Step 9. Decision Alternatives 3A and 3B meet
objectives and constraints about equally well but
construction cost of either is very close to the
budgetary limit. Unit cost will have to be kept below
$100 per sq ft. A lower building will facilitate this,
because it will have less wall area, shorter pipe and
wiring runs, shorter stairs, less costly elevators and
lower structural framing costs.
Recommend Alternative 3B, the 25-story sheer
tower on stilts, to the owner.
3.9. SYSTEM GOALS
Before design ofa systemcanproceed,it is necessary
to have a definite design program, a list of
requirements to be satisfied by the system and of
conditions that exist before the systemis built. From
information in the program, as required by Step 1of
systems design (see Sec.3.8), goals to be met by the
systemmust be defined.
Applied to systemdesign,goals are desired results
expressed broadly. They should encompass all the
design objectives, guide generation of alternative
designs and controlselection ofthe best alternative.
Goals may be classified generally as service or
interactive.
Service Goals
Service goals indicate what the system is to ac-
complish.They apply to such factors as function,or
use, of the system, strength, aesthetics, safety, and
initial, maintenance and operating costs.
Since Step 2of systems design provides thedetails
of required system performance, the statement of
goals should be briefand to the point. For example:
Given:Lot c in City D and construction budgetof
$6,000,000
Design: A factory for the Widget Company for
production of 1,000,000 widgets annually and an
attached office area for three high-level executives
and 20 office workers.
Also,the statementofgoals shouldbe broad.Goals
that are too narrow may lead designers to overlook
favorable alternatives.Forexample, suppose that the
systemto be designedis an exteriorwall.Stating that
the goal is a brick curtain wall would be too
restrictive and might rule out suitable alternatives,
such as limestone or precast-concrete walls. A goal
calling for a curtain wall without restrictions, or
eithera curtain wall ora load-bearing wall,generally
would be better.
Interactive Goals
Interactive goals indicate how the systemwill affect
the environment and other systems.
Environmental interactive goals are those con-
cerned with the response of the systemto human
needs and feelings. Buildings are for people; hence,
a building and its components should be constructed
to appropriate human scale. It should be built with
concern forthe viewofthe building fromoutside and
the view of outside fromwithin the building. Also,
while design should recognize the importance ofthe

client’s needsand desires,the primary concernofde-
sign should be the health, welfare and safety of
building users,whethertheybeoccupants,visitorsor
the client’s employees. Another prime concern
should be the good of the community. The building
should not contribute unduly to pedestrian and
vehicularcongestion orcause shortagesofresources.
Discharges fromthe building should neither pollute
the air nor bodies of water. Nor should the building
excessively restrict movement of air, block passage
of light, or interfere with communication signals,
such as radio and television, to neighboring
buildings. For these purposes, environmental
interactive goals, as applicable, should be specified
to supplement the service goals.
Other interactive goals deal with the desired
effects ofthe systemon othersystems.Forexample,
a goal for an exterior wall might be light weight, to
lighten the load on thestructuralframe.Or a goalfor
an electric lighting system might be low power
consumption, not only for energy conservation
directly but also to decrease the heat gain from the
lights and thus to lighten the load on the building
cooling system.
Other Interaction
In addition to the statement of goals, Step 1 also
should describe how the environment or other
systems will affect the systemto be designed. The
descriptions might provide such information as lot
location and size, land surface and subsurface
conditions,constructionbudget,type ofcommunity,
type ofneighboring buildings, streets and utilities.
When known at the start of the design, the
descriptionsshouldbe included in given information.
They need not be only verbal; mapsand photographs
could be used.
When the information is not available, the effects
may have to be assumedorestimatedin synthesizing
alternative systems and in developing models. For
example, during the conceptual design phase, when
a building site might not yet have been purchased,
design might proceed on the assumption that the lot
will be flat and of ample size. When a site is
purchased later,the design might have to be revised
to accord with actual conditions. Similarly, during
this design phase, when subsoil explorations have
not yet been completed, design of the structural
frame might proceed ontheassumption thatordinary
spread footings can be used. If the foundation
investigations indicate otherwise, the design would
have to be revised. In both cases, for the revised
designs,the newinformation becomes part of given
information.
Example Goal
Given: Construction budget of $50,000 and lot A,
100 X 100 ft, in a middle-class,residentialsection of
Suburb B. Well-drained land slopes slightly toward
the street sideofthe lot.Municipalwaterand sewers
are available on the street side. Gas and electricity
also are available on the street side from
underground lines of A Gas & Electric Company.
There are existing houses on bothsides ofthe lot and
at the rear. All are one-story high andhave red brick
walls and hipped roofs. Entrances face the street.
(This information is given verbally here but in
practice would be provided on a survey map,
supplemented by photographs.)
Design: A house for Mr. and Mrs. Will B.
Homeowner and their two sons and daughter.
Children’s ages are 17,15 and 12.
The house should harmonize with the adjoining
houses on the street.
Design must be completed within 90 days.
Construction must be completed within 180 days
thereafter.
3.10. SYSTEM OBJECTIVES
An essential phase of Step 2 of systems design is
identification of system objectives (see Sec. 3.8).
These are similar to goals. But whereas goals are
broad, objectives are specific.
An objective is a desired result achieving or
assisting in theachievementofoneormore specified
goals.
Associated with an objective must be at least one
criterion or a range of values that indicates that the
objective has beenmet and that can serve as a guide
in evaluations of alternative systems.
Expressed anotherway,anobjectiveis a statement
of the response (output) required of a system to
specific conditions imposedon the system(input).A
criterion then is the range in which the measure of
the response must lie. Thus, the response must be
measurable but not necessarily quantifiable. Any
convenient measurement scale may be used to
measure it (see Sec. 3.2).

Objectives for systems design usually may be
listed starting with broad generalizations and then
developed at more detailed levels to guide designof
the system.
Basic Objectives
There are several basic objectives that are generally
imposed on building design. They specify that
requirements of building codes, zoning ordinances,
subdivision regulations, utility companies, fire
marshalls, health departments, labor departments,
OccupationalSafety andHealth Administration,etc.,
must be met. Since these objectives occur so
frequently, they may be considered imposed by
implication and not listed with other objectives in
Step 2. If they were to be waived, however, an
objective should be listed to indicate the intent of a
replacement. Also, where there may be some
ambiguity in applicability ofa code orthere are some
other reasons for specifying a code, an objective
should be given to indicate which code building
design must satisfy.
Another set of basic objectives that should be
stated explicitly deals with costs and time. These
objectives should comply with the client’s
requirements and reflect the seriousness with which
he views his proposed budget. The objectives, for
example, should indicate whether initial,
maintenance or operating costs, or any combination
of them, are to be minimized. Also, the objectives
should note whether construction time is to be
minimized. Energy conservation may be an implied
objective ifcovered by a legalregulation,orimplied
by an objective concerned with minimization of
operating cost, or required by a specific objective.
In accord with the classification ofgoalsasservice
orinteractive,objectivesmay be similarly classified.
Service Objectives
A primary objective ofbuildingdesignis toserve the
needs of the client and building users. Accordingly,
a set of objectives must be provided to insure that
those needswillbe met. If, forexample, the building
is a factory,objectivesmust indicate the size,nature
and relationship of facilities needed for production;
power, water and other resources required; wastes,
smoke and heat that must be disposed of; and
environmentsthat mustbe provided.Similarly, if the
building is a school, objectives must indicate the
size, nature and relationship of classrooms, lecture
halls, study rooms, auditoriums, gymnasiums,
offices, library and other educational facilities
needed; power, water and other resources required;
waste disposal; and environments that must be
provided. For building components, similar
objectives insuring that functionalrequirements will
be met must be compiled.
Otherservice objectives should dealwith specific
characteristics of a building and its components :
appearance,strength,durability,stiffness,operation,
maintenance and fire resistance.Stillotherobjectives
should be concerned with human aspects: safety;
convenience in moving about and in locating and
using facilities; and comfort, including thermal and
acoustical. Additional objectives usually are needed
to specify controls needed for operation of systems
provided to meet the preceding objectives.
Interactive Objectives
Those objectives that specify how the systemto be
designed will affect the environment and other
systems are secondary to the preceding objectives
but nevertheless are important.
Environmental interactive objectives should be
specified to attain environmentalinteractivegoals,as
explained in Sec.3.9. In the interests ofpublic health,
welfare and safety, these objectives seek to avoid
pollution, to respect the rights of neighbors, and to
enhance community life.
Additional interactive objectives are necessary to
attain goals concerning the effects of the systemon
other systems, as explained in Sec. 3.9.
Sources of Criteria
As mentioned previously, at least one criterion
should be associated with each objective,to be used
as an indication that the objective has been met.The
criterion should apply toa measure ofan appropriate
systemresponse.Criteria may be chosenfromany of
numerous sources, depending on the particular
objectives.Note thatonecriterion may be applicable
to more than one objective,while one objective may
be associated with more than one criterion.
Criteria for objectives related to legal regulations,
such as building codes, zoning ordinances, health
laws and labor department rules, usually may be
obtained from those regulations. Criteria dealing
with quality of materials and methods of testing
materials often may be secured fromspecifications

of ASTM (formerly American Society for Testing
and Materials)orFederalSpecifications.Criteria for
such characteristics of systems as strength and
resistance to deformation and for fabrication and
construction methods generally may be found in
industry codes of practice, such as those of the
American Institute of Steel Construction, American
Concrete Institute and American Institute ofTimber
Construction. Also, criteria may be obtained from
recommendations of professional societies, such as
the American Institute of Architects, American
Society of Heating, Refrigerating and Air-
Conditioning Engineers and Institute of Electrical
and Electronic Engineers.
In some cases, it may be necessary to develop
criteria based onthe owner’s feelingsorestimatesof
values to him of various systemresponses. Criteria
applicable to aesthetics are of this type.
Alternatively, such criteria may be derived from a
consensus ofthe members ofthe building teamorof
building users or others who will be affected by the
objectives.In othercases,the only source ofcriteria
may be the experience and judgment of the
designers.
Relative Importance of Objectives
In addition to identifying the objectives ofa system,
the designers and analysts also must determine the
relative importance ofthe objectives.Ifmoney could
be used as a measure of importance, ranking of
objectives would be easy. Many systemvalues, or
benefits, however, are not quantifiable. Appearance
is one example. Comfort ofbuilding usersis another.
Consequently, some means must be adopted for
weighting system values in accordance with im-
portance to the client, building users and the public
(see Sec. 3.3).
One method that has been used for doing this is
described in Sec.3.2 (see Table 3.1). Othermethods
have also beentried.(See,forexample,c.E. Osgood,
G. J.Suciand p.H.Tannenbaum,“The Measurement
of Meaning,” University of Illinois Press, Urbana,
Ill., and L. L. Thurstone, “The Measurement of
Values,” University ofChicago Press, Chicago, Ill.)
3.11. SYSTEM CONSTRAINTS
As indicated in Sec. 3.10, objectivesand criteria are
related to system responses. When a system is
modeled, responses are represented by dependent
variables. The independent variables, which
represent the input to the system and system
properties, may be controllable by the designer or
uncontrollable (see Sec.3.1).The designer,however,
may not be completely free to select any values he
desires for the controllable variables. There may be
restrictions—legal, economic, physical, chemical,
temporal, psychological, sociological, aesthetic,
etc.—that either fix the values of these variables or
establish a range in which they must lie.
Constraints are restrictions on the values of
controllable variables thatrepresentproperties ofthe
system.
Associated with a constraint must be at least one
standard.A standard is a specific desired value ofa
controllable variable.A minimumstandard is a value
below which the variable should not fall. A
maximum standard is a valuethat the variable should
not exceed.
An example of a constraint is a building-code
requirement that the thickness of a one-story, load-
bearing,brick wall shallnot be less than 6in. In this
case, 6 in. is a minimum standard.
Another example of a constraint is a health-
department regulation that when the outdoor
temperatures between October 1 and April 1 fall
below 65° F buildings must be heated to maintain a
temperature of at least 68° F. In this case, 68°F is a
minimum standard.If the client were to require that
at no time should temperatures in occupied areas,
otherthan entranceways,ofa building exceed 77°F,
that temperature would be a maximumstandard.
Sometimes, it may be difficult to distinguish
between objectives, which are related to responses,
and constraints, which are related to system
properties. For example, costs may be considered a
response of a system or a property of the system,
depending on circumstances. A restriction on cost
may then be imposedaccordingly eitheras a criterion
for an objective ora standard fora constraint.More
specifically, suppose an owner wished to minimize
costs. That would be an objective. If, instead, the
owner established a budget that must not be ex-
ceeded but did not care how much less than the
budget would be spent, there would be no necessity
to minimize cost.Thus,the budgetamountwould be
a standard. Similarly, the maximum permissible
completion date forconstructionwould bea standard
if the ownerdid notcare howmuch earlierthe project
were to be completed. Another example is beauty,
which sometimes may be consideredtobe a response

of a systemand sometimes, a systemproperty.
For Sections 3.8-3.11
References
D. Meredith et al., Design and Planning of Engineering
1985.
s. Andriole, Interactive Computer Based Systems Design and
Development, Van Nostrand Reinhold, New York, 1983.
A. Gheorghe, Applied Systems Engineering, Wiley, NewYork,
1982.
Wordsand Terms
Constraints Criteria FeedbackGoals: service, interactive
Loop
Objectives: basic, service,interactive Standards
Steps in systems design, fromdata collectiontospecification.
Analysis, evaluation, andcomparisonof alternatives.
Anticipationof feedbackandloopingin the design process.
Purposes andrelations of goals andobjectives.Importance of
criteria in definingof objectives. Sources of criteria.
3.12. VALUE ANALYSIS
As defined in Sec. 1.3, value analysis is an in-
vestigation of the relationship between lifecycle
costs and values of a system, its components and
alternatives to these, to obtain the lowest life-cycle
cost for an acceptable performance.
Value is a measure of benefits anticipated froma
system response or from the contribution of a
component to a systemresponse. This measure is
used as a guide in a choice between alternatives.
Scales that may be used for value measures are
discussed in Sec. 3.2.
Life-cycle costs may be taken as the sum of the
present worth of initial, maintenance and operating
costs; or they may equally well be taken as the sum
of equivalent annual initial, maintenance and
operating costs. In either form, life-cycle costs
encompass money measures of such system
characteristics as quality, energy consumption and
efficiency. Furthermore, initial, or construction,
costs include tax, wage, handling, storing, shipping,
fabrication,erection,finishingand clean-up costs,in
addition to the purchase price of materials and
equipment. Requiring life-cycle costs to be
minimized, therefore, is equivalent to requiring that
the sumof all the previously mentioned component
costs be minimized.
Value analysis requires that system values
(benefits)be balanced against the costs ofproviding
them. Thus,value analysis is not merely a device for
paring down costs.Its aimis to go as far as possible
toward relevant goals and objectives while
minimizing total cost. Consequently, other values
than economic ones often must be considered. This
requires determination of the relative importance of
objectives (see Sec. 3.10) and weighting of values
accordingly (see Sec. 3.2).
Weighting ofvalues should reflect the seriousness
with which the client views the constructionbudget.
Often, the budget is established as the maximum
permissible constructioncost.Ifcosts cannot bekept
within the budget, the project may be canceled.
When the constraint of the budget is a governing
factor, minimization of life-cycle costs, as desirable
as it may be as an objective, may not be realizable.
In such cases, a prime concern of value analysis is
keeping construction costs within the budget. As a
result, space, quality, reliability and low energy
consumption may be traded off for initial cost
savings, with consequent higher maintenance and
operating costs and poorer aesthetic results. The
client may plan on correcting these at a laterdate, if
possible,when funds become available; orthe client
may be willing to accept the adverse effects
indefinitely as the price he has to payforcurrentlack
of suitable funds.
Steps in Value Analysis
Regardless of the design phase in which value
analysis is applied, the value analysts must be
thoroughly acquainted with the building program,
system goals, system objectives and criteria, and
systemconstraints and standards. Through study of
design drawings and specifications and proposed
construction contracts, if available, the analysts
should also familiarize themselves with the system
or systems to be analyzed. From information
supplied by the client and the systemdesigners, the
analysts then should determine the relative
importance of the system objectives and weight
values accordingly. The weighted values are to be
compared with estimated costs.
Forthe purposes ofcostanalyses and comparisons,

cost estimators should develop and calibrate cost
models from records of costs of previous similar
systems. When a cost estimate is obtained for
construction of a system, the result should be
compared with the budget and anindication obtained
as to how much cost cutting is needed. When the
estimate is smaller than the budget, further cost
studies may not be necessary but they still are
desirable,to insure that the client will be getting his
money’s worth.
With the aid ofthe cost models,the search forways
to cut costsis facilitated.With complicated systems,
however,it may not be practicalto investigate every
component or even every subsystem. Instead, the
analystsshouldidentify targetitems forstudy.These
may be discovered through comparisons with
previously recorded costs of similar items. For
example, a subsystemwhose cost represented a high
percentage of the total system cost in a previous
systemwould be a good target.As anotherexample,
a subsystemwhose cost differed substantially from
the cost ofa similar subsystemin a previous system
would be a suitable target.
To cut costs, the analysts may seek to eliminate
components, substitute more efficient or less costly
components, or combine components so that one
component can serve the purposes of two or more.
The effects ofthe changes on costscan be estimated
with the aid ofthe cost models.Because the changes
are also likely to affect systemvalues, the analysts
should determine new weighted values for the
revised system. Costs and weighted values should
then be compared to provide a basis forthe decision
as to whether the changes are warranted.
The cost-cutting investigation should not be
restricted just to the system itself. The analysts
should review the building program, specifications
and construction contracts as well as criteria and
standards to determine whether they are essential,
too restrictive,orin otherways add unnecessarily to
costs. If the analysts should find that a change is
necessary,they should report this to the designers.
System changes recommended by the value
analysts will result in a new system. It should be
treated as indicatedin Step 7and subsequentstepsof
systems design (see Fig. 3.4).
References
L. Miles, Techniques of Value Analysis and Engineering, 2nd
Wordsand Terms
Benefit
Benefit-cost analysis
Life-cycle costs
Tradeoffs
Relative importance of separateobjectives. Relative
flexibility of criteria andconstraints. Reconsiderationof
objectives basedon value analysis.
3.13. OPTIMUM DESIGN
OF COMPLEX SYSTEMS
Section 3.1points out thatifoptimization ofa system
is an objective, preferably only one criterion for the
selection of the best systemshould be chosen. The
criterion may be expressed in the form of an
objective function [see Eq. (3.5)]. The system,
however, also has to satisfy constraints, which may
be expressed in the formof Eqs. (3.6).
For a complicated system, such as a building, a
direct solutiongenerally is impractical.There are too
many variables and constraints. Also, it may be
necessary that otherobjectives,which,while not the
prime concern, also must be met.
Selectionof Previously UsedSystems
To meet the many objectives of a complicated
system, some designers recommend, without
thorough study, a system that has been used
previously and worked satisfactorily. They usually
offer any or all of the following reasons for this:
1. Design costs mount with time spent on design,
and the design fee that the client is willing to
pay is not sufficient to coverdesigncosts fora
thorough study.
2. The deadline for completion of design is too
close to permit a thorough study.
3. Contractors quote lowerprices for constructing
systems that have been built before and build
themfaster and better than systems with which
they are not familiar.
4. The probability of getting successful results
with a systemthat has been successful in the
past is very high.
These are good reasons and generally true. As a
result,the systemchosen may sometimes be thebest
for the client.It will actually be the bestifthe system

had been developed throughstudy andexperience to
meet certain objectives and constraints and these all
happen to be the same as those of the client. Often,
however, the client has objectives that differ from
those ofotherownersorthe constraints,such asbud-
get, building codes, zoning ordinances, foundation
conditions,orclimate, differ from those imposedon
previous systems. In such cases, if a system is
selected without adequate systems analysis, the
client either will not attain his goals or will pay too
much for what he gets.
Trial and Error
An alternative that often is used to try to attain
optimization of a systemis trial and error. In many
cases, this is the only feasible method, because of
systemcomplexity.(Simulation may be considered a
form of trial and error. See p. 63.) Trial and error
involves selection of a tentative system and a
sequence of attempts to improve it by changing
controllable variables while observing the effectson
the dependent variables. (See Example 3.4, p. 79.)
The procedure has at least the two following
disadvantages:
1. It may have to be terminated before opti-
mization has been achieved, because of design
time and cost limitations.
2. The nature ofthe initial systemselectedmay be
such that, even if the system were to be
optimized,it stillwould not be theoptimum.For
example, if a long-spanstructuralsystemwas to
be designed for lowest cost and the initial
system selected was a concrete frame,
optimization by trial and errorwould lead to the
lowest-cost concrete frame.The true optimum,
however,might be thelowest-coststeelframe or
the lowest-cost thin concrete shell, and not a
frame at all.
Recognizing these disadvantages, the designers
must rely on experience, skill, imagination and
judgment in using trial and error to attain
optimization. The aim should be to approach the
optimum if design costs and time have to halt the
design effort at any stage.
Suboptimization
The procedure most often used for a complicated
system, such as a building, is to try to attain
optimization of the systemby suboptimization; that
is, by first optimizing subsystems. This procedure,
however, for several reasons, may not yield a true
optimum. Usually, because of the interaction of
systemcomponents, design of a subsystemaffects
the design of other subsystems. Hence, a subsystem
cannot be optimized until the others have been
designed and their effects evaluated. This usually
makes necessary a trial-and-error procedure for de-
sign, which has the disadvantages previously
mentioned.
For example, in optimizing structural costs,
minimum costs will not always be obtained if, first,
costs of roof and floor framing are minimized and
then column and foundation costs are minimized.
For, though column and foundation sizes are
determined by the load from the roof and floor
framing, the minimum-cost roof and floor framing
may be heavier than other alternatives and thus
require more costly columns and foundations than
would the alternatives.The totalcostofthe framing,
therefore, may not be the optimum.
Sometimes, it may be possible to optimize a
system by suboptimization directly when com-
ponents influence each otherin series. For example,
consider a systemwith three subsystems (see Fig.
3.9a). Subsystem 1 is assumed to have a known
input.This subsystemaffects only subsystem2; that
is, the output of subsystem 1 equals the input to
subsystem2. Similarly, subsystem2 provides input
only to subsystem3, whereas subsystem3 does not
affect any other subsystem. Hence, the subsystems
are in series.
Suboptimization may be started with the end
component, subsystem 3, because optimization of
that component has no effect on input to preceding
components.
Subsystem 3, however, cannot be selected
immediately, because the input to it depends on the
design of the other subsystems and therefore is not
known at this stage. To provide the needed input
information, preliminary designs of possible
optimum subsystems may be made in sequence,
beginning with the first subsystem, subsystem1, to
obtain estimates of their outputs. With a potential
input or a range of inputs assumed, one or more
optimum designs may be prepared for subsystem3,
the end subsystem.Next, subsystems 2and 3 can be
optimized togetherfor an assumed input orrange of
inputs, with no effect on subsystem 1. Then, the
process can be repeated with subsystem1, the three
subsystems being optimized in combination. Since
the input to subsystem 1 is known, the optimum

system can be selected from the alternatives
considered.
The procedure may be illustratedby a hypothetical
example. Assume that the system is a one-story
structural frame (see Fig. 3.9/?) and that inputs and
outputs are loads (see Fig. 3.9c). The roof would
correspond to subsystem1 in Fig. 3.9a, columns to
subsystem2 and footings to subsystem3. As shown
in Table 3.2, p. 92, and Fig. 3.9c, the load (input)on
the roof is 400 lb. Load is transmitted in sequence
from the roof through the columns to the footings.
Cost of the whole structural system is to be
minimized.
Suboptimization therefore can be started with the
footings. The load on the footings, however, is not
known initially, because the weight of roof and
columns to be added to the 400-lb roof load cannot
be determined until they have been designed. So
preliminary designsofroofand columns are made to
obtain estimates of the probable weights. As
indicated in Table 3.2, three alternative designs are
prepared for the roof, 1A, IB and 1C (Step 1). With
the weights of those alternatives added to the roof
load, three alternative designs are prepared for the
columns,2A, 2B and 2C(Step 2). A set of loads that
might be expected to be imposed on the footings is
now determined by the output of Step 2.
Suboptimization, starting with the footings,

Fig. 3.9. A system consisting of subsystems in series.
can now begin. As shown in Table 3.2, optimum
footing designs, 3AO,3BO and 3CO are prepared for
the range ofloads that might be expected (Step 1of
suboptimization). Costs are estimated for each
design. Next, for the range of loads anticipated,
columns are selected to make the cost of columns
and footings a minimum (Step 2). Finally, for the
load imposed on the roof, which is given as 4001b,
rhe roofand framing are selected tomake the cost of
roof, columns and footings a minimum (Step 3). In
this example, subsystem1CO which has the highest
cost ($2,700 - $1,000 = $1,700), is selected for the
roof, because, when combined with optimum
columns and footings, that roof yields the lowest-
cost structural frame.
Reference
F. Jelen andJ. Black, Cost and OptimizationEngineering,
2nded., McGraw-Hill, NewYork, 1982.
Wordsand Terms
Suboptimization
Subsystem
Trial anderror
Subsystem
1
(Roof)
Output from 1
= Input to 2
(Load from Roof
= Load on Columns)
Subsystem
2
(Columns)
Output from 2
= Input to 3
(Load from Columns
= Load on Footings)
Subsystem
3
(Footings)
System Output
(Load on Soil)
— )
(a)
(b)
1. Roof
System Symmetrical:
Data for This Side
Same as other Side
Total System Output
Tuice That for One
Side
Input = 400 lb
ị Output = 400 + UR
Input = 400 + UR
2.
Column
Output = 400 + u
3. Footing
+ uc

Problems of selectingpreviously usedsystems. Difficulties
of optimization ofcomplexsystems.
Give and take of suboptimization; need for interactive
analysis.
FOR ADDITIONAL STUDY, CHAP. 3
These are books for general reference, grouped
underthe five categories shown.Referencesrelating
to the individual chapter sections are listed at the
ends of the sections.
Modelsand Optimization
F. Jelen andJ. Black, Cost OptimizationEngineering, 2nded.,
R. Stark and R. Nicholls, Mathematical Foundation for
Design, McGraw-Hill, New York, 1972.
Comparisonsof Alternatives
c. Churchman, Prediction and Optimal Decision: Philo-
sophical Issues of a Science of Values, Greenwood,
1982.
E. Grant et al., Principles of Engineering Economy, 7th ed.,
w. Fabrycky andG. Thuesen, Engineering Economy, 6th ed.,
Prentice-Hall, Englewood Cliffs, NJ, 1984.
Value Analysis
M. Macedo et al., Value Management for Construction,
L. Miles, Techniques of Value Analysis andEngineering, 2nd
A. Mudge, Value Engineering, Society of American Value
Engineers, 1981.
p. O’Connor, Practical Reliability Engineering, Wiley, New
York, 1985.
A. Dell’Isola, Value Engineeringin the Construction Industry,
Van Nostrand Reinhold, New York, 1983.
L.Zimmerman and G. Hart, Value Engineering: A Practical
Approach for Owners, Designers, and Contractors, Van
Systems Design
M. Sanders and E. McCormick, Human Factors in Engi-
neering and Design, 6th ed., McGraw-Hill, New York,
1987.
D. Meridith, et al., Design and Planning of Engineering
Systems, 2nd ed., 1985.
s. Andriole, Interactive Computer Based Systems Design
and Development, Van Nostrand Reinhold, New York,
1983.
A. Gheorghe, Applied Systems Engineering, Wiley, New
York, 1982.
Table 3.2. Suboptimization of a Simple Frame
Preliminary Design
Step 1 Step 2
Load (input)
Subsystem
type
Load +
weight
(output)
Load
(input)
Subsystem
type
Load + weight (output)
400 1A 2,700 2,700 2A 3,000
400 IB 1,800 1,800 2B 2,000
400 1C 800 800 2C 1,000
Step 3 Step 2 Step 1
Input
Optimum subsystems
Lowest
cost
Input
Optimum
subsystems
Lowest
cost
Input
Optimum
subsystem
Lowest
cost
Output
400 1^0 +
+ 3>lơ $2,800 2,700 2T4Ơ + 3/lơ $1,800 3,000 3XO $1,000 4,000
400 1BO + 2BO + 3BO $2,900 1,800 2BƠ + 3BO $1,400 2,000 3BÕ $8002,700
400 1CO + 2CO + 3CO $2,700 800 2CƠ + 3 co $1,000 1,000 3c; $6001,500
Suboptimization
Note. The lowest-cost system consists of the optimum subsystems of types 1C, 2C, and 3C.

Building Codes
Uniform BuildingCode, 1988ed., International Conference of
Building Officials. (New edition every three years.)
The Standard Building Code, 1988 ed., Southern Building
Code Congress International. (New edition every three
years.)
EXERCISES
The following questionsand problems are provided
for review of the individual sections and Chapter 3
as a whole.
Section 3.1
1. What is the most important requirement for a
model? What should be done to insure that a
model meets this requirement?
2. Compare the role of models in systems analysis
with that ofhypothesis in the scientific method.
3. What do iconic models and analog models have
in common?
4. What are the principal advantages of symbolic
models?
5. A beamwith length L is attached with a bolt to
the top ofeach of two columns.One column is
placed at one end of the beam, and the second
column at a distance a (a < L) fromthat end.A
load p is set on the unsupported end of the
beam. Construct a symbolic model that gives,
for every load p, the loads imposed on the
columns.Define the symbols usedin the model.
Test the modelto verify its validity,by (1) set-
ting a = LI 2 and (2) letting a approach L in
magnitude.
6. (1) At the startofdesignofan industrialbuilding
to produce 1,000,000 widgets annually, the
owner establishes a budget for the project of
$3,000,000. Studies ofexisting widget factories
indicate that construction costs, adjusted for
time and regional differences, ranged from
$2,500 to $3,500 per thousand widgets
produced annually. Is the project likely to be
feasible? (2)The ownerestablishesanobjective
of 150,000 sq ft of floor area for the proposed
$3,000,000 widget factory. Studies show that
adjusted construction costs for similar
buildings range from $25 to $30 per sq ft of
floor area. Is the project likely to be
economically feasible?
7. During design of an office building with a
proposedfloorarea of100,000 sq ft and budget
of $3,000,000, cost is estimatedat $16 persq ft
of floor area for architectural components, $5
per sq ft for the structural systemand $12 per
sq ft for mechanicaland electrical systems.To
how many square feet should the floor area be
changed to meet the budget?
8. Excavation for a 9 X 6-ft by 1-ft thick concrete
footing is predicted to take 2 hr for a workman
with payrollcost of$15perhour.Formworkfor
the footing concrete is estimated to cost $40.
Concrete and reinforcing steel in place is
expected to cost $50 per cu yd of concrete.
Overhead and profit is assumed at 20% of
material and labor costs. How much will the
footing cost?
9. Cost records foran existing factory indicate that
building maintenance costs have averaged $30
per yearper 1,000 sq ft of floor area. A similar
proposed factory will have 1,000,000 sq ft of
floor area. Estimate the average annual
maintenance cost for the proposed building on
the assumption that costs will increase 100%
during the service life of the factory.
Sections 3.2 to 3.4
10. If a businessmancan get a rate ofreturn of15%
annually by investing $10,000 in his business,
howmuch money will he have at the end of 10
years if he reinvests the return every year?
Assume annual income tax at 5 % of the total
invested each year.
11. A $200 blowerpurchased todayis estimated to
have a salvage value of $20 after 5 years of
service.
(1) For a rate of return of 10%, what is the
present worth of the blower?
(2) What is the present worth of the salvage
value for a 10% return?
12. Howmuch shouldcapitalrecoverybe each year
for 20 years if a building costs $1,000,000 and
the desired rate of return is 10%?
13. An industrialist is contemplating installing in
his factory a labor-saving device at a cost of
$10,000. Annual savings of $5,000 will be
sufficient to enable the industrialist to recover
his investment in 3years,thoughthedevice has

a life of 10 years. Show that the rate of return
in the first 3 years will be about 23%.
14. (1) What is the present worth of annual
revenues of $117,460 for 20 years if the
rate of return is 10 %?
(2) What is the present worth of annual
revenues of $117,460 continued indef-
initely if the rate of return is 10 %?
15. Howmuch shouldcapitalrecoverybe eachyear
for a $5,000 industrial crane if the salvage
value after 5 years is $1,000? Assume a 10%
rate of return.
16. A factory is being designed with plans for
doubling its size after 10 years. The owner
wants an emergency electric power-generating
plant installed. Two plans are being
considered:
Plan 1. Purchase equipment initially for the
planned future size of factory. The equipment will
cost $100,000 initially and will have a probable life
of 25 years, but no salvage value. Annual
maintenance and operating costs are estimated at
$12,000.
Plan 2. Purchase equipment for the initial size of
factory and add more generating equipment when
the factory is expanded 10 years later. Initial
equipment will cost $60,000. It is estimated that the
added equipment will cost $80,000. In both cases,
equipment is estimated to have a life of 25 years
with no salvage value; but at the end of 15 years,
salvage value is estimated at $20,000. Annual
operating andmaintenancecostsare estimated to be
$7,200 for the initial equipment and $14,400 for the
final installation.
Which plan will be more economical with an 8%
rate of return?
17. A $50,000 house is initially designed with no
roof insulation. The HVAC installation will
cost $4,000. Maintenance and operating costs
will be $700 annually for HVAC. Addition of
insulation in theroofwillresult in the following
costs:
INSU-
LATION
THICK-
NESS, IN.
COST
INSTALLED
HVAC COST
INSTALLED
ANNUAL
HVAC
COSTS
2 $100 $3,700 $600
3 $125 $3,700 $590
4 $150 $3,500 $585
5 $175 $3,500 $580
6 $200 $3,300 $575
What is the most economical insulation thickness?
Assume a 10% rate of return.
18. Incrementalbenefit-cost ratio forAlternative 1
overAlternative 2is 0.86, and ofAlternative 2
over Alternative 3, 2.10. Which alternative is
best?
Section 3.5
19. Who enforces building codes?
20. A building code states thatthe minimumsize of
copperelectricalconductorpermitted is No.14.
An electricalengineerspecifies a minimumsize
of No. 12, which is larger and more costly,for
a residence,although calculations indicatethat
No. 14 is more than adequate in some cases.
What justification does the engineer have for
his specification?
21. What document does a contractor need froma
building department before construction of a
building may start?
22. What document does an owner need to show
that he has building-department permission to
occupy a new building?
23. What are the principal differences between
specification-type and performance-type
codes?
24. Where would you find information as to
whether a wood school building may be built
along a specific city street?
25. What provisions do building codes contain for
prevention of spread of fire in any story of a
large building?
26. What provisions do building codes have to
insure egress for occupants in emergencies?
Section 3.6
27. What are the purposes of a zoning code?
28. What is the relationship between zoning and
subdivision regulations?
29. What two types ofzoning regulations should be
checked to determine if a woodframe factory
may be built on a lot fronting on a specific
street?
30. A builder plans a 60-story building in a city.
The city zoning ordinance will ordinarily

permit this height on the size of lot owned by
the building and the lot location. What other
zoning regulations should the builder check?
31. A developer plans to erect 100 houses on land
zoned by a county for residential construction.
(1) What ordinance should the developer
consult for limits on minimum lot size? (2)
What regulations govern street layout? (3)
What regulations specify how far each house
must be fromits lot lines.
32. A developer owns a 500-ft-long strip of land,
wide enoughforonly one rowofhouses,along
a street. The zoning code requires a minimum
frontage of20 ft for lots along that street.What
is the maximum number of lots into which the
land may be subdivided?
33. A builderowns a 10,000-sq ft lot.Ifhe provides
a plaza at street level, the zoning code permits
a floor-area ratio of 15 if the average area of
each floordoes notexceed 55% of the lot area.
How many stories high may a sheet tower be
constructed on the lot?
Section 3.8
34. What are the purposes of Steps 1 and 2 of the
systems design procedure?
35. What does Step 4 of the systems design
procedure accomplish?
36. What is the purpose of value analysis?
37. What action specifically does Step 9 call for?
38. A one-story building with 2,500 sq ft of floor
area is to be enclosedwith a 10-ft-high exterior
wall. If the wall is built in straight sections, it
will cost $8 per sq ft of wall area; if built in
curved sections, $10 per sq ft. Comers cost
$250 each to build. What shape should the
building have in plan and what should its
dimensions be to minimize construction cost?
39. Explain the relationship between systemgoals
and objectives.
40. How does a system objective differ from a
systemconstraint?
41. What purposesdo criteria serve with respect to
systemobjectives?
42. What purposesdo standards serve with respect
to systemconstraints?
43. When a model of a systemis formulated, to
what do criteria and standards, respectively,
apply?
44. A manufacturer of heavily advertised,
consumerproducts is the client fordesignofan
office building to be built along a heavily
traveled highway.He requires that the building
be a showpiece, because of the advertising
value to his products.In this case,wouldbeauty
be an objective or a constraint?
45. A factory is being designedforconstructionin
an industrialpark.The ownerstates thatit must
be built for the least possible cost and sets a
tight budget. Management of the industrial
park, however,will not permit buildings in the
park that are not sufficiently handsome to
obtain approval of its architectural committee.
In this case,would beauty be an objective ora
constraint?
Section 3.12
46. Basically, what is a systemvalue?
47. Name at least three components ofconstruction
cost of an installed window.
48. What kind of costs are included in lifecycle
costs besides initial cost?
49. Describe two alternative ways ofconvertingthe
components oflife-cycle costs to the same basis
so that they can be added.
50. A change is beingconsideredin a systemunder
design. If value is expressed in mon- etaiy
terms, what should the minimum ratio ofvalue
added by the change to the resulting cost
increase be to justify an improvement in the
system? What should the maximum ratio of
value lost by the change to the resulting cost
saving be to justify the change?
General
51. Define systems design.
52. What steps in systems design are called for by
“Model the systemand apply the model”?
53. What is the purpose ofthe objective function?
54. Why should interest rates be used in making
economic comparisons of alternatives?
55. A client owns a building that he expects to sell

in 5 years for $100,000. If the rate of return is
10%, what is the presentworth ofthe building?
56. A client anticipatesthat he will have to replace
his $500,000 building in 5 years.Salvage value
is estimated at $100,000. How much money
should the client put aside annually at 6%
interest to have $500,000 in 5 years for
purchase of a new building?
57. Maintenance costs of a building are averaging
$30,000 peryear.Ifthe interestrate is 6%,what
is the present worthofthese costsfora 10-year
period? What would the present worthbe ifthe
costs continued indefinitely?
58. An owneris considering two typesofbuildings
for a proposed factory. Revenues fromuse of
the buildings willnot be affected by his choice.
Estimates for cost of the alternatives are as
follows:
BUILDING1 BUILDING2
First cost $100,00 $240,000
Life, years 20 40
Salvage value $20,000 $40,000
Annual
disbursements $18,000 $12,000
Rate of return, % 8 8
Which building will be more economical?
59. In what legal documents should you look for
requirements for:
(a) Number of street-level exits from a
building?
(b) Minimum distance of a building from a
rear lot line?
(c) Height ofbuilding and numberofstories?
(d) Minimum width of streets in a new de-
velopment?
(e) Electrical conduit to beused in a building?
60. Why should building designers be familiarwith
the requirements of OSHA for factoiy
conditions?Why should contractors be familiar
with OSHA requirements?
61. Describe the advantages and disadvantages of
using standard plans and specifications for
severalbuildings ofthe same type forthe same
ownerbut to be constructed on different sites.

96
Chapter 4
Application of Systems Design to
Buildings
In Chap. 3, systems design is proposed as a precise
procedure for development of an optimum system.
The method consists of six stages: data collection
and problemformulation, synthesis, analysis, value
analysis, appraisal and decision. In addition to data
collection, which could be a continuous activity
feeding information to every design step, there are
nine basic design steps (see Fig. 3.4). These
generally should be executed in sequence; however,
the procedure also calls for loops from advanced
steps back to earlier steps and then ahead again, as
new information that can be used to improve the
systemis generated.
In brief, systems designrequiresdesignersto start
with a list of goals, objectives and constraints.
Criteria must then be established, as a measure of
system response, to indicate whether or not
objectives have been met. Also, standards must be
set as a measure of the constraints on properties of
the system. Next, designers must propose one or
more designs that will satisfy the objectives and
constraints. With the aid of models, the designers
should analyze the proposedsystems and attempt to
obtain an optimumdesign for each. The alternative
systems should be evaluated and compared. After
evaluation by the designers,one ormore of the best
systems should besubjected tovalueanalysis.In this
process, the systems may be changed to improve
theircost effectivenessorsuggestionsforalternative
designs may be proposed. In either case, the
designers should analyze the alternatives, evaluate
them and seek new improvements. With this
procedure, the design should improve as new
information develops and therefore should converge
on the optimum for the given objectives and
constraints.
Application ofsystems designto buildings is made
difficult by the following factors:
1. A building is a very complicated system.
Design of any of its component systems may
affect the design ofmany, perhaps all, others.
2. Design costs generally mount rapidly with
additionalinvestigations ofalternative systems.
Design fees may not be sufficient to cover the
costs of numerous studies.
3. Time available for design often is limited and
thus restricts the number of investigations that
can be made.
Systems design, therefore, rqust be adapted to
building design with these factors in mind. This
chapterdescribes one way ofapplyingthe method to
buildings.
The design process requires the designers to make
tentative decisions as various requirements are
considered and various parts of the system are
tackled. The results of these decisions must then be
tested for validity against the results of previous
decisions. The resulting facility must be a well
integrated unit, not just an assembly of solutions to
individual objectives. Thus, every component or
subsystemshould exist only to serve the purposes of
the whole system.

Application of Systems Design to Buildings 97
4.1. CONSIDERATIONS IN ADAPTATION OF
SYSTEMS DESIGN
For complex buildings,the probability is very small
that direct application of systems design to whole
systems will be completely successful. There is so
much interaction to such a high degree among
building components that usually designers can
attain an optimumbuilding only by suboptimization.
This optimization procedure, however, because of
the effects component systems have on each other,
usually has to be executed by further
suboptimization or, more likely, by trial and error.
The latter process requires that one or more
alternatives be synthesized,analyzed and evaluated,
then discarded, improved or replaced by other
alternatives, and the process repeated continuously
in a search for the best solution.
The trial-and-error approach to design has long
been accepted practice in traditional design. In fact,
the traditional building procedure described in Sec.
1.2 evolved overa long period oftime to handle the
trial-and-error process effectively. For the purpose,
the traditionalbuilding procedure providesa phased
approach to selection of a final system. The phases,
varying fromthe generalto the specific in sequence,
comprise:
1. A conceptual phase, in which alternative
building systems are synthesized and in-
vestigated.
2. A design development phase, in which al-
ternative component systems are synthesized
and investigated.
3. A contract documents phase, in which details
are worked out.
4. A construction phase, in which the building is
erected.
The procedure gives designers an opportunity in
each phase to submit results to owners for approval
and to start subsequent phases with previous results
approved.
There appear to be at least two good reasons for
adapting systems design to the traditional building
procedure. One reason is that, despite the defects
discussed in Sec.1.2, it has worked well in practice.
The second is that building designers are familiar
with it and are more likely to adopt modifications of
it than to discard it for something completely new
with probable higherdesign costs.Hence,therest of
this chapterwill be concernedwith considerationsin
adapting systems design tothe traditionalprocedure.
Design by Building Team
The greatest change in traditional practice required
by systems design,in additionto the orderly step-by-
step convergenceto an optimumdesign,is design by
a building team, as discussed in Sec. 1.4.
In traditional practice, a prime professional,
generally an architect, assumes responsibility for
building design. He is assisted by consultants, each
ofwhomworks individually in applying his specialty
to meet design objectives. The prime professional
correlates the work of the specialists. Usually,
however,there is little or no effort to integrate their
work to produce economies by making one
component serve several functions.
In design by a building team, there still is a prime
professionalbut his prime taskis to serve as the team
leader. Throughout design,all members of the team
contribute their knowledge, experience, skill and
imagination. Their work is not only correlated but
also guided and integrated. Also, since construction
experts and building operators may be members of
the team, the results ofteamdesign should be better
designs and buildings with lower life-cycle costs.
Suboptimization in Building Design
Because ofthecomplexity ofbuildings,optimization
usually is feasible only by suboptimization. This
process, discussed in Sec. 3.13, is fraught with
pitfalls. The most treacherous pit- fall is that use of
the process may give the impressionthatan optimum
has beenattainedwhentheresult actually may not be
a true optimum. Experience and judgment are the
only means of avoiding the pitfalls.
The technique ofsuboptimization ofa systemwith
subsystems in series is likely to have limited
application in building design.Suchsuboptimization
may be useful only for small subsystems or
subsubsystems, because most building components
affect or are affected by many other components.
The generalprinciple,however,may be adaptedto
suboptimization of larger subsystems where the
effects of interaction are small enough that the
components may be treated as ifthey were in series.
Errors introduced by this assumption then may be
corrected, if substantial, after the interaction effects
have been evaluated.

When construction duration and costs are im-
portant considerations,greatereconomies may result
from integration of subsystems than from
suboptimization ofindividualsubsystems.Consider,
for example, a floor systemcomposedofa deckand
beams, with lowest cost as the design objective.
Optimization of the floor cost conceivably could
result in a more costly building.The designmight be
such that costs of installing HVAC ducts, placing
electric wiring, lengthening vertical pipe runs and
building higher exterior walls would be larger than
with other types of floors. Results closer to the true
optimum are more likely to be attained by in-
corporating ducts, wiring conduit and piping in the
floor system and optimizing that system. Since
knowledge of several specialties is required for
design of the system, this example points to the
desirability of design by a building team.
Construction Considerations
Whether traditional or systems design is used,
designers should take into account construction
conditions that not only normally exist but also
special conditions that are likely to exist when the
building is constructed.
For example, designers should insure that it is
feasible to fabricate and erect building components
as drawn and specified. For this, designers need a
knowledge of fabrication and erection methods. In
addition, a construction expert should check the
designsas soon aspossible,certainly before bidsare
requested. This is only one of many useful services
that can be performed by the constructionconsultant
on the building team.
Another useful service that the construction
consultant can perform is to advise the other team
members of construction market conditions that are
likely to exist when the building is constructed. He
should forecast the availability of materials and
equipment that the designers are considering
specifying. There is no sense, for example, in
specifying a windowtype that the manufacturerwill
be unable to deliver when it is needed for the
building. Also, the construction consultant should
predict the availability ofcontractors,subcontractors
and labor that might be required. Shortages of one
type or another not only might require substitutions
for specified materials and equipment but also
rescheduling of construction contract awards.
When the owner needs a building in a hurry and
design and construction time consequently must be
minimized, the construction consultant should, in
addition, assist in scheduling all phases of the work
to insure that the deadline will be met at minimum
cost.
Phased Construction (Fast Track)
Construction cost and project duration are
interrelated.
Cost increases when construction time surpasses
the optimum. That happens because the decrease in
wages through use of fewer workers is more than
offset by constant overheadcosts,which continue as
long as the building is under construction, and
because ofthe costofdelays due to inefficiency,bad
weather or other causes.
Also, cost tends to increase when construction
time is shorter than optimum. That happens
generally because wages rise due to use of more
workers or overtime payments and bonuses.
Usually, therefore, contractors strive to optimize
construction time.
Design,though,also influences construction time,
for designers can speed construction by calling for
systems that can be erected quickly.
Also, designers can shorten project duration by
cooperating with the construction consultant and
construction contractors in a speed-up technique
known as phased construction, or fast track.
In this process, construction starts before design
has beencompleted.Early phases ofconstructionare
begun while later phases are still being designed.
Contracts are awarded for subsequent phases as
rapidly as designis completed.Forexample, as soon
as foundation drawings have been completed, site
work on the foundations commences. As the floor
framing plans are finished,the contractor orders the
structuralsteeland concrete reinforcing bars needed.
Structural members for the lower floors of a tall
building are erected while the upper floors are still
being designed.Similarly, an early start can be made
on placement of exterior walls and windows,
construction of partitions and even finishing
operations.
Whetherconstructionbe normalorphased,design
and construction must be integrated. The building
team must work together as a unit from project
inception to completion to insure that the owner

attains his goals. Balancing design quality,
construction cost and project duration, the team
should aimat production of an optimumproduct.
Prefabrication and Industrialized Building
As mentioned previously, designers can speed
construction by specifying components that can be
erected quickly. Designers have many options for
doing this.
One option is to specify systems that have been
coordinated so that they can be assembled swiftly in
the field without the necessityofcuttingthemto fit.
Another option is to specify systems that have
been preassembled in a factory. Such systems are
likely to have also the advantage of better quality,
because ofassembly undercontrolled conditionsand
close supervision. They are likely to be lower cost
too, because of mass production, use of fast,
powerfulmachines and lowerwages thanthosepaid
construction workers.Preassembledsystems are also
known as prefabricatedcomponentsor,in the case of
concrete, as precast concrete.
Buildings formed with large preassembled sys-
tems are often referred to as industrialized buildings.
The goalgenerally is to employ tothegreatest extent
possible, in shop and field, the mass-production
techniques that have proved successful in factories.
Before specifying such buildings, however,
designers should take precautions to insure that use
of preassembly will not be counterproductive. For
one thing, designers should check that the owner’s
objectiveswillbe met and that constraints,especially
building-code requirements, will be satisfied. For
another, they should verify that shipping, handling,
storing and erectioncostswill not exceed savingsin
purchase price andpreassembly andthat thesystems
will be delivered when needed.
Designers should bear in mind that traditional
building is difficult to compete with because it often
employs a form of mass, or assembly-line,
production. In factories, a product being assembled
usually moves paststationaryworkers,who perform
a taskon it. In building construction,in contrast,the
product is stationary and the workers move from
product to product to perform the same task. The
major disadvantages of this type of production are
limited use of machines and uncontrolled
environment (climate),which can halt workoraffect
quality.
Design Priorities
With many options open to them to speed con-
struction and cut costs, designers should logically
consider the options in order of potential for
achieving objectives.A possible sequence would be
the following:
1. Selection ofan available industrialized building
2. Design of an industrialized building (if the
client needs many buildings ofthe same type)
3. Forming a building with prefabricated
components or systems
4. Specification of as many prefabricated and
standard components as possible.
5. Repetition of elements of the design as many
times as possible. This may permit mass
production of some components. Also, as
workers become familiar with those elements,
erection will be speeded.
6. Design of elements for erection so that trades
will be employed continuously. For example,
suppose designers ofa multistory building were
to call for a brick interior wall to support steel
beams supported at the other end by steel
columns. Bricks are laid by masons, whereas
steel beams and columns are placed by
ironworkers. Since the steel columns usually
can be erected faster than a brick wall can be
constructed,the ironworkers will be idle while
waiting forthe masons to finish.Thus,this type
of construction would be slower than all-steel
framing.
When to Apply Systems Design
In general,systems design may be used in allphases
of the building procedure. Systems design should
start in the conceptual phase and should be used
continuously thereafter. The procedure is especially
advantageous in the early design phases because
design changes then involve little or no cost.
In the contract documents phase, systems design
preferably shouldbe applied only to the details being
worked out in that phase and not to revisions of
major systems or subsystems. Such changes are
likely to be costly in that phase. Value analysis,
however,could be costeffectivewhen applied to the
specifications and owner-contractor agreements.
In the construction phase, systems design should

be applied only when design is required because of
changes that have to be made in the plans and
specifications.Time may be too short,however,for
thorough studies, but at least value analysis should
be used.
References
Architects Handbook of Professional Practice, American
w. Caudill, Architecture by Team, Van NostrandReinhold(out
of print).
Words and Terms
Building design team
Design priorities
Fast-track (phased construction)
Industrialized buildings
Prefabrication
Suboptimization
Phases of the traditional design procedure: conceptual, de-
velopment, contract documents, construction.
Use of suboptimization for complex systems; problems of
effective integration.
Overlapping of design and construction phases: fast-track.
Utilization of predesigned components and industrialized
buildings for faster design and construction.
4.2. ROLE OF OWNER
When systems design is used, the duties and
responsibilities of the owner during the building
process are substantially the same as for the
traditional building procedure. There are some
differences, however, in the initial steps.
Generally, the basic stepstakenby anownerin the
process of having a building designed and
constructed are as follows:
1. Recognizes the need for a new building.
2. Establishes goals and determines project
feasibility.
3. Establishes building program, budget and
time schedule.
4. Makes preliminary financial arrangements.
5. Selects construction program manager or
construction representative to act as au-
thorizing agent and project overseer, unless
the owner will act in that capacity.
6. Selects prime professional, construction
manager and other members of the building
team.
7. Approves schematic drawings androughcost
estimate.
8. Purchases a building site and arranges for
surveys and subsurface explorations to
provide information for building placement,
foundation design and construction, and
landscaping.
9. Develops harmonious relations with the
community in which the building will be
constructed.
10. Assists with critical design decisions and
approves preliminary drawings, outline
specifications andpreliminary cost estimate.
11. Makes payments offees to designers as work
progresses.
12. Approves contract documents and final cost
estimates.
13. Makes final financial arrangements, obtains
construction loan.
14. Awards construction contracts and orders
construction to start.
15. Obtains liability,property and otherdesirable
insurance.
16. Inspects construction as it proceeds.
17. Makes payments to contractors as work
progresses.
18. Approves completed project.
In many cases,there may be additionalsteps.For
example, the owner may have to make such
decisions as to whether or not phased construction
must be used,whetherseparate contracts ormultiple
contracts should be used or whether the general
contractor should also be the construction manager,
serving on the building team.Note alsothat thesteps
may not all be exactly in the order listed and that
some steps may overlap.
Some of the steps require additional comment.
Selection of Construction Representative
An early decision the ownerhas to make is whether
he will personally manage the construction
program—act as authorizing agent and project
overseer,provide information needed fordesignand
construction, make decisions, approve plans,
specifications and contracts, engage surveyors and
consultants, approve payments for all work and

expedite design and construction, if necessary—or
will designateoneormore representativesto assume
those duties. If he decides to assign a construction
representative, the owner nevertheless retains the
power to set goals, establish a construction budget
and completion date, and make final decisions, ap-
provals and changes.
For large and complex buildings, involving
expenditures of large sums of money, appointment
of a construction programmanager, who manages
both design and construction, or at least a
construction representative, usually is desirable.
Large corporations and public agencies with a big
construction program, for example, often have a
construction department,fromwhich a staffengineer
is assigned to serve as owner’s representative. For
less complicated buildings, the owner may not
require a representative but may rely instead for
assistance on the members of the building team.
There usually are additionalfees,however,when the
consultantsprovideservicesin additionto theirbasic
services.
Selection of Building Team
The skills, knowledge, experience and imagination
of the members of the building teamare critical to
the results.Poordesign can produce a defectiveand
inefficient building,high maintenance andoperating
costs or unnecessarily high construction costs, or a
combination of these. The fees paid the consultants
usually are a relatively small percentage ofthe total
construction cost, and in any event, competent
designers can easily save the owner more than the
amount of the fees. Consequently, the owner will
find it advisable to engage the best talents to serve
on the building team.
In selecting the prime professional, who assumes
responsibility forcomplete design,the ownershould
evaluate the firm’s technical qualifications,
experience, reputation, financial standing, past
accomplishments in related fields and ability to
absorb an additional work load. In addition, the
owner should learn whom the firm will place in
charge ofthe projecttoserve asleaderofthe building
team. The ownershould verify thatthis managerhas
the experience and the capabilities required for a
teamleader, as outlined in Sec. 1.4.
Similar considerationsshould apply in selectionof
a construction consultant, construction manager, or
general contractor, or any other member of the
building team; but, in addition, it is important that
the owner learn whether these professionals have
demonstrated on past projects a capability and
personality suitable for teamwork. Those who have
not should be avoided.
Community Relations
Efforts to establish good relations with the
community in which a building is to be constructed
should start before a site for the building is
purchased.This is especially important ifchanges in
the zoning ordinance will have to be requested to
permit the type of building contemplated. Before a
variance will be granted, the planning commission
will hold public hearings and solicit opinions from
the community. Hence, it is desirable to informthe
public of the nature and purpose of the proposed
building and to indicate the benefits to and potential
harmful effects on the community.The report should
discuss objectively the environmental impact
anticipated, including effects on local and regional
economics, recreation, ecology, aesthetics, housing
and resources.Such information,however,should be
provided the public even when zoning changes are
not needed, because it will promote good public
relations.
A public relations programis the responsibility of
the owner; however,the building teamshould assist
the owner, and if necessary, suggest and guide the
program, because poor public relations can halt or
delay the project or produce other adverse effects.
Goals and Program
Design cannot start until the owner establishes the
goals and objectives forthe building.In addition,the
owner must give some indication as to the relative
importance of each objective for use in evaluations
of alternative systems.
Preparation of the building program, or list of
requirements forspace,services and environment,is
also the responsibility of the owner. The building
team will assist with the program, but there usually
is an additional fee for such service.
4.3. CONCEPTUAL PHASE
OF SYSTEMS DESIGN
The conceptual phase of design is the start of the
search for the best system for a specific set of

objectives and constraints.
The purpose ofthephaseis to convert thebuilding
program, goals, objectives, constraints, data on site
conditions and other relevant information into a
building system that has high potential for client
approval and that, if approved by the client, will be
the basis for design development.
The results of the phase should be schematics—
floorplans,simple elevationsandsections,sketches,
renderings, perspective drawings or models—and
project descriptions that will give the client a broad
picture of how the building and its site will look
when completed. Accompanying these illustrations
should be a rough cost estimate to indicate the
approximate cost of the facility planned.
During the conceptual phase, many alternative
designs may have to be investigated by the building
team. To begin, each member of the team will
generate initial concepts for his specialty. Most
likely, these concepts will have to be adjusted or
discarded asnewinformation is developed.Changes
especially will occur on interaction with concepts
developed by other members of the team.
Eventually, some concepts will stand out as being
worth developingin detailin the next design phase.
Since it is the purpose of the conceptual phase to
present a broad picture ofthe proposedbuilding,the
design effort usually concentratesonly on important
features, such as those effecting the goals, or
functions, of the building, those representing a high
proportion ofthetotalconstructionorlife-cycle costs
and those having significant effectsonaesthetics,the
environment and the community.
The effort involves all members of the team, but
one member usually playsa majorrole. Forordinary
buildings, such as houses, hospitals, schools, office
buildings andchurches,an architect hasthis role.He
has responsibility for aesthetics, environmental
impact and planning the functional spaces, and the
areas used for activities and services. For more
special types of buildings, an engineer most likely
will be assigned the role.Forexample,responsibility
for environmental impact and planning the func-
tional spaces may be assigned to a mechanical
engineer for an industrial plant, to an electrical
engineerfora powerplant and to a civilengineerfor
a sewage or water treatment plant.
This team member initiates the design effort by
synthesizing one or more functional-space systems
to meet relevant objectives, constraints and site
information. His initial concepts are provided to the
other teammembers in the form of floor plans and
simple elevations and sections, with other pertinent
information. After studying them, the consultants
first offer suggestions for improvement and later
develop schematic designs fortheirown specialties,
such as HVAC, structural and electrical systems, to
correlate with the proposedfunctional-space system.
In the following discussions ofthe conceptualphase,
an ordinary building will be assumed as the goal of
design,in which case an architect willplay the major
role in design. The procedure when another team
member plans the functionalspaces would notdiffer
significantly.
Preliminary Information Needed
Before conceptual design can proceed, essential
basic design data must be obtained fromthe owner.
The building team may have to call the owner’s
attention to the need for this information and assist
him in providing it. Predesign information should
include the following:
Feasibility Study. A feasibility study may be made
with the owner’s own staffora building committee,
or with outside specialist consultants or the prime
professionalforbuilding design.The last alternative,
often requiring payment of an additional fee for the
study, has the advantage of familiarizing the prime
professionalwith the owner’s operations andgeneral
requirements for the building. The study should:
1. Anticipate facilities needed.
2. Estimate construction and operating costs.
3. Make economic comparisons of proposed
facilities and of alternatives such as renovation
of existing buildings or leasing instead of
constructing a new building.
4. Anticipate capital financing requirements and
the feasibility ofproviding the funds as needed.
5. Estimate future personnel requirements.
6. Indicate resources orservices,such as electricity,
gas and transportation, required.
7. Indicate potential locations for the facilities
and pertinent requirements for markets,
environment and legislation affecting
construction and operation.
8. Recommend a specific course of action.
If the feasibility study recommends a new building,

design may proceed.
Building Program. The list ofrequirements forthe
building should include the following:
1. Scope and type of project.
2. Relationship ofthe building to otherbuildings
on the site or adjacent to the site.
3. Characteristics of the occupants.
4. Special requirements for the building.
5. Functional requirements, including circulation
of people, material handling and work flow.
6. Priority of requirements.
7. Relationship of activities to be carried out in
the building pertinent to the location ofspaces
for those activities with respect to each other
and the amount of flexibility permitted in
assigning the spaces.
8. Site development requirements.
9. Equipment to be supplied by the owner and
equipment to be supplied by the construction
contractor.
Budget. The owner should generally indicate the
maximum amount ofmoney he is willing to pay for
design andconstruction ofthebuilding.He may also
require that construction cost be minimized or that
life-cycle cost be minimized.
The budget usually is based on the sum of the
following estimated costs based on cost records for
previously built similar buildings:
1. Cost of spaces for activities and services, as
required by the program;
2. Foundation costs;
3. Cost of site preparation and improvement;
4. Equipment costs;
5. Contingency costs, including design fees,
inspection fees, costs of site surveys and
subsurface explorations, legal fees, financing
costs,administrationcostsandcostsofchanges
Contingency costs generally are estimated at about
15% of the sumof the other costs.
In addition,sincedesignand constructionmay take
one ortwo years ormore,the budget should make an
additionalallowance forrising wagesand pricesand
other inflationary effects during that period.
Completion Date. Theownermay set a deadline for
completion of the project and occupancy of the
building. This deadline, in turn, may impose
restrictions on the time available forbuilding design.
The deadlines may be necessary because of
commitments made by the owner for use of the
building,because ofhigh interestcosts forfinancing
overthe periodofdesignand construction orbecause
of revenues desired fromuse of the building on its
early completion. In any event, a practical schedule
should be prepared as soon as possible for both
design and construction. The design schedule
preferably should allot reasonable amounts of time
to each of the design phases. The construction
schedule, if possible, should permit construction at
normal speed to keep construction costs at the
optimum. If necessary, however, phased
construction may have to be used iftime allotted for
construction is too short.
ManagementDecisions. The ownershould make as
soon as possible some basic decisions affecting the
execution of design and construction:
1. Whether to appoint a construction rep-
resentative ora constructionprogrammanager.
2. Whetherto engage a construction managerora
construction consultant to serveon the building
team.
3. Whetherphasedornormalconstructionis to be
used.
4. Whether the construction contract will be
awarded to a general contractor, who will
engage all subcontractors, or whether separate
contracts will be given to several prime
contractors.
5. Type of contract to be used-lump sumor cost
plus fixed fee.
6. Formof generalconditions ofthe contractto be
used.
7. Whetherdesign is to be executed by a building
team or by an architect assisted by consulting
engineers.
Predesign Activities. The prime professional may
organize a building teambefore preparing a proposal
for design of a building, after being asked to do so
by the client, or after signing the design agreement
with the client, depending on particular
circumstances. After being assembled, the building
teamassigns personnel to the project.
The first tasktackled by the teamis review of the
building program, construction budget and
construction schedule. Besides familiarizing
themselves with the requirements,the designers also

insure that it is feasible to comply with them. Next,
from the program and other information elicited
from the owner,the prime professionalcompiles the
goals and objectivesforthe project and providesthe
list to the team members for study. Also, the team
assembles the constraints on design. From the
objectives and constraints, the designers develop
criteria and standards that the systemmust meet. In
the process,the teamassemblesand reviews building
codes, zoning ordinances, health department
regulations,OSHA rules, etc.In addition,the prime
professionalinforms the teamofthe designschedule
to be met. Finally, a preliminary report of the
environmentalimpact ofthe projectmay be prepared
by a teammember.
If a site for the building has not been purchased,
the prime professional may assist the owner in
selecting a site.Ifone hasbeenpurchased,the owner
should provide site information, if necessary
engaging for the purpose surveyors and soil
consultants. Members of the building team also
should visit the site to become personally acquainted
with conditions there.
Design of Functional-Space System
As pointed out previously, an architect usually has
responsibility for planning the spaces required for
activities and services.He should find it worthwhile
to apply the systems-design approach to this task.
From the building programand other information
supplied by the owner,the architect should compile
a list of spaces that will be needed and the
approximate floor area that will

be required foreach space.The othermembers ofthe
building teamshould supply additional information
on spaces needed for their specialties. The architect
also should allow space for horizontal and vertical
circulation,reception ofvisitors,lounges,etc.Then,
the architect should compile otherobjectivesandlist
constraints,forwhich heshould establish criteria and
standards. Next, following the systems-design pro-
cedure, he should generate alternative systems,
modeland evaluate them.Systems may be judgedby
how well they meet objectives and constraints,
construction cost, operating efficiency and space
efficiency, as indicated by the ratio of useful floor
area to gross floor area. The result should be
schematic floorplansthatthearchitectshould submit
to the othermembers of the building teamand value
analysts for study and recommendations.
Example. As an example of the development ofa
floor plan in the conceptual phase, consider a one-
story house with basement for a family with two
small children. The programindicates that the main
floor will have to contain spacesforthe 11 elements
represented in Fig. 4.1(a).
The family requires three bedrooms,BR 1 for the
parents and BR2and BR3 forthe two children.Two
bathrooms are needed,with accessto B 1 only from
BR 1. The family also requires a foyer at the front
entrance, with access to stairs to the basement. A
kitchen is wanted,next to the dining roomand close
to an enclosed porch. In addition, the family would
like a large living room accessible directly fromthe
foyer.
From anticipated furniture, closet and activity
requirements given in the program, areas of the
elements are estimated and shapes are assumed as
shown in Fig. 4.1(Z?). Then, the desired
relationshipsbetween spacesare noted in table form
(see Fig. 4.2).
In Fig. 4.2, the relative closeness desired and the
relative importance ofproximity are indicated,in the
orderofimportance,by the letters A, E, I, o, u and X.
The reason forthedecision is indicatedby a number.
For example, the requirement that B1 be next to BR
1 is indicated by an A at the intersection of the row
la-
150 ft:
DR
130 ft2
LR
350 ft2
Foyer
beled Bathroom 1 and the column marked BR 1.
The reason for the requirement is indicated by the
number2 at the same intersection.In the summary
of reasons at the right in Fig. 4.2, 2
35 ft2 35 ft2
Fig. 4.1. {a} Schematic drawing indicating owner's
basic needs for a one-storyhouse with a basement. BR
= bedroom, B = bath, p = porch, LR = living room, DR =
dining room, K = kitchen, (b} Schematic drawing made
to indicate probable floor-area requirements and room
shapes to meet needs shown in (a), (c) Schematic
drawing showing desired relative locations of spaces
to meet the needs shown in (a).

Bedroom 1 BR 1 Ualue:
Closeness:
A Absolutely necessary
Bedroom 2
A4
^
/
1<
Value E Especially important
BR 2 I Important
* Reason Ũ Ordinary
Bedroom 3
A
/
1
0
/
4
BR 3
u Unimportant
X Undesirable
Bathroom 1
A
/
2
u
/
u
/ B 1
Reasons:
1. To observe small children
9
Bathroom 2
u
/
I
/
5
I
/
5
I
/
6
B 2
z. • 1 UL jJLiuauy
3. For quietness
4. For supervisory convenience
R Fnr nnn/Qn i anno nF nhilrl
Kitchen
X
/
3
X
/
3
X
/
3
I
/
6
I
/
6
K
6. For plumbing economy
7. For general convenience
Dining Room
X
/
3
X
/
3
X
/
3
u
/
0
/
7
A
/
7
DR
Living Room
X
/
3
u
/
u
/
u
/
0
/
7
0
/
7
0
/
7
LR
Stairs
u
/
u
/
u
/
u
/
u
/
u
/
u
/
u
/
ST
Enclosed Porch
u
/
u
/
u
/
u
/
0
/
7
I
/
7
u
/
u
/
u
/
p
Foyer
X
/
3
X
/
3
X
/
3
u
/
u
/
E
/
7
u
/
E
/
7
A
/
7
u
/
Fig. 4.2. Activity relationships for a small house.
corresponds to “For privacy.” Similarly, the
requirement that the dining room be next to the
kitchen is notedbyan A attheintersectionofthe row
for dining room and the column marked K. The
reason is “7. For general convenience.”
Figure 4.1(c) represents an early attempt to place
the elements shown in Fig. 4.1(7?) in positions that
satisfy the proximity requirements of Fig. 4.2. With
the elements in these places, however, the room
shapes do not lend themselves to formation of a
regularshape forthebuilding.With modificationsof
the roomshapes,the floorplan shownin Fig. 4.3 re-
sults.Ifthe roughcost estimate is within the owner’s
budget and the owner approves the
Fig. 4.3. Schematic floor plan with rooms located, stairs
positioned, corridors shown. Window locations have not
yet been determined.
floor plan, it may be developed in greater detail.
For multistory buildings, a floor plan may be
developed in a similar manner for each floor. If
several floors will be identical, however, a typ

ical plan may be prepared for them, and the title of
the drawing should indicate to what floors the plan
applies.
In the development of the floor plans, con-
sideration must be given to entrances to and exits
from the building, access to each floor and internal
circulation,ortraffic flow. Also,the floorplansmust
be developed in conjunction with considerations of
site conditions.Forthis to be done,the placement of
the building on the site must be taken into account.
Positions of walks, driveways and parking areas
must be included in these considerations.
Information Flow
The flow of information in the conceptual phase
when the architect plays the major role is shown in
Figs.4.4 to 4.7. In all cases,information passesfrom
the owner to the prime professional and other
members of the building team. Also, recommended
concepts flow from the members of the building
teamto the prime professional and the owner.
Figure 4.4 shows the flow of information to the
architect for execution of his main tasks. The
diagram indicates that information given the
architect also is given to the other members of the
building team and that he confers with them for
comment and suggestions. He then develops
schematic architectural drawings, which are
submitted to value analysts for comment and
suggestions. Next, the drawings, modified as
required by the analysis, are reviewed by the
building team.Finally, the drawings,again modified
as required by the re
Owner
Fig. 4.4. Flow of information to and from the architect during conceptual design for an ordinary building.

Fig. 4.5. Flow of information to and from the structural
engineer during the conceptual design phase for an
ordinary building.
view,are forwarded to theprime professionalandthe
owner for approval.
Figure 4.5 shows the flow of information to the
structuralconsultantforexecution ofhis main tasks.
This diagramalso indicatesthe informationgiventhe
structuralengineeris given to the othermembers of
the building team, too. He then develops schematic
structural drawings, which are subjected to value
analysis and toreviewbythe otherconsultants.Next,
the drawings,modified as required by the studies,are
forwarded to the prime professional and the owner
for approval.
Similarly, Figures 4.6 and 4.7 show the flow of
information to the mechanical and electrical
consultants, respectively.
Owner
Fig. 4.6. Flow of information to and from the mechanical
engineer during the conceptual design phase of an
ordinary building.
Design of Systems
Each of the members of the building team should
apply systems design to the systems forwhich he is
responsible.
For illustrative purposes, Fig. 4.8 shows possible
steps in systems design of a structural systemfor a
multistory building.The diagramfollows closely the
steps in Fig. 3.4 for general systems design.
FOR SECTIONS 4.2 AND 4.3
References
AIA, Architect’s Handbook of Professional Practice,
American Institute of Architects.
w. Caudill, Architecture by Team,Van NostrandReinhold(out
of print).

Wordsand Terms
Budget
Building program
Feasibility study
Predesign activities
Prime design professional
Owner’s decision to maintain personal control or assign
management of design and construction to others.
Needto manage community relations forlarge projects.
Owner’s responsibility toestablishgoals andobjectives for
the project.
Owner’s selectionof primedesign professional; relatedto
nature of project.
Critical management decisions of owner.
4.4 DESIGN DEVELOPMENT PHASE
OF SYSTEMS DESIGN
After the client approves the schematic drawings,
project descriptions and cost projections, the
desirability of the building concepts proposed is
established. The technological feasibility, however,
is still open to question. Can the systembe made to
function as presently conceived? Can it be
constructed with currently available methods and
equipment? Can it be constructed speedily,
efficiently and reliably at expected costs and with
low maintenance? If the answers to these questions
are negative,the development ofalternative concepts
may be required, depending on what the designers
learn as they develop the design in greater detail.
The purposes of the design development phase
Fig. 4.7. Flow of information to and from the electrical
engineer during the conceptual design phase for an
ordinary building.
Space analysis techniques for development ofbuilding
plans.
Flow of information in conceptual design phase.

therefore are:
1. To bring the proposed system into clearer
focus by determining materials to be used for,
and sizes of components of, the important
features synthesized in the conceptual phase.
2. To develop further the concepts of the
conceptual phase by proposing concepts of
other essential features and the materials and
sizes to be used.
3. To determine the technological feasibility of
the developed design.
4. To prepare design drawings and project de-
scriptions that will be the basis forpreparation
of contract documents.
The results of this phase should be preliminary
design drawings—floor plans, elevations, sections,
some details,renderingsand perhapsalsoa model—
giving building dimensionsandshowinglocationsof
equipment,pipes,ducts,wiring and controls;outline
specifications and a more refined, although still
preliminary cost estimate andconstructionschedule.
At the start ofdesign development,the ownerand
the building team should review the program,
objectives and constraints to insure that they are all
still valid. The owner should at that time impose
additional or special requirements previously
overlooked, if any are necessary. The designers
should verify compliance ofthe schematicswith the
programand building and zoning codesand with all
otherlegalregulations.In addition,theownershould
supply more detailed information concerning the
site, if required, especially information on
subsurfaceconditionsand soiltypesand properties.
In the conceptual phase, effort is concentrated
only on important features. In design development,
all systems must be determined and analyzed.
Additional elements to be specified include fire
protection and other life-safety systems; security
systems; lighting; telephone; paging systems
intercommunication systems; sound control;
conveyors, cranes and other materialhandling
equipment; closed-circuit and cable television;
clocks; and suchsupplies as vacuum,steam,heating
gas, compressed air, oxygen and distilled water.
Optimization
Each member of the building team develops the
design forhis specialty(see Sec.1.2),but because of
the consequences ofdecisions byeach specialist,the
team members must confer frequently with each
other and advise the others of the current status of
their designs. The designers also should compare
drawings of proposed systems, to determine space
requirements and tolerances and to eliminate
incompatible or undesirable situations. Flow of
information during the design development phaseis
similar to that shown in Figs. 4.4 to
4.7.
The prime professional,with an overallviewofall
team accomplishments, should insure integration of
components and subsystems to form the optimum
system for the given objectives and constraints.
Initially, each team member should apply systems
design and endeavorto obtain the optimumsystems
for his specialty.The teamshould then examine the
results to see if the component systems when
combined forma true optimum.
At the start,the building systemmay be treated as
though it were composed of subsystems in series.
The functional-space system and systems having
small effects on the others (for example, partition,
electrical and plumbing systems)may be tentatively
considered true optimums. Then, the exterior-wall
system may be combined with those systems and
optimized. Next, the HVAC system may be
combined with the preceding combination and
optimized. After that, the structural systemmay be
combined with all the others andoptimized.Finally,
the optimized result should be restudied as a system
to determine if integration of components would
produce a better system.
If an alternative systemis not evident, the cycle
should be repeated.This cycle,however,to make all
the systems compatible, should start with changes
necessary in the functional-space system, including
internalcirculation,and the component systems that
had been tentatively treatedas trueoptimums.These
adjustedsystems shouldthen beoptimized.Next, the
effects of the new optimized systems on the others
should be determined and, if necessary, new
optimumsystems should be designed.Ifchanges are
substantial,the cycle may have to be repeated again.
At the termination of the second cycle and
subsequent cycles, if any, the results should be
subjected to value analysis. The building team
should then evaluate and act on suggested mod-
ifications and alternatives.

Costs and Time
Also,at the end ofeach cycle,an estimate should
be made of construction and life-cycle costs and
construction time. If any of these do not meet
objectives and constraints, the system should be
modified accordingly. If, for example, construction
costsare too high,thebuildingmay have to be made
smaller, less expensive materials or equipment may
have to be specified,orsome requirementsmay have
to be changed. If shortages of materials, equipment
or certain types of construction workers will delay
construction, substitutes should be specified.
With more detailed information on the com-
position of the building and its equipment available
than at the end of the conceptual phase, a more
accurate estimate of construction cost is now
feasible. The cost, for instance, may be based on
historical unit costs for each of the systems
comprising the building. Typical elements of the
estimate would include items coveredby the general
conditions of the contract and the contractor’s fee,
sitework, foundations, masonry, concrete, structural
steel, ornamental metal, carpentry, roofing,
windows, doors, hardware, glass, curtain walls,
plasterand gypsumboard,metalpartitions,tile work,
ceilings, HVAC, elevators, plumbing, electrical
systemand painting.
Specifications
Each member of the building team during the
design development phase should keep notes of
decisions made, the date they were made and the
reasons for them. The notes dealing with materials
and equipment to be installed should be compiled as
outline specifications. These will form the basis for
the final specifications.
Approvals
Important questions should be submitted to the
owner for decision as they arise. Also, the owner’s
approval of resources, especially fuels, to be used
should be obtained. Preliminary drawings, outline
specificationsand preliminary estimatesofcostsand
construction time should be submitted to the owner
for approvalat the end ofthe second cycle and later
cycles when convergence ornearconvergenceto the
optimumsystemis evident.
As drawings take final shape, designers should
obtain tentative approval of regulatory agencies
concerned, especially the building department and
zoning commission,state and localfire departments
and health department.In some cases,opinions may
be desirable from a state labor department and the
Occupational Safety and Health Administration.
Mechanicaland electricalengineers should obtain
the approval of all utility companies concerned for
service connections.
Basic purposes of the design development phase.
Cyclic integrationby suboptimizationin series andsequential
combinations of subsystems.
Transitions to contract documents phase: outline specifi-
cations, preliminary drawings, preliminary approvals.
These are generalreferences forthe chapter; see
also the references listed at the ends ofchapter
subsections.
w. Caudill, Architecture by Team,Van NostrandReinhold(out
of print).
A. Gheorge, Applied Systems Engineering, Wiley, 1982.
ed., McGraw-Hill, 1982.
EXERCISES
for review of the individualsections andthe chapter
as a whole.
Section 4.1
1. When systems designis usedwith the traditional
building procedure,what are the major changes
required in traditional practice?
2. What are the advantages of phased design?
3. Why is teamworkdesirable in systems design?
4. What are the duties of the prime professional
designer on the building team?
5. Why is it desirable that structural, mechanical
and electricalengineers cooperate in design ofa

floor system?
6. What are the duties of a construction consultant
during design?
7. Explain the variation of construction costs with
construction duration.
8. What are the advantagesofphased construction?
9. Why must design and construction of buildings
be integrated?
10. In what way does traditional field assembly of
buildings resemble factory assembly-line
production?
11. Discuss the advantages and disadvantages of
prefabrication.
12. What are the advantages of repetition of
components in building construction?
13. Why is it desirable that different building
components be dimensionally coordinated?
14. A grocery store chain wants to construct 10
large identical market buildings in a region. If
businessthen goeswell,the chain plans to erect
more such markets. Use of an industrialized
building appears to have good potentialforthis
application. But investigation indicates that no
design currently available is suitable for the
client’s needs. What should the building team
recommend as the best alternative? Justify your
answer.
15. A 20-story building has 18floors with identical
structural framing. Framing for the roof,
however, could be lighter and less costly than
that for the floors. Discuss the advantages of
using the floor framing also for the roof.
Section 4.2
16. What are the advantages to an owner of
engaging a construction representative to assist
him in administering designandconstructionof
a building?
17. What is the difference between duties of a
construction programmanager and those of a
construction manager?
18. What information should a building program
provide?
19. Who is responsible for providing information
concerning the building site?
20. An owneremploys a constructionmanagerfora
building to be constructed. The manager
negotiates a contract for construction with a
general contractor. Who should sign the
contract and assume legal responsibility for
payments for construction?
21. What are the advantages to an owner of
assigning to one member of the building team
the duties of prime professional?
22. What are some of the most important char-
acteristics that members of the building team
should have?
23. Why is a public relations programaimed at the
community where a building is to be
constructed important to the owner? To the
building team? When should the programstart?
What should be its purposes?
Section 4.3
24. What is accomplished in the conceptual phase
of building design?
25. What are the primary design concerns in the
conceptual phase?
26. Describe briefly the basic predesign data
needed.
27. What design information should the building
team provide for the start of the conceptual
phase?
28. A one-story school building requires six
classrooms,each with a floor area of 700 sq ft,
a 2,000-sq ft auditorium, a 2,500-sq ft
gymnasium, a 500-sq ft library, a 600- sq ft
cafeteria, two 60-sq ft toilets and a 1,000-sq ft
administration area. Compile a closeness table
and draw a schematic plan for the main floor.
29. At completion of the conceptual phase of
design, a building teamhas produced an office
building with a floor area of 100,000 sq ft.
(a) Estimate the construction cost if similar
buildings in the same city constructed
recently have averaged $40 per sq ft.
(b) What would the estimate be if a pile
foundation is required and will cost about
$100,000 more than the spreadfooting
foundations used for the other office
buildings?
(c) What would the estimate be if costs are
expected to increase at a rate of 10% per
year during the 2 years the building (with
pile foundations) will be under design and
construction?
30. Which member of the building team is re-
sponsible for drawings for:

(a) Exterior walls?
(b) Foundations?
(c) Plumbing?
(d) Telephone wiring?
(e) Site grading?
Section 4.4
31. What are the purposes of the design de-
velopment phase?
32. A construction consultant estimates that a
multistory office building with a structuralsteel
frame can be erected in 15 months at a cost of
$4,000,000. He also estimates that the building
with a concrete frame can be constructed in 18
months at a cost of $3,800,000. The owner
anticipates a net revenue of$100,000 permonth
when the building is occupied. On the basis of
this information alone, which type of frame
should the building teamrecommend?

114
Chapter 5
Contract Documents and
Construction Methods
After owner approval of the preliminary drawings,
outline specifications,and preliminary cost estimate
and construction schedule, the contract documents
phase begins. In this phase, the building team
developsworking drawings,specifications,and final
cost estimate and construction schedule. Design in
this phase differs fromthe traditional principally in
closer coordination of the work of the various
specialists and tighter integration of the building
systems. Changes of major systems are undesirable
in this phase because they will be time consuming
and costly. Systems design and especially value
analysis,however,may still be profitably applied to
details being worked out, final specifications, and
general and special conditions of the contract.
Afterthe ownerapprovesthe contract documents,
construction contracts may be awarded and
construction may proceed. (In phased construction,
construction may begin before all the working
drawings and specifications have been completed.)
Design changes may be made after construction
starts, but they will be more costly than if made
before award of the construction contract.
The contract documents are graphic and written
means of conveying concepts ofthe structure to the
builders and assigning duties and responsibilities
during the construction phase. The documents
enable the ownerto obtain the building portrayed in
them.They allowthe designers toindicatewhat is to
be constructed. They specify to the selected
contractors the materials to be used, the equipment
to be installed and the assemblage ofthe materials to
produce the desired building. Also, the documents
detail the payments to be made for this work.
5.1. RESPONSIBILITIES ASSIGNED BY THE
CONSTRUCTION CONTRACT
The contract for construction is solely between the
owner and the contractor. The prime professional
(responsible forexecution ofdesign)unless alsothe
ownerof the building,is not a party to the contract.
Nevertheless, he prepares some of the contract
documents-the working drawings and
specifications-andassists the ownerin preparing the
owner-contractor agreement and conditions of the
contract. For preparation of the agreement and
conditions of the contract, legal counsel is at least
desirable and generally necessary. Contract law
differs from state to state, making it necessary to
obtain information from the owner’s legal counsel
regarding the law of the state in which the building
is to be erected.
While it is feasible for an owner to make an oral
contract for construction of a building, in general,
this is very risky for both the owner and the
contractor. No construction should be undertaken
without a written contract. Similarly, all changes in
the contract before bidding and all modifications
after the contract has been awarded, including
change orders, should be in writing. Otherwise,
costly disputes may arise.
Contractor Responsibilities
A construction contract generally assigns the
following responsibilities to the general contractor

Contract Documents and ConstructionMethods 115
for a project to be built:
1. Performance of all work in accordance with
working drawings and specifications and
change orders issued by the owner. Thus, the
contractor also is responsible for the
performance of all subcontractors and
workmen.
2. Starting and completing the project on the dates
specified in the contract.
3. Quality of workmanship.The generalcontractor
is required to correct any work that does not
conformwith plans and specifications.
4. Payments ofalltaxes,fees,licensesandroyalties
and for all labor, materials, equipment, tools,
utilities and other services necessary. The
general contractor also is responsible for
reimbursement ofall subcontractorshe engages
for work they perform.
5. Securing all permits and fees necessary and
compliance with all legal regulations.
6. Checking and submitting for approval to the
owner or his agent all samples and shop
drawings as required by the plans and
specifications.
7. Use of safety measures and good housekeeping
on the building site,plus provision ofinsurance
coverage, to protect the owner, building
designers and other owner agents against
financial losses from property damage or
personal injuries to employees, visitors or the
general public during construction.
8. Cooperation with other contractors, if any,
engaged by the owner.
9. Providing access to the work to the owner and
his agents.
Owner Responsibilities
A construction contract usually assigns the fol-
lowing responsibilities to the owner of a project to
be constructed. (The owner may delegate authority
for carrying out theseresponsibilities to oneormore
agents.)
1. Preparation of working drawings and
specifications that clearly define what is to be
built and either:
(a) Stipulate materials to be used and their
quality and the equipment to be installed
or:
(b) Present performance requirements for the
building, its structure and installed
equipment, but not both.
2. Approving work as completed, making de-
cisions that become necessary as work pro-
ceeds, approving subcontractors, approving
samples and shop drawings, and issuing
instructions to the contractor. The contract
should indicate who has authority to act as the
owner’s agents during construction and the
limits on the authority given to each.
Specifically, the contract should make clear
who has authoritytoissueontheowner’s behalf
instructions to the contractor.
3. Payments to thegeneralcontractorforall work,
including changes and extra work ordered by
the owner. The owner also may be required to
pay for extra work arising from unexpected
conditions,such as subsurfaceconditions onthe
site that were not disclosed because of
inadequate orinaccurateinformation the owner
provided.
4. Furnishing surveys and subsurface information
concerning the site.
5. Securing and paying for easements in per-
manent structures or permanent changes in
existing facilities.
6. Inspection of the work to insure compliance
with the contract documents and rejection of
nonconforming work. When necessary, the
owner should especially advise the contractor
of the likelihood of cost overruns or late
completion, when
such conditions are discovered,and ofthe need
for better control of costs and time.
7. Supplying materials and equipment and in-
stallation labor not covered by the working
drawings and specifications.
8. Provision of insurance against financial loss
from property damage and personal injuries
before, during and after construction.
Responsibilities of Owner's Agents
The owner, while retaining the right to exert his
authority underthe contractat any time, may assign
complete authority to act on his behalf during
construction to one agent or may divide this
authority among several agents.
Public agencies and corporations that have their
own construction departments, for example, may

assign complete authority to a staff architect or
engineer. Some owners may give the authority to a
construction programmanagerortotheprime design
professional.
In some cases, authority may be divided between
the prime professional and a construction
representative or a construction manager.
The prime design professional, in any case, has
responsibility for preparation of working drawings
and specifications.The contract usually also assigns
him the responsibility for interpreting these
documents when the contractor has questions or a
dispute arisesbetweenthecontractorandthe owner.
The contract may, in addition, oblige the prime
professional to inspect construction to insure
compliance with plans and specifications, approve
samples and shop drawings submitted by the
contractor, and to design work required by change
orders during construction. (These duties, which
often require payment by the owner of additional
fees, must also be covered in a separate owner-
designer agreement.) Responsibility for assessing
construction progress and authorizing periodic
payments tothe contractorforworkin place,in some
cases,may be assigned to the prime professionalor,
in other cases, to a construction representative or a
construction manager.
General administration of the construction
contract may, at the owner’s option, be assigned to
the prime professional,a constructionrepresentative,
or a construction manager. The contract
administratoris given authority toissue instructions,
including change orders, to the contractor on the
owner’s behalf.He also is assigned responsibility for
approving subcontractors.In addition,he is charged
with responsibility for insuring that costs are
controlled, that proper insurance coverage is
maintained, that the contractor complies with all
legal regulations, and that the project is kept on
schedule.Ifinspection dutiesare not assignedto the
prime professional, the contract administrator will
have to engage inspectors. Furthermore, he or the
prime professional may be given authority to settle
all claims or disputes between the owner and the
contractor; but under the contract, such decisions
may be subject to arbitration by outside parties
named in the contract.
While some of these responsibilities may involve
a conflict ofinterest,many years ofexperience have
indicated that professionals can execute theseduties
responsibly and with fairness to both parties to the
contract.
What but Not How to Build
One aspect of the contract documents is worthy of
special note. They always endeavor to specify
precisely what the designers intend to have built.
They avoid, whenever possible, instructions to the
contractors concerning methods to be used for
construction. The reason for this is that if the
contractoruses the specified methods andthe results
are unsatisfactory, the responsibility for the
unacceptable workfalls on the designer.On theother
hand, if the contract documents indicate only the
results to be obtained and leave the methods to be
used at the option ofthecontractor,theresponsibility
for the outcome rests on him.
References
AIA, Architect’s Handbook of Professional Practice, Vol. 1,
J. Sweet, Legal Aspects of Architecture,Engineering, and the
Words and Terms
Prime design professional
Specifications
Working drawings
Responsibilities of the contractors.
Responsibilities of the owner.
Owner’s assigned agents: prime design professional, con-
struction representative, construction manager.
Basic function ofcontract documents: control of what is built,
not how it is built.
5.2 COMPONENTS OF
THE CONTRACT DOCUMENTS
Basically, the construction contract documents
consist of:
1. Owner-contractor agreement
2. General conditions
3. Supplementary conditions
4. Drawings
5. Specifications
6. Addenda

7. Modifications
The owner-contractor agreement indicates what
the contractoris to do,for howmuch money and in
what period of time.
The general conditions contain requirements
generally applicable to all types of building
construction.
The supplementary conditions extend or modify
the general conditions to meet the requirements of
the specific project.
The drawings showgraphically the building to be
constructed.
The specifications list the materials to be used and
equipment to beinstalled in the structure and provide
necessary information about themthat cannot easily
be given in the drawings.
If it is necessary to make changesin the preceding
documentsbefore executionofthe owner-contractor
agreement, the prime professional, who is
responsible fordesign,issueson behalfofthe owner
addenda incorporatingthe revisions.These addenda
should be givensimultaneously toallbidders so that
all bids can be prepared on an equalbasis.Addenda
are part of the contract documents.
If changesbecome necessaryafterexecutionofthe
agreement,the ownerand the contractormust agree
on the modifications, which include change orders
and interpretations of drawings and specifications.
(See also Secs. 5.3 and 5.4.)
Project Manual
For the convenience of those concerned with the
contract documents, all the documents except the
drawings may be bound in a volume,called a project
manual, to provide an orderly, systematic
arrangement of project requirements. In addition,
bidding requirements, though not contract
documents,are desirably incorporatedin the manual
for the convenience of bidders. Bidding
requirements, which govern preparation and
submission of proposals by contractors, are
described in Sec. 5.5.
Project manuals are generally organized as
follows:
1. Table of contents
2. Addenda
3. Bidding requirements
4. Owner-contractor agreement
5. General conditions
6. Supplementary conditions
7. Schedule of drawings
8. Specifications
For large projects,however,a single volume may
be inconvenient.In such cases,some ofthe divisions
of the specifications, such as the mechanical, or the
electrical, or specialty items, may be bound as
separate volumes. Each volume should also contain
the addenda,biddingrequirements,conditions ofthe
contract, and the division of the specifications that
presents general requirements.
Construction Contract Forms
A typical owner-contractor agreement is presented
for illustrative purposes only. An agreement is a
legal document and therefore advice of an attorney
in its preparation is advisable.
AGREEMENT
made this __ day of ________in the year____
BETWEEN
ABC Company,the owner,and IMA Building
Corp., the contractor.The ownerandthe contractor
agree as follows:
Article 1. The Contract Documents
The contractdocuments consistofthis agreement,
conditions of the contract (general, supplementary
and other conditions), drawings, specifications, all
addenda issued before execution of this agreement
and all modifications issued afterward. All the
documents formthe contract, and all are as fully a
part of the contract as if attached to this agreement
or repeated in it.
Article 2. The Work
The contractorshallperformall the work required
by the contract documents for the ABC Office
Building to be located at _________________
Street and _________ Avenue,________ City,

State.
Article 3. Prime Professional
The prime professionalforthis project is
Article 4. Times of Commencement
and Completion
The work to be performed underthe terms ofthis
contract shall begin not later than and be
completed not later than
Article 5. Contract Payments
The owner shall pay the contractor for the
performance of the work, subject to additions and
deductions by change order as provided in the
conditions of the contract, in current funds, the
contract sumof________________ .
Article 6. Progress Payments
Based uponapplicationsforpaymentsubmittedto
the prime professional by the contractor and
certificates for payment issued by the prime
professional, the owner shall make progress
payments on account of the contract sum to the
contractor as provided in the conditions of the
contract as follows:_____________________
Article 7. Final Payment
The entire unpaid balanceofthe contract sumshall
be paid by the owner to the contractor days
after substantial completion of the work unless
otherwise stipulatedin the Certificate of Substantial
Completion, if the work has then been completed,
the contract fully performed and a final Certificate
for Payment has been issued by the prime
professional.
Article 8. Miscellaneous Provisions
Terms used in this agreement and defined in the
conditions of the contract shall have the meanings
designated in those conditions.
The contract documents that constitute the entire
agreement betweenthe ownerand the contractorare
listed in Article 1 and, except for modifications
issued after execution of this agreement, are as
follows: [Documents should be listed with page or
sheet number and dates where applicable.]
This agreement executed the day and year first
written above.
Owner Contractor
The owner-contractor agreement specifies the
method of payment to the general contractor for
constructing the building. Consequently, the
payment method selected strongly influences the
terms of the agreement and the conditions of the
contract. Contracts, therefore, may be classified in
accordance with payment method as lump-sum,
guaranteed-upset-price, cost-plus-fixed-fee, or
management contracts.
Standard forms are available for some of these
types. The American Institute of Architects, for
example, publishes standard forms forlumpsumand
cost-plus contracts. Some government agencies and
large corporations with extensive construction
programs have developed theirown standard forms.
The advantages of such forms are that contractors
become familiar with themand readily accept them,
and the chances ofomitting important requirements
are reduced.If modifications ofa standard formare
required, the owner’s legal counsel should draft the
agreement.
General Conditions of the Contract
Applicable to building construction in general, the
general conditions are made a part of each
construction contract by reference in the owner-
contractor agreement (see preceding subsection
Construction Contract Forms). Because of
variations in local and project requirements,
extension and modificationofthe generalconditions
usually are necessary. These are accomplished by
also making special, or supplementary, conditions
part of the same contract (see next subsection).
If separate prime contracts are awarded, the
general conditions should be made a part of each
prime contract. For example, if the owner should
engage directly an electrical contractor and a
plumbing and heatingcontractor,as wellas a general
contractor, the general conditions should be
incorporated into each contract.
A major portion of the general conditions is
devotedto descriptions ofthe rights,responsibilities,
duties and relationships of the parties to the
construction contract and their authorized agents,

generally as listed in Sec. 5.1.
The first article of the general conditions,
however, usually is broad in scope. It defines the
contract documents, the work and the project. The
article also points out that the contract documents
formthe contractandindicateshowthe contractmay
be amended or modified. In addition, the article
notes that the contract documents are
complementary, and what is required by any one
shallbe as binding as if required by all. (This clause
is the reason why requirements in the drawings
should not be inconsistent or conflict with those in
the specifications.)
Other requirements usually included in the first
article are that:
The owner and the contractorshould sign at least
three copies of the contract documents.
The owner will furnish the contractor without
charge all copies of drawings and specifications
reasonably necessaryforexecution ofthe work.The
drawings and specifications, being the property of
the prime design professional, may not be used on
any other project and should be returned to himon
request on completion of the work.
By executing the contract, the contractor rep-
resents that he has visited the site. Consequently, it
is presumed that he has familiarized himself with
conditionsunderwhich workis to be performed and
has correlated his observations with the
requirements of the contract documents.
On request, the prime design professional will
deliver, in writing or in the form of drawings,
interpretations necessary for proper execution or
progress of the work.
The final article of the general conditions usually
deals with circumstances under which the contract
may be terminated by either party, other than by
completion ofthe work,and describesthe meansfor
so doing.
Supplementary Conditions of the Contract
Because requirementsdifferfrom project to project,
supplementary conditions are generally needed to
extend or modify the general conditions of the
construction contract.The supplementaryconditions
are made a part of each construction contract by
reference in the owner-contractor agreement (see
preceding subsection, Construction Contract
Forms). They usually are prepared by the prime
design professionalwith the aid ofthe owner’s legal
and insurance counsels.
Nothing should be incorporated into the sup-
plementary conditions that can be covered in the
specifications. Being a well organized listing of
requirements,the specifications make it easy forthe
various trades to determine what workis to be done
and what their responsibilities and duties are. A
requirement placed in the supplementary conditions
when it should be in the specifications runs the risk
of being overlooked during construction.
The supplementary conditions may consist of
modifications of the standard form of general
conditions as required fora project andofadditional
conditions. Any of many additional conditions may
be included. Among the more common are
provisions for substitution of materials and
equipment for those specified, accident prevention,
allowances forunpredictable items,and payments of
bonuses to thecontractorforearly completion of the
project or cutting costs or of liquidated damages by
the contractorforlate completion ofthe project.Also
often included are provisions for bracing and
shoring, project offices and other temporary
facilities, postingnotices andsigns,andprovisionof
water,electricity,temporary heat,scaffolding,hoists
and ladders during construction. In addition, the
supplementary conditions may deal with the
influence of weather on construction.
5.3. CONTRACT DRAWINGS
The construction, or working, drawings the
contractor uses to determine what is to be built are
given legalstatus by beingmade part ofthe contract
by reference in the owner-contractor agreement
agreement (see Sec. 5.2, Construction Contract
Forms). The purpose of the drawings, which are
often also called the plans, is to depict graphically
the extent and characteristics oftheworkcoveredby
the contract.The drawings are complemented bythe
specifications,also part ofthe contract,in which in-
formation is compiled concerning the building and
its components that cannot be shown graphically.
Changes made in the drawings before the owner-
contractor agreement is signed are incorporated in
the contract as addenda. Later changes are included
as modifications of the contract.
The drawings show the site to scale and the
location of the building on the site. Sufficient
dimensions are given to enable the contractor to

position the structure precisely where the designers
intend it to be and toorient it properly.The drawings
also showhowthe building will look on the outside
when viewed from various angles. Plan views are
included foreach level,fromthe lowest basement to
the highest roof, to show the arrangement of the
interior. Other drawings show the foundations,
structural framing, electrical installation, plumbing,
stairs, elevators, HVAC, and other components.
On every drawing,sufficient dimensionsare given
to enable the contractortolocateeveryitem,observe
its size, and determine how it is to be assembled in
the building. Overall dimensions also are included.
Where necessary,details are shown to a large scale.
Numbering of Drawings
All sheets should be numbered for identification.
The numbers also are useful in referring the plan
reader from one sheet to related information
contained on another sheet.
The first sheet of the set of working drawings is
the title sheet. It contains the name of the project,
location, name of owner, project identification
number and names of designers. Usually, it also
provides a table ofcontents forthe drawings.It may
also provide a list and explanation of the symbols
and abbreviations used in the drawings.
The following sheets are grouped in accordance
with the type of practice of the designers who
prepared them. The architectural sheets are
assembled in sequence and often are assigned a
number prefixed with the letter A. They generally
are followed by the structural drawings, each given
a number with the prefix s. Next come the
mechanical drawings, often with each plumbing
sheet numbered in sequence with the prefix p and
with each HVAC sheet numbered in sequence with
the prefix HVAC. After that come the electrical
drawings,each assigned a numberwith the prefixE.
If otherdrawings are necessary,they followand are
similarly identified by lettersandnumbers.A typical
sequence is indicated in Table 5.1.
Title Block
Each sheet carries at thebottom,usually at the lower
right-hand corner, a title block (see Fig. 5.1) that
contains the sheet identification and general
information about theproject and thesheet.The title
blockprominently displaysthe name andlocationof
the project,the name and address ofthe design firm
responsible for the drawing, and the sheet number.
The block also contains the project identification
number, the

Contract Documents and ConstructionMethods
121
Table 5.1. Suggested
Sequence of ContractDrawings
Title sheet
Table of contents, symbols, abbreviations
Architectural drawings
Topographical survey, site plan, landscaping plan
Elevations
Floor plans, starting with lowest basement
Roof plan
Sections
Details
Schedules
Structural drawings
Soil test borings
Foundations
Floor plans, startingwith lowest floor
Roof plan
Sections
Details
Schedules
Mechanical drawings
Site plan
Plumbing plans
Plumbing details, schedules, and stack diagrams
Heating, ventilation, andair-conditioningplans
HVAC details and schedules
Electrical drawings
Site plan
Electrical power and lighting plans
Details and schedules
initials of the draftsman, the date of completion of
the drawing, the initials of the person who checked
the drawing, the date the checking was completed,
and the date ofissuance ofthe sheet.In addition,the
title of the sheet,such asNorthElevation,First Floor
Plan, or Details, is prominently displayed. Space is
also provided for listing revisions made at var-
Rev ision No. Date Description
First Floor Plan
Drawn Job No.
Hotel Palm Beach, Fla. Checked S' Date Issued
A. Professional, AIA, Architect
Okeechobee Blv d.
West Palm Beach, Fla. 33409
Sheet No.
A4
Fig. 5.1. Example of title block for a drawing.
ious times on the sheet.Consultantsmay be listed in
the title block or nearby.
Additionalnecessaryinformation is providednear
the title block.If the drawing contains a plan view,a
north arrowis shown.Ifa single scale is used forthe
whole drawing,the scale,ifnot given belowthe title
of the sheet,should be indicated nearthe title block.
If the sheet shows a plan that is only part of the
overall view, a blockplan may be drawn to indicate
the location ofthe part shownonthedrawingrelative
to the rest oftheplan (see Fig.5.2).When necessary,
a key may be provided to explain notations used for
identifying and locating sections and details. In the
same area of the drawing as the title block, other
information required by the local building
department or the state boards of architecture and
engineering may be included,such as signatures and
registration seals of the architectural or engineering
firm responsible for the drawing. The signature of
the owner or his representative accepting the
drawing should be adjacent to those signatures.
Notes and Schedules
The working drawings alsocontain notes and listings
of materials and equipment, called schedules.
The notes support and explain some items shown
in the drawings. Because writing clutters the
drawings and because the information the notes
contain may be overlooked during preparation of a
cost estimate or, even worse, during construction,
notes should be kept to a minimum. Preferably, the
information they would provide should be
incorporatedin the specifications.(It is notadvisable
Fig. 5.2. {a} Plan view of part of a building (shown here
to a much smaller scale than that used on the
construction drawings), (b} Block plan of the building,
with cross-hatching indicating the location in the
building of the plan view in (a). (The block plan is
shown to about the same scale as might be used on the
drawing.)

to put written information both on the drawings and
in the specifications, for emphasis, to prevent
oversight orforany otherreason.Repetition can be
the source of inconsistencies and the cause of con-
flicts between the contractor and the owner.)
The schedules provide information that is con-
veniently tabulated, such as a listing of doors and
their types,sizes and hand; windows andtheirtypes
and sizes; room finishes; builders’ hardware; and
structural columns and their components and
dimensions.
Relationship ofDrawingsand Specifications
The working drawings and specifications, equal
componentsofthe contract documents,complement
each other. They serve different purposes.
The drawings are a diagrammatic representation
of the building to be constructed.The specifications
are a written description(see Sec.5.4).They present
requirements that cannot be readily shown
graphically but can be conveniently expressed in
words. Thus, specifications prescribe the type and
quality of materials required, the performance
characteristics of equipment to be installed, and
workmanship desired in installation ofmaterials and
equipment. The specifications may also name ac-
ceptable sources from whom the contractor may
purchase the required materials and equipment.
Information provided bywordson drawings,such
as notes, should be brief and general. Notes should
describe a type of construction and its location and
quantity required.The specifications should expand
on the characteristics of the materials involved and
the quality of workmanship required for their
installation. For example, a note on a drawing may
read “Insulation.”The specificationswillcompletely
describe the insulation, either by naming several
acceptable proprietary products and their
manufacturers or by giving a desired thermal
coefficient, indicating the desired physical state,
such as board, granular, reflective, or blanket, and
specifying quality requirements. The specifications
also will dictate the method to be used in fastening
the insulation in the positions indicated in the
drawings and describe the results to be achieved.
Reference
AIA, Architect’s Handbook of Professional Practice,
Wordsand Terms
Addenda
Change orders
Contract documents Contract drawings Contract
specifications General conditions Interpretations
Modifications Owner-contractoragreement Project manual
Supplementary conditions Title block
Issues
Components of the contract documents. Articles of the
owner-contractoragreement.Relationshipofdrawings and
specifications.
5.4 SPECIFICATIONS
The specifications fora building are made partofthe
contract by reference in the owner-contractor
agreement (see Sec. 5.2, Construction Contract
Forms). A written description of construction
requirements, the specifications complement the
working drawings. Neither takes precedence over
the other.
Because specifications are a legal document,
specification writers tend to use language as precise
as lawyers use. Specifications, however, are
primarily intended for the use of prime contractors
and subcontractors and should, however, be written
so that they can easily understand the requirements.
Hence, specifications should be brief, clear, and
precise.They should be organized in an orderly and
logical manner, and generally accepted practices
should be followed.
Master Specifications
Design organizations that have been in existence for
several years build up a file of specifications. From
these, they can develop a generally applicable type,
called a master specification. They adapt this to a
specific project bydeletinginapplicable portions and
adding appropriate requirements.
Use of a master specification may be expedited
with computers. The master specification can be
stored in the computermemory. Parts applicable to a
specific project may be recalled for viewing on a
monitor,revised ifdesired orexpanded,thenprinted
or stored for later printing.
The American Institute of Architects established
in 1969 a nonprofit corporation,Production Systems
for Architects andEngineers,Inc.,which developed

a computerized master specification, called
MASTERSPEC. Available to allprofessionals onan
annual subscription basis, the program enables a
central facility to receive, maintain, evaluate and
transmit specification information in concise form.
Afterediting the masterspecification,the subscriber
can secure a computer printout fromwhich he can
obtain copies needed, without any intermediate
typing steps.
Basic Principles
A fundamentalconcept is that specificationsshould
be in accordance with the general prevailing
practices in the construction industry.
Specification organization therefore should
correlate with the common practice in which prime
contractors prepare their proposals from bids
submitted by subcontractors. These bids may
represent as much as 85% ormore of the work for a
project. Consequently, the specifications should be
written and organized for the convenience of
subcontractors as well as for prime contractors.
All items of work covered by the contract should
be specified in the specifications.
It follows therefore that every itemshown on the
drawings should be prescribed in the specifications.
This precaution will reduce the chances of a
subcontractor overlooking an item that is required
only by graphical depiction on the drawings. As
indicated in Sec. 5.3, Relationship of Drawings
and Specifications, however, the specifications
should supply complementary information, such as
quality and workmanship desired, not repeat the
information provided in the drawings, such as size,
shape, location and quantity required.
Specifications should be divided into sections,
each applicable to part orallof the workof only one
subcontractor.
Each item of work covered by the contract should
be treated once,andonly once,in the specifications,
and only in the appropriate section.
Each section should give the scope of and fully
describe the work to be performed by the sub-
contractor.Separate sectionsalso should beprovided
for work to be performed by the prime contractors.
When a subcontractor may perform different
construction operations,a separatesectionshould be
devoted to each operation. For example, a masonry
subcontractor may lay brick, concrete block, glass
block, structural clay tile and similar materials. A
single section dealing with all of these would be too
complex and omissions and duplications might go
undiscovered. Preferably, a separate section should
be provided for each type of work.
Divisions
For convenience, related sections are grouped into
divisions. The divisions, in turn, usually are
organized in accordance with the Uniform
Construction index favored by the Construction
Specifications Institute and others. Recommended
divisions andtheirsequence are given in Table 5.2.
The first division, general requirements, deals
with items of the contractor’s work that are general
in nature.The divisionshould providea summary of
the work to be done by the contractor, work to be
done by othercontractors,andworkto be postponed.
Materials and equipment to be provided by the
ownershould be listed.Whetherconstruction willbe
performed under a single general contract or under
separate contracts should be indicated. Also, a
description of the site should be included. In
addition, the division should indicate how tests,
Table 5.2. RecommendedDivisions of Specifications
1. General requirements
2. Site work
3. Concrete
4. Masonry
5. Metals
6. Wood and plastics
7. Thermal and moisture protection
8. Doors and windows
9. Finishes
10. Specialties
11. Equipment
12. Furnishings
13. Special construction
14. Conveying systems
15. Mechanical
16. Electrical
reports and construction progress schedules should
be handled, and how allowances and alternates
should be treated.Furthermore,reference should be
made to applicable building standards,suchas those
of the American National Standards Institute,
ASTM, American Institute of Steel Construction,
and American Concrete Institute.
There may be some difficulty in deciding whether
an item should be dealt with in supplementary
conditions to the contract orin the specifications.In
general,ifthe requirements canlogically be included
in the specifications, preferably they should be
placed there. If, however, the item is of a legal

nature, closely related to the general conditions,
especially an extension of them, it should be
incorporated into the supplementary conditions. If
the item concerns the work of the contractor at the
site,the itemshouldbe treatedin Division 1ofTable
5.2.
Sections
Each division is composed ofsections.Those in the
divisions after Division 1 deal with specific
construction operations and are often referred to as
technical,ortrade,sections.Every sectionshould be
assigned a number indicating its sequence in its
division and a title indicating the workthe contractor
or subcontractor is to perform.
It is advantageous to standardize the format
Table 5.3. Recommended Format for Technical
Sections
Preface: reference to conditions of the contract and
Division 1
General provisions
Scope of the work: materials or equipment to be
furnished and installed under this section; materials
or equipment furnished but not installed; materials
or equipment installed under this section but not
furnished under this section
Notes
Quality control: necessity for prior approval of ma-
terials or equipment; industry standards to be met
Delivery and storage of materials or equipment
Protection and cleaning
Materials or Equipment
Acceptable manufacturers
Substitutions: prohibition or procedure for obtaining
approval
Specifications for materials or equipment
Fabrication, Installation, and Testing Closeout and
Continuing Requirements
Schedules
Inspections
Guarantees, warranties, and bonds
Closeout
Submissions: samples, shop drawings, test reports,
maintenance and operating instructions
Alternates
of technical sections, because then contractors
become familiar with the arrangement and are
likelier to make fewer mistakes in preparing
proposals and in performing the work. Because of
the wide variety of work involved in building
construction, however, variations from a standard
format often are desirable forsimplification, clarity,
and convenience. Table 5.3 gives a recommended
format.
Forlegal reasons,it is desirable that each technical
section be prefaced with the statement:The general
provisions of the contract, including the conditions
of the contractandDivision 1,as appropriate,apply
to the work specified in this section.
Since a separate subcontract is concerned with
each section, this statement insures that the
subcontractorhas been informed that the conditions
of the prime contract and Division 1 are part of his
subcontract.Thus,those requirements are given only
once in the project manualand need not be repeated
for each section.
Types of Specifications
The material or equipment specifications in the
technical sections may be written in any of several
different ways.Types ofspecifications that are used
include performance, descriptive, reference,
proprietary, and base-bid specifications.
Performance Specifications
This type defines the workby specifying the results
desired. It does not give dimensions, specific
materials, finishes, nor methods of manufacture. It
does not tellthe contractorhowto do the work.The
specification delegates to the contractor the
responsibility for the design or selection of the
product and determination of the method of
installation.He has complete freedomto employ his
knowledge and experience to achieve the results
itemized in the specifications. The prime design
professionalhas the taskofevaluatingin detaileach
bidder’s proposal to determine whether the items
proposed by the bidders will meet the performance
requirements and of recommending the best pro-
posal to the owner. Because of the difficulty of
evaluating results and the undesirability of with-
holding payment from the contractor until results
have been determined, the contract should obligate
each prime contractor to supply the owner with a
written guarantee that laborand materials furnished
and work performed are in accordance with the
requirements of the contract. The guarantee should
apply for at least 1 year. In a similar fashion, the
prime contractor should get guarantees from
fabricators, manufacturers, and subcontractors who

supply products or performthe work.
To illustrate the type of requirements that might
be incorporated in a performance specification, the
following is an example ofwhat might be written for
insulation for a hot pipe:
Pipe insulation shallbe completely in contactwith
the pipe, fully enclosing it, and firmly fastened in
place.Thickness ofthe insulationshallnot exceed 1
in. The insulation material shall have the following
properties:Passage ofheat throughthe materialshall
not exceed 0.30 Btu per hr per sq ft per °F. It shall
be suitable for use at temperatures up to l,200°F
without mechanicalfailure.The material shallbe in-
combustible, insoluble in water, odorless, ver-
minproof, rotproof, mildewproof, strong enough to
resist light wear and light accidental blows without
permanent deformations or damage, and capable of
retaining its shape in normal usage.
The architect or engineer who writes such a
specification knows of at least one material that
meets the specificationrequirementsand also knows
the generally accepted practice ofinstalling it.If the
contractor proposes that material and installation
method,he willobtain readyapproval.Ifhe proposes
a different material or method, the architect or
engineer will have to determine whether
specification requirementswill be satisfied and will
make a comparison of properties and costs with
those for the material that was contemplated when
the specification was written.
Because ofthedifficulty ofwriting andevaluating
performance specifications,many specificationsare
a combination ofthis type and anothertype,usually
the descriptive type.
Descriptive Specifications
This type describesthe componentsofa productand
how they are to be assembled. Every material is
identified; the structure is fully described; the
method offasteningis specified;andthesequenceof
assembly is prescribed.The contractoris required to
furnish and installthe product in accordance with the
description. If the installation passes inspection,
responsibility for functioning and performance of
the product rests on the specifier. Consequently,
unless the specifieris certain that the product,when
properly installed,will function properly,he should
not use a descriptive specification.
The following is an example of a descriptive
specification for insulation for a hot pipe:
Pipe insulation shallbe ofthe block(sectionaland
segmental) type, molded of a chemically reacted
hydrous calciumsilicate consisting of at least 75%
hydrous calciumsilicate and between 15 and 20%
graded asbestos fiber. The fiber shall be well
distributedso that neithermaterialshallbe in excess
in samples taken at random. The insulation material
shallbe suitable foruse at temperatures uptol,200°F
without mechanicalfailure.Average densityshallbe
about 11lb percu ft, oven dried.Modulus ofrupture
shallaverage 50psifor three samples 6in. wide and
1| in. thicksupportedon a 10-in.span and carryinga
midspan concentrated load distributed over the
width of the block. Maximum linear shrinkage
should not exceed 11% when the material is heated
to l,000°F for 24 hr. The material shall be insoluble
in water.Conductivity at200°Fshould average 0.44.
Reference Specifications
This type may be basically a performance or
descriptive type but may refer to a standard
specification to indicate properties and quality
desired and methods of test required. Standard
specifications usually adopted by reference include
those of the American National Standards Institute,
ASTM,and the federalgovernment.Following is an
example of a reference specification:
Cement shall be portland cement conforming to
ASTM C150-86, “Standard Specification for
Portland Cement,” Type I.
Many companies manufacture products to
conform to such standard specifications and will
furnish, on request, independent laboratory reports
substantiating the performance of their products.
Such products can be specified with confidencethat
minimum requirements will be met.
Proprietary Specifications
This type specifies products by trade name, model
number, and manufacturer. It eliminates the task of
determining whether a product meets specification
requirements. Use of this type of specification is
risky,however,because a lengthyperiod may elapse
between writing of a specification and ordering of
the product, during which time the manufacturer
may make undesirable changes in the product.
Another disadvantage is that proprietary

specificationsmay permit useofalternativeproducts
that are not equalin every respect. Hence,whensuch
specifications are used, the specifier should be fa-
miliar with the products and their past performance
and with the reputationsofthe manufacturersand the
subcontractors in servicing those products.
Naming only one proprietary product as ac-
ceptable in a specification is very risky. If the
product should not be available when needed for
construction, the work may be delayed until a
suitable substitute is obtained. Also, with only one
product considered acceptable, there is no price
competition for furnishing it, and costs therefore
may be unduly high. Consequently, two or more
names should be providedforeach product to insure
competition and availability.Permitting the use ofa
product “or equal” is not satisfactory because the
proposed equal may not actually be so.
Base-Bid Specifications
This type indicates acceptable productsby listing at
least three trade names and corresponding model
numbers and manufacturers, but the bidder is
permitted to offer substitutes.The bidderis required
to prepare his proposal with prices fromthe named
suppliers as base bids and to indicate for each
proposed alternate the price and properties. The
owner selects the product to be used. Base-bid
specifications offer the greatest control of product
quality.
References
H. Meier, Construction Specifications Handbook, Prentice-
Hall, 1983.
c. Dunham et al., Contracts,Specifications, andLaw for
Engineers, 3rded., McGraw-Hill, 1979.
Wordsand Terms
Base-bid specifications Descriptive specifications Master
specifications
Performance specifications Proprietary specifications
Reference specifications Uniform Construction Index
Issues
Standarddivisions of the specifications, basedon theUniform
Construction Index.
Types of specifications: master, performance, descriptive,
reference, proprietary, base-bid.
5.5 BIDDING REQUIREMENTS
Bidding documents and requirements are in-
corporatedin the project manualfora building to be
constructed to inform prospective bidders of all
provisions for submission of proposals. These
documents are not part of the contract documents.
The intent is to provide fair competition, that is, to
have allbidders invited tosubmit proposals compete
on an equal basis.
The documents andrequirements include:
1. An advertisement for bids if any competent
contractor will be considered, or an invitation
to bid if only prequalified contractors will be
considered
2. Instructions to bidders
3. Proposalform
4. Sample form for the owner-contractor
agreement
5. Contractor’s qualification statement, if
required
6. Requirements forvarious types ofbonds
7. Consent ofsurety
8. Noncollusionaffidavit,if required
Advertisement for Bids
This is a printed notice in newspapers or other
periodicals.It advises that proposals willbe received
by the owner for construction ofthe building.If the
advertisementis required by law, the statute usually
indicates how many consecutive times the notice
must be published. The notice should contain the
following:
1. Name of owner,name of contract and location
of project ,
2. Time and place forreceiving bids
3. Brief description of the project
4. Places and times for examination of drawings
and specifications or indication from whom
they may be borrowed and deposit required
5. Information on required guarantees, such as a

bid bond
6. Information on a performance and payment
bond, if one is required
Invitation to Bid
An invitation to bid contains practically the same
information as an advertisement forbids and is used
to invite proposals from prequalified contractors,
selected for experience, qualifications and financial
ability. Usually, the invitation is in the form of a
letter, signed by the owner, construction
representative or prime design professional.
Bonds
A performance and payment bond is a guarantee to
the owner, equalto the total amount ofthe bid, that
everythingrequiredby the constructioncontractwill
be faithfully done.Also,thecontractoris required to
pay all lawful claims of subcontractors, material
suppliers and labor for all work done and all
materials supplied in performance ofworkunderthe
terms of the contract.In addition,theownermust be
protected against suits by those persons, in-
fringement by the contractor of patents and
copyrights, and claims for property damage or
personal injury incurred by anyone during per-
formance of the work.
This bondusually is providedbya suretycompany
on behalfofa contractor,basedon knowledgeofhis
competency and financial condition. Liability
protection against suits and other claims may be
provided by an insurance company.
A bid bond is a guarantee to the owner that the
bidder, if offered the construction contract at the
prices he bid, will sign it. This bond also may be
supplied by a surety company; however, the
company usually will issue a bid bond only afterthe
performance bond for the project has been
underwritten andapproved.Sometimes,a contractor
may be permitted to submit a certified checkinstead
of a bid bond. He should not do so unless he has
assurances that his surety will approve a
performance bond forhis execution ofthe contract.
Instructions to Bidders
The bidding instructionsshould describe procedures
for preparation, submission, receipt, opening,
withdrawal and rejection of bids. The instructions
also should indicate who will answer questions
concerningthedrawings andspecifications.Usually,
to be certain that all bidders are treated fairly, the
owner’s representative will answer all questions in
writing by issuing addenda. These documents, part
of the contract, change, modify or clarify the
drawings, specifications or contract conditions and
are sent to all known bidders.
The bidding instructions, in addition, should
require bidders to visit the site to ascertain pertinent
local conditions.
For projects for which bid advertisements are
published, the bidding instructions should cover
qualifications of bidders, submission and return of
bidders’ guarantees, payment of taxes and wage
rates to be paid. Sometimes, also, the general
contractor may be informed of the need to submit a
list of subcontractors and material suppliers to be
engaged for the project. In addition, for public
works, a noncollusion affidavit may be required
fromeach bidder,to discourageagreements between
the bidders.
Proposal Form
Foruniformity in presentationofbidders’proposals,
the bidding requirements provide a formto be used
by allbidders in submitting bids.In signingtheform,
the bidderacknowledges that he is familiar with the
contract documents, has examined the building site
and has receivedthe addenda issued.Thebidderalso
states the price for which he agrees to furnish all
materials and perform all work required by the
construction contract.He furtheragrees to complete
the project in the stipulated time and to execute,
within a specified period,a contractforthe projectif
his proposal is accepted.
The proposal form usually also contains blank
spaces for prices that may be added to or deducted
from the total sum quoted for construction of the
project if the ownerelects to make changes orselect
an alternate given in the drawings or specifications.
If unit prices apply to changes,the formshould have
spaces for the unit prices for each type of work to
which they apply.
The proposal should be submitted sealed to the
owner or designated representative at the specified
location and within the required time.
Opening of Bids
Sealed proposals should be acceptedbytheownerup
to the time specified in the advertisement forbids or

invitation to bid.At the specified time and place,the
owner or his representative should open the sealed
bids in the presence of the bidders and disclose the
complete contents of each to those present. For
public works, the owner’s representative should
announce publicly the lump sums or unit prices bid.
Final tabulation ofthe results,however,need notbe
made at the bid opening norat award ofthe contract.
Often, the tabulation requires considerable study,
especially whentheownerhasthe optionofselecting
various alternatesgiven in the contract documents.
Unless required to do so by law, the owner need
not award the contract to the lowest bidder. For
reasons peculiar to a specific project or because of
special conditions, the owner may choose another
bidder, despite his higher price.
Shortly after the bid opening, the owner should
return the bid quarantees submitted by bidders not
likely to be selected.He may retain some,say three,
of the bid guarantees while bid studies continue.
These three should be returnedlater,afterthe owner
and the selected contractor sign the construction
contract.
The agreement between the owner and contractor
must be signed by the owner or a duly authorized
representative and by an authorized officer of the
contracting company.
References
Architect's Handbook of Professional Practice, American
Words and Terms
Advertisement for bids
Bid proposal form
Bonds: performance and payment, bid
Instructions to bidders
Invitation to bid
Type ofbiddingprocedure: by advertisement, by invitation.
Bonds as protection for owner.
Need for uniformity of information to all bidders.
Process of receiving, opening, andevaluatingof the bids. Use
of bids as a basis for the construction contract (agreement
between owner and contractor).
5.6 CONTRACTORS DRAWINGS
It is typical on building projects for some of the
subcontractors to be required to submit drawings for
the completion oftheirwork.These drawings may in
some cases consist of a final level of completion of
the design work, as is the case for subcontractors
whose work involves custom designed
installations—specialcabinetryandworks ofart,for
example. The basic contract drawings will allow for
this work,but leave theactualdetails tobedeveloped
by the installers, with a formal approval process
spelled out in the contract. The drawings submitted
by the subcontractorwill constitute both a submittal
ofthe detailed workfor approvaland thedescription
of the actual work for completion of the contract.
More frequently, contractors drawings consist of
those required for clear indication of how the work
is to be done. In these cases the final detail of the
work is still required to conformwith that shown on
the earlier contract drawings prepared by the
building designers.These contractdrawings are also
submitted for approval—usually meaning approval
by the professionals who prepared the contract
drawings. Approval, however, does not relieve the
contractors fromresponsibility forcompletion ofthe
work as spelled out onthe contract drawings andthe
specifications.Ifthe contractors intend to make any
changes or substitutions, these must be clearly
indicated andspecifically negotiatedwith theowner.
Many subcontractors work essentially as in-
stallers; merely obtaining the items indicated on the
contract drawings and describedin thespecifications
and proceeding to place them properly in the
building. In other cases, however, subcontractors
must also fabricate orproducethecomponents ofthe
systems they install, which may involve some
amount of final detail development of the
components.Arrangements forthis vary in terms of
the process forapprovaland the roles of the owner,
design professionals,generalcontractor,and the par-
ticular subcontractors involved.
5.7. CONSTRUCTION AND OCCUPANCY
PERMITS
Before constructionofa building may start,thelocal
building department usually requires that the
drawings and specifications be approved and a
building permit be obtained from the department.
Obtaining the permit generally is the responsibility
of the owner; his signature often is required on the
application for the permit. The drawings, however,

may be submitted on his behalfby the prime design
professional, or the construction contract may
require the generalcontractorto obtain the building
permit and pay required fees.
Note that a building department willapprove only
drawings prepared by an architect or engineer
licensed by the state and so certified by seal and
signature.
Because the building department may require
revisions of the drawings so that the building will
comply with all building-code and zoningcode
regulations,it generally is advisable forthe ownerto
have the drawings submitted to the department
before bids are requested.Then,therevisionscan be
made before receipt of bids or signing of the
construction contract.If the changes are made later,
the prime professional will have to issue addenda
before bids are received or, after the contract has
been signed, issue change orders, an even more
costly practice.
The owner also is generally responsible for
obtaining any otherpermits requiredforconstruction
of the project under the contract, such as those for
temporary closing of a street, trucking of very long
loads, or temporary shutoff of utilities that have to
be relocated. The contractor, however, has the
responsibility of securing the necessary permits for
work done at his option on the project but not
required by the contract.Forexample, if he elects to
use a crane operating from a street for erection of
steel or placement of concrete and a permit is
required for that purpose, the contractor should
obtain the permit and pay the required fee.
After construction starts, the building department
periodically sends inspectors to inspect the building
to insure conformance with building-code and
zoning-code regulations. The department also may
require the contractor to notify it when certain
critical stageshave beenreached orcriticalitems are
ready so that an inspector may be dispatched to
check compliance.
In addition othermunicipaland stateagencies may
send inspectors to insure that items under their
jurisdiction comply with legal requirements. The
state fire marshall or local fire department, for
example, may inspect construction; so may the state
labordepartment,state housingdivision,ora federal
housing agency, if it is concerned. If violations are
observed, the contractor is informed of them and
required to correct them.He is subject to penaltiesif
he does not remove the violations.
When construction has been completed, the
contractor notifies the building department, as well
as the owner, that the project is ready for final
inspection.The department then sends inspectors to
the building for that purpose. Any violations
discoveredmust beremoved.Whennoviolations are
found, the department issues a certificate of
occupancy.This gives to the ownerthe department’s
permission to occupy the premises.
5.8 CONSTRUCTION PROCEDURES
Construction usually starts shortly after the owner
and the general contractor have signed the owner-
contractor agreement. The owner should send the
contractor a written notice to proceed. The notice
should also advise the contractorwhen he can enter
the property and begin work.The contractorhas the
numberofdays stipulatedin the contractin which to
start construction.
When theproject has a tight constructionschedule,
the owner may want an early construction start. He
may ask the contractor to begin work before the
formal signing ofthe contract.In this case,theowner
may issue to the contractor a letter of intent. This
letter indicates that the contract will be awarded to
the contractor and gives himnotice to proceed with
construction. The letter should provide for
compensation to the contractor if the owner should
not award the contractto the contractor.Both parties
must sign the letter of intent to make it effective.
Construction Supervision
The head of the construction company may
personally take charge ofconstruction operations or
if the company is doingseveraljobs simultaneously,
he may assigna company officerorproject manager
for that purpose. To assist the manager, a field
superintendent usually is assigned to the building
site with responsibility for all activities there.
The owner may assign a representative to the site
for surveillance of the work. The representative
would have the responsibility of keeping progress
records, supervising inspectors, and in some cases,
keeping cost records. The representative may have
the title clerk of the works, architect's
superintendent, engineer's superintendent or
resident engineer. When a construction manager is
engaged, he generally assumes responsibility for
construction surveillance. Members of the building

team may be required to visit the site only
occasionally. Alternatively, the prime design
professional may be assigned the responsibility for
surveillance and engagement of the project
representative.
The basic stepsin construction are summarized in
Table 5.4.
Subcontract Awards
On receipt ofthe notice to proceedorletterofintent,
the contractormobilizes his forces andequipment to
start work. In accordance with a construction
schedule he has planned, he notifies subcontractors
that he is ready to sign contracts with themand, if
necessary, issues letters of intent to those
subcontractors required for the early stages of
construction. After he signs
Table 5.4. Basic Steps in Construction
1. Obtaining of permits and issuance by owner of letter
of intent or written notice to proceed
2. Planningand scheduling of construction operations
in detail
3. Mobilization of equipment and personnel for project
4. Notification to subcontractors of contract award,
issuance of letters of intent, awarding of subcon-
tracts, advance ordering of materials and equipment,
issuance to subcontractors of notice to proceed
5. Survey of adjacent structures and terrain
6. Survey for construction layout
7. Establishment of field offices
8. Erection of fences and bridges
9. Demolition, site preparation, andexcavation,
including bracing of earth sides, drainage, and utility
relocation
10. Construction of foundations
11. Erection of structural framing and stairs
12. Placement of temporary flooring, if needed
13. Installation of pipes, ducts, and electric conduit
14. Erection of material hoists, if needed
15. Construction of permanent floors
16. Installation of elevators in tall buildings
17. Placement of exterior walls and windows
18. Fireproofingof steel framing, if required
19. Construction of fixed partitions
20. Construction of roof and placement of roofing
21. Finishing operations
22. Removal of temporary structures and clean up
23. Landscaping
24. Final inspections and project acceptance
25. Issuance by building department of certificate of
occupancy
26. Final payment to contractor andoccupation of
premises
contracts with the others, he advises them of the
dates on which they are scheduled to begin workon
the project.
Scheduling
A subcontractorwho arrives on the job readyto start
work before the project has reached the appropriate
stage generally is unable to begin. One who starts
late may delay the project.Consequently,workmust
be so scheduled that subcontractors report for work
exactly when needed. Similarly, materials must be
delivered close to the time when they are needed.If
they arrive late, work is delayed. If they arrive too
soon, sufficient storage space may not be available.
Consequently, the contractor must plan his
operations wellin advance,carefully and accurately.
Surveying
One of the first steps is to survey the building site
and surroundingterrain and property.The survey of
existing conditions is needed to determine
conditions of adjacent structures that may possibly
be damaged by the contractor’s operations. This
survey must be supplemented by readings of
elevations at the foundations ofthe nearbybuildings
for use in later determinations of the occurrence of
settlement or lateral movement.
Also, a survey is needed to provide a general
layout for construction, including base lines, offset
lines, and reference points, such as bench marks
(points of known elevation). These lines and points
are used for geometric control during construction.
Measuring from them, the surveyors locate and
orient structural members, such as columns and
walls, and maintain verti- cality of vertical
components. Also, the surveyors determine the
elevations of foundations, floors and roofs. In
addition, they establish control points inside the
building,fromwhich they make othermeasurements
of distance and elevation.
Construction Offices
Another early step the contractor takes is estab-
lishment ofconstructionoffices onoradjacent tothe
building site. The space is needed for housing
records, permits, and construction documents,
administrative and supervisory personnel when not
in the field, and clerical and secretarial help. The
offices also are useful for communication and

meeting purposes.Jobmeetingsare held periodically
with the owner’s representatives and subcontractors
for dissemination of information, to settle
controversies, and to avoid problems. Similarly,
subcontractors set up offices, usually close to those
ofthe generalcontractor,butonly fortheirown staff.
The owner too may set up offices for his repre-
sentatives.Temporary buildings may be used forall
of these offices.
Fences and Bridges
Anotherearly step the contractortakesis to fence in
the property, especially if excavation will extend
near the lot boundaries. Fencing, however, often is
omitted if the contractor believes that there is
practically no chance that the public will be injured
by construction activities.
As construction advances above ground, the
contractorusually erectsa shed,orbridge,along the
fence above streets or walkways that adjoin the
fence. The purpose of the bridge is to protect
passersby from objects accidentally dropped from
the structure during its erection.
Site Preparation
If the lot already contains buildings or other
structuresnotto beincorporatedin the newbuilding,
they must be removed. For this purpose, a
demolition subcontractor is employed. If the site is
heavily wooded, the area to be occupied by the
building and other facilities must be cleared. Often,
the land has to be graded.
Also, substantial excavation may be required; for
example, when the building has abasement or deep
foundations are needed. This work may be
performed by the foundation subcontractor or a
separate earthwork subcontractor. In addition, the
earthwork subcontract may call for removal or
relocation of existing underground utilities. If
special provisions must be made for draining the
excavation to prevent water that seeps into it from
hindering construction,a specialsubcontractmay be
let for pumping out thewater,forinstance,toa well-
point subcontractor.Ifextensive trenchingis needed
for water supply and sewage lines, the earthwork
contract also may include that work; otherwise, it
may be covered by the plumbing subcontract.
Foundations
As excavation proceeds, it usually becomes
necessaryto support theearth around theboundaries
to preventit fromcaving in orfrommoving laterally.
Earth movements might cause nearby structures to
settle or move laterally and damage them. A
common method of providing support is to drive
sheetpiles around the excavation, and then, in some
manner, brace the sheeting.
If piles are needed tosupport thebuilding,they are
driven to required depths into the bottom of the
excavation and capped with concrete footings. If
spread footings are specified, soil is excavated to
required depths and concrete is placed to form the
footings.Also,foundation walls are concreted along
the perimeter of the excavation. Earth backfill then
is placed behind the walls, if necessary, to prevent
movement of adjoining soil when the sheeting
supporting it is removed.
Structural Framing
If the framing of the building is to be structuralsteel,
the general contractor may award a contract for
fabrication and erection of the steel to a single
subcontractor, or one contract to a steel fabricator
and a second to an erection subcontractor. If the
framing is to be concrete, a concrete subcontractor
will be employed. A concrete subcontractor will be
engaged in any event if the floors, walls, or other
parts of the structure are made of concrete.
Erection of walls and columns can start as soonas
the concrete in the foundations has gained sufficient
strength, usually at least a week after the concrete
was cast.Beams and girders,ifrequired,orconcrete
floors are placed between the vertical structural
members as soon as possible. The horizontal
members are needed tobracetheverticals,toprevent
them from toppling over. Additional diagonal
bracing also may be installed, to keep columns in
vertical alignment. The beams and girders, in
addition,provide support fortemporary flooring for
workmen. (To avoid interference with erection of
structuralsteelframing,permanentfloors usually are
not installed in multistory buildings untilthe framing
is in place several stories above. Building codes,
however, for safety reasons, often place a limit on
the number of stories the framing may be advanced
above the floors.) Load-bearing walls must be
constructed before the skeleton framing (beams or
floor slabs and columns), because the walls have to
support the beams or floor slabs.

Other Components
Installation ofstairsgenerally follows closely behind
erection of the framing to enable workmen to reach
the levels at which they have to work. Piping,
ductwork, and electric conduit to be embedded in
permanent construction also are installed early.
The generalcontractorusually provideshoistsfor
use by the subcontractors to raise materials and
equipment to the floors where they will be needed.
The subcontractors also may use cranes or derricks
for hoisting materials and equipment. Also, for tall
buildings, when the framing becomes high enough,
elevators are installed to lift workmen to working
levels.
As the framing rises, permanent floors are in-
stalled at successive levels. Placement of exterior
walls follows closely behind.Windowsare set in the
walls,often without glazing to prevent the glassfrom
being broken accidentally while construction
proceeds. Meanwhile, electrical, plumbing, and
HVAC subcontractors continue with installation of
wiring, piping, and ductwork. If the framing is
structural steel and the underside requires
fireproofing,fire-resistant materialshould be placed
to protect the framing, unless the ceiling will serve
that purpose. Fixed partitions may be constructed
next. By this time, usually,the roofcan be installed.
Finishing Operations
Before the building can be considered completed,
however, there are numerous operations still to be
performed. Ceilings have to be placed, roofing and
flashing laid down, wallboard or panelling attached
to interiorwall surfacesand tile set.Electric lighting
fixtures have to be mounted and switches,electrical
outlets and electrical controls installed. Plumbing
fixtures have to be seated in place. Furnaces, air-
conditioning equipment, permanent elevators and
escalators, heating and cooling devices for rooms,
electric motors and other items called for in the
drawings and specificationsmust be installed.Glass
must be placed in the windows,floor coverings laid
down, movable partitions set in place, doors hung
and finishing hardware installed.Alltemporary con-
struction, such as field offices, fences and bridges,
must be removed. The site must be landscaped and
paved.Finally,the building interiormust be painted
and cleaned.
When the generalcontractorbelieves the building
has been completed, he notifies, in writing, the
owner and his site representative. The owner then
should apply to the building department for a
certificate ofoccupancy anddetermine by inspection
whether the work has, in fact, been completed in
accordance with the drawings and specifications. If
it has not,the ownershould report,in writing and in
detail,to the contractortheadditionalworkrequired.
The owner should make a careful final inspection
and not rely on the building departmentinspectionto
protect his interests.Building department inspectors
are primarily concerned with discovering violations
of the building code.
When the workhas been satisfactorily completed,
the ownermust determine accurately the amount due
the contractor, including the value of work done
under change orders and extra work authorized
during construction.Within a periodstipulatedin the
contract, usually 30 days, the owner must pay the
contractor the amount due, less any money the
owner,underthe contract,may be permitted to with-
hold tentatively.He alsoshould promptly furnish the
contractor and his surety a statement of acceptance
of the project or of exceptions. On receipt of the
certificate of occupancy,the ownermay occupy the
building.
These are books that deal generally with topics
covered in the chapter. Topic-specific references
relating to the individual chapter sections are listed
at the ends of the sections.
The Architect's Handbook of Professional Practice, Vol. 1,
R. Hershberger, Programming for Architecture, Van Nostrand
Reinhold, 1987.
c. Dunham et al., Contracts, Specifications, and Law for
Engineers, 3rded., McGraw-Hill, 1979.
J. Clark, Understanding and Using Engineering Service and
Construction Contracts, Van Nostrand Reinhold, 1986.
R. McHugh, Working Drawing Handbook, 2nd ed., Van
Nostrand Reinhold, 1982.
H. Meier, Construction Specifications Handbook, Prentice-
Hall, 1983.
EXERCISES

for review of the individualsectionsand the chapter
as a whole.
Section 5.1
1. Who besides the owner and members of the
building teamshould help prepare the contract
documents?
2. Name and describe briefly the contract
documents.
3. Who are the parties (signatories) to the
construction contracts?
4. If, during constructionofa building,the owner
asks the contractorto performworknot covered
by the drawingsandspecifications,what should
the contractordo ifhe is willing to do the extra
work?
5. Why should contracts and change orders be in
writing?
6. Why are modifications of the contract during
construction undesirable?
7. Besides maintenance ofa goodreputation,what
incentive does a contractor have to provide
good workmanship?
8. What risks are incurred whenthe specifications
list in detailthe proceduresthe contractormust
follow and the required results?
9. Who is responsible for securing construction
permits?
10. Under what circumstances should a contractor
use substitute materials not called for in the
contract documents?
SECTION 5.2
11. How do addenda and modifications of the
contract differ?
12. What is the purpose of the project manual?
13. (a) Which of the documents in the project
manual are not contract documents?
(b) Which of the contract documents are not
normally incorporated in the manual?
14. What requirements usually are contained in the
owner-contractor agreement?
15. What are the advantages of using a standard
construction contract?
16. Is it necessary to repeat in the specifications a
requirement given in the conditions of the
contract? Explain your answer.
(a) General conditions of the contract?
(b) Supplementary conditions ofthe contract?
18. If working drawings showto scale and labelall
items comprising a building, why are
specifications still necessary?
19. A contractor preparing a construction proposal
discovers a conflict between the working
drawings and the specifications. The prime
professional corrects the conflict and notifies
the observent contractor. What else should the
prime professionaldo before bids are received?
20. During construction of a building, the general
contractornotifies the prime professionalthat a
window type specified is no longer being
manufactured and is not available forpurchase.
What should the prime professional do?
21. In what contract document for a 10-stoiy
building should you look to determine:
(a) Beam spacing for the fifth floor?
(b) The tolerances permitted in fabrication of
steel beams for the fifth floor?
(c) Layout of air ducts for the fifth story?
(d) Quality of material used for the air ducts
for the fifth story?
22. What information is provided by a door
schedule?
23. Why should every item shown in the drawing
also be specified in the specification?
Why is repetition of a requirement in both
documents undesirable?
24. What are the advantages of a master spec-
ification?
25. What is the relationship of the organization of
specifications and the subcontract method of
construction?
26. What are the advantages to the building owner
of a product specification that gives the
contractor a choice of several products?
27. What type of information should be given by
notes on working drawings and what type by
specifications?
28. A drawing of a foundation wall does not show
a drain at the base ofthe wall, but a note on the
drawing states:“Install4in.cast-iron drain pipe
completely around foundation and connection

to sewer.” Is the contractor required to furnish
and installthe pipe without additionalcompen-
sation? Justify your answer.
Section 5.5
29. Describe briefly the usual bidding requirement
documents.
30. Compare the advantages and disadvantages of
an advertisement for bids and an invitation to
bid.
31. What should be the value of the performance
and payment bond a contractor is required to
post for a building he seeks to construct?
32. What is the purpose ofa bid bond?
33. The prime professional for a project receives a
telephone call from a prospective bidder who
questions some items in the drawings and
specifications. What should the prime
professional do?
34. In what document should a builderlook to find
information on the opening of bids?
35. Shortly after bids have been requested for
building construction, the prime professional
receives a telephone call from a material
supplier requesting additional information.
How should the prime professional handle the
request?
Sections 5.6 to 5.8
36. Why must an owner or a competent rep-
resentative inspect construction despite
frequent building department inspections?
37. After a building permit has been issued, a
company president, on recommendation of the
building architect,decides to request bids from
six general contractors:
(a) What means should the president use to
request bids?
(b) How does the president insure that the
selected bidder will sign the construction
contract?
(c) Are bids usually examined as they are
received?
(d) Must the company president sign the
contract with the low bidder?
38. A city public works department has obtained a
building permit for a proposed building. The
city engineer,in accordancewith city law,must
accept proposals fromall interestedcontractors
and engage the contractor who submits the
lowest bid.
(a) What means should the engineer use to
request bids?
(b) How does the engineer insure that the
bidder selected will complete the work
after signing the contract?
39. A company president engages for design and
construction of a factory a general contractor
who is neither a registered architect nor a
professional engineer.
(a) Will the building department issue a
building permit for plans drawn by the
contractor that satisfy the building code?
Explain your answer.
(b) How will the building department know
from inspection ofthedrawings whetheror
not the person who prepared them is an
architect or an engineer?
40. Afterselecting a generalcontractor,howcan an
owner get construction started immediately
without signing a construction contract?
41. Compare the responsibilities and duties of the
contractor’s field superintendent with those of
the clerk of the works.

135
Chapter 6
Life Safety Concerns
Buildings must be designed for both normal and
emergency conditions.Building designersshould,in
initial design ofbuildings,take precautionstoprotect
property from major damage, and especially from
collapse,due to accidentsordisasters; but designers
must also provide for life safety of occupants,
neighbors and passersby in emergency situations.
Such situationsmay be caused byhigh winds,earth-
quake, intruders or fire. Cost-effective protection
against theiradverse effectscan beachieved with the
systems-design approach, applied from the start of
conceptual design.
Building codes contain many requirements for
prevention of major property damage and for life
safety. But codes do not always cover extreme
conditions or special cases. Safety requirements in
codes generally are minimumstandardsapplicable to
ordinary buildings, those not unusually large or tall
and those not used forpurposeswith which therehas
been little experience,such as production ofnuclear
power. Building designers therefore must use
judgment in adopting code provisions and apply
more stringent requirements when specific con-
ditions warrant them.
Economic and sometimes sociological factors
often rule out provisions for full protection against
extreme conditions that are possible but highly
unlikely to occur.Forexample,it is possible but very
costly to build a one-family house that canwithstand
a violent tornado.Furthermore,becausesucha house
would have smallorno windows,a family preferring
large windows would choose suchwindowsandrisk
the possibility of injuries from tornadoes. Con-
sequently, building designers should weigh the
possibility of extreme conditions occurring and
balance risks and costs.
Fromstatisticalstudies ofsuchnaturalphenomena
as snowfalls, high winds and earthquakes,
probabilities of extreme conditions being exceeded
in a year in various parts of the United States have
been determined. For example, the probability is
0.04, orfourchances in one hundred,ofa wind faster
than 80 mph blowing through New York City, or
0.02, two chances in one hundred, of a wind faster
than 60 mph blowing through Los Angeles.
The reciprocalofthe probability is called themean
recurrence interval. This gives the average time in
years between the occurrence of any condition that
exceeds the specific extreme condition. Thus, the
mean recurrence interval of a wind faster than 80
mph in New York City is 0J04’ or
25 years,and ofa
wind faster than 60 mph in Los Angeles, 50 years.
Designers can use mean recurrence intervals to
establish reasonable design values. For example, if
the expected life of a building to be erected in Los
Angeles is 50years,it would be logicalto design the
building for a 60-mph wind, which would be
unlikely to be exceeded in the next 50 years.(Mean
recurrence intervals for snowfalls, winds and
earthquakes are given in ANSI “Building Code
Requirements for Minimum Design Loads in
Buildings and Other Structures,” A58.1-1982,
American National Standards Institute.)
6.1. WINDSTORMS
Every year, high winds in the United States cause
property damage costing many millions of dollars

and kill and injure many persons. Deaths from
tornadoesaloneaverage about100personsannually.
Many of these deaths and injuries result from
collapse of buildings. Better building design and
construction therefore not only could prevent much
of the wind damage but also could savemany lives.
Furthermore, with the systems-design approach,
designers could incorporate adequate wind
resistance in buildingsandprotect lives with little or
no increase in costs over former inadequate
measures.
Wind Characteristics
Experience has shown that probably no area in the
United States is immune fromincidence ofwinds of
100 mph. Furthermore,tornadoeshave beenreported
in all states except for four or five western states.
Tornado winds have been estimated as high as 600
mph. Hurricanes have struck areas of the country
with winds as high as 200 mph.
Straight Winds. Generally, wind damage appears
to be caused bysevere straightwinds,althoughairin
the storms may be rotating about a nearly vertical
axis. In the case of hurricanes with rotating winds,
the radius ofcurvature is solarge that thepathofthe
wind may be considered straight. In the case of
tornadoes with winds rotating in a narrow funnel,
damage appears to be caused by severe windsin the
same general direction as the funnel movement.
Gusts. Wind velocity, however, usually does not
remain constant for long. The wind often strikes a
building as gusts. Wind velocity in such cases rises
rapidly and may drop off just as fast. Hence, wind
actually imposes dynamic loads on buildings.
Effects of Friction. Because of natural and man-
made obstructionsalong the ground,wind velocityis
lower along the ground than higher up. Ground
characteristics within a range of at least 1 mile of a
building are likely to affect velocity of the wind
striking the building. The rougher the terrain the
more the air will be slowed. Building codes often
take this effect into account by permitting lower
design wind loads for buildings in the center of a
large city than for buildings in a suburban area and
woods, and allowing lower loads for buildings in
suburban areas than for buildings in flat, open
country.
The effects ofground roughness on wind velocity
diminish with height above ground and eventually
become negligible.In the center ofa large city,wind
velocity above an elevationofabout1,500 ft relative
to the ground may be unaffected by the ground
surface and buildings. For suburban areas and
woods, wind velocity may be considered nearly
constant above an elevation of about 1,200 ft. For
flat, open country, the limiting elevation for
roughness effects may be about 900 ft, and for flat,
coastal areas, 700 ft.
Velocity Measurement. For standardization
purposes, wind velocities are reported for an
elevation of 10 m (32.8 ft) above ground. If winds
are not measured at the level, the wind velocities
recorded at another elevation are converted to
velocities at the 10-m level. Building codes often
require buildings up to30to 50ft high to be designed
for wind velocities at the 10-mlevel.
Variation with Height. With the velocity knownat
the 10-m height, the velocity at any height above
ground up to the limiting elevations previously
mentioned may be estimated fromEq. (6.1).
=
(ẩs) (6J)
where
Vz — velocity at height z above ground
^10 = velocity 32.8 ft above ground
z = elevation above ground, ft
(32.8 < z < 900, 1,200 or 1,400) n =
exponent with value depending on
roughness of terrain
For centers of large cities and very rough, hilly
terrain,n may be taken equalto |.Forsuburbanareas,
towns, city outskirts, wooded areas and rolling
terrain, n may be taken equal to ^5. For flat open
country and grassland, n may be taken equalto 7and
for flat, coastal areas, 7Q.
Shielding. A building may be shielded from the
wind fromcertain directions byadjacentbuildingsor
hills. But it would not be conservative to design a
building for lesser wind loads because of such
shielding.In the future,the shielding buildings may
be removed or the hill modified, with resulting
increases in wind buffeting.

Life Safety Concerns in SystemsDesign 137
Channeling Effects. Man-made or natural ob-
structions might channel wind toward a building or
increase the intensitiesofgusts.In such cases,if the
increased wind loads can be estimated, they should
be providedforin designofthe building. Often,wind
tunnel tests of a model of a building, neighboring
buildings and the nearby terrain are useful in
predicting wind behavior.
Orientation. In many parts of the United States,
high winds generally may come from a specific
direction.Nevertheless, it is possible forhigh winds
to come from other directions too. Consequently, it
is advisable in building design to assume that wind
may come fromany direction.
Inclination. In many cases, it is reasonable to
assume wind velocities as horizontal vectors. This
assumption may be adequate for design of vertical
walls and structuralframing otherthan in roofs; but
because of possible turbulence in the vicinity of a
building or because ofthe slope ofthe terrain, wind
velocity may be inclined 10°or15° or more from the
horizontal, up or down. The vertical component of
the wind in such casesmay imposesevere loadingon
roofs, balconies, eaves and other overhangs.
Design Loads. The preceding description ofwind
characteristics should make it evident that wind
loads are uncontrollable, random variables. They
also are dynamic ratherthan static.Nevertheless,for
ordinary buildings, it is usual practice to assume
probable maximum wind velocities and to treat the
associated pressures on the buildings as constant
loads. For unusually tall or slender buildings,
detailed structural analyses aided by wind tunnel
tests ofmodels generally is advisable,with the wind
treated as a dynamic load.
Wind Pressures and Suctions
For a wind velocity Ư, mph, the basic velocity
pressure p, psf, on a flat surface normal to the
velocity is defined by
p = Kv2
(6.2)
where K = 0.00052 when n - I
= 0.0013 when fl = 43
= 0.0026 when fl = Ặ
= 0.0036 when fl = -jL
Table 6.1 lists some basic pressures for winds with
50-yearrecurrence intervalforvarious regions ofthe
United States and forvarious heights above ground.
These pressures can serve as a guide in the absence
of building-code requirements. Note, however, that
Table 6.1 does not allow for tornado winds or
extreme hurricanes.
The basic total force p, lb, due to a basic wind
pressure p is given by
P = Ap (63)
where A = area of perpendicular surface, sq ft.
The effects ofgusts may be taken into accountby
applying an appropriate gust factor G. With gusts,
the wind force equals
P=GAp = Aq (6.4)
where q = Gp.
Dependent on type of exposure and dynamic
response characteristics of the obstruction, G is
probably best determined fromwind tunnel tests of
models or from observations of similar existing
structures.
The effective pressure acting on a building or a
building component depends on the building
geometry.The effect of geometry is generally taken
into account by multiplying q by a pressure
coefficient c. For example, external pressure on the
windward wall of a building may be

Table 6.1. Basic Wind Pressuresfor Design of Framing, Vertical Wallsand Windowsof
Ordinary Rectangular Buildings, psf*
Types of exposures
Ab B0 cd
Ab cd
Ab
Bc cd
Height zone, Coastal areas, N.w. and Northern and central Other parts of
ft above curb S.E. UnitedStates^ United States*^ United States^
0-50 20 40 65 15 25 40 15 20 35
51-100 30 50 75 20 35 50 15 25 40
101-300 40 65 85 25 45 60 20 35 45
301-600 65 85 105 40 55 70 35 45 55
Over 600 85 100 120 60 70 80 45 55 65
a
For winds with 50-year recurrence interval. For computation of more exact wind pressures, see ANSI Standard
A58.1-1982.
^Centers of large cities and very rough, hilly terrain.
c
Suburban areas, towns, city outskirts, wooded areas, and rolling terrain.
ư
Flat open country, flat open coastal belts, and grassland.
e
100-mph basic wind speed.
^90-mph basic wind speed.
^80-mph basic wind speed.
computed from
pe = CpAqe (6.5)
where
A = projected area of the structure on a vertical
plane normal to the wind direction
Cp - external-pressure coefficient
Building codes give recommendedminimum values
for pressure coefficients for ordinary buildings. For
unusual buildings, they may be determined from
wind tunnel tests of models.
Pressure coefficients are given a positive sign
when the pressure tends to push a building
component toward the building interior. They are
given a negativesignwhenthe pressuretendsto pull
a building component outward. Negative pressures
also are called suctions or, for a roof, uplift.
Figure 6.1a illustrates wind flow over a sloping
roof of a low building. As indicated in Fig. 6.1Z>,
the wind creates a positivepressure on the windward
wall normal to the wind direction and a negative
pressure on the leeward wall. For the roof slope
shown,it is likely that the wind will create an uplift
over the whole roof. Pressure coefficients for the
windward wall therefore will be positive and those
for the leeward wall and the roof, negative.
If there are openings in thebuildingwalls,internal
pressures will be imposed on the walls, floors and
roofs.
The net pressure acting on a building component
then is the difference between the pressures acting
on opposite faces (vector sumof forces acting).
Fig. 6.1. Effect of wind on a low building with sloping roof, (a) Wind flow, (b) Wind pressures.

Design for Wind
Every building and its components should be
designed to withstand, without collapsing, tearing
away, breaking or cracking, maximum winds that
are likely to occurwithin the anticipatedservice life
of the building. Generally, a 50-year mean
recurrence intervalshould be the basis forselection
of a maximum basic wind velocity for a permanent
building. But for unusual buildings or for those
presenting an unusually high hazard to life and
property in case of failure, a 100-year mean
recurrence interval should be used.
For economic reasons, it is impractical to design
buildings to resist violent tornadoes without
considerable building damage. Conservative
designs,however,usually incorporatea safety factor
to provide reserve strengthagainst unexpected loads,
poorquality materials and low- grade workmanship
that escapes attention. Hence, a building properly
designed to withstand probable wind loads without
damage should have sufficient reserve strength to
resist much strongerwindswith little or no damage.
For light construction,such asone-and two-story
houses,which tend to collapse whenin the path ofa
tornado, it is advisable to incorporate a well-
protected shelter.It may be located in the basement
or on the ground floor of basementless buildings.
The shelter should be enclosed on all sides with a
strong material, such as thick, reinforced concrete.
The entrance preferably should be inside the
building and should provide a 90° turn to prevent
flying debris fromentering the shelter.In a tornado,
debris, such as wood beams, can become flying
missiles and penetrate several ordinary building
walls.
The systems-design approach can be helpful in
reducing damage fromhigh winds,especially when
systems design is used from the start of the
conceptual phase of design. For example, though a
building may be designed for a probable maximum
wind from any direction, the building may be
oriented to resist extremely high winds in the
direction from which they are likely to come. In the
midwestemregion ofthe United States,forinstance,
tornadoes generally move from southwest to
northeast.Hence,in that region,a building could be
placed on its site and shaped to have low exposure
to the southwestandstrengthened tohave highresis-
tance to such tornadoes.
As another example, all connections, from
foundation to roof, between building components
could be given adequate strength to withstand
extreme winds without failing at only a slight
increase in construction cost.
As stillanotherexample,measures canbe taken to
reduce wind pressures. This may be accomplished
with appendages on the walls or roofline
irregularities; or vents may be placed in roofs to
relieve uplift. Wind tunnel tests may give clues.
Wind resistance should be anintegralpart of every
building system. Designing a systeminitially only
for gravity loads and then adding strengthening
elements for wind resistance is likely to be more
costly and not so structurally effective as providing
strength and stiffness forbothgravity andwind loads
from the start of design.
Designers should consider the possibilities of
different failure modes under wind loads and
provide against them.
Overturning. Wind loads are often referred to as
lateral forces, because they act against the sides of
buildings as substantially horizontal forces,
compared with gravity loads, which act vertically.
Note that a wind striking the sides ofa rectangular
building obliquely may be resolved into two
components, each component perpendicular to a
windward side. In analysis of the effects of wind
loads then, the response of the building to each
component canbe studiedseparately and the effects
of both components determined.
Considered as a rigid body, a building subjected
to horizontal forces w may be overturned. It would
tend to rotate about the edge of its base on the
leeward side (see Fig. 6.2a). The tendency to
overturn is resisted by the weightM ofthe building.
Building codes usually require that the resistance to
overturning be at least 50% greater than the
overturning force.

If Wh is the overturning moment about the baseand
Me is the resisting moment about the leeward edge
of the base,
Me>1.5Wh (6.6)
The resistance tooverturningcanbeaugmentedby
anchoring the building firmly to its foundations.The
weight of earth atop footings then may be included
with the weight of the building in computation of
Me.
Sliding. In addition to tending to overturn a
building, wind forces also tend to push a building
horizontally. This movement is resisted by friction,
earth pressure and connections between
superstructure and substructure.
Like overturningresistance,sliding resistance due
to friction depends on the weight ofthe building.If
a building subjected to high winds is firmly
connected to foundations that are located near the
ground surface, the foundations may slide in the
direction of the wind unless there is sufficient
friction between them and the soil or unless the
foundations are anchored to the ground (see Fig.
6.2ft). For a building with deep foundations, earth
between footings and ground surface will assist the
friction forces in resisting sliding (see Fig. 6.2c).
(With some soils,however,resistance to movement
may decrease when the ground gets wet. The
possibility ofthis occurring should be consideredby
the designers.)
To insure development of required sliding re-
sistance,whetherfoundations are shallowordeep,it
is essentialthat designers callforstrong connections
between superstructure and foundations. In the
absence of such connections, strong winds have
pushed many small buildings off their foundations,
with disastrous consequences to occupants and
property (see Fig. 6.2d). Buildings should be
Fig. 6.2. Some potential modes of failure for buildings subjected to high winds, (a) Overturning. (Ô) Sliding,
unresisted, (c) Sliding, resisted by weak SOĨI.Ỉd} Sliding off foundations. (e} Roof uplift.
(d)

securely anchored to prevent both sliding and
overturning.
Roof Uplift or Sliding. Flat roofs and roofs with
slopes up to about 45° may be subjected to suction
over the whole area. The uplift may be severe
enoughto drawthe roof,orpartsofit,away fromthe
rest of the building, unless the roof is firmly
anchored to the building frame and its components
are securely attachedto each otherand to theframe.
Often, when high winds peela roof from a building
with loadbearing walls, one or more of these walls
also topples.
The weight ofa roofcannot be relied on to hold it
in place in strong winds. Positive anchorage should
be provided between the roof and its supports.
Steeply sloped roofsmay be subjected to positive
pressures orsuctions,depending on the directionof
inclination (see Fig. 6.2e). The resulting forces may
slide a roof from its supports or suck components
loose. Such damage can also be prevented by
positive anchorage.
Sway and Collapse. Strong winds may collapse a
building,without overturningit orcausingit to slide,
unless adequate means are provided to transmit the
wind loads through foundations into ground strong
enough to resist the loads.
Load-bearing walls have to be braced against
caving in or being sucked outward by winds.Floors
and roof,if securely attachedto the walls,can serve
as bracing, but some means must be present to
transmit the wind loads to the ground. If not, the
floors and roofwill shift underthe horizontalforces
and permit the walls to topple.
Curtain walls should be anchored to the structural
frame of the building or to floors and roof attached
to the frame. Connections should be strong enough
to transmit wind loads fromthe walls to the frame.
Then,some means must be provided to transmit the
loads fromthe frame through the foundationsto the
ground. If this is not done, the building may topple
like a house of cards (see Fig. 6.3«).
Any of several structural devices may be used to
carry wind loads to the ground. Figures 6.3b to d
illustrate some of the most commonly used ones.
Figure 6.3b shows a shear wall, which may be
used to brace load-bearing walls directly or to
withstand wind loads on floors and roof. The wall
has high resistance to horizontalforces parallelto its
length.Iftwo such walls are placed perpendicularto
each other,they can resist wind from any direction,
since any wind force can be resolved into
components parallel to each of the walls.
Figure 6.3c shows a structural frame with di-
agonal structural members to carry the wind loads
wto the ground.The diagonals are called X bracing.
The arrows in Fig.6.3c showthepaths takenbywind
forces until they reach the ground. Note that the
diagonals and the girders (majorbeams)transmit the
horizontal forces w to the leeward columns, which
carry the forces vertically to the ground. The
windward columns, in contrast, carry vertically
upward forces from the ground that keep the
building fromoverturning.
Figure 6.3d shows a rigid frame subjected to
horizontalwind forces.The wind tries to topple the
building in the manner indicated in Fig. 6.3«;
however,in the rigid frame in Fig. 6.3d,the girders
and columns are rigidly connected to each other.
Any tendencyforthe ends ofthe girders to rotate is
resisted by the columns, because the connections
maintain the right angle at eachjoint.The frame may
shift a little in the direction ofthe wind,butthe frame
cannot collapse until the strength of the members
and connections is exhausted. As in the X-braced
frame, the leeward columns transmit the horizontal
forces vertically to the ground. The windward
columns carry upward the forces from the ground
that prevent overturning.
Designers must bearin mind that the objective of
shear walls, bracing and rigid frames is to convey
loads to ground that can withstand those loads.Any
gap in the load path to such ground, i.e. any failure
to transmit load, can lead to disaster.Consequently,
not only must designers provide a continuous load
path but also they must make every element along
the path strong enough to carry imposed loads.

This means that connections as well as girders,
columns, bracing, foundations and soil must have
adequate capacity.
Sway or Drift. Strength, however, cannot be the
sole consideration. Potential movements of the
building also must be considered.Windforces,even
when static,cause sidesway,ordrift,a shifting ofthe
upperpart ofa building in the direction ofthe wind.
Winds, though, are dynamic loads and they can
cause a building to sway violently back and forth
until it falls apart, unless the building is made stiff
enough to resist suchmovements.So design against
wind must have two other objectives besides
provision of sufficient strength. Total drift of a
building must be limited to prevent damage to
building components, especially cracking of brittle
materials, such as plaster or concrete walls. In
addition, vibration of buildings must be controlled
so as not to damage building components or annoy
occupants.
These objectives canbeattainedbypropershaping
ofa building,arrangements ofstructuralcomponents
to resist drift, and selection of members with
adequate dimensions and geometry to withstand
changes in dimensions. For example, low, squat
buildings have less sidesway than tall, slender
buildings. Hence, decreasing the ratio of building
height to least base dimension,width orlength, will
reduce drift. As another example, thin rectangular
buildings have more sidesway than square or
circular buildings with the same floorarea perstory.
Thus, making buildings more compact will reduce
drift. But thin rectangles can be used with reduced
drift if they are arranged in perpendicular wings, to
brace each other. Buildings T or H shaped in plan
can consequently be efficient in resisting sidesway
because, regardless of the direction fromwhich the
(a)
ị I
(d)
(c)
Fig. 6.3. (a) Wind loads w topple an unbraced building. This maybe prevented byuse of (Ồ) shear wall, (c)
diagonal bracing, or (</) rigid-frame action.

wind blows, they have long walls or long lines of
columns with high resistance towind in thedirection
of wind components.
Design of a building as a system requires that
gravity and lateral loads be considered simulta-
neously, to achieve optimum results. Often, it
becomes possible to provide wind resistancethrough
this approach with no increase in cost over that for
supporting gravity loads alone.
Structuralframing is discussedfurtherin Sec. 6.2
and Chap. 8.
6.2 EARTHQUAKES
Earthquakes may occur anywhere in the United
States. Therefore, all buildings should be designed
to withstand them. Proper aseismic design should
produce buildings capable of surviving minor
temblors with no damage. With good systems
design, this should be done with no increase in
construction cost over that for gravity and wind
loads. Also, proper aseismic design should produce
buildings capable of surviving major earthquakes
without collapsing. Good systems design should be
helpful in minimizing the cost of achieving this
objective.
The probability of a violent temblor occurring at
the same time as a high wind appears to be very
small. Hence, building codes generally do not
require buildings to be designed for simultaneous
occurrence of wind and seismic loads. As a result,
the full strengthandstiffnessprovideda building for
resistance to seismic loads are also considered
available to resist wind loads.
If a strong earthquake should occur, sidesway of
buildings is likely to be severerthan forwinds.Asa
result,even ifstructuralcomponentsare made strong
enough to prevent collapse, buildings may suffer
considerable damage. Nonstructural components
especially may be vulnerable. For example, walls
may be stifferthan the structuralcomponentsbutnot
so strong. Being stiffer, the walls will be subjected
to greaterforces,which can causeseverecracking of
the walls or their collapse. Also, the walls may
interfere with planned actions of the structural
components and thus cause additional damage.
Consequently, aseismic design requires thorough
knowledge of structural engineering and building
material properties and also calls for exercise of
good judgment to save lives and minimize property
damage.
Characteristics of Earthquakes
Earthquakes occur because of sudden movements
inside the earth, with simultaneous release of
tremendous amounts of energy. The location at
which the temblor originates is called the
hypocenter. The point on the surface of the earth
directly above the hypocenteris called the epicenter.
The shock produces both longitudinal and
transverse vibrations in the earth’s crust.The shock
waves travel at different velocities away from the
hypocenter,some traveling throughthe earth’s crust
and some along the ground surface. The waves
consequently arrive at distant locations at different
times. Hence, at points away from the hypocenter,
seismic vibrations are a combination oflongitudinal,
transverse and surface waves. The effects are made
even more complicated by reflection ofwaves from
dense portions of the crust and consequent
magnification or reduction of vibration amplitudes
where waves meet.
Normally, an earthquake starts with faint
vibrations of the ground surface, which last only a
short time. These usually are followed by severe
shock waves, which continue for a longer period.
Then, the vibrations gradually vanish. The initial
faint vibration registers arrival of the first
longitudinal waves. The shocks occur because
longitudinal, transverse and surface waves arrive
simultaneously.
Movements of the earth at any point during an
earthquake may be recorded with seismographs and
plotted as seismograms. These diagrams show the
variation with time of components of the
displacements. Seismograms of earthquakes that
have occurred indicate that seismic wave forms are
very complex.
Measurements of ground accelerations that occur
during a temblor also are important. Newton’s law
states:
_ _ w _ _
F = Ma = —a (6.6)
s
where
F= force, lb
M= mass accelerated
a = acceleration,ft persec2
w = weight accelerated,lb
g = acceleration due to gravity = 32.2 ft per
__o sec
Hence, inertial forces resisting earthquake ac-
celerations are proportional to those accelerations.
Accelerations may be plotted as accelerograms,
which show the variation with time of components

of the ground accelerations.
Seismic Severity. Several scales are in use for
measuring the severity of earthquakes.
A scale commonly used in the United States for
indicating seismic intensityis the Modified Mercalli
Scale, which is based on subjective criteria. The
scale has twelve divisions. The more severe an
earthquake is, the higher the number assigned to it.
Mercalli intensity I indicates vibrations detected
only by sensitive instruments. Intensity V denotes
waves felt by nearly everyone. Intensity IX marks
occurrence ofconsiderable damageto welldesigned
structures. Intensity XII registers total damage.
Thus,the Mercalli scale indicates the severity ofan
earthquake at a specific location.
Another scale used in the United States is the
Richter scale, which measures the magnitude of an
earthquake. The scale is based on the maximum
amplitude ofgroundmotionanddistance ofthe point
ofmeasurement ofthe amplitude fromthe epicenter.
Richter magnitudes range from zero to 8.9. The
smallest values correspond to the smallest Mercalli
intensities and the value of 8 approximately to
Mercalli intensity XI.
Influence of GroundConditions. Investigationsof
earthquake damage indicate that there is a marked
difference in the degree of damage in similar
structures at different points at the same distance
froman epicenter.The difference in damage appears
to be due totypesofsoilat thosepoints.(Sometimes,
though, variations in damage may be due to
magnification or reduction of vibration amplitudes
as a result of wave reflections.)
Soil type affects intensity and wave form of
motion.Furthermore,some soils may suffera lossof
strength in a temblor and allow large, uneven
settlements of foundations, with large consequent
property damage.Not only soils nearthesurface but
also earth deep down may have these effects.
Observations indicate that movements are very
much larger in alluvial soils (sands or clays
deposited by flowing water) than in rocky areas or
diluvial soils (material deposited by glaciers).
Behaviorofreclaimed land (fills) appears to beeven
poorer than alluvial soils when subjected to
earthquakes. Seismic intensity seems to increase in
the following order: hard ground, sand and gravel,
sand, clay.
It seems,therefore,that disasters could be averted
by not placing buildings on sites with soils that will
have large displacements in earthquakes.
Ground Motions. Seismic waves may reach a
building site from any direction. The ground
motions are vibratory in three dimensions—up and
down, back and forth horizontally. A building
supported by the ground subjected to an earthquake
has to move with the ground and therefore also
moves up and down and backandforth horizontally.
In accordancewith Newton’s law[see Eq.(6.6)] ,the
accelerations are accompanied by inertial forces
equal to the product of mass being accelerated and
the acceleration. The inertial forces act in the same
directions as the accelerations of the building.
Consequently, buildings should be designed to
resist seismic forces from any direction. These
forces are uncontrollable,randomvariables.Varying
in intensity and direction with time, they also are
dynamic loads.
Design Loads
Seismic loads can be resolved into vertical and
horizontal components. Vertical components,
however, usually are of little concern in building
design.Buildings are designed forgravity loads with
a conservative safety factor and therefore have
considerable reserve forresisting additionalvertical
loads. Also, the added strength and stiffness
provided forwithstandinghighwinds is available for
resisting earthquakes.
Majordamage usually is caused by the horizontal
component of the seismic loads. Consequently,
buildings should be designed to resist the maximum
likely horizontal component. (Note that the
horizontal component can be resolved into two
perpendicularcomponents forconveniencein design
and analysis.)
Seismic loads can be determined from the ac-
celerations ofthe various parts ofthe building.These
motions depend on the ground motions and the
dynamic properties of the building.
With the aid of computers, probable seismic
design loads can be computed from historical
earthquake records and dynamic structural analysis
of the building. The calculations, however, are
complex and their accuracy may be questionable,
because the historicalrecords may not be applicable
to the site conditions and future earthquakes may be

completely different fromprevious ones.
Building codes may permit use of an alternative
static loading for which structural analysis is much
simpler. This loading applies forces to the partsofa
building in proportion to their weight.
To begin with, a total lateral force is specified.
This load is determined by multiplying the total
weight of the building by various coefficients. The
coefficients account for the seismic history of the
zone in which the building will be erected,the type
of structural framing and the dynamic properties of
the building.
The static seismic loads are assumed to act
horizontally at each floor level. For buildings more
than two-stories high,a part of the totallateral load
is distributed to each floor in proportion to the
weight of building parts attributable to that level.
The roof, however, in recognition of the dynamic
behavior of buildings under seismic loads, is
assigned a force that dependsonthebuildingheight-
width ratio.For one-story and two-storybuildings,a
uniformly distributed seismic loading may be
specified because oftheir relatively large stiffness.
Response of Structures
Seismic resistanceshould be anintegralpart of every
building system. As for wind loads, seismic loads
must be transmittedalongcontinuouspathsfromthe
various parts ofa building to ground strong enough
to withstand those loads. In addition, the building
should be made stiff enough to keep the amplitude
of sidesway within acceptable limits. Furthermore,
since the response ofa building to seismic loads is a
vibratory motion, provision must be made to damp
the vibrations through absorption of the energy of
motion.For economy,systems designshould utilize
the lateral-force-resisting systemfor both wind and
earthquake resistance.
Designers should consider the possibilities of
different modes of failure in earthquakes and
provide against them. The failure modes possible
generally are overturning or sliding, as for wind
loads; collapse like a house ofcards; severe twisting
and excessive sidesway. Destructive sway may
occur not only because of the magnitude of the
seismic forces but also, since they are transient
dynamic loads, because of build up of vibrations.
Design Measures
A primary concern in aseismic design should be to
transmit seismic loads to ground strong enough to
resist them. Structural members provided for this
purpose should be strong enough to transmit the
imposed forces andshould be capable ofcontrolling
sidesway. Also, the members should be ductile, so
they can absorb large amounts of energy without
breaking. Connections between members also
should be strong and ductile.
As for wind resistance, many devices, including
rigid frames,X bracing andshearwalls,may be used
to transmit seismic loads to the ground and to resist
twisting of the building. Ductile rigid frames,
however, generally are advantageous because of
large energy-absorption capacity.
Floors and roofs are usually relied on to transmit
the lateral forces to the resisting elements. In this
role, a floor orroof may act as a diaphragm,ordeep
horizontalbeam.(Horizontalbracing,however,may
be used instead.) Diaphragms with openings, for
stairs or elevators, should be reinforced around the
openings to bypass the horizontal forces.
Overturning and sliding can be resisted, as for
wind, by utilizing the weight of the building and
anchoring the building firmly to its foundations. In
addition, it is desirable that individual footings,
especially pile and caisson footings, be tied to each
other to prevent relative movement.
As for wind loads,sidesway can be controlled by
proper shaping of a building, arrangements of
structuralcomponents to resistdrift,and selection of
members with adequatedimensions andgeometryto
withstandchanges in dimensions.No precise criteria
placing limitations on sidesway are available.Some
engineers have suggested that,forbuildings over13
stories high and with ratios of height to least base
dimension exceeding 2.5, drift in any story should
not be more than 0.25% of the story height forwind
or 0.5% of the story height for earthquakes
(computed for the equivalent static load previously
described).
Curtain walls and partitions should be capable of
accommodating building movements caused by
lateral forces or temperature changes. Connections
and intersections should allow for a relative
movement between stories ofat least twice the drift
per story. Also, sufficient separation should be
provided betweenadjacent buildings orbetweentwo
elements of an irregular building to prevent them
from striking each other during vibratory motion.
Structuralframing is furtherdiscussed in Chap.8.

SECTIONS 6.1 and 6.2
References
American National Standard Minimum Design Loads for
Buildings and Other Structures, American National
Standards Institute, 1982.
Uniform Building Code,International Conferenceof Building
Officials, 1988.
International, 1988.
J. Ambrose andD. Vergun, Design for Lateral Forces, Wiley,
1987
c. Arnold and R. Reitherman, Building Configuration and
Seismic Design, Wiley, 1982.
Words and Terms
Aseismic Bracing
Braced frame Damping
Diaphragm Richter scale
Drift Overturn
Dyanamic loads Rigid frame
Earthquake Shear wall
Gust Torsion
ModifiedMercalli Scale Uplift
Issues
Influence of buildingsize, form, weight, andlocationonwind
and earthquake effects.
General nature of critical wind and earthquake effects on
building components (roof, walls, bracing) andthebuilding
as a whole.
Computation ofwindandearthquake effects fordesign.
Basic types anddetails of lateral bracingsystems.
6.3. FIRE
Loss of life, injuries and property damage in
building fires in the past have been tragically large.
In an effort to curtail these losses,building officials
devote farmore than halfofthe usualbuildingcodes
to fire protection. As a result, owners must spend
considerable sums of money to provide fire
protection in buildings to meet code requirements.
Designers therefore are professionally obligatednot
only to abide by the word of the law but also by its
spirit.Also,obligatedto the economic welfare ofthe
owners, designers, in addition, should seek ways to
provide life safety in buildings and to avoid or
minimize property damage due to fires at least cost
to the owners.
An ownerpays forfire protectionin severalways.
Initially, he pays for installation of fire protection
when a building is constructed. Then, he pays for
maintenance and operation of the fire-protection
system. Also, usually as long as he maintains
ownership, he pays fire- insurance premiums every
yearto coverpossible fire losses.The last payments
may amount to a considerable sum over a long
period.
Building designers can help lower those costs by
providing fire protection that will secure for the
owner lower fire-insurance premiums. This,
however, may result in higher construction and
operation costs. The design effort nevertheless
should aimat optimizing life-cycle costs, the
sum of construction, operation, maintenance and
insurance costs.
Because of insurance companies’ concern with
fire protection, they have promulgated many
standards forthepurpose that are widely used.Many
have been adopted by reference in building codes
and are specified by government agencies.
Generally, insurance-oriented standards, such as
those ofthe NationalFire ProtectionAssociationand
Factory Mutual System, are primarily concerned
with avoiding property losses by fire, whereas
municipal building codes mainly aim at life safety.
Building designers therefore should consider both
standards for life safety and those protecting the
owners’ economic interests by preventing property
damage. Standards, however, usually present
minimum requirements.Often,public safetyand the
owners’ special needs require more stringent fire
protection and emergency measures than those
specified in building codes and standards.
The multivolume “National Fire Codes” of the
National Fire Protection Association, Quincy, MA
02269, contains more than 200standards,which are
updated annually.
The Factory Mutual Engineering Corporation,
Norwood, MA 02062, publishes standards
applicable to properties insured by the Factory
Mutual System. FM also has available a list of
devices it has tested and approved.
Underwriters Laboratories, Inc., 333 Pfing- sten
Road, Northbrook, IL 60062, makes fire tests in its
laboratories and reports the fire resistance foundfor
various types of constructions. UL reports the
devices and systems it approves in “Fire Protection
Equipment List,” which is updated bimonthly and
annually. Also, UL lists approved building

components in “Building Materials List.”
Forfederalgovernment buildings,requirementsof
the General Services Administration must be
observed.
Many othergovernmentagenciesalso promulgate
standards that must be adhered to, even for
nongovernmental buildings. Many standards of the
federal Occupational Safety and Health
Administration,forexample,are concernedwith life
safety in fires. Also, many states have safety codes
applicable to commercial and industrial buildings.
These codes may be administered by a state
Department of Labor, Fire Marshal’s office,
Education Department or Health Department.
The American National Standards Institute, Inc.,
also promulgates standards affecting life safety in
buildings. In particular, ANSI Al 17.1,
“Specifications for Making Buildings and Facilities
Accessible to and Usable by the Physically
Handicapped,” is applicable to building design for
both normal and emergency conditions.
Fire Loads and Resistance Ratings
Fires occur in buildings because they contain
combustibles,materials that burn when ignited.The
potential severity of a fire depends on the amount
and arrangement of these materials.
Combustibles may be present within a building or
in the building structure. Contents of a building are
related to the type of occupancy, whereas
combustibility of structure is related to type of
construction. Accordingly, building codes classify
buildings by occupancy and construction, as
described in Sec. 3.5.
Fire load,measured in poundspersquare foot(psf)
of floor area, is defined as the amount of
combustibles present in a building. Heat content
liberated in a fire may range from7,000 to 8,000 Btu
per lb for materials such as paper or wood to more
than twice as much for materials such as petroleum
products, fats, waxes and alcohol.
Fire load appears to be closely related to fire
severity. Burnout tests made by the National
Institute of Science and Technology indicate the
relationship shown in Table 6.2.
Fire resistance of building materials and as-
semblies of materials is determined in standardized
fire tests.In these tests,temperature is made to vary
with time in a controlled manner. Figure 6.4 shows
a standard time-temperature curveusually followed.
The ability ofconstructions to withstand fire in these
tests is expressed as a fire rating in hours. Fire
ratings determined by Underwriters Laboratories,
Inc., are tabulated in the UL “Building Materials
List.”
Building codes classify types of construction in
accordance with fire ratings of structural members,
exterior walls, fire divisions, fire
Table 6.2. Relation betweenWeight of Com-
bustibles and Fire Severity*
Average
Weight of Combustibles,
Psf Equivalent Fire
Severity, Hr
5 1
2
10 1
20 2
30 3
40 4
50 6~
60 7Ỉ-
'2
"Based on National Bureau of Standards Report BMS92,
“Classifications of Building Constructions,’’ U.S. Gov-
ernment Printing Office, Washington, D.c.
Fig. 6.4. Standard time-temperature curvefor fire tests
of building components.
separations and ceiling-floor assemblies. Codes
usually also specify the ratings required for interior
finishes of walls, ceilings and floors. Methods for
determining such ratings are described in standards
of ASTM, formerly American Society for Testing
and Materials, such as E84 and El 19. The ƯL
“Building Materials List’’ also reports such ratings.
Building codes, however, do not relate lifesafety
hazards directly to fire load.Instead,codes dealwith
hazards through requirements for interior finishes,

ventilation and means of egress in event of fire.
Height and Area Restrictions
To limit the spread offire and the length oftravelof
occupants to places of refuge, buildings may be
compartmented horizontally and vertically. Fire-
resistant floors and ceilings are used to prevent fire
from spreading from story to story. Fire-resistant
walls, called fire walls,are used to prevent fire from
spreading horizontally. Openings in these fire
barriers for passage of occupants in normal or
emergency circumstances also must be fire
protected.
Building codes may restrict building height and
floor areas included between fire walls in
accordance with potential fire hazards associated
with type of occupancy and type of construction.
Usually, the greater the fire resistance of the
structure the greaterthepermissible heightandfloor
area. Because of the excellent past record of
sprinklers in early extinguishmentorcontroloffires,
greater heights and larger floor areas are often
permitted when automatic sprinklers are installed.
Classes of Fires
Methods used for extinguishing some burning
materials may not be suitable forothers.Hence,for
convenience in indicating the effectiveness of
extinguishing media, such as water, powders, gases
or foam, fires may be classified in accordance with
the type of combustible material burning. A
classification system developed by Underwriters
Laboratories, Inc., defines the following four types
of fires:
Class A fires. Ordinary combustibles. Extin-
guishable with water or by cooling or by coating
with a suitable chemical powder.
Class B fires. Flammable liquids. Extinguishable
by smothering or careful application of a cooling
agent.
Class c fires. Live electrical equipment. Ex-
tinguishable with a nonconducting medium. A
conducting agent can be used if the circuit is in-
terrupted.
Class D fires. Metals, such as magnesium,
powdered aluminum and sodium, that burn.
Extinguishable by specially trained personnel
applying special powders.
6.4 FIRE EXTINGUISHMENT
Writers of building codes and concerned building
designers generally take the position that a fire will
occur in any building and then proceed to consider
what can be done about it. For preservation of the
building, as well as the safety of the occupants, a
major concern is for the rapid extinguishing of the
fire. The means for achieving this vary, depending
on the building form and construction, the
occupancy and the nature of the combustible
materials that fuel the fire. This section discusses
some of the ordinary means for extinguishing
building fires.
Sprinklers
Automatic sprinklers have proven very effective in
early extinguishment of fires. In fact, that is their
main purpose; but they are also useful in curtailing
the spread of fire and hot gases by cooling the
environment around a fire.Sprinklers are suitable for
extinguishing Class A fires. Sprinklers also may be
used for some Class B and Class c fires.
A sprinkler system basically consists of fire
detectors, water for extinguishing fires, heads for
discharging the water when actuated by the
detectors, and piping for delivering the water to the
heads. Heads should be located at ceiling and roof
levels to completely cover the interior of the
building. Intervals between heads on the piping
should be small enough to provide desired
concentrationofwateron everysquarefoot offloor.
Requirements governingdesignandinstallationof
sprinklersystems are given in building codes andin
standards of the National Fire Protection
Associationand Factory MutualSystem.Generally,
the requirements of the local code will govern, but
designers should check with the owner’s insurance
carrier to determine if other standards may also
apply.If such standards are ignored,the ownermay
have to pay higher than necessary fire-insurance
premiums.
Standpipes
A standpipe is a water pipe within a building to
which hoses may be attached for fire fighting.
Standpipes are required in buildings in which fires
may occur too high to be reached by ground-based

fire-department equipment.These pipesalsomay be
necessaryin lowbuildingswith large floorareas,the
interiors ofwhich may be difficult to reachwith hose
streams fromthe outside.
Sprinklers and standpipesare furtherdiscussedas
part of the plumbing systemin Sec. 9.4.
Chemical Extinguishing Systems
Small fires in buildings in ordinary materials, such
as paper,wood andfabrics,when first starting,often
may be rapidly extinguished with water, propelled
by compressedgases,fromhand-held extinguishers.
Building codes may require suchextinguishersto be
located at convenientplacesin buildings.Occupants
should be taught to operate the extinguishers.There
is a risk in their use,however,in that the attempt to
fight a fire with an extinguisher may delay
notification of the fire department or other better-
equipped fire fighters of the presence of the fire.
Instead of plain water for extinguishing fires,
chemicals or water plus chemicals may be used.
Applied by automatic sprinklers, hoses, handheld
extinguishers,portable wheeled equipment orlarger
devices,chemicals may be desirable ornecessary for
fires in certain materials.
Foams. Forflammable liquids,such as gasoline,
a foamed chemical, mostly a conglomeration ofair-
orgas-filled bubbles,may be useful.Three types are
suitable forfire extinguishment:chemicalfoam; air,
or mechanical, foam; and high-expansion foam.
Chemical foam is formed by the reaction of water
with powders.Usually,sodiumbicarbonate andalu-
minum sulfate are used, forming carbon-dioxide
bubbles. Air, or mechanical, foam is produced by
mixing water with a protein-based chemical
concentrate. High-expansion foam is generated by
passage ofairthrougha screenconstantly wettedby
a chemical solution, usually with a detergent base.
The volume of foam produced by this method
relative to the volume of waterused is a great many
times the volume produced by the other methods.
The foams extinguish a fire by smothering it and
cooling the surface.
Carbon Dioxide. Forflammable liquids or live
electrical fires, carbon dioxide may be usefill. It is
also suitable for equipment fires, such as those in
gasoline or diesel engines, because the gas requires
no cleanup.Storedin containersunderpressure,it is
immediately ready for discharge when a valve is
opened. Heavier than air, the gas tends to drop into
the base of a fire and extinguish it by reducing the
oxygen concentration.
Halon 1301. For use in the same circumstances
as carbon dioxide, bromotrifluoromethane (CBrF3),
or Halon 1301, acts much faster. This gas also
requires no cleanup. It extinguishes fires by
interfering with the chain reaction necessary to
maintain combustion.
Dry Chemicals. For Class B and c fires, dry
chemicals, such as sodium bicarbonate, may be
suitable. They tend to extinguish fires by breaking
the chain reaction for combustion. When dry
chemicals are used, cleanup after a fire may be
difficult.
Dry Powders. For combustible metals, dry
powders, different from the dry chemicals pre-
viously mentioned, usually are the most suitable
extinguishing agent.Specific metals require specific
dry powders. Fires in metals should be fought only
by properly trained personnel.
6.5. EMERGENCY EGRESS
For life safety in buildings in event of fire or other
emergencies, provisions must be made for safe,
rapid egress of occupants, at least from the
dangerous areas and preferably also from the
buildings. The escape routes must be fire protected
and smoke free to allow safe passage ofoccupants.
An exit is a means ofegress fromthe interior ofa
building to an open exterior space beyond the reach
of a building fire. The means of egress may be
provided by exterior door openings and enclosed
horizontal and vertical passageways.
Section 6.3 points out the desirability ofusing fire
walls to compartment buildings, to limit the spread
of fire and the length oftravelto places ofrefuge.It
is also necessary within compartments to use on
floors, ceilings and walls interior finishes that will
not spread flames.
In addition, structural members should have
sufficiently high fire ratings to prevent collapse,for
a few hours at least. The objectives of this are to
allow all occupants to be evacuated and to give fire
fighters time to extinguish the fire. If structural
members are inadequate for the purpose, they may

be fire protected with othermaterials. For example,
beams and columns may be encased in concrete,
enclosed with plaster, gypsum blocks or
gypsumboard, or sprayed with insulating material.
Section 6.4 discusses the use of automatic
sprinklers to extinguish firesassoon astheystartand
to cool surrounding areas. Also, it is important, as
soon asfire is detected,to soundan alarmand notify
the fire department. In addition, a communications
systemshould instruct occupants on the evacuation
procedure to be followed or other precautionary
measures.
There is great danger of panic in emergency
situations. Panic, however, seldom develops if
occupantscan move freely towardexits that theycan
see clearly, that are within a short distance and that
can be reached by safe, unobstructed, uncongested
paths. Thus, the objective of life-safety design
should be to provide suchrapid,safe egressfromall
areas ofbuildings thatwill preclude developmentof
panic. Moreover, more than one path to safety
should be provided in case onesafe meansofescape
becomes unavailable. All paths must be accessible
to and usable by handicapped persons, including
those in wheelchairs, if they may be occupants.
To permit prompt escape of occupants from
danger, building codes specify the number, size,
arrangement and marking of exit facilities, in
addition to other life-safety measures. The re-
quirements depend on the types of occupancy and
construction.
Generally, building codes require a building to
have at least two means of egress fromevery floor
of a building. These exits should be remote from
each other,to minimize any possibility that both may
become blocked in an emergency.
Codes usually also specify that exits and other
verticalopeningsbetweenfloorsofa buildingbe fire
protected,to prevent spread offire, smoke or fumes
between stories.
In addition, codes limit the size of openings
Table 6.3. Maximum Sizes of Openings in Fire Walls
Protection of adjoining
spaces
Max area, sq
ft
Max
dimension, ft
Unsprinklered Sprinklers on
both sides Building fully
sprinklered
120°
150a
Unlimited0
1?
15“
Unlimited6
*
a
But not more than 25% of the wall length or 56 sq ft per
door if the fire barrier serves as a horizontal exit. ^But not
more than 25% of the wall length. Based on New York
City Building Code.
in fire walls (see Table 6.3). Furthermore,openings
must be fire protected.Forexample, a doorused for
an opening in a fire wall should be a fire door, one
that has a fire rating commensurate with that of the
wall, as required by the building code.
Required Exit Capacity
Means ofegress in eventoffire orotheremergencies
should have sufficient capacity to permit rapid
passage ofthe anticipated number ofescapees.This
numberdepends on a factorcalled theoccupant load.
Occupant load ofa building spaceis the maximum
number of persons that may be in the space at any
time. Building codes may specify the minimum
permitted capacityofexits in terms of occupant load,
given as net floorarea, sq ft, perperson,forvarious
types of occupancy (see Table 6.4). In such cases,
the numberofoccupants perspacecan be computed
by dividing the floor area, sq ft, by the specified
occupant load.
The occupantload ofanyspaceshould include the
occupant load ofotherspaces if the occupants have
to pass through that space to reach an exit.
With the occupant load known, the required
opening width for exits can be determined by
dividing the number of occupants per space by the
capacity of the exit.
Capacity of exits is measured in units of 22 in. of
width. (Fractions of a unit of width less than 12 in.
should be ignored,but12in. or more added to a full
unit may be counted as one-half unit.) Building
codes may specify the
Table 6.4. Typical Occupant Load Requirements
for Buildings
Occupancy
Net floor area
per occupant,
sq ft
Bowling alleys 50
Classrooms 20
Dance floors 10
Dining spaces (nonresidential) 12
Garages and open parking structures 250
Gymnasiums 15
Habitable rooms 140
Industrial shops 200
Institutional sleepingrooms
Adults 75
Children 50
Infants 25

Kindergartens 35
Libraries 25
Offices 100
Passenger terminals or platforms 1.5Ca
Sales areas (retail)
Fhst floor or basement 25
Other floors 50
Seating areas (audience) in places of
assembly
Fixed seats Db
Movable seats 10
a
c - capacity of all passenger vehicles that can be un-
loaded simultaneously.
b
D = number of seats or occupants for which space is to
be used.
Based on New York City Building Code.
maximum design capacity of an opening as the
numberof persons per22-in. unit,for various types
of occupancy (see Table 6.5).
When occupant load is dividedby unit capacityto
determine the minimumrequired exit width,a mixed
fraction may result. In such cases, the next larger
integer or integer plus one-half should be used to
determine the exit dimensions.
Building codes,however,also specify a minimum
width for exits (see Table 6.5) and may require at
least two separated exits. These requirements
govern. Generally, building codes set the minimum
width ofcorridors at 44in. and exit dooropeningsat
36 in. (See also Sec. 16.2.)
Example. Determination of Door Width
An office has 20,000 sq ft of open floor area. The
building code requires at least two exits,
Table 6.5. Capacity of Exits, Persons per 22-in. Unit
of Exit Width
Occupancy type
To
outdoors at
grade
Other
doors
Min
corridor
width, in.
High hazard 50 40 36
Storage 75 60 36
Mercantile 100 80 44
Industrial 100 80 44
Business 100 80 44
Educational 100 80 66
Institutional
For detention 50
40 44
For handicapped 30 30 96
Hotels, motels,
apartments 50 40 44
From From
assembly safe
place area
Assembly 44
Theaters 50 100
Concert halls 80 125
Churches 80 125
Outdoor structures 400 500
Museums 80 125
Restaurants 50 100
each protected by 2-hr fire doors. The exits lead to
stairways.Howwide should eachdooropening be?
Table 6.4 gives the occupant load for offices as
100 sq ft per occupant.Therefore,the space may be
occupied by 20,000/100, or 200 persons. (If the
designerknows thattheownerplans to employmore
than 200 persons in that office area, calculations
should be based on the actual number to be
employed.) Table 6.5 gives the allowable exit
capacity per unit for business occupancies as 80
persons.The numberofunits ofwidth required then
is 200/80, or 2.5 units. If these are divided equally
into two openings,each exit would be 2.5/2, or 1.25
units wide. Width of each opening required,
therefore,is 1 X 22 + 12 = 34 in. Use the minimum
permitted opening of 36 in.
Travel Distance and Dead-End Limits
To insure that occupants will have sufficient time to
escape froma dangerous area, building codes limit
the traveldistancefromthe most remote point in any
room or space to a door that opens to an outdoor
space, stairway or exit passageway. The maximum
distance permitted depends onthe typeofoccupancy
and whether the space is sprinklered. For
unsprinklered spaces, for example, maximum
permitted travel may range from 100 ft for storage
and institutional buildings to 150 ft for residential,
mercantile and industrial occupancies. For sprin-
klered spaces,maximum permitted travelmay range
from 150 ft for high-hazard and storage buildings to
300 ft for businesses, with 200 ft usually permitted
for other types of occupancy.
Lengths of passageways or courts that lead to a
dead end also are restricted or prohibited (for high-
hazard occupancies). For example, a code may set
the maximum length to a dead end as 30 ft for
assembly,educationalandinstitutionalbuildings,40
ft for residential buildings and 50 ft for all other
occupancies, except high hazard.

Location of Exits
All exits and access facilities should be placed soas
to be clearly visible to occupants who may have to
use them, or their locations should be clearly
marked. Ifan exit is not immediately accessible from
an open floor area, a safe continuous passageway
should be provided directly to the exit. The path
should be kept unobstructed at all times.
Furthermore, it should be so located that occupants
will not have to traveltoward anyhigh-hazard areas
not fully shielded.
Types of Exits
Building codes generally indicate what types of
facilities may qualify as exits.These usually include:
Corridors—enclosed public passageways, which
lead from rooms or spaces to exits.Minimumfloor-
to-ceiling height is 7 ft 6 in., although 7 ft may be
permitted for short stretches. Minimum width
depends on type of occupancy (see Table 6.5).
Building codes may require subdivision ofcorridors
into lengths not exceeding 300 ft for educational
buildings and 150 ft for institutional buildings. The
subdivision should be accomplished with
noncombustible partitionsincorporating smoke-stop
doors. Codes also may require the corridor
enclosures to have a fire rating of 1 or 2 hrs.
Exit Passageways—horizontal extensions of
vertical exits, or a passage leading from a yard or
court to an outdoorspace.Minimumfloor-to-ceiling
height is the same as for corridors.Width should be
at least that ofthe verticalexit. Building codes may
require the passagewayenclosuresto have a 2-hrfire
rating. A streetfloor lobby may serve as an exit
passageway ifit is sufficiently wide toaccommodate
the occupant load of all contributing spaces on the
lobby floor.
Exit Doors—doors providing access to streets
(these doorsneednothave a fire rating)and doorsto
stairs and exit passageways (|-hr fire rating). (See
also Sec. 16.2.)
Horizontal Exit—access to a refuge area. The exit
may consist of doors through walls with 2- hr fire
rating,balcony offeringpassagearounda fire barrier
to another compartment or building, or a bridge or
tunnel between two buildings. Doors should have a
fire rating of 1| hr, except that doors in fire barriers
with 3- or 4-hr fire rating should have a 1 |-hr rated
door on each face of the fire division. Balconies,
bridges and tunnels should be at least as wide as the
doors opening onthemand theirenclosures orsides
should have a fire rating of 2 hr. Exterior-wall
openings below any open bridge or balcony, or
within 30 ft horizontally ofsuch constructionshould
have |-hr fire protection.
Interior Stairs—stairs within a building that serve
as an exit. Building codes generally require such
stairs to be constructed ofnoncombustible materials
but may except one-story or two-story, low-hazard
buildings. Stair enclosures should have a 2-hr fire
rating,except in low dwellings,where no enclosure
may be required. (See also Sec. 14.2.)
Exterior Stairs—stairs thatare opento the outdoors
and that serve as an exit to ground level. Building
codes limit the height of such stairs, often to not
more than 75 ft or six stories. The stairs usually
should be constructed of noncombustible materials
and topped with a fire- resistant roof. Openings in
walls within 10 ft of the stairs should have |-hr fire
protection.
Smokeproof Tower—a continuous fire-resistant
enclosure protecting a stairway fromfire or smoke
in a building. Passage between building and tower
should be provided on every floor by vestibules or
balconies directly open to the outdoors. Enclosures
should have a 2-hr fire rating. Access to the
vestibules or balconies and entrances to the tower
should be through doorways at least 40 in. wide,
protectedby selfclosingfire doors.Thevestibules or
balconies should be at least as wide and long as the
required doorway width.
Escalators—moving stairs. These may be used as
exits instead ofinteriorstairs ifthey meet applicable
requirements of such stairs and if they move in the
direction of exit travel or stop gradually when an
automatic fire detection systemsignals a fire.
Moving Walks-horizontal or inclined conveyor
belts for passengers. These may be used as exits if
they meet the requirements forexit passagewaysand

move in the direction ofexit travelor stop gradually
when an automatic fire detection systemsignals a
fire.
Fire Escapes—exterior stairs, with railings, that
are open to the outdoors, except possibly along a
building exterior wall. These formerly were
permitted but generally no longer are.
Elevators are not recognized asa reliable means of
egress in a fire.
Refuge Areas
A refuge area is a space safe fromfire. The refuge
should be at about thesame levelas the areasserved
and separated from them by construction with at
least a 2-hr fire rating.Fire doors to the refuge area
should have at least a l|-hr fire rating.
Size of the refuge area should be adequate forthe
occupant load of the areas served, in addition to its
own occupant load, allowing 3 sq ft of open space
per person (30 sq ft per person for hospital or
nursing-home patients).There shouldbe at least one
vertical exit and, in locations over 11 stories above
ground, one elevator for evacuation of occupants
from the refuge area.
6.6. FIRE PROTECTION
Preceding sections have considered two of the
primary concerns with regard to building fires: the
rapid control and extinguishing of the fire and the
egress ofthe building’s occupants in a safe manner.
There are many other factors relating to potential
damage or injury from fires that may have some
bearing on the building design. This section
discusses some of the other major concerns for
general protection fromthe hazards of fires.
Fire-Detection Devices
The next best thing to preventing a fire from
occurring is to detect it as soon as it starts or in an
incipient stage.Manydevicesare available forearly
detection of fires. When a fire occurs near one, the
device can performautomatically serveralimportant
operations,such as sound an alarmlocally; notify a
central station and the fire department; open
automatic sprinklers; start and stop fans, industrial
processes,escalatorsandelevators; shut fire doors.
Underwriters Laboratories, Inc. (ƯL) has tested
and reported on many fire-detection devices. On
approving a device, ƯL specifies the maximum
distance between detectors giving area coverage.
Often, however, building conditions may make
closer spacing advisable.
Detectors may be classified into five types,
depending on method of operation: fixed-
temperature,rate-of-rise,photoelectric,combustion-
products and flame.
Fixed-Temperature Detectors. These devices
are set to signala fire when one element is subjected
to a specific temperature.There may,however,be a
delay between the time when ambient (room)
temperatures rise beyond this temperature and the
element attains it.Forexample,ambient temperature
may reach about 200°F by the time the detector
reaches its rated temperature of 135°F. Several
different types of fixed-temperature detectors are
available. They usually are designed to close an
electric circuit when the rated temperature is
reached.
Rate-of-Rise Detectors. Operating inde-
pendently of heat level, these detectors signal a fire
when temperature rises rapidly. For example, a
detectormay operate whenit registers a temperature
rise at the rate of10°F ormore per min. Rate-of-rise
detectors do nothave the disadvantageofthermallag
as do fixed-temperature devices. Several different
types of rate- of-rise detectors are available.
Photoelectric Detectors. These are actuated
when visibility is decreased by smoke. In a
photoelectric detector,a light ray is directedacross a
chamber so as not to strike a photoelectric cell. If
smoke particles collect in the chamber, they deflect
the ray so that it impinges on the cell, thus causing
an electric current to flow in a warning circuit.
Photoelectric detectors are useful where a potential
fire may generate considerable smoke before much
heat develops or flames can be observed.
Combustion-Products Detectors. As the
name implies, these devices signal a fire when they
detect products of combustion. They may be
ionization or resistance-bridgetypes.The ionization
type employs gases ionized by alpha particles from
radioactive material to detect a change in the
composition of ambient air. The resistance-bridge

type operateswhen combustionproductschange the
electrical impedance of an electric bridge grid
circuit. Both types are useful for giving early
warning ofa fire, when combustionproductsare still
invisible.
Flame Detectors. These devices signal a fire
when they detect light from combustion. One type
detectslight in theultraviolet range,whereasanother
type detects light in the infrared range.
Smoke and Heat Stops and Vents
A fire gives offheatandoften a considerable amount
of smoke. Both products can build up rapidly to
lethalconcentrationsand spreadthe fire,if confined
within the building. Consequently, in addition to
immediate application oflarge quantitiesofwateror
chemicals to smotherthe fire or coolthe fire source
and surrounding space, speedy removal of the heat
and smoke from the building is necessary.Methods
of doing this depend on the size of buildings and
whether they are one story high or multistory.
Small buildings can release heat and smoke
through open or broken windows or through roof
vents.
Large, one-story buildings,such as those usedfor
manufacturing and storage, may have interior areas
cut offby fire walls ortoo farfrom exterior walls for
effective venting through windows. Often, such
buildings are impracticable to vent around the
perimeter because they are windowless. Hence, for
large,one-storybuildings,the only practicalmethod
for removing heat and smoke froma fire usually is
through openings in the roof. (Venting is desirable
as an auxiliary safety measure even when buildings
are equipped with automatic sprinklers.)
Generally, smoke and heat should be ventedfrom
large, one-story buildings by natural draft. The
discharge apertures of the vents should always be
open orotherwise shouldopen automatically when a
fire is detected.Vents that may be closed should be
openable by fire fighters fromthe outside. Venting
may be done with monitors (openable windows that
project above the main roof), continuous vents
(narrow slots with a weather hood above), unittype
vents or sawtooth skylights.
As a guide, Table 6.6 gives an approximate ratio
for determination of vent area. In deciding on the
area to be used, designers should consider the
quantity, size, shape and combustibility of building
contents and structure. They should provide
sufficient vent area to prevent dangerous
accumulations of smoke during the time necessary
for evacuation ofthe floor area to be served,with a
margin of safety to allowfor unforeseensituations.
Table 6.6. Approximate Areas and Spacings for
Roof Vents
Type of contents
Ratio of vent area to
floor area
Maximum
spacing, ft
Low heat release 1:150 150
Moderate heat release 1:100 120
High heat release 1:30 75
Unit-type vents come in sizes from4 X 4 ft to 10
X 10 ft. The maximum distance between vents
usually should not exceed the spacinggivenin Table
6.6. Generally, a large number of closely spaced,
small vents is better than a few large vents. The
reason for this is that with close spacing the
probability is greaterthat a vent will be close to any
location where a fire may occur.
In multistory buildings, only the top story can be
vented through the roof. Often, the windows are
normally closed, and even when openable, they are
not operable automatically. Consequently, heat and
smoke in lower-story fires must be collected at the
source, ducted through the stories above and
dischargedabove theroof.Shafts should be provided
for this purpose.
Each smoke shaft should be equipped with an
exhaust fan. In buildings with air-conditioning
ducts, return-air ducts, which will pick up smoke,
should be controlled with dampers to discharge into
a smoke shaft when smoke is detected. A smoke
detector installed at the inlet to each return-air duct
should actuate the smoke exhaust fan and the
dampers. When smoke is detected, the smoke
exhaust fan should start and supply-air blowers
should stopautomatically.Manualoverride controls,
however, should be installed in a location that will
be accessible under all conditions. Smoke-detector
operation should be supervised from a central
station.
To prevent spread of fire from one part of a
building to another and to confine the smoke and
heat of a fire to one area from which they can be
exhausted safely, building codes require
compartmentation of a building by fire divisions.
The floor area permitted to be included betweenfire

divisions depends on types of occupancy and
construction and whetherthebuildingis sprinklered.
A fire division is any construction with the fire-
resistance rating and structural stability under fire
conditions required for the types of occupancy and
construction of the building to bar spread of fire
between adjoining buildingsorbetween parts ofthe
same building on opposite sides of the division.
A fire division may be an exterior wall, fire
window, fire wall, fire door, floor, ceiling or
firestop.
A fir estop is a solid or compact, tight closure
incorporated in a concealed space in a building to
retard spread offlames or hot gases.Every partition
and wall should be firestoppedat eachfloorlevel,at
the top-storyceiling leveland at the levelofsupport
for roofs. Also, every large unoccupied attic space
should besubdivided byfirestopsinto areasof3,000
sq ft or less. In addition, any large plenumor space
between a ceiling and floor or roof should be
subdivided.Firestopsextendingthe fulldepth ofthe
space should be placed along the line ofsupportsof
the structural members and elsewhere to enclose
spaces between ceiling and floor with areas not
exceeding 1,000 sq ft nor3,000 sq ft when between
ceiling and roof.
For life safety of occupants during evacuation
from multistory buildings through smokeproof
towers, it is desirable to pump fresh air into the
towers to pressurize them.Maintenance ofa higher-
than-normal air pressure is intended to prevent
smoke from entering the towersthrough openingsin
the enclosurethat may not becompletely closed.The
procedure,however,hassome disadvantages.One is
that the pressure may make opening doors to leave
the towerdifficult.Anotheris that in many buildings
standpipe connectionsare located in the towers and
fire fighters haveto open thedoorto the fire floorto
move a hose toward the fire. This disadvantage can
be overcome by placing the hose valves within the
building at the tower doors, if permitted by the
building code, while leaving the standpipe, as
customary, in the smokeproof tower.
Systems Design for Fire Protection
Sections 6.3-6.6 described the elements necessary
for life safety and protection ofproperty in event of
fire or otheremergencies in buildings.In summary,
these elements are:
1. Limitation of potentialfire loads,with respect
to both combustibility and ability to generate
smoke and toxic gases.
2. Compartmentation of buildings by fire di-
visions to confine a fire to a limited space.
3. Provision of refuge areas and safe evacuation
routes to outdoors.
4. Prompt detection of fires, with warning to
occupants who may be affected and notifi-
cation of presence of fire to fire fighters.
5. Communication ofinstructions tooccupants as
to procedures to adopt for safety, such as to
stay in place, proceed to a designated refuge
area or evacuate the building.
6. Early extinguishment of any fire that may
occur, primarily by automatic sprinklers but
also by trained fire fighters.
7. Provision, for fire fighting, of adequate water
supply, appropriate chemicals, adequate-sized
piping, conveniently located valves, hoses,
pumps and other equipment necessary.
8. Removal of heat and smoke from the building
as rapidly as possible without exposing
occupants to them, with the HVAC system, if
one is present,assistingin venting the building
and by pressurizing smokeproof towers,
elevator shafts and other exits.
Emergency Power
In addition, not discussed before, a standby electric
power and light systemshould be installed in large
buildings. The system should be equipped with a
generator that will start automatically on failure of
normal electric service. The emergency electric
supply should be capable ofoperatingallemergency
electric equipment at full power within 60 seconds
of failure of normal service. Emergency equipment
to be operated includes lights forexits,elevators for
fire fighters, escalators and moving walks desig-
nated as exits, exhaust fans and pressurizing
blowers, communications systems, detectors, and
controls needed for fire fighting and life safety
during evacuation of occupants.
Emergency Elevators
The vertical transportation system should make
available at least one elevator for control by fire
fighters, to give them access to any floor from the
street-floor lobby. Elevator controls should be
designed to preclude elevators from stopping

automatically at floors affected by fire. In the past,
lives have been lost when fires damaged elevator
signaling devices, stopping elevators with
passengersat the fire floor and openingthe elevator
doors.
Systems Design for Life Safety
For maximum protection of life and property in
event offire or otheremergency at least cost,all the
preceding elementsshould be integratedintoa single
life-safety system so that they work in unison to
meet all objectives.
Some of the elements may be considered per-
manent.They require no supervisionotherthan that
necessaryforordinary maintenance.These elements
include the various fire divisions, structural
members and exits. With the systems design
approach, cost of the fire-resistance functions of
these building components can be offset by
assigningthemadditionalfunctions,where feasible.
Other elements, such as detectors, automatic
sprinklers and the emergency HVACsystem,require
at least frequent observation oftheircondition,ifnot
constant supervision.
Supervision can be efficiently provided by
personnel at a properly equipped control center,
which may include an electronic computer,
supplemented by personnel performing scheduled
maintenance. The control center can continuously
monitor alarms, gate valves, temperatures, air and
water pressures and perform other pertinent
functions. In addition, in emergencies, the control
center can hold two-way conversations with
occupantsthroughout the building and notify the fire
and police departments. Furthermore, the control
center can dispatch investigators to sources of
potential trouble or send maintenance personnel to
make emergency repairs, when necessary.
For more efficient operation of the total building
systemand greater economy, the control center can
also be assigned many other functions. The center
can become the key element of a systemthat, for
example:
1. Meets life-safety objectives
2. Warns ofintruders
3. Controls HVAC to conserve energy
4. Switches on emergency power
5. Turns lights on andoff
6. Communicates with building occupants,when
necessary
7. Schedules building maintenance and repair
8. Puts elevators under manual control for
emergencies
SECTIONS 6.3 TO 6.6
References
Officials, 1988.
International, 1988.
Life Safety Code, National FireProtectionAssociation, 1988.
Fire Protection Handbook, NFPA
Wordsand Terms
Class of fire, A to D
Combustible
Egress in emergency
Extinguishment
Exit andoccupant load
Fire division
Fire load
Fire severity,in hours
Occupant load
Refuge area
Smoke andheat stops
Smokeproof tower
Sprinklers
Standpipe
Venting
Width of exits, individual andtotal
Significant Relations, Functionsand
Issues
Fire/cost relations: long term benefits of design to lower risk
and reduce insurance premiums.
Rating of building construction components and systems for
fire resistance.
Building height and floor area restrictions related to occu-
pancy and fire resistance of construction.
Means for fire extinguishing related to type (class) of fire.
Exit requirements relatedtooccupant load. Fire control by use
of stops, divisions and vents.
6.7. SECURITY
Means for prevention of theft and vandalism in
buildings aftertheowners occupythemshould bean
integral part of the building system.
Provision should be made fromthe start ofdesign

for control of access to buildings and to specific
areas, if desired by the owner. For some buildings,
tight security may be essential for certain sections,
such as rooms housing valuable materials or
expensive equipment, like a large computer.
Fordetection ofintruders,televisionmonitorsand
intrusion alarms may be installed. For control of
access, doors may be equipped with locks operated
by keys or by devices that read identification cards,
hand prints or voice vibrations. For protection of
valuables, thick steel safes may be provided.
Fora small building,alarmsystems may be rigged
to soundan alarmand to notify thepolice theinstant
an intruder attempts to enter the locked building or
security area.
Fora large building,guardsare neededto monitor
the various devices or to patrol the building.
Therefore, a control center should be provided for
observation purposes. In addition, communications
should be established between the center, various
parts ofthe building and police andfire departments.
Also, a guard room should be provided for guards
not on duty and for files and lockers.
With the use of electronic devices, security
systems can be installed to do the following:
1. Sound an alarm when an intruder attempts to
enter.
2. Identify the point of intrusion.
3. Turn on lights.
4. Display the intruder on television and record
observations on video tape.
5. Call police automatically.
6. Restrict entry to specific areas only toproperly
identified personnel and at permitted times.
7. Change locks automatically.
Costs forsecuritycanbe cutifthe systems-design
approach is used to combine security measures with
other controls. For example, the control center and
its equipment, including a computer, if desired, can
be used not only for security but also for HVAC
controls and firesafety equipment. In addition,
personnel,televisionmonitorsandsensorsaswellas
electric wiring can share tasks related to security,
HVAC and fire detection, extinguishment and
communications.
6.8. BARRIER-FREE ENVIRONMENTS
Ordinary building safety concerns are based
primarily on an assumption that the building
occupants are able-bodied and in full possession of
the faculties of a normal adult. It is assumed that
occupants canwalk(use stairs),see (readexit signs),
hear(be alerted byfire alarms),use theirhands (open
doors), and generally function adequately in panic
situations (not retarded, not very young, not
marginally senile,etc.).However, in almost alltypes
of building occupancies there will be some persons
who do not have allofthese faculties intact.In recent
times, the building codes have been made to
recognize this situation, and most buildings must
nowbe designedwith some recognition ofthe need
for barrier-free environments. Barriers are anything
that interfere with use ofthe building—inparticular,
devices and components involving entrances, exits,
warning systems, rest rooms, and general vertical
and horizontal movement through the building.
Specialefforts to create barrier-free environments
must be made forbuildings thathave a large number
of occupants with special needs: day care centers,
convalescent hospitals,andhealthcare facilities,for
example. However, the same accommodations are
also generally required forany buildingthat involves
use by the public or houses employees. These con-
cerns may be principally addressed to usage and
access but at some level may involve safety when
hazardous conditions are at issue.
It is virtually impossible to produce a physical
environment that is optimally accommodating to a
range ofpeople thatincludes normal,healthy adults,
small children, enfeebled and easily disoriented
elderly persons, and persons who are blind or
wheelchairconfined.In some instances,whatis best
for one group is bad for another. The elaborate
facilities required to provide access and egress for
persons in wheelchairs may in effect represent
confusing barriers for blind, very young, or elderly
persons. Where occupancy is more specific, some
level of optimization may be feasible,but where the
public as a whole must be facilitated, considerable
compromise must be anticipated.
Building codes, design practices, and the de-
velopment of construction components—notably
hardware, signage, elevator controls, paving and
floor finishes—are steadily being designed with a
concern for a wider range of occupant capabilities.
Hard design data are being developedfromresearch
and the experience deriving from experimentation
and design implementations.
SECTIONS 6.7 AND 6.8

References
p. Hopf, Handbook ofBuilding Security Planningand Design,
McGraw-Hill, 1979.
p. Hopf and J. Raeber, Access for the Handicapped, Van
Nostrand Reinhold, 1984.
M. Valins, Housing for Elderly People, Van Nostrand
Reinhold, 1987.
Specifications for Making Buildings and Facilities Accessible
to and Usuable by the Physically Handicapped, ANSI Al
17.1, AmericanNational Standards Institute, New York.
Wordsand Terms
Detection and alarm systems Entrance control Handicapped
access Selective reduction of barriers
Issues
Access control relatedto degree ofsecurityrequired. Need
for entranceby controlledmeans.
Needfor reductionof barriers andhazards forselectedgroups
of persons with diminished faculties.
6.9. TOXIC MATERIALS
There is a great range ofmaterials used forbuilding
construction.Some materials are used essentially in
raw, natural form as in the case of wood used for
structural purposes. In most cases, however,
building products are produced from synthesized,
processed, materials. For example, wood is often
used as an ingredient in a synthesized material for
paper, cardboard, and particleboard products. In
some caseswoodis also processed bybeingimpreg-
nated or coated with materials, thus involving a
composite material in its finished form.
General experience together with extensive
medical research has produced a long list of po-
tentially dangerous materials, posing the possibility
of sickness, injury or death upon exposure to them.
Some cases are long-standingas in the case oflead,
which has virtually been eliminated as an ingredient
in paints. More recent cases involve construction
products containing asbestos, formaldehyde, and
chlorine. Publicity from legal actions and the work
of advocacy groups has brought pressure on man-
ufacturers, builders, designers, and the admin-
istrators ofbuilding codesto respondby restricting,
eliminating, or otherwise controlling the use ofsuch
materials.
Danger may be present merely in exposure to
some toxic materials on a continuing basis. Thus,
when many house paints were leadbased, the
chipping and flaking of the painted surfaces over
time led to an accumulation of particles containing
lead that sometimes were picked up and ingestedby
the building occupants. Another danger is that
occurring duringa fire when products ofcombustion
may include highly toxic materials—particularly,le-
thalgases.These have been the main cause ofdeath
in most fires in recent times,the major culprit being
various plastic materials used for furnishings,
decorations,andbuildingconstructionproductssuch
as piping and insulation.
Althoughdangerto building occupants is a major
design concern,potentialdangerto construction and
maintenance workers also should be investigated to
determine the need for modification or elimination
of hazardous buildingproducts.One such product is
asbestos, the hazard of which was dramatized by
massive law suits brought by workers. Only as a
secondary effect did the public become alarmed
about the hazards represented by the dormant
presenceofthe material in many existing buildings.
As is usually the case,the originalreason foruse
in construction of a particular material is positive.
For example, one factor that led to widespread use
of asbestos was its high resistance to fire. Thus, an
optimized design process, with fire resistance as a
major value, could easily serve as justification for
use ofthe material.Add the otherplus factors foruse
of the inert mineral material (water-resistive, non-
rotting,etc.)and the result (as it actually developed)
quickly produced quite popular, widespread use of
the material. Only much later did the dangeroflung
infection from ingestion of asbestos fibers become
evident.
Both public awareness and industry caution
concerningliability are steadily growing in this area.
This will hopefully both rectify some ofthe errors of
the past and allowforsome confidence in the useof
new products. However, development of new
materials and products and the slow feedback of
medical research results call for considerable
restraint in acceptance of unproven items for
building construction.This is unavoidably inhibiting
to creative, pioneering designers, but is an ethical
issue of major proportions.
6.10. CONSTRUCTION SAFETY
Pressures brought by trade unions and various
advocacygroups havegreatly increasedconcerns for

the reduction of hazards during the construction
process. This form of pressureresulting in legal
actions and the creation of legislation and agencies
for enforcement—falls most heavily on
manufacturers and contractors, adding to the
overhead expense forvarioustypesofwork.As this
causes some shifts in the relative cost of certain
types of construction, such influence bears on
designers who make basic choices of materials,
products, and entire systems.
Direct-cost factors involving required safety
measures are routinely reflected in unit prices used
for cost estimating.Less easy to dealwith are more
subtle effects such as the general reluctance of
workers or contractors to deal with some forms of
construction because of the complexity or general
annoyance of complying with the actions or
documentations required because of safety
requirements. The latter can in effect sometimes
result in a form of boycott, which may be quite
regional or only shortlived, but can have major
influence in bidding on particular forms of
construction. This can be a major factor in
establishing what is defined as “local practice”.
references relating to individualchaptersectionsare
listed at the end of each individual section.
Buildings and Other Structures, ANSI A58.1-1982,
American NationalStandards Institute, New York, 1982.
Officials, Whittier, CA, 1988 (new editions every three
years).
International, Birmingham, AL.
Life Safety Code, NFPA 101, National Fire Protection As-
sociation, Quincy, MA, 1988.
J. Lathrop, Life Safety Code Handbook, National Fire Pro-
tection Association, Quincy, MA, 1988.
J. Ambrose andD. Vergun, Design for Lateral Forces, Wiley,
New York, 1987.
p. Hopf, Handbook ofBuilding Security Planningand Design,
p. Hopf and J. Raeber, Access for the Handicapped, Van
EXERCISES
for review ofthe individualsections andthe chapter
as a whole.
1. Why should lateral loads on buildings be
treated as dynamic loads?Whymight dynamic
loads have severer effects on buildings than
static lateral loads of the same magnitude?
2. The walls of a building face north-south and
east-west.The maximum wind may blow from
any direction.Explain why the building should
be designed to withstand full design wind
pressures againstthe northand southwalls and
also separately against the east andwest walls.
3. Wind pressure ona building 32.8ft (10 m) above
ground is 20 psf. What is the pressure 240 ft
above grade if the building is located in the
center of a large city?
4. A factory building, 30 ft high, is 20 X 100 ft in
plan. For wind pressure of 20 psf, what is the
lateral wind force on each wall?
5. At what value should the mean recurrence
interval be taken for design of a permanent
ordinary building?
6. A symmetrical building 40 ft wide weighs 200
tons.Lateralforces may total100 tons andtheir
resultant is 40 ft above grade. If the building
relies only on its weight for stability, can it be
considered safe against overturning by the
lateral forces. Justify your answer.
7. A 30 X 60-ft roof weighs 10 tons and relies for
stability on its own weight. If basic wind
pressure on theroofmay average 40psfand the
pressure coefficient is —0.5, is the roofstable?
Justify your answer.
8. Wind velocity is measured at 50mph at a station
32.8 ft (10 m) above ground. The station is
located in rough, hilly terrain.
(1) What would the velocity have been 240 ft
above ground?
(2) What would the basic velocity pressure
have been 240 ft above ground?
9. A building code requires that a 30-ft-high
building be designed for a minimum effective
velocity pressure, including gust effects, of 10
psf. The building is 100 sq ft in plan and has a
flat roof.The building code specifies anexternal

pressure coefficient Cp of 0.8 for windward
walls and —0.5 for leeward walls. For what
minimum lateral wind forces should the build-
ing be designed to prevent overturning and
sliding at the base?
10. Explain the importance of anchoring a roof to
its supports.
11. Why are seismic forces assumed to be pro-
portional to weight?
12. The probability of an earthquake of Modified
Mercalli Scale intensity V at City A is 0.01.
What is the mean recurrence interval of
earthquakes of that intensity?
13. A developeris considering two sites fora high-
rise apartment building in southern California,a
state where severe earthquakeshave occurred in
the past. One site is the remains of an ancient
river bed and has deep layersofclay.The other
site is on high ground and has deep layers of
sand with some clay. Which site should be se-
lected? Why?
14. Why is ductility important in aseismic design?
15. Describe a shear wall and explain its purpose.
16. Describe a rigid frame and explain its purpose.
Sections 6.3 to 6.6
17. Why should standards for fire protection
specified by insurance companiesbe applied in
design of a building for a private or
governmental owner?
18. Why is type of occupancy important in de-
termining fire-protection requirements for a
building?
19. Why is type of construction important in
determining fire-protection requirements for a
building?
20. Define fire load.
21. What is meant when a building component is
reported to have a 4-hr fire rating?
22. What is a fire wall?
23. How should a burningliquid be extinguished?
24. What are the basic components of a sprinkler
system?
25. An office has a fire load of 10 psf. What is the
equivalent fire severity?
26. What means should be usedto prevent fire from
spreading:
(a) Vertically from story to story?
(b) Horizontally throughout a complete story?
27. What is the main advantage of automatic
sprinklers?
28. In multistory buildings, where are standpipe
risers usually placed?
29. What may be usedto extinguisha fire around an
electric motor?
30. What elements may be incorporated in a
building to reduce chances of panic if a fire
occurs?
31. A restaurant has a 2,400-sq ft dining area.
(a) From Table 6.4, determine the maximum
number of persons permitted in the dining
room.
(b) From Table 6.5, determine the minimum
numberand size of exits, if maximum door
size is limited to 44 in.
32. How much floorarea, as a minimum, should be
allotted to a refuge area for 100 persons?
33. Compare advantages and disadvantages of
fixed-temperature and rate-of-rise detectors.
34. What types of fire detectors are useful for
detecting a smoldering fire?
35. A one-story factory contains 30,000 sq ft of
floor area. Materials and equipment handledor
installed may be classified as low heat release.
What is the minimum vent area that should be
provided in the roof?
36. Where must firestops be used?
37. What are the advantages of a multipurpose
control center?
38. What is the objective of life-safety design for
emergencies demanding evacuation of
occupants fromdangerous areas?
39. How do foams extinguish a fire?
40. What is the purpose of exits?
41. Name and describe briefly at least three fa-
cilities that building codes generally recognize
as a reliable exit.
42. Under what conditions can an escalator be
considered an exit?
43. A two-story industrial laboratory building has
5,000 sq ft of floor area on each level. It will
have exit stairs at each end ofthe building with
2-hr fire doors.
(1) On the secondfloor,howwide should each
door opening be?
(2) What is the minimum width permitted for
the corridors to the exits?
44. Why must structural members be fire pro-
tected?
45. How can a communication systembe used to

prevent occupant panic?
46. What is the purpose of a refuge area?
47. Describe at least four tasks a security system
should performto prevent theft and vandalism.
48. With regard to establishment of barrier-free
environments, what is meant by the term
“barrier”?
49. Why is it difficult to optimize barrier-free
facilities for all types of building users?
50. How does undue concentration on a single
favorable property of a material or product
sometimes result in major use of a toxic
material?
51. How may concerns for worker safety affect
designer’s choices for materials or products?

162
Chapter 7
Building Sites and Foundations
The building site is subject to design manipulation
in a limited way.Site boundariesconstitutethe most
fixed set of conditions. In addition, the nature of
adjacent properties and other boundary conditions
provide major constraints. Surface contours and
existing site landscaping may be altered to some
degree, but must conformto site drainage, erosion,
zoning,and environmentalimpact considerationson
a general neighborhood or regional basis.
Site materials can be a resource for construction
and must be dealt with as such. Surface materials,
however, may be unsuitable for the site and may
need to be replaced. The general excavation and
recontouring of the site should be accomplished as
much as possible without requiring excess removal
or importing of ground materials. Excavation work
and support ofthe building will involve subsurface
materials that present simple and uncomplicated or
challenging and expensive problems.
This chapter discusses the general problems and
design factorsrelating to specific building sitesand
to the development of site and foundation
constructions.
7.1. SITE CONSIDERATIONS
Building designers frequently are confronted with
situationswhere the ownerhas alreadypurchased a
site and they are required to design a building for
that site.In such cases,theywill adapt a building to
the site,if it is practical to do so,and will endeavor
to keep construction costs as low as possible under
existing conditions. Sometimes, however, it is
necessaryordesirable to chooseanothersite.In one
case, for example, soil investigations at a site indi-
cated that foundation construction would cost
severalhundred thousand dollars more than if good
ground were available. The owner decided to buy
another site.
The decisions as to which site to purchase, when
to buy it, howmuch land to include,and howmuch
money to pay for it are strictly the owner’s. It is to
his advantage, though, to have the advice of
consultants,especially his design consultants,in site
selection. They, however, usually will charge for
this service,becausesiteevaluations orcomparisons
are not ordinarily included in the basic services
provided by architects and engineers.
The best time for selecting a site occurs after the
design program has been established and a good
estimate has beenmade ofthe owner’s space needs.
Schematic studies then can indicate how many
buildings will be required, how much land will be
needed for each building, how much space will be
needed around each building and characteristics
desired of the site and surrounding property.
Estimates also can be made of utilities needed.The
data derived from these studies are basic
considerations in selecting a site.
Land Costs
Final selection of a site, however, is likely to be
determined by other considerations than just the
suitability of the lot for the building. Initial cost of
the lot, for example, may be a significant factor.
It is important, though, that the consultants call
the owner’s attention to the fact that the purchase
price ofa lot is not the only initial cost.While there
are broker fees, legal fees, registration fees, title

Building Sites and Foundations 163
insurance premiumand other costs that the owner
may be aware of, there are likely to be other
considerably larger costs that he may not expect,
unless advised of them by his consultants. These
costs arise fromzoning or subdivision regulations,
provision of access to the building, obtaining of
utilities, site preparation, foundation construction
and other conditions, depending on the type of
building. Such costs vary from site to site. In
comparing prices of proposed building sites,
therefore, the owner should be advised to add or
subtractcost differentials to accountforthesecosts.
Site Selection
Table 7.1 provides a partial checklist as a guide in
site selection. The check list is partial in the sense
that the factors included should always be
investigated,but,in addition,otherfactorsaffecting
a specific project also should be investigated.
For example, for an industrial or commercial
project, availability of a labor supply and housing
for executives and labor should be determined and
taken into account. For a residential development,
the distancestoschools,shopping,medicalfacilities
and religious institutionsmay be criticalfactors.For
a shopping center, the number of potential
customers and the range of incomes are crucial.
Inclusion of an item in the check list is not an
implication that its presence or absence at a site is
favorable or unfavorable to a decision to purchase
the site.Each factormust be evaluated with respect
to the specific project being considered.
Physical Features
Various physical characteristics of the site may
exert influence on the design of buildings for the
site. If site space is restricted, it may be
Table 7.1. Check List for Site Selection
Considerations
Internal Site Characteristics
Area and shape of lot—need for parking, storage areas,
future expansion
Topology—slopes, surface water, trees, drainage, rock
outcroppings
Geological conditions—surface soils, subsoils, watertable,
risk of landslide, flood, earthquake
Location
Owner preferencefor region, urban,suburban, or rural area
Distance from population centers and facilities for
education, recreation, medical service
Transportation
Accessibility of site—easements andrights ofway needed
Highways, airports, railroads, waterways, surface
transportation
Costs and Legal Concerns
Initial price, fees, taxes, insurance, permits
Clear title, easements, rights of way granted to others
Building codes, zoning, subdivision ordinances
Site work, access roads, services, utilities
Utilities and Services Required
Water, sewer, electricity, gas, telephone
Mail service and fire and police protection
Environmental Impact on Proposed Project
Business and political climate, local labor-management
relations, local employment conditions, available labor
Character of neighborhood, attitude of nearby residents
Proposed development or highway construction in area
Congestion, noise, trends of neighborhood, proximity to
airports
Views from site, appearance of approaches to site
Climate, prevailingwinds, fog, smog, dust storms, odors
Environmental Impact of Project
Congestion, pollution, noise, parking, housing, schools
Services required—utilities, police, fire, transportation
Taxes and assessments
Economic, educational, sociological, cultural
necessary to have a high-rise building, instead of a
less costly low-rise building. If the site boundaries
are not rectangular,it may be necessary to mold the
building plan to thesite shape,which is likely to add
complexity and some compromising to the general
planning of the building. For tight sites it is often
necessary to provide some parking in lower levels
of the building, the planning for which adds con-
straints to the layout of vertical structural elements
in the upper levels of the building.
Slope of the terrain also is an important con-
sideration. Moderately sloping or rolling terrain is
preferable to flat or steep land.Flat land is difficult
to drain of rainwater. For steep slopes (surfaces
rising or falling more than 10 ft vertically in 100 ft
horizontally), improvement costs rise rapidly.
Heavy gradingto flatten slopes notonlyadds to land
costs but also creates the risk of later uneven
building settlementorland erosion.In addition,fast
runoffofrainwaterfromslopes,as wellas collection
of water in marshes, swamps or wet pockets, must
be prevented, and this type of work is costly.

Rock at a convenient distance below the ground
surface often is advantageous for foundations of
buildings, but rock outcroppings that interfere with
building or road construction may have to be
removed with explosives,at considerable expense.
The difference in foundation construction costs
for good land and bad land may be sufficient for
rejection of an otherwise suitable site. One of the
earliest stepsin site evaluation,therefore,should be
an investigation ofsubsurfaceconditionsat the site.
Transportation
For most types of buildings, easy access to a main
thoroughfareis a prime requisite.Forcommuting of
employees fromhome to work, receipt of supplies,
and dispatch of output, building operations usually
depend heavily on transportation by automobile.
Note, however, that it is easy access to a major
highway, not its nearness, that is important. A
building fronting on a limited-access highway, for
example, may not be able to discharge traffic to it
without inconvenient, lengthy detours. Similarly, a
building near a major interchange may be
undesirable,because ofcongested traffic,difficulty
of access and egress, confusion caused by the
interchange layout,and noise andvibrationfromthe
traffic.
For some industrialplants,the type ofproduct to
be shipped may be such that shipmentby railroad is
economically necessary. In such cases, not only
must the site selectedbelocatedalonga railroad,but
also an agreement should be reached with the
railroad forprovision offreightserviceat acceptable
rates and intervals of time. For companies oriented
to air transportation,a location nearan airport may
be a prime requirement.
Zoning
Zoning or subdivision regulations often may
determine how a site under consideration may be
used,the typesofbuildingsthat may be constructed,
the types ofoccupanciesthat may be permitted and
the nature ofthe construction(seeSec.3.6).In some
cases,the type ofbuilding contemplated forthe site
may be prohibited, or land costs may be too high
relative to the expected return on investment when
the parcel of land is subdivided as required by law.
Similarly, limits on building height or floor area
may make a contemplated building uneconomical.
Sometimes,however,with the help oflegalcounsel,
the owner may be able to obtain a variance from
zoning requirements that will permit the proposed
building.
Building codes are not likely to have suchdrastic
effects on a proposed project. They may, however,
be a factorin site comparisons when the sites lie in
different jurisdictions, inasmuch as building-code
requirements are likely to be different in different
communities.
References
H. Rubinstein, Guide toSite andEnvironmental Planning, 3rd
ed., Wiley, New York, 1987.
J. Simonds, Landscape Architecture: A Manual of Site
Planning and Design, 2nd ed., McGraw-Hill, New York,
1987.
Site selection criteria.
Building-to-site relations: elevation, site plan, grading, ac-
cess, neighborhood, environment.
Site recontouring: drainage, topology, construction, site
boundaries.
Zoning, rights-of-way, easements, subdivision ordinances.
Feasibility of site and foundations, regarding site topology,
access for equipment, subsurface conditions, water.
7.2. SITE SURVEYS
When a site is being consideredforpurchase,a site
survey is conducted to provide information needed
for making a decision regarding that purchase. The
information provided should be that necessary for
evaluation and comparison of alternative sites and
in determination of the suitability of a specific lot
for the building and its uses. After a site has been
selected andpurchased,the purposes ofsite surveys
are to provide information needed for planning the
use of the land in detail, locating the building and
other facilities on the lot, installing utilities and
constructing foundations. In either case, the in-
formation is given diagrammatically and, to a
limited extent, by notes on two or more maps.
Additional information is provided in written
reports on surface and subsurface conditions and
their significance in design and construction of the
proposed building.

One type of map is used primarily to indicate the
location ofthe site with respect topopulation centers
or other points of interest to the building owner.
Another type of map, the survey plan described in
Sec. 2.23, shows property lines, topography and
utility locations.The plot plandescribedin Sec.2.23
shows the proposed location and orientation of the
building to be constructed, site grading to be done,
parking areas to be provided, driveways and other
installations planned. The plot plan is developed
from the survey plan.
Site Location Map
This map is useful, in the early stages of site-
selection studiesaswellas afterpurchaseofa lot,in
showing where the new building would be located
relative to existing facilities.The map may be drawn
to a very small scale, compatible with provision of
the following information:
1. location of site relative to nearby population
centers
2. jurisdictional boundaries
3. major highways and streets
4. principal approaches to the site
5. transportation lines
6. employment centers
7. shopping centers, schools, religious insti-
tutions, recreational facilities
8. appropriate zoning regulations, such as those
governing land use, for example, nearby
parcels restricted only to residential,oronly to
industrial construction
Survey Plan
This map delineates the boundaries of the lot. The
map need not be drawn to a large scale unless
considerable detail must be shown. For large
parcels, a scale of 1 in. = 100 ft may be adequate.
The map should show the following:
1. Lengths,bearings (directions),curve data and
angles at intersections of all boundary lines
2. Locations and dimensions ofstreets alongthe
boundaries andofstreets,easementsand rights
of way within the parcel, with deed or
dedication references
3. Location of intersection lines of adjoining
tracts and any encroachmenton boundaries of
the lot
4. Names of owners of adjoining property or
reference to recorded subdivision of that
property
5. Position and descriptionofphysicalboundary
markers and of official bench marks,
triangulation stations and surveying
monuments within or near the property
6. Area of the site and each parcel comprising it
7. Topography of the site—contours, lakes,
marshes, rock outcroppings, etc.
8. True and magnetic meridian (north arrow) on
the date of survey
9. Utility installations adjoining or passing
through the site
Topographic Map
A separate topographic map should be prepared
when considerable detailmust be shown fora site or
when a lot has steepslopes.Topographic maps show
the nature ofthe terrain and locate naturalfeatures,
such as lakes,streams,rockoutcroppings,boulders
and important trees, as well as structures and other
man-made items existing on the site. The scale
should not be smaller than 1 in. = 100 ft.
Slopes are indicated on such maps by contour
lines. Each line represents a specific level above a
base elevation,ordatum, as explained in Sec. 2.23.
The steeper the slope of the terrain, the closer will
be the contourlines.For relatively flat land (slopes
up to about 3 %; that is, 3 ft vertically in 100 ft
horizontally), contours may be drawn for height
intervals of 1 ft. For slopes up to about 15%, the
contourintervalmay be 2 ft, and for steeperslopes,
5 ft.
The location of test pits or borings for soil
investigations of the site may be added to the
topographic map.
Utilities Map
A separate map showing type,locationand sizes,if
appropriate,ofutilities adjacent to orwithin the site
should be preparedifthe amount ofdatato be given
would make a single map with combined
information confusing or difficult to read.

The utilities map should be drawn to a scale not
smaller than 1 in. = 100 ft. In addition to location,it
should provide the following information:
1. Sizes and invert elevationsofexisting sewers,
open drainage channels, catchbasins and
manholes
2. Sizes of water, gas and steam pipes and
underground electrical conduit
3. Widths of railroad tracks and rights of way
4. Police and fire-alarm call boxes and similar
devices
5. Dimensions of utility easements or rights of
way
Surveying Methods
Site surveys are not included in the basic services
provided by architectsandengineers.The owner,or
the architect or engineer on his behalf, should
engage a licensed surveyor to make land surveys
and drawthe maps.Geotechnicalconsultantsshould
be engaged for subsurface investigations and
reports.
Property-line lengthsanddirectionsandsettingof
boundary markers require land surveysofrelatively
high accuracy.These surveysare usually made with
a transit or a theodolite and tape. Topographic and
utility surveysmay be made with a transit ora plane
table and a stadia rod. Also, such surveys may be
made with electronic instruments, such as a
tellurometer, which uses micro waves to determine
distances; an electrotape, which uses radio-
frequency signals; or a geodimeter, which employs
light. For large parcels, aerial surveys offer
economy and speed in obtaining topographic
information. By photogrammetric methods,
contours and natural and artificial features can be
plotted on an aerial photograph of the site.
References
9th ed., Wiley, 1988.
J. DeChiara andL. E. Koppelman, Time-Saver Standards for
Site Planning, McGraw-Hill, 1984.
F. Merritt,BuildingDesignandConstructionHandbook, 4th
ed., McGraw-Hill, 1982, Sec. 23.
Wordsand Terms
Site Location Map Survey Plan Topographic Map Utilities
Map
Significant Relations, Functionsand
Issues
Site development, regarding: existing topology, location of
streets and utilities, control of water runoff.
Building positioning on site, regarding: grading, utility
connections, excavation for construction.
7.3. SOIL CONSIDERATIONS FOR SITE
AND FOUNDATION DESIGN
Surface and near-surface ground materials are
generally composed of combinations of the fol-
lowing:
1. Rock, solid or fractured
2. Soil, in naturally formed deposits

3. Fill materials of recent origin
4. Organic materials in partially decomposed
form
5. Liquids, mostly water
A number of considerations must be taken into
account in design of the building foundations and
the general site development. With respect to site
ground conditions, some typical concerns are the
following:
1. The relative ease of excavation
2. Site water conditions: ease of and possible
effects of any required site dewatering for
construction
3. Feasibility of using excavated site materials
for fill and site finish grading
4. Ability of the soil to stand on a relatively
vertical cut in an excavation
5. Effects of construction activities—notably
the movement of workers and equipment—
on surface soils
6. Reliability and structural capacity of near-
surface materials for foundation support
7. Long-time effects of site changes: paving,
irrigating, recontouring
8. Necessary provisions for frost protection,
soil shrinkage, subsidence, consolidation,
expansion, erosion
9. Need fordampproofingand/orwaterproofing
of subgrade constructionofoccupied spaces
10. Ease ofinstallation ofburied services:water,
gas, sewer, utilities, phones
11. Specialprovisionsforexisting features:large
trees, buildings (abandoned or remaining),
existing underground services or easements
for same
tion deals with a discussion of various ground
materials, their significant properties, how they
behave with respect to effects of building and site
construction, and the problems of establishing
criteria for design.
Soil Properties and Identification
Of the various ground materials previously de-
scribed, we are concerned primarily with soil and
rock. Fill materials of recent geological- formation
origin and those with a high percentage of organic
materials are generally not useful for site
construction or foundation support, although they
may have potential for backfill or finish grading to
support plantings.A precisedistinctionbetweensoil
and rock is somewhat difficult, as some soils are
quite hard when dry and cemented,while some rock
formations are highly weatheredanddecomposedor
have extensive fractures. At the extreme, the
distinction is simple and clear: for example, loose
sand versus solid granite. A precise definition for
engineering purposes must be made on the basis of
various responses of the materials to handling and
to investigativetests.Some ofthese are describedin
other portions of this chapter, relating to specific
materials, property definitions, and excavation and
construction problems.
Soil is generally defined as materialconsistingof
discrete particles that are relatively easy to separate
by moderate pulverizing actionorbysaturationwith
water. A specific soil mass is visualized as
consisting of three parts: solid, liquid and air. By
either volume or weight, these are represented as
shown in Fig. 7-1. The nonsolid portion of the
volume is called the void and is typically filled
partly with liquid (usually
Ground conditions at the site constitute a given
condition which must be dealt with in some feasible
manner.If building and site designrequirementsdo
not mesh well with given conditions, a lot of
adjustment and compensation must be made.
Investigations of the site conditions must be made
to inventory the existing ground materials, with
special attention to properties critical to building
and site design concerns.The following materialin
this sec-

water)and partly with air,unlessthe soilis saturated
or is baked totally dry.
Soil weight (density)is determined bytheweights
of the solid and liquid portions. The weight of the
solids may be determined by weighing an oven-
dried sample.The weight ofthe waterpresentbefore
drying is given by the difference in weight between
that sample and the weight of the sample before
drying. The specific gravity of primary soil
materials (sand, silt, clay, rock) vary over a short
range—fromabout2.60to 2.75—so thatthevolume
of the solids is easily predictedfromthe weight; or,
if the volume is known, the weight is easily
predicted.
Various significant engineering propertiesofsoils
are defined in terms of the proportionsofmaterials
as represented in Fig. 7.1. Major ones are the
following:
1. Void ratio (e). This generally expresses the
relative porosity or density of the soil mass,
and is defined as follows:
volume of the voids e =
—:
------------------, ---------——
volume of the solids
2. Porosity (n). This is the actual percentage of
the void, defined as
volume of the voids
n = " “ “ (100)
total soil volume
This generally defines the rate at which water
will flow into orout ofsoils with coarsegrains
(sand and gravel), although water flow is
measured by tests and expressed as relative
permeability, which is also affected by actual
particle size and gradation of particle sizes.
3. Water content (w). This is one means of
expressing the amount of water, defined as
w (in percent)
weight of water in the sample
weight of solids in the sample
of wateras a ratio,similar to the void ra
tio, thus:
volume of water
volume of voids
Oversaturation, with s greater than one, is
possible in some soils, when some of the soil
particles are made to float.
Particle size is a major factorin soilclassification,
as the majortypes ofsoils are essentially definedon
this basis. Figure 7.2 indicates the general formof
the graph thatis usedforclassifications on the basis
ofparticle size. Size is displayedhorizontally on the
graph, using a log scale, and indicating the usual
boundaries for common soil types. Distinctions
become less clear for very fine materials, so that
otherfactors must be usedto clearly distinguish be-
tween sand and silt and between silt and clay. Soil
deposits typically consist of mixtures of a range of
particles, and the vertical scale in the graph in Fig.
7.2 indicates the percentage of the soilvolume that
is represented by various particle sizes.The curved
lines on the graph indicate typical displays of size
analyses for soil samples; the forms of the curves
represent different soil types, as follows:
1. Well-graded soil. This is indicated by a
smooth curve, spanning a considerable range
of size.
2. Uniformsoil.This is indicated by a curve that
is mostly vertical in a short range of size.
3. Gap-graded soil. This curve is significantly
flexed, indicating a significantlackof middle-
sized soil particles.
Particle size alone, together with grading eval-
uations, will provide indications of major en-
gineering properties.
Particle sizes of coarsermaterials are determined
by passing the loose soil materials through
increasingly finer sieves, as indicated at the top of
the graph in Fig.7.2. For finegrained materials,size
is measured by the rate of settlement ofparticles in
an agitated soilwater mixture.
Particle shape is also significant, being mostly
bulky in rounded or angular form, although flaky
and needlelike shapes are also possible. Soil
mobility, compaction, and settlement may be
affected by shape—this often being critical with
specific types of soils.
A major distinctionis made between cohesive and
and cohesionless soils. Sand and gravel generally
represent cohesionless soil materials, while clay is
cohesive. Soils, though, usually
(100)
Saturation (S).This expressesthe amount
4.

are mixtures of various materials, taking on a
general character on the basis of the types of soil
materials as well as their relative amounts in the
overall soil volume. A quite small percentage of
clay, for example, can give considerable cohesive
character to predominantly sandy soils.
At the extreme, cohesive and cohesionless soils
are quite different in many regards,the propertiesof
critical concern being quite different. For
consideration of structural capacity, we may
compare sand and clay as follows:
Sand. Has little compression resistance without
some confinement; principle stress mechanismis
shear resistance; important data are penetration
resistance (measured as number of blows (A) for
advancing a soil sampler), density (measured as
weight), grain shape, predominant grain size and
nature of size gradation; some loss of strength
when saturated.
Clay. Principal stress resistance in tension;
confinement is of concern only when clay is wet
(oozes); important are the unconfined
compressive strength (qu), liquid limit (wz),
plastic index(Ip) and relative consistency (soft to
hard).
On the basis of various observed and tested
properties, soils are typically classified by various
systems. The systems used are based on user
concerns—major ones being those used by the
highway constructioninterests and byagriculturists.
Forengineering purposes,the principalsystemused
is the Unified System(ASTM DesignationD-2487),
abbreviated in Fig. 7.3. This systemdefines fifteen
soil types,each represented by a two-lettersymbol,
and establishes the specific properties that identify
each type.Most building codes use this as the basic
reference for establishing foundation soil re-
quirements. Codes often provide tables of lim-
Grain Diameter in Millimeters - Log Scale
7.2. Grain size measurement and plot for soil particles. Standard-size sievesare used to determine gradation of
size by percent. Both size and gradation are critical to soil properties.

Well-graded gravels and gravel-sand mixtures,
little or no fines
Poorly graded gravels and gravel-sand mixtures,
little or no fines
Silty gravels, gravel-sand-silt mixtures
Clayey gravels, gravel-sand-clay mixtures
Well-graded sands and gravelly sands,
little or no fines
Poorly graded sands and gravelly
sands, little or no fines
Silty sands, sand-silt mixtures
Clayey sands, sand-clay mixtures
Peat, muck and other highly organic soils
Fig. 7.3. Unified Soil Classification System. Used generallyfor
basic identification of soil type. Various criteria (not shown here) based on tests are used to establish
classification. (After ASTM D2487-85.)
iting values for foundation design (called pre-
sumptive values) based on some amount of pre-
scribed soil identification. Table 7.2 is reprinted
from the UniformBuilding Code and indicates the
Unified Systemas the basic classificationreference.
The following are some of the most common
ground materials. These are commonly named for
ourpurpose here,although some have quite specific
engineering definitionsin the various classification
systems.
Loam, or topsoil, is a mixture of humus, or
organic material, and sand,silt or clay.It generally
is not suitable for supporting foundations.
Bedrock is sound, hard rock lying in the po-
sition where it was formed and underlain by no
othermaterial but rock.Usually,bedrockis capable
of withstanding very high pressures from
foundations and therefore is very desirable for
supporting buildings. When bedrock is found near
the ground surface, excavation of overlying soil to
expose the rock and set footings on it often is the
most economicalalternative.Whenbedrockis deep
down and overlain by
Major Divisions
Group
Symbols
Descriptive Names
ML Inorganic silts, very fine sands, rock
flour, silty or clayey fine sands
CL Inorganic clays of low to medium plast-
icity, gravelly clays, sandy clays,
silty clays, lean clays
ŨL Organic silts and organic silty clays
of low plasticity
MH Inorganic silts, micaceous or diato-
maceous fine sands or silts, elastic
silts
CH Inorganic clays of high plasticity, fat
clays
ŨH Organic clays of medium to high
plasticity '
Highly Organic Pt
Soils

Table 7.2. Allowable Foundation and Lateral Pressure*
CLASS OF MATERIALS2
ALLOW A BLE
FOUN DA TIO N
PRESSU R E. LB/SQ.
FT.5
LATER AL
BEARIN G
LB/SQ ./FTJ FT.
OF DEPTH
BELOW
NATUR A L
GRADE4
LATERAL SLIDING1
COEFFICIENTS
RESIS TAN C E
LBISQ . FT.6
1. Massive Crystalline Bedrock 4000 1200 .70
2. Sedimentary and Foliated
Rock 2000 400 .35
3. Sandy Gravel and/or Gravel
(GWandGP) 2000 200 .35
4. Sand, Silty Sand, Clayey
Sand, Silty Gravel and
Clayey Gravel (SW, SP,
SM, SC, GM and GC) 1500 150 .25
5. Clay, Sandy Clay, Silty Clay
and Clayey Silt (CL, ML,
MH and CH)
10007
100 130
’Lateral bearing and lateral sliding resistance may be combined.
2
For soil classifications OL, OH and PT (i.e., organic clays and peat), a foundation
investigation shall be required.
3
All values of allowable foundation pressure are for footings having a minimum width
of 12 inches and a minimum depth of 12 inches into natural grade. Except as in
Footnote 7 below, increase of 20 percent allowed for each additional foot of width
and/or depth to a maximum value of three times the designated value.
4
May be increased the amount of the designated value for each additional foot of depth
to a maximum of 15 times the designated value. Isolated poles for uses such as
flagpoles or signs and poles used to support buildings which are not adversely
affected by a Vz-inch motion at ground surface due to short-term lateral loads may
be designed using lateral bearing values equal to two times the tabulated values.
Coefficient to be multiplied by the dead load.
6
Lateral sliding resistance value to be multiplied by the contact area. In no case shall
the lateral sliding resistance exceed one half the dead load.
7
No increase for width is allowed.
"Source: Reproduced from the Uniform Building Code, 1988 edition, with permission
of the publishers, International Conference of Building Officials.
weak soils,however,it may be more economicalto
drive supports, such as piles, from the ground
surface through the weak soil to the rock to carry a
building.Care should be takenin soilinvestigations
not to mistake weathered rock or boulders for
bedrock.
Weathered rock is the name applied to ma-
terials at some stage in the deterioration ofbedrock
into soil.This type ofrockcannotbe trustedto carry
heavy loads.
Bouldersare rockfragments overabout10in.in
maximum dimension.They too cannot be trusted to
carry heavy loads,because,whenembeddedin weak
soils, they may tip over when loaded.
Gravel consistsofrockfragmentsbetween2 mm
and 6 in. in size. When composed of hard, sound
rock, it makes a good foundation material.
Sand consists ofrockparticles between 0.05and
2 mm in size. The smallest particles may be
classified as fine sand,the largest as coarsesand,and
the intermediate sizes as mediumsand.Dense sands
usually make a good foundationmaterial.Fine sands
may be converted by water into quicksand, which
may flow out from undereven a very lightly loaded
foundation.
Silt and clay consist of particles so small that
individual particles cannot readily be distinguished
with the unaided eye. In one classification system,
silt comprises particles larger than those in clay. In
another classification system, silt is defined as a
fine-grained, inorganic soil that cannot be made
plastic by adjustment of water content and that

exhibits little or no strength when air-dried.Clay is
defined as a fine-grained,inorganic soilthat can be
made plastic by adjustment ofwatercontent andex-
hibits considerable strength when air-dried. Thus,
clay loses its plasticity when dried and its strength
when wetted.It may make a satisfactory foundation
material under certain conditions. Silt is not a
desirable foundation material, because when it gets
wet its strength cannot be relied on.
Sand and gravel are considered cohesionless
materials, because their particles do not adhere to
each other.They derive their strength frominternal
friction. In contrast, silt and clay are considered
cohesive materials, because their particles tend to
adhere when the water content is low.
Hardpan consists of cemented material con-
taining rock fragments. Some hardpans consist of
mixtures of sand, gravel and clay or silt. Glacial
hardpans may be composed of particles, ranging in
size from clay to boulders, that were at least partly
cemented together by high pressures fromglaciers.
Some hardpans, depending on the degree of
consolidation,make very good foundation material.
Till is a glacial deposit of mixtures of clay, silt,
sand, gravel and boulders. If highly compressed in
the naturalstate,tillmay serve as a goodfoundation
material. Loose tills vary in characterand may cause
uneven settlement ofbuildings supported on them.
Muck, or mud, is a sticky mixture of soil and
water. Because ofits lack of stability,muckseldom
can be used as a foundation material or as a fill to
build up ground to a desired level.
Foundation Design Criteria
Investigation of site conditions is aimed partly at
establishing data forthe building foundation design
and planning of the site work and foundation
construction. Information and recommendations
must be obtained that address the following
concerns.
Allowable Bearing Pressure. This is the
limiting value forthe verticalpressure undershallow
bearing foundation elements. It will be affected by
the type of soil materials encountered, by seasonal
fluctuations of the ground water level, by any deep
frost conditions, by the depth of the footing below
the ground surface (called surcharge), by the
sensitivity of the type of building construction to
settlements, and—in special situations—by
numerous otherpossible data and circumstances.In
simple situations,formodest sized buildings where
considerable previous constructionhas beenin place
forsome time, design values may be primarily based
on recommended presumptive values; often
stipulated by local building codes. For large
projects, or where unusual conditions exist, it is
common to seek recommendations from
experienced geotechnical engineers, supplied with
considerable investigative data.
Settlement. Downward movement of foun-
dations, as the building is progressively stacked
upon them,is an unavoidable eventuality,except for
foundations bearing directly on massive bedrock.
The precise magnitude of movements of complex
constructions on multilayered soil masses is quite
difficult to predict. In most cases, movements will
be small, and the primary concern may be for a
uniformity of the settlement, rather than a precise
prediction of the magnitude. Again, for modest
structures,bearing on firm soils with relatively low
imposed vertical pressure, settlement is seldom a
major concern. However, if any of the following
situations occur, settlements should be very
carefully studied:
1. When soils of a highly unstable or com-
pressible nature are encountered
.2. When vertical pressures are considerable and
bearing footings are used—especially when
any of the following situations 3 and 4 exist
3. When the construction is sensitive to
movements (notablyto differentialsettlements
of separate foundation elements), as are
concrete rigid frames,tall towers and masonry
or plastered walls
4. When nonuniform settlements may cause
serious misalignment of sensitive equipment,
or even of tall elevators, large doors, or other
building elements requiring careful fit or
joining
In some instances,the design verticalpressure may

be reduced to limit the magnitude of settlements.
WaterEffects. Water—is typically present in all
soils,except forthose in very dry,desert conditions.
At building sites, the effects of precipitation plus
irrigation for plantings will often keep a notable
magnitude of moisture in soils near the ground
surface.A specialconcern is that for the free-water
level (sometimes called the water table) in the
ground,belowwhich relatively porous soils will be
essentially saturated. This level normally fluctuates
overtime as precipitationamountsvary—especially
in areas where long periods occur with no precip-
itation.Repeated changesin the moisture contentof
soils, from saturated to near dry, can be the source
of various problems—most notably in fine-grained
soils subject to erosion,flotation orhigh magnitude
of volume change due to shrinkage and expansion.
A high free-waterlevelcan also bea problemduring
construction where considerable deep excavationis
required. Regrading of the site, covering of major
portions of the site surface with buildings and
paving and provision of extensive irrigation are all
effects constituting major adjustments of the
previous naturalsite environment and may result in
major changes in some soil materials near the
ground surface.
Horizontal Force Effects. Horizontally di-
rected force effects are usually of one of the
following origins.
1. Horizontal stressesfromverticalforces. When
a large vertical force is imposed on soil the
resulting stresses in the soil are three-
dimensional in nature. The soil mass tends to
bulge out horizontally. This effect can be a
major one in some situations—most notably in
soils with a high clay content. Adjacent
foundations may experience horizontal
movements or nearby excavations may be
pushed outward.
2. Active lateral pressure. This is the horizontal
force effect exerted by a soil mass against
some'vertical retaining structure, such as a
basement wall.This is generally visualized by
considering the soil to behave like a fluid,
exerting pressure in proportion to the distance
belowthe top ofthe fluid mass (ground level).
If the groundslopes upward behindthe retain-
ing structure(as with a hillside retaining wall),
or some additional load (such as a heavy
vehicle) imposes additional vertical load on
the ground surface,this pressurewillbe further
increased. Water conditions and the type of
soil will also cause variations in both the
magnitude and nature of distribution of this
type of pressure.
3. Passive lateral pressure. This represents the
resistance developedbya soilmass against the
horizontal movement of some object through
the soil. This is the basic means by which the
actual horizontal forces caused by wind and
seismic action are transferred to the ground—
by soilmass pressures against the basement
walls or sides offoundation elements.As with
active pressures, this effect varies in its
potential magnitude with depth below the
ground surface, although some limiting total
magnitude exists.
Frictional Resistance. When combined with
vertical forces, horizontal stresses will also be
resisted by friction on the soilin the case ofbearing
type foundations (friction on the bottomoffootings
resisting lateral sliding). For coarse-grained soils
(sand and gravel) the potential friction resistance
varies with the vertical force and is generally
independent of the contact area. For clays, the
resistance will vary with the cohesion per unit of
contact area,with theverticalforce being considered
only in terms of a certain minimum amount to
develop the friction effect.
Both passive lateralbearing and frictionalsliding
resistances as well as presumptive vertical bearing
pressures are often stipulatedin building codes (see
Table 7.2).
Stability. The likelihood for a soil mass to
remain in its present structural state depends on its
relative stability. Significant lack of stability may
result in erosion, subsidence, lateral movement,
viscous floworliquefaction.Alloftheseactions can
have disastrous effects on supported structures and
their potentialoccurrence is a major concern in soil
investigation.During excavation work as well as in
final site grading, a major concern is that for the
stability ofslopes,as discussedin Sec.7.8.Principal

destabilizing effects are those due to fluctuationsin
water content, unbalancing of the equilibrium of
pressures caused by deep excavations or heavy
surface loads and dynamic shocks such as those
caused by earthquakes. Loose sands, highly plastic
soft clays and cemented soils with high voids are
examples of potentially unstable soils.Modification
of some soils may be necessary and various
techniques are employed, as described in Sec. 7.7.
Excavation and Construction Concerns.
Performance of necessary excavation and site
grading and the general advancement of site and
building construction work must be planned with
consideration of various factors relating to soil
conditions. Need for bracing and possibly
dewatering oflarge excavations is a major task; this
is discussed in Sec. 7.9. Surface materials that can
be used for backfill, pavement subgrades or for
finish grading as topsoil should be stockpiled for
future use before they are lostduring the excavation
and construction processes.In some cases,existence
of large boulders, tree roots, old wells, cesspools,
underground tanksorburied constructionforutility
tunnels and vaults may present major tasks during
excavation as well as possibly requiring some
reconsideration in siting of buildings and design of
foundation elements. For urban sites, these matters
may be of heightened concern because they may re-
quire protectionofadjacentbuildings,streets,buried
utilities, and other structures.
Pile Foundations. These are discussed in
general in Sec. 7.5. A critical factor is the de-
termination at an early stage of design of the need
for deep foundations and the type to be used. For
piles,critical early decisionsmust be made as to the
likely required length,the useoffriction versusend-
bearing piles and any specialproblems thatmight be
encountered in advancing the piles. Heavy
equipment must be used for pile driving and the
movement of the equipment to and on the site may
be a problem in some cases. Pile driving is also
disturbing to the neighbors and may present
problems in this regard.
Pier (Caisson) Foundations. These are also
discussed in general in Sec. 7.5. They represent a
need for a very deep foundation, two primary
concerns being for the effects of water and the
potentialcollapse ofthesides ofthe excavation.The
excavation must be successfully advanced and then
filled up with concrete; in some cases requiring the
lining ofthe walls ofthe dug shaft anda dewatering
process. The term “caisson” derives from a tech-
nique used primarily for bridge piers, in which an
airtight chamber is sunkby digging out fromunder
it; then is filled with concrete once in place. The
deep foundation that is not driven as a pile is more
generally described as a pier. In some cases,it may
be advanced a great distance below grade, and its
design (and development of the construction
planning) may require quite deep soil explorations.
Piers—like end-bearing piles—oftenhavetheirsafe
load capacities verified by actual load tests; how-
ever, as the size of the pier increases, this becomes
less feasible. If load tests are not performed, the
necessity forreliable and complete soilinformation
becomes essential.
References
J. Ambrose, Simplified Design of Building Foundations,
2nded., Wiley, 1988.
J. Bowles, Foundation Analysis and Design, 3rd ed.,
McGraw-Hill, 1982.
G. Sowers, Introductory Soil Mechanics and Foundations:
Geotechnic Engineering, 4th ed., Macmillan, 1979.
Words and Terms
Clay
Cohesionless
Cohesive
Density
Fill
Grain size
Gravel
Penetration Resistance
Permeability
Porosity
Presumptivebearingpressure
Rock
Sand
Settlement: allowable, differential
Silt
Surcharge
Unified System of soil classification
Void

SignificantRelations, Functions, and Issues
Excavation: extent, ease, dewatering for, bracing for.
Effects of constructionactivity on thesite andexcavatedsoils
for bearing.
Site development in general related to building foundation
design.
Soil identification andevaluationforuse.
Establishment of design criteria for site and foundation
systems.
Settlement: computation of, control, effects on building.
7.4. SHALLOW BEARING FOUNDATIONS
In situations where reasonably stable, bearing-
resistive soils occur near the ground surface, the
commonly employed foundation system is that
using shallow bearing footings. The most common
forms of such footings are the simple strip footing
used beneath bearing walls and the rectangular pad
under individual columns. There are, however,
various other forms of footings for different
elements of building construction or special
situations. Some of the most common types of
footings are shown in Fig.
7.4.
The principal function of bearing foundations is
mainly transfer of vertical force through contact
pressure on the bottomof the footings. A primary
design decision is selection of the maximum
permitted bearing pressure, which is important in
determining the area of contact (plan size of the
footing). This area may be calculated from
. p
^=7 Í7
-1
)
q
in which A is the required footing area, p the total
load including the weight ofthe footing and q is the
unit ofallowable soilpressure.Designofthe footing
may proceed as for a reinforced concrete flexural
member: a single-direction cantilever for a wall
footing and a twoway cantilever for a column
footing.
Forsmall to medium-size projects,constructionof
footings is often quite crude, involving a minimum
of forming—especially in soils where a vertical cut
for the footing sides can be made for a shallow
excavation. In such cases, construction consists
essentially of casting concrete in a hole in the
ground. Economy is generally obtained by using a
relatively low grade ofconcrete,a bare minimumof
reinforcing,and a minimum of forming—often only
that required to obtain a reasonably true top surface
for the beginning of the construction of the sup-
ported object.Froma construction detailing point of
view, this latter function is of primary concern: the
providing of a platform for the building
construction. Concerns in this regard are for the
accurate location of the top of the footing, the
centering ofthefootingbeneaththe supported object
and the accurate installation of any anchorage
devices, such as anchor bolts or dowels for
reinforcement.
Wall and column footings are usedso repetitively
in common situations that their designs are mostly
achieved by using tabulated data, such as those in
the CRSỈ Handbook (see References at end of this
Section). Complete structural design is usually
limited to special foot-

ings, such as combined column footings or
rectangular footings for individual columns.
A major concern for shallow bearing footings is
the anticipated vertical movement caused by the
loads on the footing,called settlement.Some amount
of settlement must be expected if the footing bears
on anything other than solid rock, and solid rock is
not often available. The magnitude of settlement is
frequently the principal factor in determining the
limiting soil pressure fora footing.Settlements can
quite often be predicted with acceptable accuracy on
the basis of the soil materials, the thickness of
individual strata (layers) of different soil materials,
the magnitude ofthe verticalloads and bearing area
of the footings. The prediction, however, should
preferably be made by a qualified, experienced,
geotechnical engineer, as it requires expert
interpretation of investigative data and collation of
many factors.
Settlement mechanisms develop differently in
various types of soils and in response to various
actions.The initial settlement caused by the weight
of building and contents, however, may be most
significant, especially in loose sands and sand-
gravelmixtures. In soft wet clays,onthe otherhand,
settlement may occur over time as the clay mass
readjusts tothechanges in pressure—oozing in three
dimensions in the directions of less restraint. The
potential critical nature of settlements is largely
predictable from investigative data, if the data are
properly obtained and carefully analyzed.
How serious settlement effects are depends
Fig. 7.4. Shallow bearing foundations (also called spread footings), (a) Single footings for column, (b) Combined
footings for closely-spaced columns, (c) Cantilever, or strapped, footing, used at building edge on tight sites, (d)
Continuuous strip footing for wall, (e) Continuous footing for a row of columns, (f) Large single footing for
number of columns or a whole building, called a mat or raft.

not only onthe magnitude ofthe settlementsbutalso
on characteristics of the construction. Tilting of
towerstructures,crackingofplasterormasonry,and
misalignment of elevators or other sensitive
equipment are examples ofthe effectsofmovements
of the building supports. Especially critical is the
effect ofdifferential movements ofsupports ofstiff,
rigid-frame structures. Differential settlements are,
in fact,ofmore frequent concernthan the magnitude
Any Combination of Compression and Moment
Uhere: e = M/N
Producing: Compression Stress
Bending Stress
Resulting in One of Four Possible
Stress Combinations:
1. Uhen moment is small.
2. Uhen moment produces the same maximum stress
as the compression force.
3. Uhen moment produces a stress greater than that due
to the compression force.
4. Uhen the stressed section is incapable of
developing tensile stress.
Fig. 7.5. Combined stress produced by compression plus bending, (a) Development of stress, (b) Kern limits for
common sections; indicates limit for eccentric load without tension stress or uplift.
Eccentric Compression
is Equivalent to
Plus

of the vertical movements.If all of the footings for
a building settle the same amount, there will be
essentially no damage to the construction. If the
uniformsettlement is small,orif adequateprovision
can be made to compensate for it (such as simply
building the footings a bit high), the magnitude of
the settlement may be inconsequential.
In some situations differential settlements are
partly controlled by designingspecifically to control
them. This involves an analysis of the nature of
settlementsin terms ofboth the soilmechanismsand
the loads that cause them.Forsettlementsthatoccur
mostly at the time of loading, footing sizes may be
proportioned on the basis of the loads, with some
emphasis on the dead loads which are more
predictable. For long-time settlements of
considerable magnitude, it is sometimes necessary
to place adjustable elements between the footings
and the supported construction, with adjustments
made periodically as settlements are monitored.
In addition to their resistance to vertical loads,
bearing footings are often required to develop
resistance to the effects of lateral, uplift, or
overturningactions.Theproblems ofhorizontalsoil
pressures and general resistance to uplift are
discussed in Sec. 7.6. Footings subjected to
combinations of vertical compression and
overturning moment, such as the supports for
freestanding walls,towers,and isolatedshearwalls,
must resolve the combined effects of compression
and bending as shown in Fig.
7.5. As it is not feasible to develop tension re-
sistance at the contact face between the footing and
the soil, the total resistive effort must be achieved
with compression stress. Eccentric loadings may
result in development of a partly loaded contact
face, or cracked section, when the magnitude of
bending stress exceeds that of the direct
compression. This stress distribution is not very
desirable for a footing because of the implications
of rotational settlement. Thus, the usual
conservative design limit is the condition forwhich
maximum tensile bending stresses and direct
compressive stresses are equal. Visualizing the
combined actions as equivalent to those produced
by a mislocation (eccentricity) of the compression
force, it is possible to derive the maximum
eccentricity forthe limiting stress condition.This is
the basis forestablishing the kern limit for an area;
the formof such a limit for simple areas is shownin
Fig. 7.5.
References
J. Ambrose, Simplified Design of Building Foundations,
McGraw-Hill, 1982.
F. Merritt,BuildingDesignandConstructionHandbook, 4th
ed., McGraw-Hill, 1982, Sections 6 and 10.
Design Aids
CRSI Handbook and CRSI Manual of Standard Practice,
Concrete Reinforcing Steel Institute, 1984.
Words and Terms
Shallow bearing foundations
Footings: wall, column, cantilever, rectangular, combined,
mat
Lateral pressure
Soil friction
Kern limit
Geotechnical engineer
Vertical bearing: magnitude of, dispersion in soil mass,
settlement from.
Lateral, uplift and overturning moments on footings.
7.5. DEEP FOUNDATIONS
In many situations the ground mass immediately
below the bottomofthe building is not suitable for
use of direct bearing of footings. For tall buildings
this may simply be due to the magnitude of the
loads. In most cases, however, there is some
problemwith the soil itself or with some potential
destabilizing effect, such as washout erosion in
waterfront locations.Forsuch situations it becomes
necessary to go deeper into the ground for the
transfer of the bearing loads. (See Fig. 7.6.)
If the distance to good bearing material is rel-

atively short,it may be possible to simply excavate
into that soil, construct the usual bearing footings,
then build short columns (called piers or pedestals)
up to the bottomofthe superstructure(Fig.7.6a). In
some situations, there are other motivations for the
use of such transitional elements, such as cases
where supported elements (wood or steel columns,
for example) must be kept out of contact with soil.
If short pedestals are used, the additional cost may
be minor, consisting mostly only of the additional
Pedestals and foundation
footings to better soil
walls used to lower
Friction piles driven to develop lower soil
mass
bearing in a
End-bearing piles driven to seat in some lower, highly-resistive
soil or in rock
Concrete-filled, excavated shaft with belled bottom, bearing
on lower soil
Concrete-filled, excavated shaft, extended (socketed)
into rock
Fig. 7.6. Types of deep foundations.
3
(e)

excavation and the construction of the pedestals.
When it becomes necessary to lower the bearing
transfera considerable distance (say 15ft or more),
the usualsolution consists ofthe use ofeitherpiles
orpiers.This decisionis not lightly made,asthecost
of such foundation systems is usually much more
than that of simple footings. Use of piles or piers
consistsessentially oferectingthe building onstilts,
the stilts being used to transfer the vertical bearing
to some point significantly distant fromthe bottom
of the building. The distinction between piles and
piers has to do with the means for placing themin
the ground: piles are dynamically inserted (much
like pounding a nail into a board) while piers are
essentially concrete columns, the concrete being
cast in excavated shafts.
Because of the means of their installation, the
precision of the location of piles is difficult to
control. It is thus typical to use groups of piles for
support of loads that require precise location, such
as single building columns.Piers,on the otherhand,
are mostly used singly, except where a very large
single platform must be supported. Building loads
may be placed directly on top of piers, while a
transitionalconcrete cap(not unlike a thickfooting)
is required between a group of piles and a column
base.
Piles may consist of timber poles (stripped tree
trunks), rolled steel sections (H-shaped), thick-
walled or fluted-walled steel pipe, or precast
concrete. These elements are driven to one of two
forms of resistance development: simple skin
friction (Fig. 7.6Z?) orend point bearing (Fig.7.6c).
For friction piles, the load capacity is ordinarily
establishedby the difficulty ofdrivingit the lastfew
feet.With the aid of a calibrated driving device,the
numberof blows required to advance a pile the last
foot orso can be convertedto an extrapolatedstatic
force resistance.Building codesusually have empir-
ical formulas that can be used for this, although
more complex analyses may be possible using
additional factors and a computer-aided inves-
tigation.
When piles are closely clustered in a group, the
group capacity determines the load that may be
supported. It may be calculated by treating the pile
cluster as a large single block, equivalent to a
bearing footing with a plan size of that of the pile
group.
End bearing piles driven into rockpresent a much
different situation. This type of foundation is
generally feasible only with steel piles and
capacities must usually be determined byload tests.
The load tests are more for the purpose of
determining the proper seating of the piles in the
rock; the actualload capacity is usually that forthe
steel pile acting as a column.
Piles are installed by specialty contractors, often
using patented equipment or special pile systems.
As the necessary heavy equipment is difficult to
move over great distances, the type of pile
foundation used is often restricted by the local
availability of individualcontracting organizations.
Since a particular type of pile or pile-driving
technique is usually best suited to particular soil
conditions,localmarketing ofservices willtypically
favor particular systems. The following discussion
deals with some typical types of piles and driving
methods and some general considerations for their
use.
Pile Types
Timber Piles. Timberpiles consist ofstraight tree
trunks,similarto thoseusedforutility poles,that are
driven with the smallend down,primarily as friction
piles.Their length is limited to that obtainable from
the species of tree available. In most areas where
timber is plentiful, lengths up to 50 or 60 ft are
obtainable, whereas piles up to 80 or 90 ft may be
obtained in some areas. The maximum driving
force, and consequently the usable load, is limited
by the problems of shattering either the leading
point or the driven end. It is generally not possible
to drive timber piles through very hardsoilstrataor
through soil containing large rocks. Usable design
working loads are typically limited to 50 to 60 k (1
k = 1 kip = 1,000 lb).
Decay ofthe wood is a major problem, especially
where the tops of piles are above the groundwater
line. Treatment with creosote will prolong the pile
life but is only a delaying measure, not one of
permanent protection.One technique is to drive the
wood piles below the waterline and then build
concrete piers on top of them up to the desired
support level for the building.
For driving through difficult soils, or to end
bearing, wood piles are sometimes fitted with steel
points. This reduces the problemof damage at the

leading point, but does not increase resistance to
shattering at the driven end.
Because of their relative flexibility, long timber
piles may be relatively easily diverted during
driving,with the pile ending up in something other
than a straight,verticalposition.The smallerthe pile
group,the more this effect can produce an unstable
structural condition. Where this is considered to be
a strong possibility,piles are sometimes deliberately
driven at an angle, with the outer piles in a group
splayed out for increased lateral stability of the
group. While not often utilized in buildings, this
splaying out, called battering, of the outer piles is
done routinely for foundations for isolated towers
and bridge piers in order to develop resistance to
lateral forces.
Timber piles are somewhat limited in their ability
to accommodate to variations in driven length. In
some situationsthe finished lengthofpiles can only
be approximated, as the actual driving resistance
encountered establishes the required length for an
individual pile. Thus the specific length of the pile
to be driven may be either too long or too short. If
too long, the timber pile can easily be cut off.
However,if it is too short,it is not so easy to splice
on additional length. Typically, the lengths chosen
for the piles are quite conservatively long, with
considerable cutting off tolerated in order to avoid
the need for splicing.
Cast-in-Place Concrete Piles. Variousmethodsare
used forinstalling concretepiles forwhich the shaft
of the pile is cast in place in the ground. Most of
these systems utilize materials or equipment
producedby a particularmanufacturer,who in some
cases is alsothe installationcontractor.The systems
are as follows:
1. Armco system. In this system a thin-walled
steel cylinder is driven by inserting a heavy
steeldriving core,called a mandrel, inside the
cylinder.The cylinderis then dragged intothe
ground asthe mandrelis driven.Oncein place,
the mandrel is removed for reuse and the
hollow cylinder is filled with concrete.
2. Raymond Step-Taper pile. This is similar to
the Armco systemin that a heavy core is used
to insert a thin-walled cylinderinto the ground.
In this case the cylinder is made of spirally
corrugated sheet steel and has a tapered
verticalprofile, both ofwhich tend to increase
the skin friction.
3. Union Metal Monotube pile. With this system
the hollow cylinder is fluted longitudinally to
increase its stiffness,permitting it to be driven
without the mandrel.The flutingalsoincreases
the surface area, which tends to add to the
friction resistance for supporting loads.
4. Franki pile with permanent steel shell. The
Franki pile is created by depositing a mass of
concrete into a shallow hole and then driving
this concrete “plug” into the ground.Where a
permanent liner is desired for the pile shaft, a
spirally corrugatedsteelshellis engagedto the
concrete plug and is dragged down with the
driven plug. When the plug has arrived at the
desired depth,thesteelshellis then filled with
concrete.
5. Franki pile without permanent shell. In this
case the plug is driven without the permanent
shell.If conditions require it,a smooth shellis
used and is withdrawn as the concrete is
deposited. The concrete fill is additionally
rammed into the hole as it is deposited,which
assures a tight fit for better friction between
the concrete and the soil.
Both length and load range is limited for these
systems,based on the size ofelements,the strength
of materials, and the driving techniques. The load
range generally extends from timber piles at the
lower end up to as much as 400 kips for some
systems.

Precast Concrete Piles. Some of the largest and
highest-load-capacity piles have been built of
precast concrete. In larger sizes these are usually
made hollow cylinders, to reduce both the amount
of material used and the weight forhandling.These
are more generally used for bridges and waterfront
construction. A problem with these piles is
establishing their precise in-place length. They are
usually difficult to cut off as well as to splice. One
solution is to produce themin modular lengthswith
a typicalsplice joint,which permits some degree of
adjustment. The final finished top is then produced
as a cast-in-place concrete cap.
In smaller sizes thesepiles are competitivein load
capacity with those of cast-in-place concrete and
steel.Fordeep waterinstallationshugepiles several
hundred feet in length have been produced. These
are floated into place and thendropped intoposition
with their own dead weight ramming them home.
Precast concrete piles often are prestressed with
high-strength steel bars or wires to limit tensile
stresses during driving.
Steel Piles. Steelpipes andH-sectionsare widely
used forpiles,especially where great lengthorload
capacity is required orwhere driving is difficult and
requires excessive driving force.Althoughthe piles
themselves are quite expensive, their ability to
achieve great length,theirhigherload capacity,and
the relative ease of cutting orsplicing themmay be
sufficient advantages to offset their price. As with
timber piles ofgreat length,their relative flexibility
presentsthe problems ofassuringexact straightness
during driving.
Pile Caps. When a group of piles support a
column or pier, load transfer is accomplished
through a pile cap. The piles are driven close
together to keep cap size to a minimum. The exact
spacing allowable is related to the pile size and the
driving technique. Ordinary spacings are 2 ft 6 in.
for small timber piles and 3ft for most otherpiles of
the size range ordinarily used in building
foundations.
Pile caps function much like column foot-
ings,and will generally be of a size close to that of
a column footing for the same total load with a
relatively high soil pressure. Pile layouts typically
follow classical patterns, based on the number of
piles in the group.Typicallayouts are shownin Fig.
7.7. Special layouts, of course, may be used for
groups carryingbearing walls,shearwalls, elevator
towers, combined foundations for closely spaced
columns, and other special situations.
Although the three-pile group is ordinarily
preferred as the minimum for a column, the use of
lateral bracing between groups may offer a degree
of additional stability permitting the possibility of
using a two-pile group, or even a single pile, for
lightly loaded columns. This may extend the
feasibility of using piles for a given situation,
especially where column loads are less than that
developed by even a single pile, which is not
uncommon for single-story buildings of light
construction and a low roof live load. Lateral
bracing may be provided by foundation walls or
grade beams or by the addition ofties between pile
caps.
Drilled-in Piers
When loads are relatively light, the most common
form of pier is the drilled-in pier consisting of a
vertical round shaft and a bell-shaped bottom, as
shown in Fig.7.6d.Whensoilconditions permit,the
pier shaft is excavated with a large auger-type drill
similar to that used for large post holes and water
wells. When the shaft has reached the desired
bearing soil strata, the auger is withdrawn and an
expansion element is inserted to formthe bell. The
decision to use sucha foundation,the determination
of the necessary sizes and details for the piers, and
the development of any necessary inspection or
testing during the constructionshouldallbe done by
persons with experience in this type ofconstruction.
This type of foundation is usually feasible only
when a reasonably strong soilcan be reachedwith a
minimum-length pier. The pier shaft is usually
Fig. 7.7. Caps used for groups of three, four and five
piles.

designed as an unreinforced concrete column,
althoughtheupperpart oftheshaft is oftenprovided
with some reinforcement. This is done to give the
upper part of the pier some additional resistance to
bending caused by lateral forces or column loads
that are slightly eccentric fromthe pier centroid.
The usuallimit forthe belldiameteris three times
the shaft diameter.Withthisasanupperlimit,actual
bell diameters are sometimes determined at the time
of drilling on the basis of field tests performed on
the soil actually encountered at the bottomof the
shaft.
Where subgrade rock is within a practical depth,
the bell may be eliminated. Reinforced with a
structuralshape,such asan H-beam,socketedin the
rock (Fig. 7.6e), a drilled in pier can support very
large loads.
One of the advantagesofdrilled piers is that they
may usually be installed with a higher degree of
control on the final position of the pier tops than is
possible with driven piles. It thus becomes more
feasible to consider the use of a single pier for the
support of a column load. For the support of walls,
shear walls, elevator pits, or groups of closely
spaced columns, however, it may be necessary to
use clusters or rows of piers.
References
McGraw-Hill, 1982.
H. Winterkom and H. Fang, Foundation Engineering
Handbook, Van Nostrand Reinhold, 1975.
Sweets Architectural File, for various priority systems for
piles and drilled piers.
Words and Terms
Pile: friction, end-bearing, (see next Section7.6), capfor Pier:
caisson, belled, drilled.
Kips
Need for deep foundation.
Selection of foundation type and construction method.
Provisions for lateral and uplift forces.
Determination of vertical load capacity. Required testing,
before, during, and after installation.
7.6. LATERAL AND UPLIFT FORCES ON
STRUCTURES
While resistance to vertical force is the primary
function offoundations,there are many situations in
which horizontal and uplift loads develop. The
following are some types ofstructures andsituations
involving such actions.
Basement Walls
Basement walls are vertical load-bearing walls,but
they must also resist inward soil pressures on their
outside surfaces. The horizontal soil pressure is
usually assumed to vary in magnitude with the
distance belowgrade,as shown in Fig.7.8, with the
soilacting in the mannerofa fluid.Forinvestigation
the equivalent fluid soil is assumed to have a unit
density of approximately one third of its actual
weight.It is also common to assume some surcharge
effect,due to eitheran overburden ofsoilabovethe
surface, a sloping ground surface, or a wheel load
from some vehicle near the building. The typical
horizontal pressure loading for a basement wall is
therefore that represented by the trapezoidal
distributionshownin Fig.7.8Z?.In addition tothese
functions,basement walls may also serve as beams
when they must support columns directly or must
span between isolatedfootings orpile caps.Finally,
they must serve as exterior walls for any subgrade
occupied spaces, and must prohibit water
penetration and limit thermal transmission.
Freestanding Walls
These are walls supported only by their foundation
bases.They may occurinside buildings as partition
walls, but occur more often as ex-

7.10a.Ifthe shearwallis an interiorwall, it may be
built as a freestandingwall,with the combination of
active and resistive forces shownin Fig. 7.10b.The
single interior shear wall is seldom actually free,
however,and may resolvehorizontalforces through
elements of the floor or basement construction, as
shown in Fig. 7.10c.
teriorwalls orfences.The foundationsmust support
the weight of the wall, but must also develop
resistance to the horizontal forces of wind or
earthquakes.Thecombination of verticaland lateral
forces results in pressures on the bottom of the
foundation that vary as illustrated in Fig. 7.5. The
lateral loads will be resisted by a combination of
passive soil pressure on the side of the footing and
pressure on the buried portion of the wall, plus
sliding friction on the bottomof the footing. The
action of the active and resistive forces is shownin
Fig. 7.9.
Shear Walls
Shear walls (Sec. 8.16) often occur as portions of
exterior walls, with theirsupport provided by either
a continuousbasementwallora grade beam(a beam
at ground level).In such cases,horizontalforces on
the wall will produce shear and bending in the
supports as shown in Fig.
Retaining Walls
Changes in ground elevations that occur gradually
can be achieved by simply sloping the soil. When
abrupt changes must be made, however, some type
of soil-retaining structure is required; the type used
depending largely on the height difference to be
achieved. Small changes of a foot or so can be
accomplished with a simple curb, but for greater
heights, a cantilevered retaining wall often is used.
For heights from a few feet up to 10 ft or so, a
common form is that shown in Fig. 7.1 Ifl. The wall
may be built of masonry or solid concrete or core-
grouted,concreteblock.Forvery tallwalls it is com-
mon to use some form of bracing,as shown in Fig.
7.11/?.
Low walls may be designed for the equivalent
fluid pressure described for basement walls,
although a more rigorous investigation relating to
specific properties of the retained
Fig. 7.8. Horizontal soil pressure on basement wall (a)
without surcharge, (b] with surcharge.
Fig. 7.9. Total effect of gravity and lateral forces on a
freestanding wall. w n = weight of wall, w2 = weight of
footing, w3 and w4 = weight of soil, s = passive soil
pressure, F = friction.

Fig. 7.10. Actions of shear wall foundations, (a) Wall on
continous foundation, (b) Freestanding wall, (c) Wall
restrained by the building construction.
soilis usually made forhigh walls.Whentheground
surface slopessignificantly (at more than 1:5 or so)
there is some added pressure which is usually
accounted forby usinga surchargeeffect,as shown
in Fig. 7.8. A major objective for retaining walls is
to prevent collection of water in the retained soil
behind the wall, usually achieved by installing
through- the-wall drains and a coarse-grained,
porous fill behind the wall.
Abutments
It is occasionally necessary to provide a form of
foundation fora permanent combination ofvertical
and horizontalforces,suchas at thebase ofan arch.
This structure is called an abutment, and the
simplest form is that shown in Fig. 7.12ớ. Whereas
footings that are subject to lateral loads fromwind
or earthquakes may be designed forthe unevensoil
pressures shown in Fig. 7.5, such pressures, when
the lateral load is permanent, will result in some
tilting of the foundation. It is therefore desirable to
have the line of action of the resultant load pass
through the centroid of the footing bearing area, as
shown in Fig. 7.12Z?. When the horizontalforce is
large, or the resultant load on the abutment is at a
very low angle, or the load application occurs a
considerable distance above the footing, it may be
necessary to use an off-centerfooting orone with a
non-rectangular bearing area, to get the footing
centroid in the properlocation.The structure in Fig.
7.12c indicates the useofa T-shaped footingforthis
purpose, and also shows the use of an intermediate
grade beamto reducethe bendingin the footing.For
structures such as arches or ga-
(a)
(b)
Fig. 7.11. Forms of retaining walls, (a) Low wall,
cantilevered from footing, (b) Tall wall with counterfort
braces.

bled frames, it may be possible to provide a cross-
tie that resiststhe horizontalforce withoutinvolving
the footing,as is shownin Fig. 7.12J; in which case
the footing is simply designed forthe vertical load.
Lateral Loads on Deep Foundations
Piles and piers offervery limited resistance tolateral
forces at theirtops.Forbuildings,the usualsolution
is to use ties and struts in the foundation
construction to transfer the horizontal forces to
basement walls or grade beams. Where this is not
possible, it may be necessary to use battered piles
(driven at an angle), drilled-in tiebacks, or other
means to establish significant lateral resistance. A
special structure sometimes used in waterfront or
hillside conditions is that shown in Fig. 7-13c, in
which piles orpiers are developed to provide a rigid
frame action with a horizontal concrete frame
system; called a downhill frame. Additional
Fig. 7.12. Forms of abutments for arches, (a) Simple abutment with rectangular footing, (b) Force resolutions to
obtain uniform soil pressure for (a), (c) Abutment with T-shaped footing, (d) Abutment for a tied arch; develops
only vertical resistance with a horizontal tie at the hinge at the base of the arch.

stiffness of such a structure is obtained if short
drilled-in piers can be inserted a sufficient distance
into solid rock to provide fixity at their lower ends.
If piles or piers must develop lateral resistance
without any ofthesemeasures,theymust usually do
so in the manner of pole structures, described as
follows.
Pole Structures
Where good timberpoles are plentiful,they may be
used for a building foundation. The poles may be
driven-in piles—mostly in waterfront locations—
but may instead be partly buried in excavated holes.
In one form of construction-called pole platform
construction— the poles extend up to provide a
platformon which the building is erected.The other
basic system—called pole frame construction—uses
the poles as building columns,with floors and roofs
framed by attachment to the extended poles. For
lateral forces,the buriedpolesfunctionin one ofthe
two ways shown in Fig.7.14. In Fig. 7.14ứ the pole
is restrained at ground level—for example, by a
concrete floor slab. This results in a rotation about
ground level and development of the lateral soil
pressure indicated. If no restraint exists, the poles
behave asshownin Fig.7.14Z?, and theirresistance
is determined by empirical formulas. (See the Uni-
form Building Code or specific references on pole
construction.)
Uplift Forces
Resistance to uplift forces may be achieved in
various ways.The magnitude ofthe force is a major
consideration, resulting in modest response for a
simple tent stake and monumental construction for
the end anchorage ofsuspension bridge cables.The
resisting force may be developed by engaging
sufficient soilmass orbycreatinga constructeddead
weight.Concrete foundations themselves tendtobe
sufficient to anchor most light structures. Large
piers may be used for the value of their own dead
weight, with some more resistance offered if they
have belled bottoms, as shown in Fig. 7.6J. Major
problems occur mostly with very tall structures, or
single-footed structures, such as signposts or light
towers,ortall shearwalls for which the overturning
moment exceeds the gravity restoring moment.
Relatively long piles will develop significant
resistance to pullout,which may be usedfortension
resistance. For these, the reliable design load
capacity must usually be determined by load
tests.For concrete piles or piers, tension
development will require considerable vertical
reinforcement,representinga majorincrease in cost.
References
J. Ambrose, Simplified Design of Building Foundations, 2nd
ed., Wiley, 1988.
McGraw-Hill, 1982.
Words and Terms
Abutment
Fig. 7.13. Action of a downhill frame, functioning as a
fixed-base rigid frame.
(b)
Fig. 7.14. Lateral resistance of buried poles, (a) with
ground-level restraint, (b) with soil resistance only.

Active soil pressure
Battered pile
Downhill frame
Overturning moment
Passive soil pressure
Pole frame construction
Soil friction
Surcharge
Drilled-in tieback
Active pressure on retaining structures: affected by height,
soil type, water, surcharge.
Development of resistance to horizontal movement in soils:
affects of soil type, depth below grade.
Selection of type of retaining structure related to height of
retained soil.
7.7. SITE DEVELOPMENT
CONSIDERATIONS
General development of the building site may be a
simple matter or a major part of the project.
Extensive site construction or need for major
corrective effortson difficult sitesmay make the site
work a considerable design and construction
planning undertaking on its own.Assite designand
construction is not the major topic of this book,we
will consideronly a fewofthe typicalsituationsthat
relate to the building planning and the design of
foundations.
Finish Grading —Cut and Fill
Most sitesrequire some degreeoffinish “trimming”
to accommodate thebuildingand develop necessary
walkways,drives,landscaping,andso on.Economy
and ease ofthe constructionis generally servedbest
if there is a minimum requirement to either take
away or bring to the site significant amountsofsoil
materials. This translates to a desire to balance the
cuts (below existing grade) with the fills (above
grade)where possible.In this regard the excavation
for the building foundations usually represents a
major cut, unless the finish level of the grade is to
be raised a significant amount.
The ability to do any cross-trading ofsoilmaterials
on the site will ofcourse depend onthenature ofthe
existing materials. Existing surface soils may not
make good backfilland excavated materials may not
be good for landscaping work.
Removal of Objectionable Materials
Site materials not useable as backfill, paving
subgrades, or planting fill may have to be re-
moved—and, if necessary, replaced with imported
materials. This can only be determined after
considerable information about the site is obtained
and the site and building designs are carried to a
relatively complete stage of design. Removal and
replacement of soil are an expense to be avoided if
possible andmay affect the sitingofthebuilding and
generalplans forsite development.It is also possible
that site materials objectionable forone project may
be useful for another, making trading of materials
possible. Some form of soil modification may also
be possible, as described in the following.
Soil Modification
The work of excavating and grading is a form of
modification of a sort; materials may be basically
unchanged, but soil structures are altered. In the
process of moving the soils, some new materials
may be introduced,resulting in some newcharacter
for the soil. Modifications may also be made of
unexcavated soils.Some possibilities forthis are as
follows:
1. Consolidation by vibration or overburden
(stacking soil on the site) or by flooding to
dissolve the bonds in highly voided,cemented
soils.
2. Surface compactionforbetterpavementbases.
3. Infiltration of fine materials, such as cement
or bentonite clay, to reduce voids and lower
the permeability of fine, loose sands.
Modifications may have the basic purpose to
improve the soilconditions,ormay be doneto cause
certain unstable effects to occur in advance of
construction. Flooding to cause collapse in
cemented void soils may be done to prevent large
settlement after construction, when extensive
irrigation for plantings may cause the ground to
sink. This is a common occurrence in arid climates
where irrigation is used around buildings.
Surface Drainage
Control of surface water runoff is a major concern
in developing the finished site contours and site

construction.Thisalso needstobe coordinatedwith
the building roofdrainage andmeasuresundertaken
to prevent waterbuildup behind retainingwalls and
on the outsides of basement walls. Care must be
taken not to create channels of water flowing onto
neighboring properties, unless they existed as
established streams before site development in
which case damming orotherwise obstructingthem
may be objectionable.
Site Construction
Construction ofpavements,retaining walls,ditches,
planting structures, pools and other site structures
may be essentially separate from or simply an
extension of the building construction. Although
overallintegrity ofthe construction is to be desired,
less conservativism may be exercised in the
ancillary design work unless safety may be
adversely affected.Exterior exposure conditionsfor
this work make detailing of the construction quite
responsive to local climate conditions. Concrete
admixtures or types of special cements, depth of
footings below grade, and control joints in
pavements are some of the variables in this regard.
Local codes may provide some guidance,but this is
more a matter of evolved local practices.
Utilities
Electric power, telephone lines, gas, water, and
sewer services may all be delivered underground.
The presence of existing main distribution or
collection lines—especially gravityflow sewers—
may offer important constraints to site planning or
to the general siting of the building. Consideration
in planning should also be given to the following:
Underground tunnels orvaultsmay require ventsor
manholes for access which must be allowed for in
the site planning. Penetration of service lines into
the building must be accommodatedby thebuilding
foundationsand basement walls.Generalaccess for
modification, maintenance or repair should also be
considered.
Landscaping
Except for very tight urban locations,most building
sites will have some formof landscapingwith some
amount of plantings. The following should be
investigated with regard to possible effects on the
building:
1. Adequate provision for plant growth.
Plantings may occur over underground
structures. Hence, adequate depth for plant
growth and space for the necessary
waterproofing are needed. Siting and vertical
positioning of building spaces must make
adequate provisions for planting re-
quirements.
2. Provision for effects of irrigation. Frequent
watering may saturate the soil and cause
uneven settlement of retaining walls,
basement walls or buried utilities, or may
cause sinking of cemented void soils.
3. Roots of trees and shrubs. These may intrude
into basements or utility tunnels, or may get
beneathsome light foundations and pushthem
up or sideways.
Provision forthese,orforotherpotentialadverse
conditions,may wellofferopportunities forsystems
integration during the design stages.
Reference
J. DeChiara andL. E. Koppelman, Time-Saver Standards for
Site Planning, McGraw-Hill, 1984.
Words and Terms
Site grading
Soil Modification
Balancing of cut and fill in grading.
Effects of construction activity on surface and subsurface
soils.
Modifications to improve soil properties.
Intrusion of buriedutilities in site development. Provisions for
and effects of landscaping and irrigation.
7.8 COFFERDAMS AND FOUNDATION
WALLS
Depending onthetype ofsoil,shallowbasements or
cellars may be excavated and foundation walls and
footings constructed in stiff soils with no lining of
the earth perimeter or, in weak soils, with braced
wood sheeting to prevent collapse of the earth
sidewalls. Deep cellars and high foundation walls

require that excavation be carried out within an
enclosure to keep out water and to prevent earth
sidewalls fromcollapsing.A cofferdamgenerally is
used for the purpose.
A cofferdam is a temporary wall used for
protecting an excavation.One of its most important
functionsusually is to permit work to be carried out
on a dry, or nearly dry, site.
There are many different types of cofferdams,
including simple earth dikes,cells filled with earth,
braced single walls and double walls with earth
between the walls. For excavations for buildings,
braced single-wall cofferdams are generally used.
Such walls though must be carefully constructed,
especially if there are streets or other buildings
nearby.Small inward movement ofsuchcofferdams
may cause caveins and damage to nearby
construction.
Such movements and consequent damage can be
prevented only by adequate bracing of the
cofferdams. Not only must the bracing be strong
enough to sustain imposed loads, such as earth and
hydrostatic pressures and the weight of traffic
outside theexcavation,but it must also be seated on
practically immovable footings, anchors or walls.
Single-Wall Cofferdams
Cofferdams for building excavations may be
constructed in any ofmany different ways.Some of
these are illustrated in Fig. 7.15.
Figure 7.15a shows a type of single-wall cof-
ferdam that is often used when dry conditions are
expected during excavation. Structural steel piles,
called soldier piles, are driven vertically into the
ground,usually at intervals of 5to 10 ft, around the
perimeter of the planned excavation. Meanwhile,
excavation proceeds in the central portion of the
enclosure toward the depth required for the cellar
and interiorwalland column footings.Asthe soldier
piles are placed with their bottoms embedded below
the required depth of excavation, excavation starts
between the piles.To support the earthsidewalls as
work proceeds,wood boards,called lagging,are set
horizontally between the soldier piles. Small gaps
are left between the laggingto permit waterto drain
through and prevent buildup of hydrostatic
pressures against the cofferdams. At intervals, as
depth ofthe excavation increases,horizontalbraces,
called wales,are attached to the soldierpiles.Also,
the wales are braced with rigid struts to an opposite
cofferdam wall or with diagonal struts, called
rakers,extending to rigid supports in the ground.
When wet conditions may occur during ex-
cavation, the single-wall cofferdammay preferably
be constructed with sheetpiles (see Fig. 7.15b to/).
Sheetpiles are thin structuralsteelshapes fabricated
to interlock with each otheralong theiredges when
they are driven into the ground. They are driven in
the same way as other piles. In cross section,
sheetpiles may be straight, channel (C) shaped, or
zees. Special sections are fabricated for special
purposes, for example, for forming cofferdam
comers. The sheetpiles, which form a continuous
wall, may be braced,as excavation proceeds,in the
same way as cofferdams with soldierpiles and lag-
ging; for example, with wales and fakers,as in Fig.
7.15b, or with cross-lot bracing, as in Fig. 7.15e
and/.
These types of bracing, however, have the
disadvantage that they tend to interfere with
construction operations within the cofferdam. To
avoid this disadvantage,means have beendeveloped
for placing bracing, other than wales, outside the
cofferdam. For shallow excavations, for example,
the top of the cofferdam may be tied back to a
concrete anchor, or dead man, buried in the soil
outside the enclo-

sure (see Fig. 7.15c). For deep excavations, for
which bracing is required at several vertical in-
tervals, wales at those levels may be restrained by
tensioned, high-strength steel bars or wire strands
anchored in rock (see Fig. 7.15J). For the purpose,
holes are drilled on a diagonal through the soil
outside the cofferdamuntilrockis penetrated.Next,
a pipe is placed in each hole tomaintain the opening.
A steelbarorseveralwire strandsare inserted in the
pipe,and one end is anchoredwith grout in the rock
socket while the opposite end is fastened to hy-
draulic jacks set on a wale. The jacks apply a high
tension to the bar or strands, which then are
anchored to the wale. The resulting forces restrain
the cofferdamagainst inward movement underearth
and hydrostatic pressures.
A cofferdam also may be constructed with
precast-concrete panels or by forming continuous
walls by casting in place concrete piles in bored
holes.
Another method that may be used is the slurry-
trench method, which permits construction of a
concrete wallin a trench.The trench is excavated in
short lengths.As excavation proceeds,the trench is
filled with a slurry of bentonite, a mixture of water
and fine inorganic particles. The fluid pressure of
the slurry prevents the sidewalls of the trench from
collapsing. Concrete is then placed in the trench,
replacing the slurry.
After excavation has been completed within a
soldier-pile or sheetpile cofferdam, form work can
be erected around the perimeter for the
Fig. 7.15. Single-wall cofferdams,(a) Lagging between soldier piles, braced with walesand rakes,(b) Sheet pile
with braces, (c) Sheet piles with tieback to deadman. (d) Wall with drilled-in tiebacks, (e) Crossbraced walls in
narrow excavation (trench), (f) Walls with two-waycross-lot bracing.

Fig. 7.16. Provision for drainage at a foundation wall.
foundation walls.Finally, concrete is placed within
the framework to form the walls. Afterthe concrete
has hardened, the formwork and cofferdamcan be
removed, for reuse elsewhere. Drains should be
placed behind the walls along wall footings, to
conduct away water, and a porous backfill, such as
gravel, should be placed against the wall to allow
water to seep down to the drain (see Fig. 7.16).
References
J. Bowles, Foundation Analysis andDesign,3rded. McGraw-
Hill, 1982.
G. Sowers, introductory Soil Mechanics and Foundations:
L. Zeevaert, Foundation Engineering for Difficult Subsoil
Conditions, 2nd ed., Van Nostrand Reinhold, 1982.
Words and Terms
Cofferdam
Dead man
Drilled-in rock anchor
Lagging Raker
Sheetpiling
Soldier beam or pile
Tieback
Wale
Slurry-trench method
Bracingfor excavationrelatedto height of cut, constructionin
excavation, andprotectionof propertyorbuildings adjacent
to cut.
Drainage of backfill along cofferdams
7.9. DEWATERING OF EXCAVATIONS
Several construction operations must be carried out
within an excavation for a building. These include
erection of formwork and placing of concrete for
footings, walls, piers, columns and floors and
perhaps also erection of steel columns and beams.
These operations canbe executed more efficiently if
the excavation is kept dry.
Provision for dewatering therefore usually has to
be made for excavations forbuildings.Dewatering,
however, also has other advantages than just
permitting construction to be carried out in the dry.
Removal of water makes excavated material lighter
and easier to handle. Dewatering also prevents loss
of soil below slopes or from the bottom of the
excavation, a loss that can cause cave-ins. In
addition, removal of water can avoid a quick or
boiling bottom in the excavation; for example,
prevent conversion of a fine sand to quicksand.
Often, an excavation becomes wet because the
water table, or level of groundwater, is above the
bottomof the excavation. To keep the excavation
dry, the water table should be at least 2 ft, and
preferably 5 ft, below the bottomof the excavation
in most soils.
Any ofseveralmethods may be usedforlowering
the watertable,when necessary,andfordraining the
bottom of the excavation. Information obtained
from site exploration should be useful for deciding
on the most suitable and economical dewatering
method.This information should covertypes ofsoil
in and below the excavation,probable groundwater
levels during construction,permeability ofthe soils
and quantities of water to be removed. Pumping

tests are useful in obtaining data for estimating
capacity of pumps needed as well as indicating the
drainage characteristics of the soils.
Dewatering Methods
When the groundwater table lies below the ex-
cavation bottom, water may enter the excavation
only during rainstorms, or by seepage through side
slopes or through or under cofferdams. In many
small excavations, or where there are dense or
cemented soils,watermay be collectedin ditchesor
sumps at the excavation bottomand pumped out.
This is the most economical dewatering method.
Where seepage fromthe excavation sides may be
considerable, it may be cut off with a sheetpile
cofferdam,grout curtains orconcrete-pile orslurry-
trench walls. For sheetpile cofferdams in pervious
soils, water should be intercepted before it reaches
the enclosure, to avoid high pressures on the
sheetpiles. Deep wells or wellpoints may be placed
outside the cofferdams for the purpose.
Deep wells, from 6 to 20 in. in diameter, are
placed around the perimeter of the excavation to
intercept seepage orto lowerthe water table.Water
collecting in the wells is removed with centrifugal
orturbine pumpsat the wellbottoms.Thepumps are
enclosed in protective well screens and a sand-
gravel filter.
Wellpoints often are used for lowering the water
table in pervious soils or for intercepting seepage
(see Fig. 7.17). Wellpoints are metal well screens,
about 2to 3in. in diameterand up to about 4ft long,
that are placed below the bottomof the excavation
and around the perimeter. A riser connects each
wellpoint to a collection pipe, or header, above
ground. A combined vacuumand centrifugal pump
removes the water fromthe header.
References
L. Zeevaert, Foundation Engineering for Difficult Subsoil
Conditions, 2nd ed., Van Nostrand Reinhold, 1982.
Wordsand Terms
Deep wells Dewatering
Quick or boilingeffect
Seepage
Well points
Conditions requiring need for dewatering.
Dewatering methods related to soil type, water level in soil
and nature of excavation and bracing of cuts.
7.10. INVESTIGATION AND TESTING
Some investigation ofsite and subsurfaceconditions
must be made forany building project.The extentof
investigation and its timing varies considerably,
depending onthe size and nature ofthe construction
and the site conditions. Cost of investigative work
must be considered, and its control may be quite
important for small building projects. However, if
serious problems exist, they must be sufficiently
Fig. 7.17. Wellpoint installation for an excavation.

investigated, regardless of the project size.
Site surveys will provide considerable infor-
mation for the general site development. For the
building design, however, some investigation must
be made of the subsurface conditions that affect the
foundations and any subgrade construction. For
small buildings with shallow foundations, a simple
soil exploration may be sufficient, possibly
conductedwith very minorequipment,such ashand
augers or post-hole diggers. Such minor
investigations performed by personsexperiencedin
geotechnical work can reveal considerable data,
which may be significant for site development and
for preliminary design of foundations.
For most building projects, however, permit-
granting agencies will require some investigation
consisting of deep soil sampling and the
performance of minimal testing. Such soil ex-
plorations should be performed by experienced
persons who will usually also make some rec-
ommendations for foundation design criteria and
any specialconditionsthatcan beanticipated during
the site work and excavation.
The form and extent ofsubsurface investigations,
the equipment usedto achieve themand the type of
tests to be performed, all vary considerably. When
the site is fully unexplored, the first investigations
may be done primarily to establish what type of
investigationis really required.In many situationsit
is possible to predict from past experience or
previous construction on the site the likelihood of
encounteringspecific conditionsin the region ofthe
site. Information is also forthcoming from various
sources such as:
1. Government engineering,building orhighway
departments.
2. Government agricultural agencies or ag-
ricultural industry organizations.
3. Various agencies that conduct studies for
water resources, such as erosion control, and
seismic activity.
4. U.S. Armed Forces studies for nonclassified
projects.
Most geotechnical engineering organizations in the
soilinvestigation and testingbusinesswillmake use
of any such information that is available forregions
they regularly serve,and theycan thus workfroma
considerable database to predict conditions on any
site.
In the end what is required is whatever in-
vestigation is necessary to assure the adequacy of
the foundation design and to provide a base for
planning of the site work and excavation for the
building construction. This may present some
problems in timing, as some soil exploration must
be made before design can be done, while the
investigation required must be based partly on
knowing the building location, the type of
construction, and the anticipated magnitude of
foundation loadings. The result of this can
sometimes produce some interaction between
design and investigation—such as when the
subsurface investigation shows that the desired
location for the building is the worst possible place
on the site for foundations.
Investigation and testing must generally address
the establishingofthree categories of information:
First is the identification of types of soils in the
various typical layers that occur at different
distances below the ground surface. Using the
Unified System (Fig. 7.3) for classification,
pertinent dataare obtained.Simply identifying soils
as one of the 15 categories in the Unified System
does not yield all of the desired information for the
engineering design work, however.
Second, depending on the soil type, additional
data may be required. For sand—in addition to
information for the classification only —structural
behavior will be determined by relative density
(from loose to dense), penetration resistance
(measured as the number of blows required to
advance a standard soil sampler), grain shape and
watercontent.Forclay the principaltestedstructural
property is unconfined compressive strength, qu.
This property may be approximated by simple field
tests, but must be more accurately determined by
laboratory tests.
Third,information may be needed to evaluate the
potentialforusing excavated soilmaterials for site-
development work—for pavement subgrade bases,
for plantings, for retaining wall backfill, for
example. This often requires more information on
surface and nearsurface materials, which are not of
major concern in the deep-soil investigation for
foundation design criteria.
For large projects, for deep excavations or
whenever major problems are anticipated during
construction, it is often necessary to performsome

tests duringthe performance ofthe excavationwork.
These may be done primarily only to verify data
from previous investigations or to confirm
assumptions made for the engineering design. For
some types of foundations, however, there are
investigations that are a normal part of the work.
Foundations on rock, typically using very high
levels of bearing pressure, require tests on the rock
at the time of excavation,involving drilling to some
length into therockmaterialencountered.End-bear-
ing piles seated in rockmust usually be load tested,
as the usual empirical formulas using pile driving
data do not work for this situation.
Soil properties are interrelated, so that a single
tested property—such as unit weight- should relate
to other tested properties, such as penetration
resistance, permeability, consolidation and water
content. This allows the inference of some
properties fromthe identification ofothers,butmore
importantly permits cross-checking to verify
reliability of investigative data.
The following is a description of various ex-
plorations and tests that are commonly made to
support site and foundation design work.
Explorations
Visual inspection is an essential preliminary step
for building designers, foundation consultants,
construction managers, and prospective
construction bidders. Visual inspection should
provide information on surface soils, rock out-
croppings, surface water, slopes, accessibility for
equipment for subsurface exploration, grading and
excavating, availability of water for drilling
equipment, existing structures on the site, former
structures on the site and adjacent structures. If
possible, inspection should determine whether
underground utilities may be passing through the
site.Small truck-mounted augerdrills,may be used
for quick visual soil analysis and location of
groundwater below grade.
Test pits are holes dug on a site to investigate
soil conditions. They permit visual examination of
soil in place and provide information on the
difficulty of digging. They also make it possible to
obtain an undisturbed sample of the soil manually.
Cost of digging a test pit, however, increases with
depth. Hence, this method is limited for economic
reasons to relatively shallow depths below grade.
Borings usually are resorted to forsampling soils
at greaterdepths than those desirable with test pits.
Boring is a drilling process in which a hole is formed
in the ground forsoilsampling orrockdrilling. The
hole may be protected by insertionofa steelcasing
or with drilling mud, a slurry of water and clay.
Borings may be carried out in several different
ways, but the most satisfactory results are usually
obtained by “dry” sampling.
“Dry sampling has the objective of obtaining a
complete sample ofthe naturalsoil.Forthe purpose,
a hole is drilled; for example, with a hollow-stem
auger.Samples are obtained by lowering a drill rod
with a sampler on the bottom end through the
hollow-stemauger to the bottomof the hole. Then,
the sampler is driven beyond the lead point of the
auger to secure a sample of the soil.
Any of several different types of samplers, also
called spoons, may be used to obtain a dry sample
from a borehole. Thin-walled types cause less soil
disturbance, but thick-walled types are preferable
for sampling stiff, nonplastic soils. Some samplers
have sectional linings for collecting samples, to
permit delivery of samples to a laboratory without
manual handling of the soil.
A sampleris driven into the bottomofa hole with
a free-falling weight. Standard practice is to use a
140-lb weight falling 30 in. on a spoon with 2-in.
outside diameter. The number of blows required to
drive the spoon are recorded for each foot of
penetration into the soil. This record is useful as a
measure of the soilresistance encountered andmay
be used for soil classification. If undisturbed soil
samples can be obtained, however, unconfined
compressiontests on themin a laboratory can be of
greatervalue to engineers thanthe numberofspoon
blows. Shearing strength, for example, equals one-
halfthe unconfined compressive strengthofthesoil.
Rock samples generally are obtained in the form
of rock cores. For the purpose, rotary drilling with
shot or diamond bits is used. A complete core,
however, may not always be obtainable. Hence,
investigators should report the percentage of
recovery ofrock,the ratio oflengthofcore obtained
to distance drilled. Generally, the higher the
percentage of recovery, the better the condition of

the rock.Note,however,that recovery alsodepends
on care taken in sampling and on type ofbit used in
drilling.
Water-table depth and its variation over a period
of time should be reported when a site investigation
is made, because the presence of groundwater can
affect foundation design and construction. One
method is to dig a permanent observation well and
take weekly or monthly readings ofthe waterlevel.
Another method is to take readings in boreholes.
Local building codes may specify the minimum
number of borings or test pits in terms of building
area, for example, one for every 2,500 sq ft of
ground area.These codesalsomay specify the depth
for the holes and pits. At least one boring, though,
should extend into bedrock.
Soil Tests in the Field
Properties of soils from which predictions of their
behavior under building loads may be made
sometimes can be determined directly in the field.
Such tests may measure soil density, permeability,
compressibility or shearing strength. The tests may
be made at the bottom of test pits or of casings
driven into the soil or inserted in boreholes. After
the casings have been cleaned out, any of several
different kinds of tests may be carried out on the
exposed bottom. Common tests include loading of
cone-shaped plungers ortight-fitting bearing plates
to measure resistance of the soil to penetration or
compression. Sometimes, a vane shear test may be
made. In this test, a rod with two to four vertical
plates,orvanes,at thetip is insertedinto the soiland
rotated. The torques required to start and maintain
rotation can be correlated with shearresistance and
internal friction. The data can be used to estimate
soilbearing capacity andpile friction resistanceand
hence pile length required.
Bearing capacity of a soil to support footings
often is estimated from load tests made in the field.
The tests are made on a small area of soilin a pit at
the levelofthe footingstobe built.In the tests,loads
are applied in increments to a bearing plate resting
on the soil.Hydraulic jacks orweights may be used
to load the plate. Settlement of the plate after each
increment has been in place 24 hr is recorded, but
sometimes sizable settlements continue for a long
time, in which case it is necessary to wait until
settlement stops.The data recordedusually are plot-
ted to forma load-settlement curve.
In load tests of a typical footing for a building,
loads are continually increased to 150 or 200% of
the expected footing design load. The design load
may be considered acceptable if,when applied in the
test,the load does not cause a settlement exceeding
a specified amount, for example, I in. Also, under
the maximum applied load, settlement must be
nearly proportional to that under the design load.
Building codes generally prescribetheprocedure for
making a load test.
Soil Tests in Laboratories
Any ofmany different laboratory tests may be made
on soils to identify those present, determine their
properties and predict theirbehaviorunderbuilding
loads. Usually, however, only a few different tests
are necessary.More tests may be neededthough for
foundations with heavy ordynamic loads andthose
on weak or unreliable soils. Among the more
commonly made tests are the following:
Mechanical analyses are performed to determine
the percentages of different size particles in a soil
sample.Different sizes ofsieves are usedtoseparate
coarse particles. Fine particles are separated by
sedimentation, usually by hydrometer test. The
gradations measuredin suchanalyses canbe usedto
indicate the type of soil and a wide variety of
properties, such as permeability, frost resistance,
compactability and shearing strength.
Density determinations are made to measure the
compressibility of soils. Loosely packed soils are
more compressible than compact ones.
Compaction tests are made to determine the
maximum density that can be achieved for a soil.
These tests provide data for later use in the field to
insure that thedesired degreeofcompactionofa fill
is achieved with compaction equipment.
Moisture-content determinations are made foruse
in estimating soil compactability and
compressibility and to predict the shearing strength
of clays at varying water contents.

Consistency tests may be made on finegrained
soils to predict their shearing strength at varying
water contents. Atterberg-limit tests, for example,
are made to determine the water contents that
change fine-grained soils fromsolids to semisolids,
then to plastic materials, and finally to liquids.
Permeability tests are conducted to estimate
subsurface water flow, such as artesian flow and
flow under sheetpiling.
Compression tests of various types are made to
determine the compressibility and shearing strength
of soils.
Consolidation tests are made to obtain in-
formation for predicting anticipated settlement of
soils under building loads.
Direct shear tests are conducted to determine the
bearing capacity of soils under building loads and
the stability of ground slopes.
The value of information obtained from lab-
oratory testsdependsgreatly on the care with which
samples are extracted,locationsfromwhich samples
are taken, and the care in storing, handling and
delivering samples to the laboratory, as well as the
execution of the tests. Intelligent interpretation of
test results also is important.
References
J. Bowles, Foundation Analysis andDesign, 3rded.,
McGraw-Hill, 1982.
G. Sowers, Introductory Soil Mechanics and Foundation:
Geotechnic Engineering, 4thed., Macmillan, 1979.
Wordsand Terms
Borings Rock cores Soil sampling(dry) Test pits Density
Penetration resistance
Compaction Consistency Consolidation
Types of investigations andtests relatedtosoil conditions
andnature of construction.
Timingof soil investigations relatedto schedule of design
work andconstruction.
Importance ofreliabilityof investigation andinterpretations
of data.
Field tests for soil density, permeability,compressibility,
shearingstrength, unconfinedcompressive strength
Laboratorytests forparticle size andgradation, density,
water content,consolidation
7.11. SYSTEMS-DESIGN APPROACH TO
SITE ADAPTATION
Two cases must be consideredin systems design of
a building.One is the situation where a site has
already been purchasedand the building mustbe
adapted to it.The secondis the situationwhere a
site has not yet been selected before design starts.
In the lattercase,the building designers may be
able to influence purchase ofa site that will permit
use ofthe most economicalfoundations andthat
will have mostly beneficialeffects on building
design and construction.
The lot and foundations may be treatedas a major
subsystemof the building, but for brevity will be
referred to as the site-foundation system. The
systems-designsteps illustratedin Fig.3.4should be
applied to this system.
There are complications, however, because the
site-foundation system plays conflicting roles in
building design. The lot is both the initial and final
subsystemin a sequence of subsystems comprising
a building. The lot affects design of the basic
subsystems, such as the building envelope (shape,
plan dimensions and number of stories, or height),
orientation of the building on the site and access to
the building from streets and highways.In contrast,
as the end subsystem, the site-foundation system
does not affect the design of the building structural
system,after the type and geometry ofthe building
systemhas been selected.In view of the associated
complications of the conflicting roles, a practical
procedure is to prepare schematics of the building
superstructure, with due consideration to site
characteristics, and then to apply systems design to
site adaptation and preliminary design of
foundations.
Data Collection and Problem Formulation
In selection of a site, reconnaissance, surveys and
preliminary soil sampling, as well as purchase-cost
comparisons, should provide information to guide
decision making. Aftera site has been bought,data
should be collected to guide site adaptation and

foundationdesign,as described in Sec. 7.2 and 7.3.
Site surveys and soil investigations should provide
information on size and shape of lot, surface
conditions, slopes, rock outcroppings, underlying
soils, water table, access to site, utilities available,
possible interferenceswith construction operations,
and neighbors and adjoining construction. In
addition, the possible effects of building
construction on neighbors and adjoining
construction should be determined.
The goal may be statedsuccinctly as:to adaptthe
building to the site orthe site to thebuildingto meet
the owner’s goal for the building.
Objectives
Start of a listing of objectives depends on whether
or not a site has been selected. When a site has not
been selected, one objective is to select a site that
gives designers freedomto design a building that
meets the owner’s goal efficiently and
economically. Given a site, one objective is to
choose sizes, shape and orientation of the building
to make the most efficient use of the site. Other
objectivesthenmay be listed to give detailson what
is required ofthe building and site.Includedshould
be the important objective of selecting the most
economicalfoundation systemfor the building size
and the site surface and subsurface conditions and
for meeting requirements for supporting super-
structure walls and columns.
Constraints
Numerous constraints may be imposed on site
adaptation and foundation design. Among the most
important are the lot size and shape, surface and
subsurfaceconditionsthatmake building design and
construction difficult orcostly,locationsofbuilding
walls and columns,site gradingand drainage,depth
of excavation required and cofferdams needed, and
provision ofaccess to the lot and the building.Also
important are considerationsthathave tobe givento
community relations, neighboring construction,
building-code requirementsandzoning regulations.
Synthesis and Analysis
Schematics ofthe superstructure should beprepared
to meet site-foundation systemobjectivesas wellas
superstructure objectives. At the same time, the
schematics should satisfy the constraints imposed
on both the site-foundation system and the
superstructure. Analysis of the proposed design
should verify that the objectives and constraints are
indeed met.
If the ownerapproves the schematics,preliminary
designs ofalternative foundation systems should be
developed. Costs of these systems should then be
estimated.
Value Analysis and Appraisal
The benefits and costs ofthe alternative foundations
should be compared. The evaluation should lead to
selection ofthe optimumtype offoundations forthe
building site.Then,the optimumfoundations ofthe
chosen type should be designed. Inasmuch as the
foundations are the final subsystemin the sequence
of subsystems composing the building system, the
type offoundations selected forthe preliminary de-
sign will be unaffected by the superstructure
preliminary design, unless it is changed from that
shown in the schematics.
severaltopics covered in this chapter.Topicspecific
references relating toindividualchaptersections are
F. Merritt, Building DesignandConstruction Handbook, 4th
ed., McGraw-Hill, 1982.
McGraw-Hill, 1982.
J. Ambrose,Simplified Design of Building Foundations,
J. De Chiara andd L. E. Koppelman, Time-Saver Standards
for Site Planning, McGraw-Hill, 1984.
EXERCISES
The following questions andproblems are provided
for review ofthe individualsections ofthe chapter.

Section 7.1
1. Why do constructionplansfora building on one
site have to be revised for use for an identical
building on a different site?
2. An owner has purchased a 20,000-sq ft site for
an office building.Studiesshowthe need forat
least 25,000 sq ft of floor area for the building.
What effect will this have on design of the
building?
3. What site ofeachofthe following pairs should a
designer recommend for a large factory?
(a) Triangular lot or square lot, both with the
same area.
(b) Level lot or one with a 2% slope.
(c) Lot with rock at the surface or one with
rock about 20 ft below the surface.
(d) Lot on a two-way service road one half
mile from a freeway entrance/exit or a lot
on a one-way service road midway
between entrance/exits one mile apart.
4. Describe at least three ways in which zoning
affects selection of a site for:
(a) A one-family dwelling.
(b) A factory.
(c) A high-rise office building.
Section 7.2
5. An architect is recommending to a client
purchase of a ten-acre parcel for development
as a shopping center. What map should be
examined to determine:
(a) The potential market to be served by the
shopping center?
(b) Availability of water, sewers, electricity
and gas?
(c) Access roads?
(d) Who owns adjoining property?
(e) Current occupancy usage of nearby
properties?
(f) Whether zoning would permit a shopping
center to be built?
6. Who should prepare the survey plan for a site?
Section 7.3
7. What two materials ordinarily take up the void
in a soil?
8. What are the principal differences between
cohesionless and cohesive soils?
9. If the specific gravity ofthe solid particles in a
soilis 2.65 and the tested void ratio is 0.3,what
is the unit weight of the dry soil in lb/ft3
?
10. What is the difference between a well- graded
soil and one that is:
(a) uniformly graded?
(b) gap-graded?
11. What are the various factors to beconsideredin
establishing thedesignunit bearing pressurefor
bearing footings?
12. What particularconditions make settlements of
increased concern in foundation design?
13. What is the difference between active and
passive lateral soil pressure?
14. How is frictional resistance determined
differently for sand and clay soils?
Section 7.4
15. A wall footing is to support a thick,reinforced
masonry wall. Besides consideration of
allowable bearing pressure, what should be
noted in establishingthe footingdimensions?
16. A one storybuildingwith shallowfootings is to
have footings bear on silty sand at
approximately 2 ft belownaturalgrade.Based
on data fromTable 7.2, find:
(a) Required width fora wall footing; load is
2.4 kips/ft; footings 12 in. thick.
(b) Side dimension for a square column
footing; column load is 80 kips; assume
footing 16 in. thick.
Section 7.5
17. What are the principal considerations that
influence a decision to use deep foundations
instead of a shallow bearing foundation?
18. Why are piles usually placed in groups?
19. What soil conditions make the installation of
piles or piers difficult?
20. What is the purpose of a belled bottomon a
drilled pier?
Section 7.6
21. What is meant by the term “equivalent fluid
pressure”?
22. Why is it desirable to have the load resultant
coincide with the plancentroidofan abutment?
23. What are some means for bracing of pile and
pier foundations for lateral load effects?

24. What is the difference betweenpole frame and
pole platformconstruction?
Section 7.7
25. In developing plans for site grading, why is it
desirable to balance the cuts and fills?
26. What are some positive changes that may be
effected by soil modification?
27. What considerations must be made in de-
veloping the site with regard to water runoff?
28. What site design considerations may be af-
fected by accommodation of service lines for
utilities?
29. Describe some of the relations between de-
velopment of landscaping and design of the
building and its foundations.
Section 7.8
30. What are the purposes of foundation walls?
31. What are the purposes of grade beams?
32. What are the purposes of cofferdams?
33. Describe the steps in forming a deep foun-
dation with a sheetpile cofferdam.
34. Describe the slurry-trench method of con-
structing a foundation wall.
35. How can a buildup of hydrostatic pressure in
permeable soil against a foundation wall be
prevented?
36. Under what conditions can horizontal bracing
between parallel foundation walls be
considered safe?
Section 7.9
37. What is the most economical method, when it
works, for dewatering an excavation?
38. Where should deep wells be placed to dewater
an excavation?
39. Describe the installationofa wellpoint system
for dewatering an excavation.
Section 7.10
40. What soilproperties can usually be adequately
determined by field tests?
41. What soilproperties require laboratorytests
for reliable determination?
42. What data are most significant forestablishing
the engineering design criteria for:
(a) sand?
(b) clay?
(c) bedrock?
43. Describe the problems involved in deciding
what kinds of investigations to make and how
and when to make them for the foundation
design of a large building project on an
extensive site in an area with no history of
building construction.

201
Chapter 8
Structural Systems
Structural systems are major subsystems incor-
porated to resist the loads in and on a budding.The
prime function of the systems is to transmit safely
the loads from the upperportion,orsuperstructure,
of the building to the foundations and the ground.
Floors, ceilings and roofs may serve simply as
working surfaces or enclosures, which transmit
loads to a structural system. More economically,
these building componentsmay also serveas part of
the structural system, participating in the load-
carrying function. Similarly, partitions and walls
may serve simply as space dividers and fire stops.
Again, these components may serve also
economically as part of the structural system. The
systems design approach encourages such
multipurpose use of building components.
Comprehension of the role of structural systems
requires a knowledge of:
1. Types and magnitudes of loads that may be
imposed on a building
2. Structural materials and their characteristics
3. Structural analysis and design theory and
practice
4. Types of structural systems, their behavior
under load and probable life-cycle cost
5. Methods of erecting structural systems
Structural analysis and design lie in the province
of specialists,called structuralengineers.They may
serve âs independentconsultantstothe prime design
professionalfor a building or,preferably,as part of
the building team. The scope of structural
engineering is broad and complex. This chapter
therefore can only describe briefly the most
significant aspects of structural systems.
8.1. BUILDING LOADS
Loads are the externalforces actingon a buildingor
a componentofa building.They tendto deformthe
structure andits components,although in a properly
designed structure, the deformations are not
noticeable.There are many ways in which loads are
classified. The more important classifications are
described below.
Types of Stress
One method classifies loads in accordance with the
deformation effect on the components resisting
them. Thus,the type ofload depends on the way in
which it is applied to a component: Tensile forces
tend to stretch a component. Compressive forces
squeeze a component.Shearing forces tend to slide
parts of a component past each other (a cubical
element becomes a parallelepiped). (See Fig. 8.1.)
These forces occur because motion produced by
loads is required to be negligible. Hence, when a
load is applied to a structural component, an equal
and opposite reaction must also be developed to
maintain static equilibrium. The function of a
structural component is to re-

202 Building
Engineering and
Systems Design
These basic
force actions
Produce
these
deformations
sist the load and
its reaction, and
in so doing, the
component is
subjected to
tension,
compression or shear, or a
combination ofthese.The reaction may be supplied
by other structural members, foundations or
supports external to the building.
Laws of Equilibrium. Because the reaction
prevents translatory motion, the sum of all the
external forces acting on a structural member in
equilibrium must be zero. If the external forces are
resolved into horizontal components Hl H2,. . . and
vertical components Vi ,v2, • • • r then
ZHi = 0 ZVị = ồ i= 1,2,... (8.1;
Because the reaction to a load also prevents
rotation, the sum of the moments of the external
forces about any point must be zero:
2M=0 (8.2)
Now imagine a structural member cut into two
parts but with each part restrained frommotion by
reactions with the other part. These reactions are
called stresses. They are the internal forces in a
structural member that resist the loads and external
reactions.Becauseeachofthe two partsare in static
equilibrium, the laws of equilibrium expressed by
Eqs. (8.1) and (8.2) hold for each part.
Because loadsare known,these laws oftenmay be
used to determine internal stresses and external
reactions.Forexample, Eqs. (8.1) and (8.2) may be
used to determine three unknowns in any
nonconcurrentcoplanarforce system.The equations
may yield the magnitude of three forces for which
the direction and point ofapplication are known,or
the magnitude,direction and point ofapplicationof
a single force.
As an illustration of the use of the laws of
equilibrium, the reactions of a simple beamwill be
computed.Line AB in Fig.8.2tf represents the beam,
which is shown to have a 20-ft span.A support at A
cannot resist rotation nor horizontal movement. It
can supply only a vertical reaction Rị. A support at
B cannot resist rotation.It can supply a reactionwith
a horizontalcomponent Hand a verticalcomponent
R2. A 10-kip load (10,000 lb) is applied at a 45° an-
gle to the beam at c, 5 ft from A. The load has
horizontal and vertical components equal to 7.07
kips (see Fig. 8.2/?). There are therefore three
unknown reactions to these components, Rị,R2 and
H, to be determined fromEqs. (8.1) and (8.2).
Because the sumofthe horizontalcomponents of
the external forces must be zero, H must be equalto
the 7.07-kip horizontal component of the load but
oppositely directed (see Fig. 8.2/?). To make the
sum of the vertical components of the external
forces vanish: R J +
Fig. 8.1. Force actions and deformations.

Structural Systems 203
R2 — 7.07 = 0, where the negative sign is assigned
to the downward acting force. To apply Eq. (8.2),
moments are taken about B, which makes the
moment arms of R2 and the horizontal forces equal
to zero. The result is 207? J - 15 X 7.07 = 0, from
which Rị = 5.30 kips. Substitution in the equation
for the sumof the vertical forces yields R2 - 7.07 -
5.30 = 1.77 kips.
If moments are taken about another point, say A,
the result will not be anotherindependent equation.
The calculations, however, will be a check on the
preceding results: 207?2 " 5 X 7.07 = 0, from which
again R2 = 1.77 kips.
Static and Dynamic Loads
Another classification method for loads takes into
account the rate of variation of load with time.
Static loads are forces that are applied slowly to a
building and thenremain nearly constant.Weight of
building components,such asfloors androof,is one
example.
Dynamic loads are forces that vary with time.
They include moving loads, such as automobiles in
a garage; repeated,andimpact loads. Repeatedloads
are forces that are applied many times and cause the
magnitude and sometimes also the direction of the
stresses in a component to change. Forces from a
machine with off-balance rotating parts are one
example. Impact loads are forces that require a
structure or a component to absorb energy quickly.
Dropping of a heavy weight on a floor is one
example.
Distributed and Concentrated Loads
Another classification method for loads takes into
accountthedegree towhich a loadis spreadout over
a supporting member and the location of the load
relative to an axis passing through the centroid of
sections of the member.
Distributed loads are forces spread out over a
relatively large area of a supporting member.
Uniformly distributed loads are those that have
constant magnitude and direction. Weight of a
concrete floorslab ofconstantthickness and density
is one example.
Concentrated loads are forces that have a small
contact area on a supporting memberrelative to the
entire surface area. One example is the load froma
beamon a girder supporting it. Concentrated loads
and loads that for practical purposes may be
consideredconcentratedmay be furtherclassified as
follows:
An axialloadon a sectionofa supportingmember
is a force that passes through the centroid of the
section and is perpendicular to the section.
An eccentric load on a section of a supporting
member is a force perpendicular to the section but
not passing through its centroid.Such loads tend to
bend the member.
A torsional load on a section of a supporting
member is a force offset from a point, called the
shear center,ofthe section.Suchloads tend totwist
the member.
Design Loads
Still another classification method is one generally
employed in building codes.It takes intoaccount the
nature of the source of the load.
Dead loads include the weight of a building and
its components and anything that may be installed
and left in place for a long time.
Fig. 8.2. Simple beam with inclined load.

Table 8.1. Minimum Design Dead Loadsfor Buildings
Type of Construction Psf
Ceilings
Plaster (on tile or concrete)
Suspended gypsum lath and plaster
Concrete slabs
Stone aggregate, reinforced, per inch of thickness
Lightweight aggregate, reinforced, per inch of thickness Floor
finishes
Cement, per inch of thickness
Ceramic or quarry tile, 1-in.
Hardwood flooring, 8-in.
Plywood subflooring, 1-in.
Resilient flooring (asphalt tile, linoleum, etc.)
Glass
Single-strength
Double-strength or 8 "in* plate
Insulation
Glass-fiber bats, per inch of thickness
Urethane, 2-in.
Partitions
Gypsum plaster, with sand, per inch of thickness
Gypsum plaster, with lightweight aggregate, per inch
Steel studs, with plaster on two sides
Wood studs, 2 X 4-in., with plaster on one side
Wood studs, 2 X 4-in., with plaster on two sides
Roof coverings
Composition, 4-ply felt andgravel
Composition, 5-ply felt andgravel
Shingles
Asbestos-cement
Asphalt
Wood
Walls
Clay or concrete brick, per 4-in. wythe
Concrete block, 8-in. hollow, with stone aggregate
Concrete block, 8-in. hollow, lightweight aggregate
Gypsum block, 4-in. hollow
Waterproofing
5-ply membrane
5
10
12.5
9
12
12
4
1.5
2
1.2
1.6
0.5
1.2
8.5
4
18
11
19
5.5
6
4
2
3
33-46
55
35
12.5
5
Materials Lb per cu ft
Ashlar masonry
Granite
Limestone
Marble
Sandstone
Cement,portland, loose
Concrete, stone aggregate, reinforced
Steel
Wood
Douglas fir
Pine
165 135-165
173
144
90
150
490
40
33-50

Live loads include occupants and installationsthat
may be relocated,removedorapply dynamic forces.
Impact loads are dynamic forces applied by live
loads. Because they are considered related to live
loads,impact loads generally are taken as a fraction
of the live loads causing them.
Wind, snow and seismic loads are forces caused,
respectively,by wind pressure,weight ofsnowand
inertia in earthquakes. Snow loads usually are
treated as additional dead load, whereas the other
two types may be considereddynamic loads ormay
be taken into account by use of approximately
equivalent static loads.
In design, structural engineers apply the
maximum probable load that may occurorthe load
required by the applicable buildingcode,whichever
is larger.Tables 8.1through 8.4illustrate thetype of
data that might be given in building codes. More
general comprehensive design data on loads are
given in the American National Standards Institute
Building Code Requirements for Minimum Design
Loads in Buildings and Other Structures.
8.2. DEFORMATIONS
OF STRUCTURAL MEMBERS
Section 8.1 points out that loads cause a structural
member to deform. In a properly designedmember,
the deformations produced by designloads are very
small. In tests, though, large deformations can be
produced.
Tension and Elongation
Figure 8.3a shows a straight structural member in
static equilibriumunderthe actionofa pairof equal
but oppositely directed axial tensile
Table 8.2. Minimum Design Uniformly DistributedLive Loads, ImpactIncluded*
Occupancy or use Psf
Auditoriums with fixed seats 60
Auditorium with movable seats 100
Garages, for passenger cars 50
Hospitals
Operatingrooms, laboratories and service areas 60
Patients’ rooms, wards and personnel areas 40
Libraries
Reading rooms 60
Stack areas (books and shelving 65 lb per cu ft) 150
Lobbies, first floor 100
Manufacturing 125-250
Office buildings
Corridors above first floor 80
Files 125
Offices 50
Residential
Apartments andhotel guest rooms 40
Attics, uninhabitable 20
Corridors (multifamily and hotels) 80
One- and two-family 40
Retail stores
Basement and first floor 100
Upper floors 75
Schools
Classrooms 40
Corridors 80
Toilet areas 40
*See local building code for permittedreductions for large loaded areas.

Table 8.3. Pressures, psf, for Windswith 50-Year Recurrence Interval
Exposures
Height zone, ft
above curb
110-mph basic wind speed*2
(Coastal areas, N.w. and S.E.
United States)
90-mph basic wind speed*2
(Northern and central United
States)
80-mph basic wind
speed*2
(Other parts of the
United States)
Ab
Bc
cd
Ab
Bc
cd
Ab
Bc
cd
0-50 20 40 65 15 25 40 15 20 35
51-100 30 50 75 20 35 50 15 25 40
101-300 40 65 85 25 45 60 20 35 45
301-600 65 85 105 40 55 70 35 45 55
Over 600 85 100 120 60 70 80 45 55 65
*At 30-ft height above ground surface.
^Centers of large cities and rough, hilly terrain. ^Suburban regions, wooded areas and rolling ground. ^Flat, open
country or coast, and grassland.
Table 8.4. Roof Design Loads, psf, for Snow
Depth with 50-Year Recurrence Interval
Regions
(other then mountainous)**
Roof angle with
horizontal, degrees
0-30 40 50 60
Southern states 5 5 5 0
Central and northwestern states 10 10 5 5
Middle Atlantic states 30 25 20 10
Northern states 50 40 30 15
a
For mountainous regions, snow load should be based on
analysis of local climate and topography.
forces T. Note that the arrows representing T are
directed away from the ends of the member. As
indicated in Fig.8.3ớ, the forces stretch the member.
The elongation occurs in the direction of the forces
and its magnitude is shown as e. Tests and
experience indicate that for a specific member, the
larger the magnitude of T the larger e will be.
Compression and Buckling
Figure 8.3Z? shows a straight structural member in
static equilibriumunderthe action ofa pair of equal
but oppositely directe4 axial compressive forces c.
Note that the arrows representing c are directed
toward the ends of the member. Two cases must be
Fig. 8.3. Deformation effects of force actions, (a) Tension. (Ô) Compression of short element, (c) Compres sion
of slender element. (Ờ) Shear.

recognized: short compression members and
columns.
A short compression memberis one with length L
in the direction of c not much larger than the
dimensions of the member perpendicular to the
length.As shownforthe short memberin Fig. 8.3/?,
c causes the member to shorten an amount e in the
direction ofc. Tests and experience indicate thatfor
a specific member,the largerthe magnitude ofc,the
larger e will be.
A column is a compression memberwith length L
in the direction ofc much largerthan the dimensions
of the member perpendicular to c. For small values
of c, the column may behave in the same way as a
short compression member; but if c is made larger,
the central portion of the member will move
perpendicularto the length (see Fig.8.3c). This sort
of movement is called buckling.A specific value of
c, called the Euler load, will hold the column in
equilibrium in the buckled position. Larger loads
will cause an increase in buckling until the column
fails. Tests and experience indicate,however,that a
relatively small force applied normalto the lengthof
the column at an appropriate point can prevent
buckling. This observation indicates that proper
bracing can stop columns frombuckling.
Shear
The rectangle in Fig. 8.3J may represent a structural
member, such as a short bracket, or an element
isolated fromthe interiorofa structuralmember.The
vertical arrow directed downward represents a
shearing force V. For equilibrium, an equal but
oppositely directed verticalforce must be provided,
by an external reaction in the case of the bracket or
by a shearstress in the case ofthe internalelement.
These forces tend to make vertical sections of the
member slide past each other.As a result,one edge
of the rectangle moves a distance e relative to the
other edge. Tests and experience indicate that the
larger the magnitude ofV, the larger e will become.
In Fig. 8.3d, the load V and its reaction are shown
a distance L apart. Thus, they forma couple with a
moment VL in the clockwise direction. For
equilibrium, a counterclockwise moment also equal
to VL must be provided by external forces or by
stresses. These are indicated in Fig. 8.3d by the
dashed-line horizontalarrows V'.Fromthis it may be
concluded that if shears act on an element in one
direction, shears must also act on the element in a
perpendicular direction.
Load-Deformation Curves
To study the behavior of a member, tests may be
performed on it to measure deformations as loadsare
increased in increments. For graphic representation
of the results, each measured deformation may be
plotted forthecorrespondingloadproducingit.Ifthe
points are connected with a line, the result is a load-
deformation curve, also known as a load-deflection
curve. While the curve provides information on the
structural behavior of the member, the results are
applicable only to that specific member. For more
generally applicable results of such tests, the
concepts ofstress and strain are more useful.These
are discussed in Sec. 8.3.
8.3. UNIT STRESSES AND STRAINS
Deformation as described in Sec. 8.2 is the total
change produced by loads in the dimension of a
member in the direction ofthe loads.Deformation is
also referred to as strain.
Unit strain,orunit deformation,in anydirection at
any point in a structural member is the deformation
per unit of length in that direction.
Types of Unit Strain
Consider the structural member in Fig. 8.3«
subjected to axial tensile forces, which cause an
elongatione ofthe member.If the unit strains can be
consideredconstantalong themember,then the unit
strain at every pointcan beobtained bydividinge by
the length L; that is, the tensile unit strain et in the
direction of T

equals
e __
et = l (8.3)
Considernowthe structuralmemberin Fig. 8.3Z?
subjectedto axialcompressiveforces,which cause a
shortening e ofthemember.Again,ifthe unit strains
ec can be considered constant along the length L of
the member, the compressive unit strain in the
direction of c equals
- Ỉ (8 4)
Finally, consider the rectangular element in Fig.
8.3J subjectedto shearing forces.Ifthe deformation
e is divided by the distance L over which it occurs,
the result is the angular rotation 7, radians, of the
sides of the rectangle when it is distorted into a
parallelogram.Thus,the shearing unit strain is given
by the angle
T = f (8-5)
In general,unit strainsare not constant in a loaded
structural member. They actually represent the
limiting value ofa ratio giving deformation perunit
length.
Unit Stresses
Section 8.1 defines stress as the internal force in a
structural member that resists loads and external
reactions.
Unit stressis the load perunit ofarea at a point in
a structural member and in a specific direction.
Consider the structural member in Fig. 8.3fl
subjected to horizontal axial tensile forces T.
Imagine the member cut into two parts by a vertical
section and still maintained in equilibrium. Thus,
each cut end must be subjected to a stress equalbut
opposite to T that is supplied by the reaction of the
other part. Assume now that the unit stresses are
constantovereach cut end (see Fig.8.4fl). Then,by
the definition ofunit stress,the productof A,the area
ofthe cut end,and the unit tensile stress / must equal
T, for equilibrium. So, for constant unit tensile
stress.
f, = (8.6)
Imagine nowthe structuralmemberin Fig. 8.3Z?,
subjected to horizontal axial compressive forces c,
cut into two parts by a vertical section and still
maintained in equilibrium. Assume that the unit
stresses are constant over each cut end (see Fig.
8.4Z?). Then, from the requirement of equilibrium,
the unit compressive stress equals
(8.7)
where A is the area of the cut end.
Tensile and compressive stresses are sometimes
referred to as normalstresses,becausethey acton an
area normal to the loads.Underthis concept,tensile
stresses are considered as positive
normal stresses andcompressivestresses as negative
normal stresses.
Shearing unit stress acts differently.The area over
Fig. 8.4. Development of unit stresses, (a) Tension stress, (b) Compressive stress, (c) Shearing stress.

which this type of stress acts is the sliding area and
therefore must be taken in the direction of the shear
force. Consider, for example, the element of a
structural member represented by a rectangle with
sides of length L and L' in Fig. 8.4c. A downward
shearing force V must be counteracted, for
equilibrium, by upward shearing unit stresses fvy. If
the sliding area A = L’t, where t is the thickness of
the member and the unit shearing stresses are
considered constant over A, then for equilibrium
L'tfvy = V. So for constant unit shear,
fVy = ^t (8.8)
Also,forequilibrium, the element must be subjected
to a horizontal shear V', which is counteracted by
horizontal unit shearing stresses fvx. These stresses
act over an area Lt. Hence,
fvx=Yt (8.9)
In addition, for equilibrium, the couple VL must
equal the couple V’L or (L'tfVy)L = (Ltfvx)L'.
Division by LtL' yields
fvy=fvx (8.10)
Consequently, the unit shearing stresses in per-
pendicular directions are equal. They therefore can
be represented simply by fv.
One othertype ofunit stressshould be considered
at this point.This type ofstress,called bearing stress,
is the same type discussedin Chap.3as the pressure
under a spread footing. Figure 8.5a shows a load p
applied to a structural member 1, which, in turn,
transmits the
I 1 I I 1 I if+1+
777/77777777/ HTH WZZ>Z7Z/Z/
2
Afb
2
(a) (b) (c)
Fig. 8.5. Bearing stress, (a) Load presses member 1
against member 2. {b} Unit bearing stress on member 1.
(c) Unit bearing stress on member 2. load to a second
structural member 2 over a bearing area A. As
indicated in Fig. 8.5/?, the reaction of 2 on 1 is a
bearing stress fh, assumed constant over A. For
equilibrium, Afh = p. Then,the bearing stresson 1is
f„ = -A (8.11) A
Also,forequilibrium,the reaction of1on 2(see Fig.
8.5c) is a bearing stress//,,oppositely directed,given
by Eq. (8.11).
In general, unit stresses are not constant in a
loaded structural member but vary from point to
point. The unit stress at any point in a specific
direction is the limiting value of the ratio of the
internal force on any small area to that area, as the
area is taken smaller and smaller.
Stress-Strain Curves
To study the behavior of a structural material, load
tests are performed on a specimen of standard size
and shape.Formaterials that havebeenin use a long
time, the specimen size and shape generally are
taken to accord with the requirements of an
applicable method of test given in an ASTM
specification. In these tests, loads are increased in
increments andthe deformationis measuredforeach
load. Then, unit stresses are computed from the
loads, and unit strains from the deformations. For
graphic representation ofthe results,eachstrain may
be plotted for the corresponding unit stress. If the
points are connected by a line, the result is a stress-
strain curve.
While a load-deflection curve provides infor-
mation on the behavior under load of the specific
member tested, a stress-strain curve supplies
information on the mechanical properties of the
material tested. This information is applicable to
practically any size and shape of structural member
made of the material. Stressstrain curves will be
discussed in more detail later.
SECTIONS 8.1-8.3
References
ANSI, American National Standards Minimum DesignLoads
for Buildings and Other structures, American National
Standards Institute, New York.

H. Parker andJ. Ambrose, SimplifiedMechanics and Strength
of Materials, 4th ed., Wiley, New York, 1986.
R. Gytkowski, Structures: Fundamental Theoryand Behavior,
2nd ed., Van Nostrand Reinhold, New York, 1987.
Wordsand Terms
Buckling
Deformation
Elongation
Force, types of,actions
Load: dead, live, static,dynamic, wind, snow, seismic, impact,
distributed, concentrated
Strain
Stress
Unit stress
Function of structure; structural role of building construction
components.
Aspects of understandingof structures.
Types of stresses; nature of unit stress; forms of deformation.
Loads: sources, effects, measurement.
8.4. IDEALIZATION OF
STRUCTURAL MATERIALS
Stress-strain curves obtained from a standard load
test of a structural material are indicative of the
behavior of structural members made of that
material. Several mechanical properties of
importance can be deduced fromsuch curves.
Material Properties and Stress-Strain
Curves
Some examples of stress-strain curves for different
materials are shown in Fig. 8.6. These were
developed from tension tests in which a specimen
was loaded in increments until it fractured.
Curve OA in Fig. 8.6iz is indicative ofthe behavior
of a brittle material. For the material tested,stress is
proportional to strain throughout the loading.
Fracture occurs suddenly at point A. The ultimate
tensile strength, or unit stress at failure, is
represented by Fu.
Ductility. The curve in Fig. 8.6Z? is indicative of
the behavior of a ductile material. Ductility is the
ability of a material to undergo large deformations
before it fractures. Initially, for the material tested,
as indicated by line OB, stress is proportional to
strain. Between points B and c, the stress-strain
curve may be irregular ornearly horizontal.Beyond
c, strains increase rapidly with little increase in
stress, or a nominal decrease, until fracture occurs.
The large deformations before fracture give ample
warning of the imminence of failure. Consequently,
ductility is a very desirable characteristic of
structural materials.
Elastic Behavior. If a material, after being
subjectedto a load,returns to its originalsize afterit
has been unloaded,it is said to be elastic.Ifthe size
is different, the material is called inelastic. The
material for which the stressstrain curve in Fig.
8.6Z? was developed is elastic up to a stress called
Fig. 8.6. Stress-strain curvesfor various materials, (a) Curve for an elastic but brittle material. (Ò) Curve for an
elastic, ductile material, (c) Curve for a material with no proportional limit.
(a)
c
o
Õ
Õ
C
D
(c)

the elastic limit. If the material is loaded to a larger
stress, it will not return to its original size when
unloaded. It has become inelastic. The curve for
slow unloading is nearly parallel to line OB, the
initial portion of the stress-strain curve. Thus, as
indicated in Fig. 8.6Z?, if the material is loaded
beyond the elastic limit until the point D on the
stress-strain curve is reached, the unloading curve
will be DE. The material will then havea permanent
set,orresidualunit strain, OE.Ifthe material is now
reloaded, the stress-strain curve will lie along ED,
back to D. It has again become elastic, but with the
permanent set OE.
The stress at which strain and stress cease to be
proportional is known as the proportional limit.
The stress Fy beyondwhich there appearsto be an
increase in strain with no increase or a small
decrease in stress is called the yield point.
The elastic limit, proportional limit and yield
point,if they exist, are located close togetheron the
stress-strain curve. For some materials,
determination of the values of these stresses is very
difficult. Furthermore,some materials do not have a
proportional limit or a recognizable yield point or
elastic limit. Figure 8.6c shows the stress-strain
curve for a material with no proportional limit and
with a yield point that is poorly defined.
For such materials, an arbitrary stress, called the
yield strength,also denoted by Fy,may be used as a
measure of the beginning of plastic strain, or
inelastic behavior. The yield strength is defined as
the stresscorresponding to a specific permanent set,
usually 0.20% (0.002 in. per in.).
The yield point and yield strengthare important in
structural design because they are used as the limit
of usefulness of a structural material. At higher
stresses, the material suffers permanent damage,
undergoes large deformations, which may damage
supportedconstruction,and is closeto failure.It has
become customary, consequently, to apply safety
factors to Fy in the determination of allowable unit
stresses or safe loads for ductile materials.
Some additional structural properties of note are
the following:
Poisson sratio(p.) is the ratio oflateralunit strain
to longitudinal unit strain in a material. Under
tension, for example, a member lengthens in the
longitudinal direction and shortens laterally. For
steelthis ratio is about0.3and forconcreteit is about
0.25.
Modulus of elasticity (E) is the ratio of normal
stress (tension or compression) to strain within the
proportional limit. On the stressstrain graph, this is
measured as the tangent of the angle of the curve
(such as line OB in Fig. 8.6Ẹ).
Toughness is the ability of a material to absorb
large amounts of energy (dynamic loading) without
failure. This is often affected by temperature,
toughness being reduced at low temperatures.
Modulus ofrigidityor shearingmodulus (G)is the
constantofproportionality whenshearing unit strain
is proportional to unit shear stress:
fv = Gy (8.12)
where
fv = shearing unit stress
y = shearing unit strain
G= modulus of rigidity, or shearing modulus of
elasticity
It is possible to determine Gfroma linearstressstrain
curve when Poisson’s ratio is known, because G is
related to the modulus of elasticity in tension and
compression:
E _ _
G = _ — (8.13)
2(1 + g)
where
ỊẤ = Poisson’s ratio for the material
Idealized Structural Materials
To simplify structuralanalysis and design,structural
materials usually are represented by a simple
mathematical model. The model often assumes that
a material is homogeneous; thatis,there is nochange
in the material frompoint to

point in a structural member. Also, the model
generally assumes that the materialis isotropic,that
it has the same properties in all directions.
For some materials, additional assumptions are
made. Some common ones for structural steel, for
example, is that the material has the same modulus
of elasticity in compression and tension and is
ductile and tough.
Hooke’s Law. Figure 8.7 shows the stressstrain
curve in tension for an idealized ductile, linearly
elastic structuralmaterial.Forthis material, Hooke’s
law applies up to the yield stress
, ........
Hooke’s law states that unit strain is proportional
to unit stress. The law can be represented by the
equation
f=Ee
where
f = unit stress
e = unit strain
E = modulus of elasticity
(also called Young’s modulus)
Accordingly, line OB, the initial portion of the
stress-strain curve, in Fig. 8.7 is a straight line with
slope E. At point B, the stress is Fy.
Plastic Behavior. The portion of the stressstrain
curve beyond B often is taken as a hori-
F
y zontal line, such as BC in Fig. 8.7. This is a
conservative assumptionforductile materials,since
they require at least a small increase in stress to
produce a large increase in strain.In the range BC,
the idealized material is said to be plastic.
This property of a material is important, because
it affects the ultimate strength of a structural
member. When a portion of the member is stressed
under load to Fy, the member does not necessarily
fail when the load is increased. That portion of the
member yields; that is, undergoes large
deformations,with the increase in load.Nonetheless,
if the rest of the member is not stressedto Fy and is
so constructed that the large deformations do not
cause failure, the member can sustain larger loads
than that causing Fy in only a few places. Thus,
plastic behavior can increase the load-carrying
capacity of the structural member beyond that for
local departure fromthe elastic range.
Departure of Actual Materials from Ideal
Few actual materials can be accurately represented
by the idealized structural material. Consequently,
for these materials,the mathematicalmodelmust be
modified.
Sometimes, the modification may be minor. For
example, for a ductile material with no proportional
limit, such as a material with a stress-strain curve
like that shown in Fig. 8.6c, a secant modulus may
be substituted for the modulus of elasticity in the
assumption of a stress-strain curve observing
Hooke’s law. The secant modulus is the slope of a
line, such as OG in Fig. 8.6c, from the origin to a
specified point on the actualstress-strain curve.The
point is chosentomake the shape ofthe linearstress-
strain curve for the idealized material approximate
that in Fig. 8.6c.
Unit Strain
Fig. 8.7. Stress-strain curve for an idealized ductile,
linearlyelastic material.
Design Bases for Structural Materials
Either of two methods is generally usedin designof
structures. In one method, allowable or working
stresses are established. Under design loads, these
stressesmay notbe exceeded.In thesecondmethod,
called ultimate-strengthdesign,limit designorload-
factor design, design loads are multiplied by
appropriate factors and the structure is permitted to
be stressed or strained to the limit of usefulness
under the factored loads.
Allowable stresses fora specific material usually
are determined by dividing the yield strengthorthe
ultimate strengthby a constant safety factorgreater
than unity. A smaller safety factor is permitted for
such combinations ofloadingas dead andlive loads
with wind or seismic loads.
When ultimate-strength design is used, load
factors greaterthan unity are so chosenas to reflect
the probability ofoccurrence ofexcessive loadings.
For example, a larger factor is applied to live loads
than to dead loads,because ofthe greaterprobability
(8.14)

of maximum design live loadings 'being exceeded
than of design dead loads being exceeded.
8.5. STRUCTURAL MATERIALS
The idealized structural material described in Sec.
8.4 is homogeneous and isotropic. It exhibits
linearly elastic behaviorup to a yield strength Fy.If
the material also is ductile, it exhibits plastic
behavior under loads greater than that causing Fy.
For structural analysis and design, mathematical
models predict the behavior of structures made of
the idealized structural material.
Actual materials, however, may not be repre-
sentedaccuratelyby the idealization.Consequently,
the idealized material and the mathematical models
must be revised to improve the accuracy of
predictions of structural behavior. For this to be
done, a knowledge of the properties of structural
materials in use is required.
In this section,the properties ofsome commonly
used structural materials are described briefly. In
following sections, mathematical models for
predictions of the behavior of these materials are
discussed.
Material and Design Specifications
Aftera material has been tested thoroughly andhas
been usedforseveralyears,a standard specification
is written for it. Material and test specifications of
ASTM (formerly American Society forTesting and
Materials) are often used for structural materials.
Building codes often adopt such specifications by
reference. Standard design specifications also are
available for commonly used structural materials.
Design specifications usually are developed and
promulgated by trade associations or engineering
societies concerned with safe, economical and
proper uses of materials. Examples of such
specifications are: for structural steel—the
American Institute of Steel Construction; for
reinforced concrete—the American Concrete
Institute;and forwood construction—the American
Institute of Timber Construction.
Structural Steel
Steel is a highly modifiable material due to the
process of production of the raw material plus the
various processes of production of finished
products. Steel is basically an alloy of iron and
carbon. For structural steel the carbon content is
kept quite small,generally less than0.35%,since the
carbon tends to decrease ductility and weldability,
although it increases the strength of the iron. Other
metals are often alloyed to the carbon and iron to
produce particular properties of the finished steel,
such as high strength, corrosion resistance,
weldability, and toughness.
Structuralsteels used in building constructionare
often specified by reference to ASTM spec-
ifications. For example, steels meeting the re-
quirements of ASTM A36, Standard Specification
for Structural Steel, are called A36 steel, which is
consideredas sufficientidentification.Some ASTM
specifications apply to steel with common
characteristics but with different yield points. In
such cases, steels with the same minimum yield
point are grouped in grade, with the grade
designation being thevalue ofthe yield point in ksi.
The plates and shapes used in structural appli-
cations are produced by hot rolling material
produced in steelmaking. This hot rolling tends to
improve grain structure in the direction of rolling.
Consequently,ductility and bendability are betterin
the direction ofrolling than in transverse directions.
Also,because more rolling is needed toproduce thin
steel products

than thick ones, thin material has larger ultimate
tensile strength and yield stress than thickmaterial.
Consequently, ASTM specifications often specify
higher minimum yield stresses as thickness is
decreased(see Table 8.5). This,in turn,permits use
of larger allowable unit stresses or load-carrying
capacity in design as thickness is decreased.
In accordance with the chemical content,
structural steels usually used in building con-
struction are classified as carbon steels; high-
strength, low-alloy steels; and high-strength, heat-
treated, low-alloy steels. As indicated in Table 8.5,
high-strength,low-alloy steels have greaterstrength
than carbonsteels.Also,the heat-treatedsteelA514
has greater strength than the other two classes of
steel.The greaterthe strength,however,the greater
the cost per unit weight of the steel.
The structural steels have stress-strain curves
similar to that shown in Fig.8.6c. Figure 8.8 shows
to an enlarged scale the portions of the curves for
some structural steels in the elastic range and
somewhat beyond. The shapes of these curves
indicate that the stress-strain curve in Fig.8.7forthe
idealized structural material
ASTM
specification
Thickness, in.
Minimum tensile
strength, ksi
Minimum yield point or
strength, ksi Relative
corrosion
resistance*1
Carbon Steels
A36 To 8 in. incl. 58-80c
36 lb
A529 To 2 in. incl. 60-85c
42 1
A441 To Ẹ in cl. 70 50 2
Over Ẹ to 12 67 46 2
Over 12 to 4 incl. 63 42 2
Over 4 to 8 incl. 60 40 2
A572 Gr 42: to 4 incl. 60 42 1
Gr 45: to lị in cl. 60 45 1
Gr 50: to lị incl. 65 50 1
Gr 55: to lỵ incl. 70 55 1
Gr 60: to 1 incl. 75 60 1
Gr 65: to ị incl. 80 65 1
A242 To ị incl. 70 50 4-8
Over to 1 ị 67 46 4-8
Over 12 to 4 incl. 63 42 4-8
A588 To 4 incl. 70 50 4
Over 4 to 5 67 46 4
Over 5 to 8 incl. 63 42 4
A514 To incl. 115-135 100 1-4
Over 4 to 2 J 115-135 100 1-4
Over 2^ to 4 incl. 105-135 90 1-4
Table 8.5. Propertiesof Structural Steels
High Strength, Low-Alloy Steels
Heat-Treated, Low-Alloy Steels
^Relative to carbon steels low in copper.
^A36 steel with 0.20% copper has a relative corrosion resistance of 2.
^Minimum tensile strength may not exceedthe higher value.

can represent, with acceptable accuracy for design
purposes, the structural steels generally used in
building construction.
Steel mills use a different classification method
for steel products. Included are structural shapes
(heavy) and (light). The former applies to shapes
with at least one cross-sectional dimension of 3 in.
or more, whereas the latter applies to shapes of
smaller size, such as bars.
Shapes are identified by their cross-sectional
geometry; forexample, wide-flange or H-shapes,I-
beams, bearing piles, miscellaneous shapes,
structuraltees,channels,angles,pipe and structural
tubing (see Fig.8.9). For convenience,these shapes
usually are designatedby lettersymbols,aslisted in
Table 8.6.
A specific shape is specified by a listing in the
following order: symbol, depth and weight.
For example, W12 X 36 specifies a wide- flange
shape with nominaldepthof12in. and weight of36
lb perlin ft.Actualdimensions are listedin the AISC
Steel Construction Manual and steel producers’
catalogs. (The X symbol in the designation is a
separatorand is read “by.”).............................
Plates are designateddifferently.The designation
lists in the following order:symbol,thickness,width
and length.Forexample,PL I X 15 X2'-6" specifies
a plate I in. thick, 15 in. wide and 2 ft 6 in. long.
Properties of Structural Steels. As indicated by
the stress-strain curves of Fig. 8.8, structural steels
are linearly elastic until stressed nearly to the yield
point. Beyond the yield point, they may be
considered plastic.
A514 Steel
Fig. 8.8. Idealized stress-strain curvesfor some grades of structural steel.

Fig. 8.9. Rolled structural steel shapes and their symbols.
Table 8.6. Structural-Steel Shape Designations
Section Symbol
Plates PL
Wide-flange (H) shapes
w
Standard I-shapes
s
Bearing-pile shapes HP
Similar shapes that cannot be included
in w, s or HP M
Structural tees made by cutting
a w, s or M shape WT, ST, MT
American standard channels
c
All other channel shapes MC
Angles L
Tubing TS
Stiffness. Structural steel is the stiffest of the
commonly used structural materials. Stiffness may
be measured bythemodulusofelasticity,whichmay
be considered the unit stress required to produce a
unit strain of1 in. perin. if the material were to stay
in the elastic range.Structuralsteelshavea modulus
of elasticity ofabout 29,000 ksi (30,000 ksi often is
used in design).The modulusofelasticity is takenas
the same value in tension and compression.
Poisson’s ratio for structural steels is about 0.3.
Stiffness is important becauseit is an indicationof
the resistanceoffered by a loadedstructuralmember
to deformations and deflections.
Weight. ASTM specificationA6 specifies thatrolled
steelshallbe assumed to weigh 0.2833 lb per cu in.
Volume Changes. Steelis a goodconductorofheat
and electricity. It has a thermal coefficient of
expansion of 0.000 0065 in. per in. per °F. This is
about the same as that for concrete but much larger
than that for wood.
Corrosion. Steeltends to forman iron oxide in the
presence of oxygen and water. Unless special
alloying elements are present,the oxide is very weak
and is called rust. The process of forming the weak
oxide is called corrosion.
The rate ofcorrosionofa steeldepends onthe type
and amount ofalloying elements incorporatedin the
material. A copper-bearing steelwith at least 0.20%
copper has about twice the corrosion resistance of
ordinary carbon steels. Some steels, such as A441,
A242 and A588, are known as weathering steels
because they can offereven greaterresistance to cor-
rosion (see Table 8.5). These steels forman oxide,
but it adheres stronglyto the basemetaland prevents
further corrosion. Other steels should be protected
against corrosionby coats ofpaint orconcrete orby
cathodic protection.
Fire Protection. Structural steels also need
protection against high temperatures, because they
tend to lose strength under such conditions.
Consequently, steel members should be protected
against the effects of fire if exposure to fire is
Plate
Bar
u Beam w Column s
Uide-Flange Shapes I Beam
HP
Bearing Pile
UT ST c l*IC
Sructural Tees (Cut) Channels
Angle Shapes
Equal Unequal
Leg Leg
Structural Tubing
TS

possible. For this purpose, the steel may be coated
with insulating,fireproofmaterials,suchasconcrete,
plaster, mineral fibers and special paints. (See also
Secs. 2.2 and 6.3.)
Steel Cables. When considered a permanent part
of structural steel framework, steel cables are
considered to be in the classification of structural
steel.Cables may be used asverticalhangersorthey
may be strung between two points in a curve to
support other building components. The types of
cables used for these purposes are known as bridge
strand or bridge rope.
A strand consistsofsteelwires coiling helically in
a symmetrical arrangement about a center wire. A
rope is formed similarly but with strands instead of
wire. The wires used in forming these products are
cold drawn and do not have a definite yield point.
Safe loads on strands and rope, therefore, are
determined by dividing the specified minimum
breaking strength for a specific nominal diameter
and type of cable by a safety factor greater than
unity.
Design Rules for Structural Steels. Structuralsteel
design often is based on the AISC Specification for
the Design, Fabrication and Erection of Structural
Steel for Buildings. This specification may be
adopted as a whole by local building codes or with
some modifications.
The design rules in this specification apply to
elastic and plastic behavior of structural steels. The
rules generally assume that the steels have a stress-
strain curve similar to that of the idealized material
in Fig. 8.7 and that the modulus of elasticity is the
same in tension and compression. The specification
is included in the AISC Manual of Steel
Construction but separate copies also are available.
Fabrication. The AISCSpecification also presents
requirements for fabrication and erection of
structuralsteelframing.Fabrication is the operation,
usually conducted in a shop, of cutting steel plates
and shapes to specified sizes and assembling the
components into finished members, ready for
shipment to the building site and for erection.
The intent of steel designers is conveyed to the
fabricating shopin detail drawings. Theyusually are
prepared by shop detailers, employed by the
fabricator, from the steel designers’ drawings. The
detail drawings are generally of two types: shop
working drawings and erection drawings. Called
details, shop drawings are prepared for every
member of the framework. They provide all
information necessary forfabricating each member.
Erection drawings guide the steel erector in
constructing theframework.They showthe location
and orientation of every member, or assembly of
components, called shipping pieces, that will be
shipped to the building site.
Fasteners for Steel Connections. Components or
members may be connectedto eachotherwith rivets
or bolts or by welding. For connections with rivets
and bolts,holes must be providedforthe fasteners in
the fabricating shop. The holes must be accurately
located and ofthe propersize for the fasteners to be
used. The holes may be formed by punching or
drilling, the former being faster and less expensive.
Punching,however,is suitable only forthin material,
usually up to about 1-in. thickness forcarbon steels
and |-in. for heat-treated steel.
A rivet consists of a cylindrical shank with an
enlarged end, or head. For making a connection
between steelmembers,the rivet is heated untilit is
cherry red, placed in aligned holes in the members
and hammered with a bullriveteror a riveting gun to
form a secondhead.When the rivet cools,it shrinks,
and the two heads force theconnected members into
tight contact.
A bolt consists ofa cylindricalshankwith a head
on one end and threads on the opposite end. For
making a connection between steel members, the
bolt is inserted in aligned holes in the members and
a nut is turned on the threaded endofthe bolt shank
to hold the members in tight contact.In some cases,
washers may be required under the nut and
sometimes also underthe bolt head.Bolts generally
are used in field connections as well as in shop
connections,but rivets usually are usedonly in shop
connections, for economic reasons.
The AISCSpecification requires that specialhigh-
strength bolts be used for major connections in tall
buildings and for connections subject to moving
loads, impact or stress reversal. These bolts should
conformto ASTM specificationA325,Specification
forHigh-Strength Bolts forStructuralSteelJoints,or
A490, Specification for Quenched and Tempered
Alloy Steel Bolts for StructuralSteelJoints (for use

with high-strengthsteels).Forsuchconnections,the
high-strength bolts are highly tensioned by
tighteningofthe nuts,andthepartsofthe connection
are so tightly clamped together that slippage is
prevented by friction.
A weld joins two steelcomponentsbyfusion.It is
economical, because it reduces the number of holes
and the amount ofconnection materialneeded from
that required with fasteners. Also, welding is less
noisy than boltingorriveting.Useofwelding in steel
construction is governed by the American Welding
Society Structural Welding Code, AWS Dl.l. The
most commonly used welding methods employ a
metal electrode to strike an electric arc that supplies
sufficient heat to melt the metalto be joined,orbase
metal, and the tip of the electrode. The electrode
supplies filler metal for building up the weld.
Welds usedforstructuralsteels are eitherfillet or
groove.Fillet welds are used to join partsat anangle
with each other, often 90°. In the process, molten
weld metal is built up in the angle (see Fig. 8.10a).
Groove welds may be used to connectpartslying in
the same plane
Fig. 8.10. Welds used for structural steel, (a) Fillet weld,
(d) Complete penetration groove weld, (c) Partial
penetration groove weld.
or at an angle with each other.Forthis purpose,one
edge to be connected is cut on a slope,so that when
the edge is placed against anotheredge orsurface in
the connection, a gap, or groove, is formed. In the
welding process,molten metal is built up in the gap
(see Fig. 8.10Z? and c).Groove welds may be either
complete (see Fig.8.10Z?)orpartialpenetration (see
Fig. 8.10c), depending onthe depthofgap and solid
weld metal.
Clearances in Steel Erection. Steel designers
should select member sizes and shapes and arrange
the components so that fabrication and erection
operations can be easily and properly performed.
There should be ample clearances, for example, for
application of riveting machines, tightening of nuts
on bolts with wrenches,andwelding with electrodes
and welding machines. Another important example
is provision of ample clearances for erection of
beams between columns. Consequently, designers
should be familiar with fabrication and erection
methods, and their designs should anticipate the
methods likely to be used. In addition, designers
should anticipate conditions underwhich pieces are
to be shipped from the fabricating shop to the
building site. Lengths and widths of trucks or
railroad cars, or height limitations on shipments by
highway or railroad, may restrict the size of pieces
that can be moved. The size restrictions may
determine whether members must be shipped in
parts and later spliced, and if so, the location of the
splices.
Erection Equipment for Steel Framing. When a
piece arrives at the building site, the steel member
may be moved to storage or immediately erected in
its final position.Often,the handling is done with a
crane (see Fig. 8.11). Depending on the terrain, the
crane may be mounted on wheels ortractortreads.It
carries a long boom,sometimes with anextensionon
the end,called a jib,overwhich steellines are passed
for picking up building components. Operating at
ground level,the crane can rotate and raise orlower
the boomand jib,while a drumwinds orunwinds the
lines.
Stiffleg derricks also are frequently used forsteel
erection. Such derricks consist of a rotat-

Fig. 8.11. Crane erecting structural steel. (Courtesyof
American Hoist and Derrick Company)
able vertical mast, held in position by two stifflegs,
a boompinned at the bottomof the mast, and steel
lines passing overthetopofthe boomforpicking up
building components.In erection ofa tallbuilding,a
stiffleg derrick usually is set on the toplevelofsteel
to erect the next tier and is jumped upward as
erection progresses. Thus, while use of a crane is
limited to framework with height less than that of
boom and jib—usually about 200 ft—a stiffleg
derrick can be used for framework of any height.
Otherequipment,such as guy derricks,also may be
used in a similar fashion.
Cold-FormedSteels
As mentionedpreviously,certain steelitems,though
used as structural components, are not considered
structural steel if not defined as such in the AISC
Code of Standard Practice for Steel Buildings and
Bridges. An important classification of structural
items made of steel but not considered structural
steelis cold-formed steel.Made generally ofsheet or
strip steel or of bars with small cross section, or of
combinations of these materials, cold-formed steel
members offer substantially the same advantages as
structural steel, although price per pound may be
greater, but are intended for use for light loads and
short beamor panel spans. These members can be
used as floororroofdeckor curtain walls as well as
beams and columns.
Like hot-rolled steel, cold-formed members must
be protected against corrosion. This usually is done
by painting or galvanizing. They also must be
protected against fire, and this is usually done with
concrete floor or roof decks and plaster or fire-
resistant acoustic ceilings.
Cold-formed steel members may be classified as
structural framing formed from sheet or strip steel;
deck and panels; or open-web steel joists.
Production of Cold-formed Shapes. Cold-formed
framing, deckand panels are made ofrelatively thin
steel formed by bending sheet or strip steel in roll-
forming machines, press brakes or bending brakes.
Shapes so produced may also be used in door and
window frames, partitions, wall studs, floor joists,
sheathing and molding.
Thickness of cold-formed sheet steel often is
designated by a gage number, but decimal parts of
an inch are preferable.Table 8.7 lists the equivalent
thickness in inches for gage numbers and
approximate unit weight. Thickness of strip steel is
always given as decimal parts of an inch.
Stress-strain curves for cold-formed steels are
similar to that ofthe idealized structuralmaterial(see
Fig. 8.7). Modulus ofelasticityis about 30,000ksiin
tension and compression. Hence, cold-formed steel
shapes may bedesigned by the same procedures used
for hot- rolled structural steel shapes. Local
buckling,however,is a greaterpossibility with cold-
formed shapes,because ofthe thinnermaterialused.
To account for this effect, the width or depth of a
shape used in design is reduced from the actual
dimensions, the reduction being
Table 8.7. Manufacturers' Standard Gage
for Steel Sheets
Gage No.
Equivalent thickness, inc.
Weight, psi
3 0.239 10.00

4 0.224 9.38
5 0.209 8.75
6 0.194 8.13
7 0.179 7.50
8 0.164 6.88
9 0.150 6.25
10 0.135 5.63
12 0.105 4.38
14 0.075 3.13
16 0 060 2.50
18 0.048 2.00
20 0.036 1.50
22 0.030 1.25
24 0.024 1.00
greater the larger the ratio of width or depth to
thickness.
Design ofcold-formed steelmembers generally is
based on the American Iron and Steel Institute
(AISI) Specification for the Design ofCold-Formed
Steel Members. This specification may be adopted
by building codesas a whole orwith modifications.
Cold-Formed Steel Shapes. Because cold-formed
steel is thin, it can be bent readily into desired
configurations or built up from bent shapes for
specific architectural and structural applications.
Some shapes used structurally are similar to hot-
rolled structural shapes. Channels, zees and angles
can be roll-formed in a single operation from one
piece ofmaterial (see Fig.8.12ứ to c). They can also
be provided with lips along flange edges to stiffen
the flangesagainst localbuckling (seeFig.8.12J to/).
I sectionsmay be produced byweldingtwo anglesto
a channel (see Fig. 8.12g and h) or by welding two
channels back to back (see Fig. 8.12/ and j). As
indicated in Fig. 8.12/1 and j, I sectionsalso may be
provided with stiffening lips.
Otherstructurally usefulsectionsmade with cold-
formed steelinclude the hat,openboxand Ưshapes
shown in Fig. 8.12fc to m. Made with two webs,
these shapes are stifferlaterally than the single-web
shapes in Fig. 8.12ứ to7.
Deck and panels may be produced by forming out
of one piece ofmaterial a wide shape with stiffening
configurations. The configurations may be rounded
corrugations or sharply bent ribs, such as the series
of hat shapes shown in Fig. 8.12M, sometimes used
for roof deck. Often, deck shapes are built up by
addition of a flat sheet on the underside of the hats
(Fig. 8.12ơ), for greaterstiffening,orby attaching a
series ofinvertedhat shapes,to formparallellines of
hollow boxes, or cells, which offer both greater
strength and stiffening.
Steel roof deck consists of ribbed sheets with
nesting or upstanding-seam side joints, for in-
terlocking adjoining panels,as shown in Fig. 8.12M
and o. The deck should be designed to support roof
loads applied between purlins,roofbeams ortrusses.
Floor deck may also be used for roofs.
Cellular panels generally are used for floor deck
(see Fig. 8.12/?). The advantage ofthe cellular type
is that the cells provide space in which electric
wiring and piping may be placed. This avoids
increasing the floor depth to incorporate the wiring
and piping and also conceals the unsightly network
from view. The cells also may be used for air
distribution in air-conditioning systems.
Consequently,cellulardeckis always a competitive
alternative to othertypes offloorsystems in systems
design of buildings.
Connections for Cold-Formed Steels. Components
of cold-formed steels may be interconnected with
bolts, rivets or welds in the same way as hot-rolled
structural components; but because cold-formed
steels are thin, other methods often may be
conveniently used. Arc welding, for example, may
be used to join parts with spot welds. As another
example, in fabricating shops, resistance welding
may be used because of speed and low cost. Spot
welds are formed by this process by clamping the
parts between two electrodes throughwhich an elec-
tric current passes, to fuse the parts. Projection
welding is anotherformof spot welding that may be
used.A projectionorprotuberanceis formed on one
of the mating parts, and when

the parts are brought together and current is passed
through, a weld is formed.
Bolts are convenient for making connections in
the field when loads have to be transmittedbetween
connected parts. Tapping screws may be used for
field joints that do not have to carry calculated
gravity loads. Tapping screws used for connecting
cold-formed siding and roofing are generally
preassembled with neoprene washers to control
leaking, squeaking, cracking and crazing.
Open-WebSteel Joists. These are truss-like,load-
carrying members suitable for direct support of
floors and roofs in buildings. The joists are usually
fabricated from relatively small bars, which form
continuous, zigzag web members between chords,
and the top and bottomchords may be made of bar-
size angles or shapes formed fromflat-rolled steel.
(Cold working in rolling chords ofsheet orstrip steel
increases the strength of the metal. Yield strengths
exceeding 150% of the minimum yield point of the
plain material may be obtained.) Components of
open-web steeljoists may be joined by resistance or
electric-arc welding.
Joists usedforshortspans are simply called open-
web steel joists. Such joists, however, may span up
to about 60ft.Thoseusedforlong spans, upto about
144 ft, are commonly known as long-span joists.
Both types ofjoists may be specified by reference to
specifications adopted jointly by AISCand theSteel
Joist Institute (SJI).
While SJI has standardized many aspects of
design, fabrication and erection of open-web steel
joists, exact details of specific joists vary with
different manufacturers.Some typicalarrangements
in elevation andcross sectionare shownin Fig. 8.13.
Some joists are produced with top chords that have
provisions for nailing of wood deck to them.
Open-web joists are very flexible laterally.
Consequently, they should be braced as soon as
possible aftererection and before construction loads
may be applied to them. Often, bracing
Flange
(a) (b) (c)
Channel Zee Angle
Plain Sections
(d) (e) (f)
Channel Zee Angle
or C-Section
Lipped (Stiffened) Sections
Flange
(g) (h)
I Sections
Hat Open Box u
Special Sections
Roof Deck
Fig. 8.12. Cold-formed, light-gage steel shapes.
Floor Deck

(a)
Fig. 8.13. Typical forms for open-web
steel joists (prefabricated light trusses).
of the top chord may be provided by a floor or roof
deckimmediately attachedandbystrutsbetweenthe
bottom chord and adjacent joists, or by bridging,
continuous rigid struts between the chords of one
joist and the corresponding chords of an adjacent
joist. Also, wall-bearing joists should be firmly
secured at the supports with masonry anchors.
Where joistsrest onsteelbeams,thejoistsshould be
welded, bolted or clipped to the beams.
Wood
Wood is an organic productofnature.Often,except
for drying, wood is used in its natural state.
This product ofnature offersnumerousadvantages
in structural applications as well as in such
architectural applications as interior and exterior
wall facings and floor coverings. Wood has high
strength but lowcost perunit ofweight.It is ductile
and resilient (high shock-absorptioncapacity).It can
be easily sawn to desired dimensions and bent to
sharp curvature.It canreadily be shopfabricated into
structural members, ready for shipment to the
building site for erection. Often, the light weight of
wood makes possible erection without the aid and
cost of mechanical hoisting equipment.
Wood, however, has some disadvantages in
structural applications. For example, for the same
load-carrying capacity, bulkier wood members are
needed as opposed to structural steel or concrete.
Where space is critical and heavy loads must be
supported, wood is at a disadvantage, despite lower
cost. Wood also has the disadvantage of being
combustible. This disadvantage, however, can be
overcome to some extent by use of bulky members,
which are slow burning and therefore permitted in
low buildings with nonhazardous contents,byuseof
fire-retardant treatments and by enclosure with fire-
resistant materials. But the two disadvantages
generally make use of wood structural members
impractical for high-rise buildings. In addition,
consideration must be given to the possibility that
wood can decay or may be attacked and destroyed
by insects.
Just as there are differenttypes ofstructuralsteels,
there are also different types ofwood.Forone thing,
wood from different species of trees have different
characteristics.Foranother,wood cut fromtwo trees
of the same species that grew side by side probably
would not have the same strength; and even if all
characteristics were initially the same,two pieces of
wood may developin a relatively short time different
defects that would influence strength differently.
Research and experience, though, have shown how
these differences can be taken into account.
Consequently, wood is a useful, reliable and
economical structural material.
Structure of Wood. Wood has a cellular, fibrous
structure that is responsible for many of its
characteristics. The cell walls, made essentially of
cellulose, are cemented together by lignin, another
organic substance. Positioned vertically in trees
before they are cut down, the cells range in length
from 0.25 to 0.33 in. and are about 1% as wide. A
cross section also has horizontally positioned bands
of cells called rays. In addition, because of the
manner in which trees grow, differences in cell
thickness occur between seasons and are displayed
in the cross section as annulargrowthrings.Because
of this composition, wood is neither homogeneous
nor isotropic; that is, it has different properties in
different directions.
Moisture Content. Unlike other structural ma-
terials, wood undergoes little dimensional change
directly due to temperature changes; however,
(b)

it may develop significant dimensionalchangesdue
to increase or decrease of moisture content.
Wood from a newly felled tree is called green
because the interior is wet. The wood may be
allowed to dry naturally (seasoned)ormay be dried
in a kiln. The first step in the drying process is
exodus of free water from the cavities in the wood.
Eventually,the cavitieswill contain only air,but the
cell walls, or fibers, will still be saturated. At this
fiber-saturation stage, the moisture content of the
wood may be between 25 to 30% of the weight of
the oven-dry wood.
Except for change in weight, very few of the
properties of wood, including dimensions, change
during removal of free water. If drying continues
past the fiber-saturation point, however, the cell
walls lose water, and the wood begins to shrink
across the grain (normal to the direction of the
fibers). Shrinkage continues nearly linearly as
moisture content decreases to zero. In ordinary
usage, however, moisture content will stabilize in
accordance with the humidity ofthe environment.If
humidity increases, the wood fibers will absorb
moisture and the wood will swell (see Table 8.8).
Many properties ofwood are affectedbyits moisture
content.
Defects. Wood also contains or develops defects
that influence its properties.Knots,for example, are
formed when a branch, embedded in the tree, is cut
through in the process of lumber manufacture.
Another example is slope of grain, cross grain or
deviation offiber from a line parallel to the sides of
a piece of wood. Other examples are shakes and
checks, lengthwise grain separations between or
through growth rings.
Property
Douglas fir,
coastal
Douglas fir,
inland
Southern pine,
longleaf
Southern pine,
shortleaf
Moisture content when green, % 38 48 63 81
Weight, lb per cu ft
When green 38.2 36.3 50.2 45.9
With 12% moisture 33.8 31.4 41.1 35.2
Add for each 1% moisture
increase 0.17 0.14 0.18 0.15
Shrinkage from green dimensions
when dried to 20% moisture, %a
Radial direction 1.7 1.4 1.6 1.6
Tangential dừection 2.6 2.5 2.6 2.6
Volumetric 3.9 3.6 4.1 4.1
Shrinkage from green dimensions
when dried to 12% moisture, %a
Radial dừection 2.7 2.2 2.7 2.7
Tangential direction 4.1 4.1 4.1 4.1
Volumetric 6.2 5.8 6.6 6.6
Modulus of elasticity, ksi
When green 1,550 1,340 1,600 1,390
With 12% moisture 1,920 1,610 1,990 1,760
Proportional limit, compression
parallel to grain, ksi
When green 3.4 2.5 3.4 2.5
With 12% moisture 6.5 5.5 6.2 5.1
Proportional limit, compression
perpendicular to grain, ksi
When green 0.5 0.5 0.6 0.4
With 12% moisture 0.9 1.0 1.2 1.0
Proportional limit, bending, ksi
When green 4.8 3.6 5.2 3.9
With 12% moisture 8.1 7.4 9.3 7.7
Table 8.8. Properties of Douglas Fir and Southern Pine
fl
Total longitudinal shrinkage of normal species from fiber saturation to oven dry is minor, usually ranges from 0.17
to 0.3% of the length when green.

To some extent,the deleteriouseffectsonstrength
of all these defects may be overcome by grading of
wood in accordance with the type, number and size
of defects present, so that appropriate material can
be selected for specific tasks, with appropriate
allowable stresses assigned.
Also, different wood pieces can be combined in
such a way as to average out the effects of solid
material and material with defects. For example,
severalpiecesoflumbermay be laminated,with glue
or nails, to form the equivalent of a large timber
member. Because of the low probability of defects
occurring in several components at the same cross
section, the laminated member will have much
greater strength than if it were made of a single
ordinary wood pieceofthe same size.Similarly, thin
sheets, or veneers, of wood can be bonded together
to form plywood,with a reduction in the probability
of defects being concentrated in any section.
Hardwoods and Softwoods. Trees whose wood is
used in construction may be dividedintotwo classes,
hardwoods and softwoods. Hardwoods have broad
leaves, which are shed at the end of each growing
season. Softwoods, or conifers, have needlelike or
scalelike leaves, and many of the species in this
category are evergreen.
The fact that a tree is classified asa softwood does
not mean that its wood is softer than that from a
hardwood tree. Some softwoods are harder than
medium density hardwoods. Two of the most
commonly used woods for structural purposes,
Douglas fir and southern pine, are softwoods.
Hardwoods, such as oak, maple, birch, beech and
pecan,usually are used for flooring or interior trim.
Softwood Lumber Standards. Softwood lumberis
generally produced to meet the requirements of
Product Standard PS 20-70, a voluntary standard
developedby the NationalInstitute ofStandardsand
Technology and wood producers, distributors and
users. This standard sets dimensional requirements
forstandardsizes,technicalrequirements,inspection
and testing procedures,and methods ofgrading and
marking lumber. The standard includes a provision
forgrading oflumberby mechanicalmeans.Lumber
so graded, called machine-stress-rated lumber, is
distinguished from lumber that is stress graded
visually in that machine-graded lumber is
nondestructively tested and marked to indicate:
Machine Rated, rated stress in bending and the
modulus of elasticity.
Glued-laminated timber is generally produced to
conformwith Product Standard PS 56- 73. This is a
voluntary standard thatgives minimumrequirements
for production,testing,inspection,identification and
certification ofstructuralglued-laminated timber.In
addition,structuralmembers should be fabricated to
conformwith AITC 117, Standard Specification for
StructuralGlued-Laminated Timber of Douglas Fir,
Western Larch, Southern Pine and California
Redwood, developed by the American Institute of
Timber Construction.
Design Specification for Structural Lumber.
Practice followed in design ofvisually stress-graded
lumber, machine-stress-rated lumber, structural
glued-laminated timber and lumber used in
repetitive-membersystems generally conforms with
the National Design Specification for Stress-Grade
Lumber and Its Fastenings, recommended by the
National Forest Products Association. (Repetitive-
member systems consist of three or more framing
members, spaced not more than 24 in. center-to-
center, that are joined by floor, roof or other load-
distributing members so that the framing members
share the load.)
Oassification of Structural Lumber. The design
specification requires that lumber grades be
specified by commercial grade names. Structural
lumber consists oflumberclassifications as follows:
dimension, beams and stringers, and posts and
timbers. The specification assigns allowable unit
stresses for each grade in these classifications.
Each lumber grade comprises pieces of lumber
that may be slightly different fromeach otherbut all
suitable for the use for which the grade is intended.
Grading rules applied by generally acceptedgrading
agencies describe the pieces thatmay be accepted in
each grade.Forthose use andsize classifications for
which stress values are assigned, the grade rules
limit strength-reducing characteristics.
Dimension lumber denotes pieces at least 2in.but
less than 5 in. thick, and at least 2 in. in nominal
width. The following classes are included: framing,
special dimension, and joists and planks, each with

several grades. The framing classification covers
studs 10 ft or less in length. The special-dimension
classification covers framing for which appearance
is important, machine-stress-rated lumber and
decking.
Beams and stringers denote pieces ofrectangular
cross section,at least 5 in. thick and 8 in. wide, and
graded with respect to strength in bending when
loaded on the narrow face.
Posts and timbers comprise lumber of square or
nearly square crosssection,graded primarily for use
as posts or columns carrying longitudinal loads but
adapted also for miscellaneous uses in which
strength in bending is not especially important.
Boards are lumberpiecesnotmore than1|in.thick
and at least 2 in. wide. The classification includes
appearance grades, sheathing and formlumber.
Methods for Establishing Allowable Stresses.
Because ofvariability in characteristics ofwood,as
previously described, it is impractical to establish
allowable design stresses by applying safety factors
to ultimate strengths,yield strengthsorproportional
limits, as is done for the more uniform structural
steels. Instead, tests are made on small specimens
substantially free of defects to determine strength
data and then factors are applied to determine basic
allowable stresses and modifications to account for
the influences of various characteristics.
The National Design Specification for Stress-
Grade Lumber and Its Fastenings, mentioned
previously,presentsallowable unit stressesbasedon
rules ofthe variousagenciesthatwrite gradingrules.
If these stressesare used,eachpiece oflumbermust
be identified by the grade mark of a competent
lumber grading or inspection agency.
Standard Sizes of Lumber. As mentioned
previously, Product Standard PS 20-70 establishes
dimensional requirements for standard sizes of
lumber. These standard sizes apply to rectangular
cross sections and are specified by their nominal
dimensions. Actual dimensions differ from the
nominal to allow for dressing the lumberto size and
for moisture content. PS 20-70 lists minimum
dressed sizes for lumber in both the dry and green
conditions. In this case, dry lumber is defined as
lumber seasoned to a moisture content of 19% or
less,and greenlumber as containing more than19%
moisture.
Generally, dry lumber with a nominal dimension
up to 7 in. is I in. smaller than the nominalsize. For
example, a 2 X 4 actually is lọ X 3|. For nominal
dimensions of 8 in. or more, actual size is I in. less
than nominal.Forboards,actualthickness is ịin.less
than nominal. Actual sizes for green lumber are
slightly larger than for dry lumber to allow for
shrinkage when moisture content drops below 19%.
Glued-laminated timbers are generally fabricated
with nominal 2-in.-thick lumber, unless they are to
be sharply curved(seeFig.8.14). Forsharply curved
members, nominal 1-in.- thick lumber is usually
used.Standardsizes forglued-laminatedtimbers are
based on the minimum dressed sizes for the
laminations and are givenin AITC113, Standard for
Dimensions of Glued-Laminated Structural
Members.
Feet Board Measure. Payment for wood is
generally based on volume, measured in feet
Fig. 8.14. Glued-laminated timber.
board measure (fbm). A board foot of a piece of
lumber is determined by multiplying the nominal
thickness, in., by the nominal width, in., and by the
length, ft.
Structural Behavior of Wood. Wood is
nonhomogeneous and anisotropic (has different
properties in different directions) because of its
cellular structure,the orientation ofits cells and the
way in which diameter increases when trees grow.
Properties of wood usually are determined in three
perpendiculardirections:longitudinally,radially and
tangentially (see Fig. 8.15). The difference between
properties in the radial and tangential directions is

seldom significant for structural purposes. In
general, it is desirable to differentiate only between
properties in the longitudinaldirection,orparallelto
the grain, and the transverse directions, per-
pendicular to, or across, the grain.
Wood has much greater strength and stiffness
parallel to the grain than across the grain, the
difference in tension being much larger than in
compression. Table 8.8 (p. 227) lists proportional
limits for Douglas fir and southern pine in
compression in the two directions for comparison.
The compressive strength ofwood at an angle other
than parallel or perpendicular to grain may be
computed from
c‘ - c, M.r ff’c, cos2# (815)
Fig. 8.15. Wood log with directions indicated for
measuring properties.
where
ce = strength at desired angle 0
with the grain
Cị = compressive strength parallel
to the grain
c2 = compressive strength perpendicular to the
grain
The stress-strain curve forwood in each principal
direction resembles that in Fig. 8.6Z? (p. 214),
except that it has no recognizable yield point. The
modulus of elasticity, as well as the proportional
limit, is different in each direction. The modulus
given in Table 8.8(p.227) is forstatic bendingloads.
Wood is designed sothat nowhere does the stress
produced by design loads exceed allowable unit
stresses that will keep the material in the elastic
range. Consequently, wood can be treated in
structuralanalysis and design in the same way as the
idealized structural material with the stress-strain
curve of Fig. 8.7 (p. 216), for the elastic range and
for each principal direction.
Fabrication may involve the following operations
in shop or field: boring, cutting, sawing, trimming,
dapping,routingandotherwise shaping,framing and
finishing lumber,sawn orlaminated,to assemble the
pieces in final position in a structure. Shop details
should be prepared in advance of fabrication and
submitted to the structural engineer for approval.
The details should give complete information
necessary for fabrication and erection of
components,including location,type,size andextent
of all connections,fastenings andamount ofcamber
(upward bending of beams to compensate for
expected deflections).
Glued-laminated timbers are fabricated by
bonding lumber laminations with adhesive so that
the grain directions ofalllaminations are essentially
parallel (see Fig. 8.14). To form a wide, deep
member, narrow boards may be edge-glued, and
short boards may be endglued, in each layer. The
resulting laminations canthenbe face-gluedto form
the large timber.
The strength, stiffness and service life of glued-
laminated timbers depend on the grade of lumber
used forthe laminations andthe gluejoint produced.
Selection of the adhesive to use should take into
account the wood species,type oftreatment,if any,
given the wood,and whetherconditionofuse ofthe
timber will be wet or dry. Casein is generally used
for dry-use timber. Resorcinol or phenol-resorcinol
resins often are used for wet-use or preservative-
treated timber.Glued joints may be cured by heatby
any of several methods.
Fasteners for Structural Lumber. Fabrication of
wood members and their erection is easily carried
out,not only because ofthe light weight ofwood and
the ease with which it can be cut to size and shape in
shop and field,but also because there are numerous
easy ways for joining wood parts.
Small, lightly loaded wood parts can readily be
joined with nails orspikes.The latterare available in
longer lengths and in larger diameters for the same
length than nails. Most nails and spikes used in

construction are made of common wire steel,with a
head on one end and a point on the otherend ofthe
shank. They also are available in hardened steel,
alloy steels, aluminumand copper. Shanks may be
smooth bright, cement coated, blued, galvanized,
etched or barbed. Some shanks come with annular
grooves or helical threads, for improved holding
power.
The unit of measure for specification ofnails and
short spikesis the penny,represented by the letterd.
Penny measure indicates length, usually measured
from under the head to the tip of the point. A two-
penny (2d) nail is 1-in. long. From this length,
lengths increase in |-in. increments per penny, to 3
in. for a lOd nail. For longernails,generally lengths
increase in |-in. increments per penny to 4 in. for a
20d nail, then in y-in. increments forevery 10d,to 6
in. for a 60d nail. Diameters are standardized for
each penny size.
Nails and spikes may be driven directly with a
hammer through wood to connect two or more
pieces. If, however, nails have to be placed closer
togetherthanhalftheirlength,holessmallerthan the
nail diameter should first be drilled at the nail
locations and then the nails may be driven in the
prebored holes.
Nails and spikes may be driven at any angle with
the grain if they are to be loaded in compression;
however, if they are to be loaded in tension or
subjected to withdrawal forces, nails and spikes
should not be placed in end grain or parallel to the
grain. On the other hand, some reliance can be
placed on toenailing (driving nails diagonally)where
two members meet at a sharp angle andthe loadsare
primarily compressive. Best results with toenailing
are obtained when eachnailis startedat one-third the
naillength fromthe end ofthe piecebeing joinedand
the nail is driven at an angle of about 30°to the face
of the piece.
Among the many factors determining the
withdrawal resistance of a nail or spike, one of the
most important is the length of penetration into the
piece receiving the point.Load tables forwithdrawal
resistance generally are based on a penetrationof11
nail or spike diameters. Penetration into the piece
receiving the point should be a minimum of 31
diameters.
Wood screwsare an alternative tonails andspikes
but with greaterholding power,because the threads
project into the wood. Common types of screws
come with flat heads, for use in countersunk holes
when a flush surface is desired,orwith ovalorround
heads, for appearance or to avoid countersinking.
Also, screws are available in steel, brass and other
metals. They should be placed in wood pieces only
perpendicular to the grain, preferably in predrilled
holes,to preventsplitting. Embedment into thepiece
holding the point should be at least seven times the
shank diameter.
Lag screws are large screws capable of resisting
large loads. They are sometimes used instead of
bolts,especially where tighteninga nutorbolt would
be difficult or where a nut would be objectionable
for appearance reasons.
Common, or machine, bolts, usually with square
heads and nuts, are often used to connect load-
carrying wood pieces. Holes with a diameter that
permits easy placement ofbolts have to be drilled in
the wood. The holes must be accurately located.
Metalwashers should be placed undernuts and bolt
heads to protect the wood when the nuts are
tightened and to distribute the pressure over the
wood surface.

Tightening of the nuts holds the pieces together,
while loads are resisted by pressure of the wood
against the bolt shank.
Exposed metal fasteners may be subjected to
corrosion or chemical attack. If so, they should be
protected by painting, galvanizing or plating with a
corrosion-resistant metal. In some cases, hot tar or
pitch may provide a suitable protective coating.
Timber connectors often are used with bolts to
provide a more efficient joint with fewer bolts.
Connectors are metal devices that transmit load
between parts to be joined, while bolts function
mainly to hold the parts in contact. Generally, a
connector is placed in a groove in the wood.
Split rings (see Fig.8.16a)are efficient forjoining
wood pieces.Made ofsteel,the rings are 2^ or 4 in.
in diameter.To make a connection,a groove foreach
ring is cut with a special tool to a depth of half the
ring depth in the contact surface ofeach piece to be
joined.Also,a hole for a bolt is drilled at the center
of the circle and througheach piece.The lowerpart
ofthe split ring is inserted in the grooveofone piece
and then the groove in the second piece is placed on
the upperpart of the ring. The ring is provided with
a tongue-and-groove split, to obtain a tight fit.
Placement of a bolt in the centerhole and tightening
ofa nut on the bolt holds the pieces ofthe connection
together (see Fig. 8.lói).
Shear plates (see Fig. 8.16c) are efficient for
joining wood to steelcomponents.Circularin shape,
they come with a smooth backface,forcontactwith
the steelpart,and a circumferentiallip, for insertion
in a round groove in thewoodcontactsurface.A bolt
hole must be provided in both the steel and wood
parts of the joint at the center of the circle. As with
split rings,the bolt holds the parts in contact(seeFig.
8.16J). Shearplates,used in pairs,backto back,may
also be used to connect wood components (see Fig.
8.16e).
Glued Lumber Joints. Still another alternative for
making connections between wood pieces is
(a)
Steel
(d)
Shear
Bolt
(a)
Fig. 8.16. Timber connectors, (a) Split ring, (b} Assembled connection with split ring, (c) Shear plate. (Ờ) Steel
member connected to wood member with shear plate and bolt, (e) Wood members connected with a pair of shear
plates and a bolt.

glueing. Adhesives described previously for fab-
ricating glued-laminated timbersare alsosuitable for
otherglued joints.In allcases,consideration mustbe
given in selection of an adhesive as to whether
service conditions will be wet or dry.
When a strong glued joint is required, pieces
should be placed with the grain direction parallel.
Only in special cases, such as fabrication of
plywood, may lumber be glued with the grain
direction at an angle in pieces to be joined.
Joints between end-grain surfacesofwood pieces
are not likely to be reliable. Consequently, joints
between ends of pieces with fibers parallel are
usually made by cutting sloping, mating surfaces at
the ends and glueingthose surfaces [scarfjoints(see
Fig. 8.17íỉ)]. Or fingers may be cut into the endsand
joined with glue by interlocking [finger joints (see
Fig. 8.17Z? and c)].
Preservative Treatments for Wood. Ifwoodcannot
be kept dry or permanently submerged in water, it
will decay. This, however, can be avoided by
application of a preservative treatment. There are
several types of preservative that may be used.
Selection of an appropriate preservative dependson
the service expected of the wood member for the
specific conditions of exposure.
Among the commonly used preservatives are
creosoteandcreosote solutions;oil-bornechemicals,
such as pentachlorphenol; and waterborne inorganic
salts, such as certain chromated zinc compounds,
copper compounds and fluorchrome compounds.
Preservatives may be applied in any of many ways.
In some cases, brushing or dipping may provide
adequate protection.For maximum effect, however,
pressure application is necessary. Effectiveness
depends on depth of penetration and amount of
retention of preservative.
Wood also may be impregnated to make it fire
retardant. For such purposes, salts containing
ammonium and phosphates are often used.They are
recommended,however,only forinterioror dry-use
service conditions, because the salts may leach out.
With proper preparation, the impregnated surfaces
may be painted. Fire- retardant surface treatments
also are available. Their effectiveness generally
depends on formation, under heat, of a blanket of
inert gas bubbles, which retards combustion and
insulates the wood below.
Glued Joint
Fig. 8.17. Wood joints, (a) Scarf joint for connecting ends of wood members, {b} Finger joint with fingers along
the width of the members, (c) Finger joint with fingers over the depth of the members.

Plywood
Plywood essentially is a wood product, just as is
glued-laminated timber. Plywood, however, is
fabricated as sheets,orpanels,often4ft wide by 8 ft
long and I to 11 in. thick for construction
applications, although other-size panels also are
available. Principal advantages over lumber are its
more nearly equal strength properties in the length
and width directions,greaterresistance to checking,
less shrinkage and swelling from changes in
moisture content,and greaterresistance to splitting.
Productionof Plywood. Plywoodis built up ofthin
wood sheets, or veneers. It contains an odd number
oflayers ofthese veneers.Each layer,orply,consists
of one ormore veneers.The plies are glued together
with the grain of adjacent layers at right angles to
each other (see Fig 8.18).
The veneersare peeled fromlogs by rotating them
against a long knife. Afterbeing dried to a moisture
content ofabout 2to 5%, each veneeris graded and
then coated on one face with glue. Next, another
veneermay be placed on the glued surfaceto forma
ply,which also is then coated onone face with glue.
Finally,plies are combined abouta centralply sothat
plies at the same distance fromthe central ply have
their grain direction parallel. This symmetry is
desirable to reduce warping, twisting and shrinking.
The glued plies are usually cured by hot pressingin
a large hydraulic press. The manufacturing process
generally conforms with the latest edition of the
voluntary product standard PS 1, for Softwood Ply
wood-Construction and Industrial.
Design Standard for Plywood. Design practice
usually complies with the Plywood Design
Specification ofthe American PlywoodAssociation.
This specificationclassifies woodspecies into five
groups in accordance with modulus of elasticity in
bending and important strength properties. It also
distinguishes betweentwotypes ofplywood,interior
and exterior, and its various grades.In addition,the
specification presents designmethods andallowable
design stresses. Various supplements to the
specification cover design of such structural
components as beams, curved panels, stressed-skin
panels and sandwich panels.
Classification Systems for Plywood. All woods
within a species group are assigned the same al-
lowable stress. The group classification is usually
determined by the species in the face and back
veneer of the plywood panel. Unless the grade
classification requires all plies to be of the same
species, inner plies may be made of a different
species than the outer plies.
Southern pineand Douglas firfromnorthern areas
fall in Group 1. Douglas fir from southern states are
included in Group 2, which is assigned lower
stresses than Group 1.
Some types of allowable stress also are lower for
interior-type plywood than for exteriortype used in
dry conditions.Shearstrength,however,depends on
the type of glue used in the plywood.
The classification into interior and exterior types
is based on resistance of the plywood to moisture.
Exterior plywood is made with waterproofglue and
high-quality veneers, incorporating only small,
minor defects, such as small knots, knotholes and
patches. Interior plywood also may be made with
waterproof glue but the veneers may be of lower
quality than that permitted for exterior plywood.
Interior plywood may be used where its moisture
contentin service willnot continuously orrepeatedly
exceed 18% or where it will not be exposed to the
Fig. 8.18. Assemblage of plywood panels, (a) Three layer, three ply. {b) Five layer, five ply. Arrows show
direction of grain in the plies.

weather. For wet conditions, exterior plywood
should be used.
Veneer is classified into the following grades:
N and A— no knots, restricted patches, N being
used for natural finishes and A for
paintable surfaces
B—small round knots, small patches,
round plugs (often used as outerfacing
of plywood forms for concrete)
C— small knots, knotholes and patches
(lowest grade permitted for exterior
plywood; often used for a facing on
sheathing),c plugged is a betterquality
c grade, often used in floor underlay
ment.
D—large knots and knotholes, used for
inner plies and back ply of interior
plywood
Plywood panels, depending on the wood species
and veneergrades in the plies,may be considered to
be in an engineered grade or an appearance grade.
Engineered grades consist mostly of unsanded
sheathing panels designated C-D Interior or C-C
Exterior,the letters referring to the veneergradesin
front and backpanels.Thesegrades are specified by
giving thickness and an identification index, which
is discussed later. C-D Interior and C-C Exterior
may additionally be graded Structural I or II,
intended for use where strength properties are
important. All plies of Structural I must be one of
the Group 1 species. Groups 2 and 3, which are
assigned lower design stresses, are permitted in
Structural II. Both structural grades are made only
with exterior glue and have additionalrestrictionson
knot size and patches. Appearance grades are
specified by thickness, veneer grades in face and
back plies, and species group.
The identification index used on sheathing is a
measure ofplywoodstiffnessandstrength parallelto
the grain ofthe face plies. The indexconsistsoftwo
numbers, written left to right, with a slash line
between them. The number on the left indicates the
maximum spacing,in.,forroofsupportsforuniform
live loads ofat least 35 psf.The numberon the right
indicates the maximum spacing, in., for floor
supportsforuniformlive loads ofat least160psfand
concentrated loads, such as pianos and refrigera-
tors.Forexample, 5" 32/16 C-C INT-APA specifies
a j-in. thick C-C interior-type plywood panel,
which could be used as roofsheathing supported by
rafters spaced not more than 32 in. center-to-center
oras subflooringwith joists spacednot more than16
in. center- to-center.
Plywood Construction. Plywood can be used
mainly as paneling or built up into structural
members, much as structuralsteelplates are usedto
build up structural steel members.
Paneling may serve as facings for interior and
exterior surfaces ofbuilding walls,as subflooring,or
as roof or wall sheathing.
Subflooring is a structural deck, which is sup-
ported on joists and on which is placed carpeting,
floor tile, linoleum or other decorative, wearing
surface.
Sheathing is an enclosure,supported by rafters in
roofs or by studs in walls, and on the outer surface
of which is usually placed waterproofing and a
decorative, weather-resistant facing.
In built-up members, plywood may be used as the
web of beams,such as the I beamin Fig. 8.19tz and
the box beam in Fig. 8.19b, with lumber top and
bottomflanges. Plywood also may be used as the
faces, or skins, of sandwich panels. In such panels,
the skins are separated by, but glued to, a structural
core capable of resisting shear(see Fig. 8.19c). The
core may be closely spaced lumber ribs, resin-
impregnated-paper honeycomb or foamed plastic.
The honeycomb or plastic, however, should not be
assumed capable of resisting flexural or direct
stresses.
As another alternative, plywood may be used as
one or both faces of a stressed-skin panel (see Fig.
8.19J). In such a panel, plywood fac-

ings are glued to lumberstringers,foruse asflooror
roof members or as wall members subjected to
bending. The skins and stringers act together as a
series ofT or I beams.The skins resist nearly all the
bending forces and also serve as sheathing or
exposed facings. The stringers resist shear on the
panel. Cross bracing, such as headers at the panel
ends and interior bridging, may be placed between
the stringers to keep themaligned,support edgesof
the skin and help distribute concentrated loads.
Concretes
Just as there are many structural steels, there are
many concretes. The concretes that are commonly
used for structural purposes in buildings consist
basically of a mixture of portland cement, fine
aggregate,coarse aggregate and water.Temporarily
plastic and moldable,the mixture soon forms a hard
mass, usually in a few hours. Just as chemicals are
added to steels to form alloys to achieve specific
results,chemicals,called admixtures,may be added
to the concrete mixture to secure desired properties.
A specific proportioning of contents of concrete is
called a mix.
A short time after the solid components of
concrete are mixed with water, the mass stiffens,or
sets. The time required for setting is controlled by
ingredients in the portland cement and sometimes
also by admixtures to allow time for placement of
concrete in molds, usually called forms, and for
producing desired surfaces. Then, additional
chemical reactions cause the mass to strengthen
gradually. The concrete may continue to gain
strength formore thanone year,althoughmost ofthe
strength gain takes place in the first few days after
hardening starts.
The chemical reactions are accompanied by
release of heat, which must be dissipated to the
atmosphere. If this heat cannot be removed during
the early stages of hardening, as may happen in hot
weatherorwhen the concrete is cast in large masses,
the concretewillget hot and crack.Precautions must
be taken to avoid suchsituations,as willbe discussed
later.
Designed by knowledgeable structural engineers
and produced and handled by reliable, competent
contractors, concrete is an excellent, economical
structuralmaterial. It offers high strengthrelative to
its cost.While plastic,it can be cast in forms on the
building site to produce almost any desired shape.
Also, it can be precast with strict quality control in
Lumber Stringers
Plywood
Top Skin
Plywood
Splice Plate,
Glued Joint
Butt joint
between plywood
skin panels (or
scarfed)
Fig. 8.19. Plywood structural members, (a) I beam, lb} Box beam, (c) Sandwich panel. (Ờ) Stressed-skin panel.

factories, then shipped to the building site and
erected in a mannersimilar to that forstructuraland
cold-formed steel members. In addition, concrete is
durable and can serveas a wearing surface forfloors
and pavementsoras an exposedsurface forwalls.It
does not need painting. Furthermore, it has high
resistance to fire and penetration of water.
Concrete, however, has disadvantages, especially
when it is cast in place on the building site.For one
thing, quality control may be difficult. Often, many
subcontractors are involved in supplying
ingredients, designing the mixes, producing the
mixes, placing the concrete and curingit,inspecting
the processand testingthe results.Ifany stepshould
be faulty and cause production of poor concrete,
responsibility for the undesirable results may be
impossible to determine.
Another disadvantage is that concrete is brittle.
While its compressive strength is substantial,tensile
strength is smalland failure in tension is sudden.As
a result,plain concrete is used only where it will be
subjected principally to compression and in
members, such as pedestals, that are bulky.
Concrete, however, can be used in members
subjectedto tensionifreinforcing materials, such as
steel, capable of resisting the tension, are
incorporated in it. Concrete can also sustain tension
if it is prestressed,held in compressionpermanently
by external forces applied before the tensile loads.
Reinforced, or prestressed, concrete serves
economically in a wide variety of structural
applications in buildings, fromfootings to roofs.
Types of Concrete. The main types of concrete
used in building construction may be classified as
normal, air-entrained or lightweight concrete.
Heavyweight concrete may be used where shielding
from high-penetration radiation, such as that from
nuclear reactors, is needed.
Normal concrete is generally used for structural
members, including foundations. It is made with
portland cement, sand as the fine aggregate, gravel
or crushedstone as the coarse aggregate,and water.
Air-entrained concrete is used where the material
will be subjected to cycles of freezing and thawing
in service. While normal concrete contains some
entrapped air, this air does not provide adequate
protection fromdamage from freezing and thawing.
So air in small, disconnected bubbles is purposely
entrained in the concrete. This may be done by
incorporationofchemicals in the portland cementor
by addition of admixtures to the concrete mix. The
tiny air bubbles in the concrete provide reservoirs
into which ice formed in concrete in cold weather
can expand and thus prevent spalling ofthe concrete.
A slight loss in strength results fromairentrainment,
but the penalty is small compared with the benefits
from improved durability.
Lightweight concrete is usedwhere less weight is
needed than that imposed by normalor airentrained
concrete or where weight reduction will cut
construction costs. Lightweight concrete may be
made by substitution oflight aggregates forsand and
gravel, by expansion of the mix before it sets by
addition ofa chemical,suchas aluminumpowder,or
by incorporation ofa stabilized foam. Concrete into
which nails can be driven can be produced by
replacement of the coarse aggregate with pine
sawdust.
Heavyweight concrete is made with heavy
aggregates,such as iron ore,barite,or iron shot and
iron punchings. This type of concrete may weigh
more than twice as much as an equal volume of
normal concrete.
Methods of selecting mixes for the various types
of concrete are described in ACI 211.1,
Recommended Practice forSelectingProportions for
Normal and HeavyweightConcrete,and ACI 211.2,
Recommended Practice forSelectingProportions for
Structural Lightweight Concrete, American
Concrete Institute.
Production, placement, finishing and testing of
concrete are describedin ACI301,Specifications for
StructuralConcreteforBuildings.This standard also
incorporates by reference applicable ASTM
specifications.Admixtures are discussed in the ACI
Guide for Use of Admixtures in Concrete. The
preceding recommended practices and many others
are incorporated in the ACI Manual of Concrete
Practice but also are usually available as separate
publications.

Portland Cements. There are several types of
portland cement,but only a few are frequently used
in building construction.Allare made by blending a
carefully proportioned mixture of calcareous, or
lime-containing, materials and argillaceous, or
clayey, materials. Burned at high temperatures in a
rotary kiln, the mixture forms hard pellets, called
clinker. The clinker is then ground with gypsumto
the fine powdercalled portland cement.The gypsum
is used to control the rate of setting of concrete
mixes. For some types of cement, an air-entraining
agent is added.
The most effective ingredientsofportlandcement
in the formation of normal concrete are tricalcium
silicate (C3S), dicalcium silicate (C2S), tricalcium
aluminate (C3A) and tetracalciumaluminum ferrite
(C4AF). The proportions of these chemicals and
requirements placed on physical properties
distinguish the various types of portland cements
from each other.
Portland cementsare usually produced tomeet the
requirements ofASTMCl50,Standard Specification
for Portland Cement. This specification details
requirements for generalpurpose cements, usually
used for structural applications; cements modified
for use where exposure to sulfate attack will be
moderate orwhere therewillbe somewhat more than
normal heat of hydration during hardening of the
concrete; high-early-strength cements; and air-
entraining cements.
Aggregates. Fine and coarse aggregates for
concretes should be treated as separate ingredients.
Aggregates for normal concrete should conform
with ASTM C33, Specifications for Concrete
Aggregates. Those for lightweight concrete should
comply with ASTM C330, Specifications for
Lightweight Aggregates for Structural Concrete.
Water. Concretesshould be made only with clean,
freshwater. If the water is drinkable, it is generally
acceptable.If not,specimens ofconcrete made with
the water should be tested to verify attainment of
desired concrete properties.
Desired Characteristics of Normal Concrete.
Within specific inherent limitations, properties of
concrete can be changed to achieve desired
objectives by changing the ingredients of the mix
and the proportions of the ingredients used. The
main variations that are usually made are:
1. Type of cement
2. Ratio of weight of water to weight of cement
(water-cement ratio)
3. Ratio of weight of cement to weight of
aggregates
4. Size of coarse aggregate '
5. Ratio of weight of fine aggregate to weight of
coarse aggregate
6. Gradation, or proportioning of sizes, of
aggregates
7. Use of admixtures
Workability. For complete hydration of cement,
about 21galofwatercombines chemically with each
sack (94 lb) of cement. But a mix with this water-
cement ratio would be too stiff for uniform mixing,
properhandling and easy placement.Consequently,
additional water is used to make the concrete flow
more readily. Workability thus is a measure of the
ease with which the ingredients of concrete can be
mixed and the resulting mixhandled and placed.The
concept of workability embraces other charac-
teristics of the plastic mix, such as consistency,
adhesiveness and plasticity.
To evaluate the workability ofa mix, a slump test
is often made,as describedin ASTM Cl43, Standard
Method of Test for Slump of Portland Cement
Concrete. In this test, which actually measures
consistency,a mold with the shapeofthe frustumof
a cone is filled with a specimen ofthe mix. The mold
is removed and the changein height,orslump,ofthe
mass is measured.The slump is used as anindication
of the workability of the mix. Slump for structural
concrete may range fromzero for a very stiff mix to
4 in., one-third the cone height, for a plastic mix.
Durability of concrete is generally achieved by
productionofa dense,high-strength concrete,made
with hard,round,chemically stable aggregates.Such
a concrete has a high resistance to abrasion. For
resistance to freezing and thawing, air-entrained
concrete is used.
Watertightness. Waterin excess ofthat neededfor
hydration of the cement evaporates eventually,
leaving voids and cavities in the concrete. If these
become connected, water can penetrate the surface

and pass through the concrete. Consequently, water
added to the concrete mix should be kept to the
minimum needed for acceptable workability.
Volume Changes. From the plastic state on,
concrete is likely to undergo changes in volume.
While in the plastic state,concretemay settle before
it sets.To reducethe amountofsettlement,concrete,
after placement in formwork, often is vibrated with
mechanical vibrators or pushed with a spade to
consolidate the mixand insure complete filling ofthe
forms. After the concrete starts to harden, it may
shrink as it dries, and cracking may occur as a
consequence. Drying shrinkage may be limited by
keeping the amount of cement and mixing water to
the minimum necessary for attaining other desired
properties ofthe concrete andby moist curing ofthe
concrete asit hardens.The cracksmay be kept small
or closed by use of reinforcing steel or prestress.
Afterthe concrete hashardened,it willexpand and
contract with temperature changes in its
environment. The coefficient of expansion of
concrete depends on many factors but averages
about 0.000 0055 in. per in. per°F, nearly the same
as that of steel.
Another cause of volume change is chemical
reaction between ingredients of the concrete. Such
changes can be avoided by selection of nonreactive
aggregates or by addition of poz- zolanic material,
such as fly ash, to the mix.
Strength. After concrete sets, it gains strength
rapidly at first and then much more slowly asit ages.
Because concrete has a low tensile strength,
engineers seldom rely on this property. Instead,
concrete strength is measured by the ultimate
compressive strength of a sample. In the United
States, it is common practice to measure this
property by testing a cylindrical sample in
compressionwhenit is 28 days old.Thesample may
be taken from the mix being placed in the forms or
by taking drilled cores from hardened concrete.
Handling and testingofthe specimensare prescribed
in various ASTM specifications and often done by
independent testing laboratories.
Concrete strength is related linearly to the water-
cement ratio. The lower the ratio, the higher the
strength of a workable mix. Hence, strength can be
increased by decreasing the amount of water or
increasing theamount ofcementin the mix. Strength
also may be raised by use of higher-strength
aggregates, grading the aggregates to reduce the
percentage ofvoids in the concrete,moist curing the
concrete afterit has set,vibrating the concretein the
forms to densify it,orsucking outexcess waterfrom
the concretein the forms by means ofvacuum.High
strength in the first fewdays can be achieved by use
of high-early-strength cement, addition of
appropriate admixtures orhigh curing temperatures,
but long-term strength may not be significantly
influenced by these measures.
Ultimate compressive strength of normal
structural concrete at 28 days usually specified
ranges from about 3,000 psi to about 10,000 psi.
Strengths exceeding 15,000 psi have been achieved
in building construction, however,by use ofspecial
admixtures and cement substitutes.
Superplasticizers, which are cement-dispersion
agents, are used to reduce water requirements and
increase strength without impairing workability.
Similarly, silica fume, or microsilica, a waste
product of electric-arc furnaces, is substituted for a
portion of the required portland cement to achieve
substantial strength increases.
Weight. Normal concrete weighs about 145lb per
cu ft. For reinforced concrete, 150 lb per cu ft is
generally assumed for design purposes, to include
the weight of steel reinforcing.
The weight of lightweight concretes depends on
aggregates usedoramount ofexpansion orfoaming,
in accordance with the technique used for reducing
weight. With vermiculite or perlite, weight may be
about 60 lb per cu ft; with scoria, pumice or
expanded clay or shale, about 100 lb per cu ft; and
with cinders,115 lb percu ft with sand and85lb per
cu ft without sand.
Heavyweight concretes made with steel shot for
fine aggregateand with steelpunchings and sheared
bars as coarse aggregates may weigh from 250 to
290 lb per cu ft.
Creep. As do other materials, concrete when
subjected to static load deforms, and the amount of
initial deformation depends on the magnitude ofthe
load. If the load remains on the concrete, the
deformation will increase.This change with time of
deformation underconstant load is called creep.The
rate of creep gradually diminishes with time and the
total creep approaches a limiting value, which may

be as large as three times the initial deformation.
Stress-Strain Curve for Concrete. When tested
in compression, concrete has a stressstrain curve
similar to that shown in Fig. 8.6c, p. 214.
Consequently, the idealized structural material with
the stress-strain curve shownin Fig.8.7, p.216, is at
best only a rough approximation of concrete in
compression.
The portion of the stress-strain curve up to about
40% of the ultimate load is sufficiently close to a
straight line that a secant modulus of elasticity may
representthatportion.The value ofthe modulusmay
be taken, in psi, for normal concrete as
Ec = 57,000 (8.16)
where fc = 28-day compressive strength of the
concrete, psi.
Poisson’s ratio for concrete is about 0.25.
Manufacture of Concretes. The mix for normal
concrete is specified by indicating the weight,lb,of
water, sand and stone to be used per 94-lb bag of
cement.Preferably also,type ofcement,gradation of
the aggregates and maximum size of coarse
aggregate should be specified. Mixes are often
briefly but not completely described by giving the
ratio of cement to sand to coarse aggregate by
weight; for instance, 1: 1|:3.
The proportion ofcomponentsshould be selected
to obtain a concrete with the desired properties for
anticipated service conditions and at lowest cost.
Although strength and other desirable properties
improve with increase in cement content of a mix,
cement is relatively expensive.Hence,foreconomy,
cement content should be kept to a minimum. Also,
because strength increases with decrease in water-
cement ratio, the amount of water should be kept to
the minimum necessary to produce acceptable
workability. Attainment of these objectives is
facilitated by selection of the largest-size coarse
aggregates consistent with job requirements and by
good gradationofthe aggregatesto keep the volume
of voids in the concrete small. Optimum mixes for
specific job requirements usually are determined by
making and testing trial batches with different
proportions of ingredients.
Batching and Mixing. While concrete may be
prepared on or near the building site, it is usually
more convenient to purchase ready-mixed concrete
batched at a centralplant and deliveredto the site in
a mechanical mixer mounted on a truck. The mix
ingredients are stored at the plant in batching
equipment before being fed to the mixer. The
equipment includes hoppers,watertank,scales,and
controls for adjusting weights of ingredients to be
supplied to themixer. Since mixing takes only a few
minutes,bestcontrolofmixing time can be achieved
by adding water to the mixer after the truck arrives
at the site, where the operation can be inspected.
Placement of Concrete. There are many ways of
conveying concrete from the mixer to its final
position in the building. In all cases, precautions
should be taken to prevent segregation of the
concrete ingredients afterdischarge fromthe mixer.
Usually,the mixer discharges into a chute.To avoid
segregation,the concrete should be fed into a length
of pipe inserted at the end

of the chute to carry the mix directly down to the
forms or into buckets, hoppers, carts or conveyor
belts that will transport it to the forms.
In multistory buildings, concrete may be lifted to
upper levels in buckets raised by cranes, hoists, or
elevators. There, it is usually discharged into
hoppers and then fed to barrows or motorized carts
for delivery to forms (see Fig. 8.20a). Alternatively,
concrete may be pumpedthrough pipesfromground
level directly to the forms (see Fig. 8.20/?). Near
ground level, concrete may be speedily placed with
conveyor belts (see Fig. 8.20c).
Concrete also may be sprayed onto a backup
surface and built up to desired thicknesses.Sprayed
concrete, also called shotcrete or gunite, is applied
by an air jet from a gun,ormechanical feeder, mixer
and compressor. Shotcrete can be made with a low
water-cement ratio to obtain high strength.
Afterthe concretehas beenplacedin finalposition
in the forms, it should be immediately spaded or
vibrated with electric or pneumatic
(a)
(b)
Fig. 8.20. Placement of concrete, (a) Motorized cart transports ready-mixed concrete to forms for floor of a
multistory building, (b} Pipes carry concrete from a pump to forms, (c) Conveyor carries concrete to column
forms, (a) Courtesy of H. H. Robertson Co.; (b} and (c) courtesy of Morgan Manufacturing Co.

vibrators. The objectives are to eliminate voids and
insure close contact of the concrete with forms,
reinforcing and other embedded objects.
Construction Joints. A construction joint is
formed when new concrete must be bonded to
concrete that has already hardened. Steps should be
taken to insure a secure bond.
First,the hardenedsurfaceto be bondedshould be
cleaned,washedwith a jet ofairand waterat 100psi,
and sandblasted or brushed vigorously with fine-
wire brooms.Next,the surface should be washedand
allowed to dry. Then, before the new concrete is
placed againstthe surface,it should be coated with I
in. of mortar, a mixture of sand, cement and water.
The newconcrete should be placedbefore themortar
dries.
Finishing of Concrete Surfaces. Afterconcretehas
been consolidated in the forms, the top surface
should be brought to the desired leveland given the
specified shape, smoothness or texture. The surface
usually is leveled or shaped by screeding. In this
process,a straightedge ora board with the specified
shape is moved alongscreeds,rigid guides setat ap-
propriate elevations. Then, if desired, as would be
the case forfloors and roofs,the top surface may be
smoothed with power floats or by hand with wood
floats. If a finer surface is desired, it may be steel-
troweled.Floating may begin as soon as the surface
has hardened sufficiently to bear a worker’s weight
without indentation. Troweling may be done when
the surface is hard enough that excess fine material
in the mix will not be drawn to the top and, for an
extra- hard finish,again when the surface has nearly
hardened. Excessive manipulation, however, can
cause the surface to check, craze and dust later.
Curing of Concrete. Although more water than
needed for hydration of the cement is incorporated
(0
Fig. 8.20. (Continued}

in a concrete mix, concrete neverthelessmustbekept
moist after it has set. If the water evaporates,
hydration of the cement may be delayed or
prevented,anda weakconcretemay result.Curing is
any operation performed after concrete has set that
improves hydration. Generally, curing is achieved
by maintaining a moist environment by addition of
water. For this purpose, water may be continuously
sprinklered orponded onthesurfacesexposedorthe
surfaces may be covered with wet burlap. Normal
concrete should be cured this way for at least 14
days. An alternative method is coating of the
surfaces with a sealer to prevent evaporation.
Precast concreteand concretecastin cold weather
may be steam-cured in enclosures to speed
hydration. Temperatures maintained usually range
between 100and 165°F. The result is a product with
high early strength. Higher 24-hr strengths can be
attained,however,ifstart ofsteamcuring is delayed
1 to 6 hr, to allow early cement reactions to take
place and sufficient hardening to occur so that the
concrete can withstand the rapid temperature
changes when curing begins. Another process that
may be used forfactory-produced concrete products
is autoclaving, or high-pressure steamcuring, with
temperatures above the boiling point of water. The
processmay providehighearly strength,lowvolume
change on drying and better chemical resistance.
Formwork for Concrete. Forms are usedto support
and shape concrete until it gains sufficient strength
to be self supporting. They also may be provided
with coatings or liners to produce desired surface
textures.
Forms for horizontal or inclined concrete
members usually must be supported on falsework,
temporary construction, of adequate strength and
sufficient rigidity to keep deflections within
acceptable limits (see Fig. 8.2ia). Forms for vertical
members must be braced to keep themplumb.
The forms themselves must also be strong and
rigid to satisfy dimensional tolerances. In addition,
they must be tight, to prevent water or mortar from
leaking out. Because forms usually are only
temporary construction devices, they must be low
cost,andwhenpossible,they should bedesignedand
scheduled for repeated reuse, for economical
reasons. Figure 8.21/? illustrates the assembly of
wall forms with identical, prefabricated panels.
Figure 8.21c shows a large, prefabricated form,
called a flying form, used repeatedly for the floors
and roofofa multistory building.Because forms are
usually temporary construction andreuse,orat least
salvage of the materials, is desirable, forms should
be lightweight and also easily and speedily erected
and removed. Materials generally used for forms
include lumber, plywood, cold-formed steel,
reinforced plastic and precast concrete.
Parallel vertical forms, such as those for walls,
often are kept at the proper distance apart by struts
or ties,the former usually being placed at the top of
the forms. Form ties that will pass through the
concrete should have as small a cross section as
possible, because the holes they form may permit
water to leak through.
Forms should be treatedbefore concrete is placed
in them to prevent the concrete from sticking to
them. Paraffin-base mineral oils generally are used
to coat wood forms,and marineengine oils for steel
forms.
While forms usually are kept immovable until
they are to be removed, continuously movable
forms, called slip forms, also may be used in
appropriate situations.In building construction,slip
forms sometimes are used for concrete walls of
multistory buildings.Theforms are slowly jackedup
on steel bars embedded in the concrete. Climbing
rates range fromabout 2 to 12 in. per hr.
In multistory buildings, floor and roof forms
usually are supported on vertical falsework, called
shores,that extend to and are supportedon the floor
below (see Fig. 8.21a). Because construction must
proceed speedily, that floor seldom is old enough
and therefore sufficiently strong to withstand the
load of falsework and newly placed concrete at the
upper level. Consequently, as soon as the forms for
a floor have been removed, the floor should be
reshored,oragain supportedonfalseworkextending
to the floorbeneath.It may be necessary to reshore

(a)
(b)
Fig. 8.21. Forming systems for sitecast concrete, (a) Falsework temporarilysupports forms for floors and roofs,
(b) Prefabricated panels used for walls, (c) Flying form for repetitive use. (CourtesySymons Manufacturing Co.)

several floors in series to support the new concrete
adequately.
Cold-Weather Concreting. Newconcreteshould be
protectedagainstfreezing during cold weatherforat
least 4 days after placement in the forms. For this
purpose,the mix may be made with water heated to
at least 140°F,and if necessary, the aggregates may
also be heated. An enclosure should be placed
around the forms or the entire construction space,
and the space within the enclosure should be heated
to maintain temperatures above freezing. Danger of
freezing and thawing may be reduced by production
of concrete with high early strength.
Hot-Weather Concreting. In hot weather, concrete
may set undesirably fast. Addition of water to
counteract this is poor practice for many reasons.
At high outdoor temperatures mixing water
evaporates swiftly,the concrete shrinks fast and the
rate of cooling of the concrete fromthe high initial
temperatures may be high. As a result, the concrete
will crack. Such conditions may be avoided by
keeping the temperature of concrete during casting
below 90°F. For this purpose, water and aggregates
may be chilled. If necessary, work may be carried
out at night.Also,forms may be sprinkled with cool
water. In addition, set-retarding admixtures may be
used in the mix to counterattackthe set-accelerating
effects of hot weather and to lessen the need for
additional mixing water to maintain workability.
Curing should be started as soonas the concrete has
hardened sufficiently to resist surface damage.
Continuous water curing gives best results.
Contraction Joints. As pointed out previously,
concrete shrinks when it dries after setting or
whenever the temperature drops. If the shrinkage is
restrained, whether by friction or obstructions, the
concrete will crack. Shrinkage and restraint are
difficult to prevent. Consequently, structural
(c)
Fig. 8.21. {Continued}

engineers design concrete components to prevent or
control cracking. Sufficient prestress, keeping the
concrete continuously under compression after it
hardens, can prevent cracks from opening. Use of
reinforcing steel can keep the size of cracks small.
Contraction joints are another crack control
measure.They are used in concretefloors,roofslabs
and long walls mainly to control location of cracks,
by creating a plane of weakness along which cracks
are likely to occur. A contraction joint is an
indentation in the concrete, in effect, a man-made
crack. Width may be I to I in. and depth one-sixth to
one-quarter the slab thickness. The joint may be
formed by grooving the surface of the slab during
finishing orwith a sawcut shortly afterthe concrete
hardens.
Expansion Joints. Temperature changescancause
large changes in length of long slabs and walls.
Provision must be made for these movements orthe
components may crack or buckle. For this purpose,
expansion joints are used. They provide complete
separation of the parts of a long component. The
opening usually is sealed with a compressible
material to prevent the gap frombecoming jammed
with dirt and, consequently, inoperative. Where
watertightness is required, a flexible water stop of
rubber, plastic or noncorrosive metal should be
placed between the separated parts.Iftransferofload
between the parts is desirable, steel bars, called
dowels,should connect the parts,with provision for
one end of each dowelto slide in a close-fitting cap
or thimble.
Reinforced Concrete
The disadvantages of the low tensile strength of
concretescan be largely overcome by incorporating
in them, in proper locations and with appropriate
anchorage lengths, steel bars or wires designed to
withstandtensile forces.The steelmay serve entirely
as reinforcing against tension, in which case, the
combination of steel and concrete is called
reinforced concrete; or the steel may be used as
tendons, to prestress the concrete.
Reinforcing steel may also be used in beams and
columns to withstand compressive forces and thus
permit use ofsmallerconcrete members.In addition,
steel may be used to control crack openings due to
shrinkage and temperature change,to distribute load
to the concrete andother reinforcing steel, or both.
Design of reinforced concrete should conform
with requirements ofthe localbuilding code orwith
ACI 318, Building Code Requirements for
Reinforced Concrete. A Commentary on ACI 318
also is available from the American Concrete
Institute.It contains explanations andinterpretations
of the requirements in ACI 318.
Reinforcing Steel. Reinforcing bars and wires
come with smooth surfaces orwith protuberances,or
deformations, for gripping the concrete. Deformed
bars are generally used in preference to smooth bars
because of superior bond with the concrete. Wires
are usually provided as welded mesh,orfabric. The
wires may be smooth, because the cross wiring of
fabric gives ẻxcellent bond with concrete. Bars and
wires are usually produced to conformwith appli-
cable ASTM specifications.
Reinforcing bars are generally used in beams,
columns, walls, footings and long-span or heavily
loaded floor or roof slabs. Welded-wire fabric is
frequently usedin short-span orlightly loaded floor
or roof slabs.The bars orwires are placed in forms,
as required by design drawings, before concrete is
placed.They are held in their specified positions by
bar supports. These are commercially available in
four general types of material: wire, precast con-
crete, molded plastic and asbestos cement.
UnderASTM specifications,reinforcingbars may
be made of billet steel (Grades 40,60 and 75), axle
steel (Grades 40 and 60) and rerolled rail steel
(Grades 50 and 60). The grade numbers indicatethe
yield strengths of the steel in ksi. Grade 60 is
generally used in building construction. It is
provided in eleven diameters, ranging from a
nominal I in. to 21 in. Sizes are denoted by integers
that are about eight times the nominalbardiameters.
Thus,a No.3barhas a nominaldiameterofIin., and
a No. 8 bar, 1 in.
Stress-strain diagrams for reinforcing steels
permit the assumption that design may be based on
the idealized structural material with stressstrain
curve shown in Fig. 8.7, p. 216.
Reinforcing bars, often referred to as rebars for
short,may be fabricated in a shop orin the field, the
choice often depending on local union restrictions.
Fabrication consists of cutting the bars to required

lengths andperforming specified bending.The rebar
supplier often details the work (prepares shop
drawings and diagrams for placing the bars in the
forms), fabricates the bars and delivers themto the
building site.Sometimes,the supplieralso placesthe
rebars in the form.
Rebars may be placed in concrete members singly
at specified spacings or in bundles at specified
locations. Bundling is advantageous where space
available for reinforcing in a concrete member is
very tight.A bundle is assembled by wiring in tight
contact up to four bars, none larger than No. 11.
Because of limits on shipping lengths of rebars,
they have to be spliced when lengths longer than
shipping lengths are required. Splices may be made
by welding.Bars up to No.11 in size,however,may
simply be overlapped and tied together. Welded-
wire fabric also may be spliced by overlapping.
For protection against fire and corrosion, re-
inforcing steel must be embedded deeply enough
that the concrete will serve as a protective cover.
Except for slabs and joists, depth of cover between
steel extreme surface and concrete exposed surface
should at least equal the bar diameter. For extreme
exposures, such as exposure to seawater or contact
with the ground, cover should be 3 to 4 in. In
unexposedconcrete,minimum covershould be ^-in.
for joists spaced not more than 30 in. center-to-
center, slabs and walls and 11 in. for beams and
girders.
Precast Concrete
When concrete products are manufactured in other
than their final position and then assembled on the
structure being erected,they are considered precast.
They may be unreinforced,reinforcedorprestressed.
Precast productsincludeblocks,pipes,slabs,beams,
columns and piles.
Precasting is advantageous when it permits
economical mass production of concrete members
with strict quality control.Because the finalproducts
must be handled several times, shipped to the site
and erected,lowweight is important.Consequently,
precast products generally are made ofhigh-strength
concrete topermit productionofthin members.Also,
they are often prestressed to withstand handling
stresses as well as loads in service.
While precasting of concrete members may be
more economicalthan productionof the members by
casting them in place, care must be taken that
precasting savings are not offset by the cost of
handling, transporting, erecting and making
satisfactory connections in the field.
Lift-slab construction is a special type of pre-
casting performed on the building site. In this
method, floor and roof slabs are cast one atop the
other at or near ground level and then lifted into
place with jacks set atop thebuildingcolumns.After
each slab, beginning with the topmost one, reaches
its final position, steel collars embedded in the slab
are welded to the columns to secure the slab in place.
Lift-slab construction thus offers many of the
advantages of precasting while eliminating many
storing,handling and transportationdisadvantages.
Tilt-up wall construction is anotherspecialtypeof
precasting performed on the building site. For low
buildings,it provides advantages similar to thosefor
lift-slab construction. In tilt-up construction, panels
are cast horizontally at ground level at their final
position. After the panels have gained sufficient
strength, they are tilted into position, braced, then
connectedto eachotherand joinedtofloors androof.
Prestressed Concrete
In the design of reinforced concrete members,
structuralengineers assume thatthe reinforcingsteel
and only the concrete in compressionare effectivein
supporting loads. Use of concrete, however, can be
made much more efficient by applying a
compressiveprestress to the concrete.Ifthe prestress
is large enough, the concrete need never be in
tension. In that case, the whole cross section of the
member becomes effective in supporting loads.
Furthermore, the prestress will either prevent
formation of cracks or will hold themclosed if they
should form. With the whole section thus effective,
it becomes more economical to use higher-strength
concrete forprestressed concrete than forreinforced
concrete, where much of the cross section is not
considered capable of supporting loads.
The usualprocedure in prestressing concrete is to
tension high-strength steel cables or bars, called
tendons, and then anchor them to the concrete.
Because the concrete resists the tendency of the
stretched steel to shorten, the concrete becomes
compressed. Prestressing often is classified in
accordance with the sequence in which concrete is

cast and hardened and the tendons tensioned and
anchored to the concrete.
Pretensioning is a method in which tendons are
tensioned between external anchorages and then
concrete is cast to form a member and embed the
tendons throughout its length. After the concrete
attains sufficient strength to withstandprestress,the
tendons are released from the anchorages. Being
bonded to the concrete, the tendons impose
compressive forces on it.
Posttensioning is a method in which concrete is
cast around but not bonded to unstressed tendons,
which may be sheathed in protectiveducts.Afterthe
concrete attains sufficient strength, the tendons are
tensioned with jacks acting against the hardened
concrete.Then,the stressed tendons are anchoredto
the concrete, imposing compressive forces on it.
Prestressneednotcompletelyeliminate tensionin
the concrete. Sometimes, it is economical to permit
small tensile stresses or to add reinforcing steel to
resist substantialtension.The lattermethodis called
partial prestressing.
The initial prestress applied by the tendons to the
concrete decreases for several reasons. For one
thing,when prestressis transferred fromthe steelto
the concrete, the concrete shortens elastically,
allowing some shorteningofthe tendons.Also,there
are losses due to friction if the tendons are curved
and due to some slip at anchorages.In addition,there
are losses that increase with time, such as thosedue
to creep or drying shrinkage of the concrete or
relaxation of the steel. The total of these losses can
be substantial. Hence, it is desirable to use high-
strength tendonsandapply a large tensionto themin
prestressing, to make the prestress losses a small
percentage of the applied prestress force.
For pretensioning, spaced wires are usually used
as tendons. As with deformed rebars, deformations
on the wires improve bond with the concrete for
transfer of prestress.
For posttensioning, where the tendons are placed
in ducts to prevent bond with the concrete initially,
bars,strandsorgroupsofparallelwires are generally
used for prestressing. Grout, a fluid mix of cement,
fine aggregate and water,is usually pumped intothe
ducts afterthe tendonshave been anchored,to estab-
lish bond between the steel and the concrete.
To protect the tendons from fire and corrosion,
sufficient concrete cover should be provided the
steel, as is done for reinforced concrete.
Anchorage devices ofmany types are available for
transfer of prestress from tendons to concrete in
posttensioning. The methods used depend on the
type of tendons. For example, bars may come with
threaded ends on which a nut may be tightened until
it bears against steelbearing plates embeddedin the
concrete. Strands may be supplied with threaded
swaged fittings on which a nut may be tightened.
Single wires may be provided with button heads to
bear against an anchorage. Also, wires may be
anchored by wedging them with a conical wedge
against the sides of a conical opening.
Unit Masonry and Mortars
Structural members and some self-supporting
enclosures often are constructed of inorganic,
nonmetallic, durable, fire-resistant components,
called masonry units,thatare smalland light enough
for a worker to handle manually. While these units
may be fabricated into a structuralmemberora panel
in an off-site shop, they usually are assembled in
their final position with a cementitious material.
Unit masonry. This is a built-up constructionor
combination ofmasonry units bonded togetherwith
mortar or other cementitious material. Mortar is a
plastic mixture of a cementitious material, usually
portland and masonry cements or portland cement
and lime, fine aggregates and water. Sometimes,
however, masonry units are bonded together with
sulfur or an organic cement (plastics).
Masonry Units. These may be solid or hollow.
Solid units have a net cross-sectional area, in every
plane parallel to the bearing surface,equalto 75% or
more of the gross cross-sectional area measured in
the same plane.Hollowunits are those with a smaller
net cross-sectional area, because of open spaces in
them.
A line of unit masonry one unit wide is called a
wythe.A line ofmasonry one unit deep is referred to
as a course. In masonry walls, a masonry unit laid
with length horizontalandparallelwith the wallface
is known as a stretcher. A header or bonder is a
masonry unit laid flat across a wall with the end

surface exposed, to bond two wythes. Separate
wythes also may be interconnected with metal ties.
Joints may be made by mortaring together
overlapping and interlocking units.
Because unit masonryand mortareach havea low
tensile strength, masonry generally is used for
members subjected principally to compression.
Units with substantial compressive strength,
however, also can be reinforced with steel or
prestressed to resist tension, as is done with
reinforced and prestressed concrete. Principal uses
for masonry,however, are for walls and partitions.
Unit masonry may be made of various materials.
Some are suitable for load-bearing construction;
some can be exposed to the weather; some are used
principally for appearance reasons; and some serve
mainly as fire protection forstructuralmembers and
shafts. Commonly used materials include brick,
concrete block,ceramic veneer,stone,gypsumblock
and glass block. Materials generally used for
structuralpurposesinclude brick,concreteblockand
stone.
Brick is a rectangular masonry unit, at least 75%
solid, made from burned clay, shale or a mixture of
these materials.
Concrete block is a machine-formed masonryunit
composedofportlandcement,aggregatesand water.
Stone is a masonry unit composed of or cut from
natural rock. Ashlar stone is a rectangular unit
usually larger than brick. Rubble stone is a roughly
shaped stone.
Mortar. The strength of a unit-masonry structural
member dependsonthe strengthsofunitsand mortar
and on the bond between units and mortar. The
strength and bond of the mortar, however, usually
govern. Allowable unit stresses for unit masonry
generally are based on theproperties of the mortar.
Structural Masonry
There is a considerable variety ofconstructionsthat
may be called by the general term masonry, but a
critical distinction is that made between structural
and nonstructuralmasonry.Both may be made with
the same units, the distinction being the intended
purpose and general character of the construction.
Masonry used to produce bearing walls, supporting
piers, and shear walls must be structural—the
principal design concern being for structural
properties of the units, mortar, and other
construction details. Whereas appearance of the
finished construction is of major importance with
nonstruc-turalmasonry,andwhile not to be ignored
with structuralmasonry,it is not the overridingcon-
cern of the structural designer.
A second structural-masonry distinction is
between reinforced and unreinforced masonry. All
forms of structural masonry use some formof joint
reinforcement to improve the resistance of the
construction to cracking and joint separations.
Reinforced masonry, however, is developed much
the same as reinforced concrete,

with steelrods used to developmajortensile forces.
When carefully designedandconstructed,reinforced
masonry structures can attain strengths competitive
with reinforced concrete and levels of raw strength
and toughness considerably beyond those capable
with the equivalent forms of unreinforced
construction. For structural applications, reinforced
masonry construction is the only formpermitted by
codes in regions of high seismic risk.
Composite Materials and Composite Construction
In previous sections, some examples of composite
materials, such as reinforced and prestressed
concretes, and some examples of composite
construction, such as drilled-in caissons, were
discussed. In the following, some additional
examples are described.
The distinction between composite materials and
composite construction is vague. In general,
production of composite materials is a manu-
facturing process, carried out in an off-site plant,
whereas composite construction is an assembly
process done with the components in their final
position in the building.
Composite materials may be basically classified as
matrix, laminate or sandwich systems.
Matrix systems (see Fig. 8.22tf) consist of a
discontinuous phase, such as particles, flakes or
fibers, embedded in a continuous phase or matrix.
Steel-fiber-reinforced concrete and glass-fiber-
reinforced plastics are examples of such systems.
Laminates (see Fig. 8.22/?) are formed by
bonding togethertwo ormore layers ofmaterials,all
ofwhich share theload-carryingfunction.Thelayers
may all be made of the same material, as is the case
with plywood and glued-laminated timbers,orthey
may be made ofdifferent materials,such assteeland
plastic. For example, bearing plates for beams are
sometimes made of layers of Teflon and steel, a
composite that permits movement of a supported
member and also provides strength.
Sandwich systems (see Fig.8.22c) comprise at
least two load-carrying layers, or skins, between
which is a core not relied on for carrying substantial
proportions ofthe loads butwhich serves to separate
and brace the skins. Sandwich panels with metal or
plywood skins andinsulationcores,forexample, are
often used in wall and roof construction.
Composite construction is primarily used to
take advantage, for economic reasons, of specific
properties of different materials. Concrete is one
material often used because it can serve
simultaneously as an enclosure, for fire protection
and as a wear- or weather-resistant surface, while
advantage can be taken of its compressive strength.
Thus, concrete often is used as the exposed surface
of a floor, ceiling or roof. Because concrete is weak
in tension or because additional compressive
strength is needed, it is advantageous to form a
composite of concrete and a material strong in
tension, such as structural steel.
One example of composite construction is the
drilled-in caisson, in which a pile is formed by
embedding a structural steel shape in concrete.
Another example is a column formed by filling a
steel pipe with concrete. Still another example is a
beamin which the top flange is a rein
Fibers or
Particles
Layers
Fig. 8.22. Composite materials, (a) Matrix system. (/?) Laminate, (c) Sandwich.

forced concrete floor or roof slab and the web and
bottom flange are structural steel. In this case,
because the concrete is intended to resist
compressivestresseswhile the steelat the same cross
section is resisting tensile stresses,some means must
be provided to bond the two materials together.
Connectors, such as headed steel studs or steel
channels,with web vertical, often are welded to the
top of the steelfor embedment in the concrete to tie
the materials together.
A characteristic of composites of materials that
share the load-carrying junction isthat at any point
where two materials or layers are integrated, the
unit strain must be the same in both.
In a homogeneousmaterialin the elastic range,the
centroid of a cross section lies at the intersection of
two perpendicularaxes so located that the moments
of the areas on opposite sidesofan axis,taken about
that axis, are zero. For a composite material in the
elastic range, in contrast, the centroid is located at
the intersection oftwo perpendicularaxes so located
that the moments ofthe productsofeach area andits
modulus of elasticity on opposite sides of an axis,
taken about that axis, are zero.
To illustrate, consider a prism of uniform cross
section composed of two materials and with a load
of 200 kips in compression (see Fig. 8.23tz).
Suppose one material is concrete, 12- in. thick and
10 in. wide,with a cross-sectionalarea of120 sq.in.
and a modulus ofelasticity of3,000ksi.Assume that
the other material is structural steel, 2-in- thick and
10-in. wide, with an area of 5 sq in. and a modulus
of elasticity of30,000 ksi. The materials are bonded
together along the 10-in. wide faces for the full
length of the prism.
To find the centroid ofthe section, moments may
be taken about the outer face of the concrete. Let X
be the distance fromthat face to the centroidal axis
parallel to the face (see Fig. 8.23b). The distance
fromthe concrete faceto thecentroid oftheconcrete
is 12/2 = 6 in. and to the centroid of the steel 12 +
0.5/2 = 12.25 in. The product of the area Ac of the
concrete and its modulus of elasticity Ec is
ACEC = 120 X 3,000 = 360,000
The product of the area As of the steel and its
modulus of elasticity Es is
ASES = 5 X 30,000 = 150,000
Prism Centroidal Axis 2
Prism Centroid
p = 200 kips
5"->
Steel Axis
Concrete Axis
Prism Centroidal
Axis 1
(b)
Fig. 8.23. (a) Short composite column. (Ô) Cross section of column.

The sumofthese productsis ACEC + ASES = 510,000.
Then, to balance the products of areas and elastic
moduli about the centroidal axis,
510,000 X = 360,000 X 6 + 150,000 X 12.25 =
3,997,500
Solving for X yields x = 7.84 in.; that is, the
centroidal axis is 7.84 in. from the outer face of the
concrete and 12.5 - 7.84 = 4.66 in. from the outer
face ofthe steel.The 200-kip load on the prismmust
pass through the intersection of this axis with the
perpendicularaxis at the midpoint of the prismor it
will cause the prismto bend.
Since at the interface ofthe concrete andthesteel,
the unit strain in eachmaterialis the same,then from
Hooke’s law [see Eq. (8.14)] and Eq. (8.7), the load
taken by each materialis proportionalto the product
of its area by its modulus ofelasticity.Also,the sum
of the loads on each material must be equal to the
total load p = 200 kips on the prism. From these
relationships, the load on each material can be
calculated andthen the stressdetermined bydividing
that load by the area of the material. Thus, for the
concrete andsteelprism,the stressin the concreteis
f , PEc
c
- ACEC + AsEs
= 200 X 3,000 =
360,000+ 150,000 1 si
and the stress in the steel is
„ PES
f =---------— ------
s
ACEC+ASES
200 X 30,000
360,000+ 150,000 ’ si
Division of the expression for fc by that for fs
indicates that the unit stress in each material is
proportional to the modulus of elasticity. This also
follows from Hooke’s law, becausethe unit strain is
the same in both materials. Consequently,
fs = nfc (Eq. 8.17) where
n = modular ratio = ESIEC
References
H. Parker andJ. Ambrose, Simplified Mechanics andStrength
H. Rosen, ConstructionMaterials for Architects, Wiley, New
York, 1985.
R. Smith, Materials of Construction, 3rd ed., McGraw- Hill,
New York, 1979.
D. Watson, Construction Materials and Practices, 3rd ed.,
E.Allen, Fundamentals of Building Construction: Materials
and Methods, Wiley, New York, 1985.
Wordsand Terms
Allowable (working) stress
Brittle: fracture, material
Composites:
Composite construction
Composite material
Laminates
Matrix systems
Modular ratio (n)
Sandwich systems
Concrete:
Admixture
Aggregate
Air-entrainedconcrete
Curing
Forms
Portland cement, types
Precast concrete
Prestressedconcrete: pretensioned, posttensionedRebar
Specified compressive strength (f')
Water-cement ratio
Workability
Design specifications
Ductility
Elastic: limit, stress/strain behavior
Hooke’s law
Masonry:
Course
Header
Masonry unit
Mortar
Reinforcedmasonry
Stretcher
Structural masonry
Wythe
Modulus of elasticity
Plastic stress/strain behavior
Poisson’s ratio
Proportional limit
Steel:
Cable, strand, rope
Cold-formedmembers
Forming: drawing, rolling
Gage, of sheet steel, of wire

Open-web joist
Rivet
Structural shapes
Weathering steels
Welding
Strain hardening
Toughness:
Ultimatestrength
Ultimate-strength design (limit design, load-factor design)
Yield: point, strength
Wood:
Defects
Fasteners: bolts, connectors (shear), nails, screws, sheet
metal
Glued-laminatedtimber
Grade (of structural lumber)
Hardwood/softwood
Moisture content
Plywood: grade, identification index
Species (tree)
Stress/strain behavior: elastic, inelastic, plastic,ductile, brittle.
Measurements of stress/strain behavior: elastic limit, yield
strength, ultimate strength, modulus of elasticity, modulus
of rigidity (shear), Poisson’s ratio.
Design (stress-based): allowable stress, safetyfactors
Design (strength-based): design loads, loadfactors Standard
design specifications
Steel: basic metallurgy, production methods, standard
products, fasteners, fabrication and erection.
Wood: material identity and grade classification, standard
structural products, design specifications, fasteners.
Plywood: production, classification, identification index.
Concrete: components of mix, control of properties, placing
and forming, finishing, curing, reinforcing.
Precast andprestressedconcrete: constructionprocedures and
applications.
Masonry: units, mortar, construction controls, structural,
reinforced and unreinforced.
Composite materials and constructions: interactive structural
behaviors, construction applications.
8.6. TYPICAL MAJOR CONSTRAINTS ON
STRUCTURAL SYSTEMS
Building codes and nationally recognized speci-
fications and standards govern certain aspects ofthe
design of a structural system, such as minimum
design loads, acceptable materials, load factors,
allowable unit stresses and often methods for
computing load-carrying capacity of components.
As a result, corresponding design variables are
controlled orconstrained,dependingon whetherthe
designeris restricted tostandardvaluesorto a range
of values for the variables.
Loads
Structural systems must be designed to support the
maximum loads that are likely to occur during
construction and their service life or the minimum
design loads specified in building codes, whichever
is larger. Design loads on buildings include dead,
snow, live, impact, wind and seismic loads, and
sometimes also earth pressures (see Sec. 8.1).
For a specific component, only part of the dead
load, the weight of building contents, such as
furniture or equipment, and the weight of
components previously designed are known at the
start of design. The weight of the component being
designed is unknown until a material is selected for
the component and its size determined. This part of
the dead load is a controllable variable. It is,
however, subject to several constraints, typical of
which are least cost, space limitations, and
requirements imposed by other building systems.
Snow load depends primarily on the climate. A
local building code, however, may specify a
minimum design load. The load used, in any event,
is a partly controllable variable, because it can be
reduced by use of sloping roofs.
Live and impact loads are uncontrollable var-
iables. They are determined by loads related to the
function of the building, the type of occupancy and
by minimum values specified by building codes.
Some building components, furnishings and
equipment may be considered dead rather than live
loads if their location is permanent. Partitions,
however,if they may be shifted in the future,should
be treated as live loads.Building codes though,often
prescribe a uniformly distributed floor load, to be
added to the dead load, to take into account the
uncertainty of partition locations. Also, codes may
specify a concentratedload thatshould be locatedto
produce maximum effects on the system and its
components, because of the possibility of
unanticipated heavy loads.
Wind, seismic and earth loads are partly con-
trollable variables.Basically,these loads depend on
local environmental conditions; but they also vary
with such characteristics of the structural systemas
exposed surface areas, mass and stiffness.
Building designers thus have an opportunity to
reduce building costs, by adjusting values of those
variables that are partly or completely controllable,
to reduce the loads on thestructuralsystemas much
as possible.

Stability
A prime requisite of a structural systemis that it be
stable, unable to move freely and permit damage to
property orinjury to occupantsorthe public,despite
the maximum loads that are likely to occur during
construction and the service life of the building.
Stability is provided by proper arrangement and
interconnection of building components that have
adequate strength and rigidity. These components
must provide a continuous path along which loads
are transmitted to the ground.
Trusses, for example, are made stable by as-
sembling a sequenceofstructuralmembers arranged
in a triangular configuration. A horizontal beam
supported at its ends and subjected to vertical loads
is made stable by restricting points of uncontrolled
rotation,orhinges,only to the two end supports.If,
however, a third hinge is inserted in the beam, for
instance, at midspan, the beam would become a
mechanismand collapse underthe verticalloads.In
contrast,an arch with hingesattwo endsupportsand
midspan is stable.
While only a single path of load transmission is
necessary for each load, it is prudent to provide
redundancy; that is, at least two paths. Then, if one
path is destroyed by an unforeseen accident, as has
happened in the past in storms or explosions, the
structuralsystemmay basically remain stable.Often,
redundancycanbe provided with little orno increase
in initial construction cost.
Strength
This is the ability of a structural system and its
components to withstand without excessive de-
formation or collapse the maximum loads that may
be imposed during construction and the service life
of the building.Both strength understatic loadsand
strength under dynamic loads, which includes
fatigue strength under cyclic loads, are important.
Static strength of a component may be measured
in either of two ways. One measure is the load that
causesexcessive deformation orcollapse.This load,
for adequate strength, must be equal to or greater
than the service load multiplied by a factor greater
than unity, as prescribed in a building code or
nationally recognized standard.
A second measure is the maximum load under
which nowhere in the component willallowable unit
stresses assigned by a building code or nationally
recognized standard be exceeded. This load, for
adequate strength, must be equal to or greater than
the service load.
Fatigue strength also may be measuredin eitherof
two ways.One measure is the loaddetermined bythe
maximum allowable unit stress assigned forfatigue,
to avoid sudden failure under repetitive loads. A
second measure is the allowable range of stresses at
any point as the unit stressfluctuates with change in
load. For stress reversal, in which stresses alternate
between tension and compression, the stress range
should be taken as the numerical sum of the
maximum repeated tensile and compressivestresses.
Fatigue strength is likely to be of concern only for
components subjected to frequently moving loads,
such as crane runways, or for supports for
machinery. While wind and seismic loads cause
fluctuating stresses, occurrence of full design loads
is usually too infrequent to governstrength design.
Strength under dynamic loads in general is
measured by the ability of the structuralsystemand
its components to absorb energy. Except for tall,
slender buildings and special structures, however,
structural systems are often permitted by building
codes tobe designedforan equivalent static loading.
Determination of energyabsorbing capacity,
however, may be required for systems to be
constructed in regions known or suspected to be
subject to heavy seismic shocks.
Rigidity
This is the ability of a structural system and its
components to withstand without excessive
deformation the maximum loads that may be
imposed during construction and the service life of
the building.Of specialconcern are controlofbeam
deflections; drift, or sway, of a building under
horizontal loads; and prevention of buckling, either
locally or overall, of components subjected to
compression.
Rigidity is necessary forcomponents subjected to
dynamic loads to control vibrations and their
transmission.
Cost
The objective of structural engineering is a stable
structuralsystemwith required strength and rigidity

that will have the lowest life-cycle cost. It is not
sufficient that the materials selected for the system
have the lowest cost or that the systemcontain the
smallest amount of materials of all possible
alternatives.
Life-cycle cost is the sumfor the whole structural
system of the costs of raw materials, fabrication,
handling, storage, shipping, erection and
maintenance after erection. Because this sum is
difficult or impracticable to estimate during the
design stage, other measures are often used in cost
comparisons.
For example, cost of a structural steel frame may
be measured by multiplying the weight, lb, of steel
by a price per lb. Cost of a wood frame may be
measured by multiplying feet board measure by a
price per ft. Cost of a concrete system may be
measured as the sum of the product of volume of
concrete,cuyd,byprice percu yd andthe product of
weight of reinforcing steel, lb, by a price per lb. In
each case,the unit price is taken as greaterthan that
forthe rawmaterialto coverfabrication,erectionand
othercosts.In selection oftheunit price,care should
be taken to incorporatethe effectsoffabrication and
erection characteristics of each structural system.
SECTION 8.6
References
Buildings and Other Structures, American National
Standards Institute, New York, 1982.
F.Merritt, Building Design and Construction Handbook, 4th
Wordsand Terms
Cost (structural): components of, life-cycle
Rigidity Stability Strength: static,dynamic, fatugue, adequate
service Loads: dead, design (service)
Issues
Control ofloads as a design variable.
Components of control of rigidityandstability. Redundancy
as a safety factor.
Types of strength.
Structural cost as a design variable.
8.7. TENSION MEMBERS
This section deals only with members subjected to
axial tension(no bending ortorsion).Designofsuch
members requires selection of a material and
determination of dimensions of a cross section
normal to the load. Also, the type of connections to
be made to othermembers and the type,numberand
size of fasteners to be used in the connections must
be decided. This decision affects the net cross-
sectionalarea at the connection and may govern the
design of the member.
The required cross-sectional area may be cal-
culated by recasting Eq. (8.6) in the form:
A=f (8.18)

If ultimate-strengthdesign is used, Trepresents the
factored load and fti the yield stress ofthe material.
If working-stressdesign is used, Tis the service
load and ft, the allowable unit-tensile stress.In
eithercase,?lis the critical net cross-sectionalarea,
overwhich failure is likely to occur.
The net section equals the gross cross-sectional
area, or the area included between the
outer surfaces of the member, less the area of any
openings orholes.Generally,tension members have
a constant cross section, except at connections.
Consequently, the critical design section occurs at
connections, where openings may be provided for
bolt holes (see Fig.8.24a, b and d) orfor connectors
(see Fig. 8.24tf, / and h) or where the area may be
reduced by threads to receive nuts.
(a)
Plan
(b)
Side
(e)
Plan
(f)
Side
Fig. 8.24. Bolted joints in tension, (a) to (d) Steel bars connected with two bolts, (e) to {h} Wood members
connected with bolts and split rings.

Figure 8.24« shows a plan viewand Fig. 8.247? a
side view of a bolted connection between two
rectangular steel bars under tension. Between
connections, bar A has the solid cross section
(normal to the tensile force T) shown in Fig. 8.24c.
At the upper bolt, however, the cross-sectional area
is reduced by thearea ofthe bolt hole,the product of
the material thickness and sumof bolt diameter and
I in. clearance (see Fig. 8.24J).
Figure 8.24e shows a plan view and Fig. 8.24/a
side view of a split-ring connection between two
pieces of lumber in tension. Between connections,
piece A has the solid cross section (normal to the
tensile force T) shown in Fig. 8.24g. At the upper
bolt,however,the cross-sectionalarea is reduced by
the sumof the projected area ofthe split ring on the
section and the portion of the bolt-hole area not
included in that projected area (Fig. 8.24/z).
The critical section need not be normal to the
tensile stress. The critical area may occur in a
diagonalplane oralong a zigzag surface where there
are two or more holes near each other. The AISC
Specification for the Design, Fabrication and
Erection of Structural Steel for Buildings and the
NFPA National Design Specification for Stress-
Grade Lumber and Its Fastenings present methods
for computing the net section of steel and wood
tension members,respectively.Similar methods may
be used for other materials.
8.8. COLUMNS
This section deals with members subjected to axial
compression. For short compression members,
dimensions ofcrosssectionsnormalto the load may
be computed with Eq. (8.7), by solving forthe area,
as is done fortension members.No reductionin area
need be made for bolt holes, however, because
fasteners are assumed to fill the holes and to be
capable of withstanding the compression.
Forsome materials,suchas concrete,thatare weak
in tension,provision should be made to resist tensile
stresses, computed with Poisson’s ratio for the
material, in directions normal to the compressive
stresses. For this purpose, concrete compression
members usually are reinforced around the
perimeter, with steel-bar ties or spirals encircling
longitudinal reinforcing bars.
Columns are long compression members. Di-
mensions of their cross sections normal to the axial
load are relatively small compared with theirlength
in the direction of the load. Although a long
compressionmembermay be straight when the load
is applied (see Fig. 8.25«), it may bend, or buckle,
suddenly and collapse when a certain load is
exceeded (see Fig. 8.257?). This load is called the
critical, or Euler, load.
Buckling may occurlong before the yield stress is
reached at any point in the column.The strengthofa
long column,therefore,is not determined bytheunit
stress in Eq. (8.7), as is the strength of short
compressionmembers,butbythemaximum load the
column can sustain without becoming unstable and
buckling. In members intermediate in length
between short and longcolumns,however,the yield
stress may be exceeded at some points before
buckling occurs.
Fig. 8.25. Effective lengths of columns for various end conditions.

Stable Equilibrium
The column with ends free to rotate shown in Fig.
8.25tf is initially straight. It will remain straight as
long as the load c is less thanthe criticalload Pc.Ifa
small transverse force is applied, the column will
deflect, but it will become straight again when the
force is removed.This behavior indicatesthat when
c < Pr, internal and external forces are in stable
equilibrium.
the strengthofa column,depends not onthestrength
of the material but, as indicated by Eq.
(8.19) , on the stiffness of the material, as mea-
sured by E.
As mentioned previously, column behavior
depends on the ratio of length to cross-sectional
dimensions. This relationship may be expressed
more precisely by representing cross-sectional
dimensions by the radius of gyration r of the cross
section.
Radius ofgyration is definedby
Unstable Equilibrium
If c acting on the column in Fig. 8.25iZ is increased
to Pc and a small transverse force is applied, the
column will deflect,as with smaller loads,but when
the force is removed, the column will remain in the
bent position (see Fig.8.25b). Repeated application
and removalofsmalltransverse forcesorapplication
of axial loads greaterthan Pc will cause the column
to fail by buckling. This behavior indicates that
when c = Pc, internal and external forces are in
unstable equilibrium.
Euler Loads
Application ofbendingtheory to analysis ofcolumn
behavior indicates that, if stresses throughout the
member do not exceed the yield stress, the smallest
value of the Euler load for a pin- ended column is
given by
r. ^EI
p = —T-
c
L2
where
E = modulus of elasticity of the material in the
column
L = length of column
1= moment of inertia about an axis through the
centroid of the column cross section
The axis for which moment of inertia is smallest
should be chosen,because buckling willoccurin the
direction normal to this axis. {Moment of inertia is
the sumof the productsofeach area comprising the
cross section bythe square ofthe distanceofthearea
from the axis.)
Note that the Euler load, which determines
(8.20)
where
A = cross-sectional area of the column
For a rectangular section, r= t/y/12 about an axis
through the centroid and in the direction of the
width,where t is the thickness.Fora circularsection,
r = dỊ4 for every axis through thecentroid,where d
is the diameter of the circle. The AISC Steel
Construction Manuallists themoment ofinertia and
radius of gyration for structural steel shapes.
Equation (8.19) for the Euler load can be ex-
pressed in terms of the radius of gyration if both
sides of the equation are divided by A and Eq.
(8.20) is used to eliminate I. The result is
The left side of the equation gives as a measure of
column strength a unit-compressivestress.Theright
side of the equation indicates that the stress is
proportionalto modulus ofelasticityandis inversely
proportional to the square of the ratio of length to
least radius of gyration.
This important ratio is known as the slenderness
ratio of the column.
Equation (8.21)applies only to pin-endedcolumns
with stresses within the elastic limit. For other end
conditions, the column formula may be written as
(8-19)
Pc _ 7Ĩ2
E
Ã~ỴẼĨrý (8.21)
pc= ^E
A (kL/f)2 (8.22)

where
k = factordetermined by end-support conditions
for the column; forexample: Both ends fixed
against translation androtation (seeFig.8.25c), k
= 0.5
One end pinned, one end completely fixed
(see Fig. 8.25d), k = 0.7
Both ends fixed against rotation,butoneend
can drift (Fig. 8.25e), k = 1.0
One end completely fixed, but the otherend
can drift and rotate (see Fig.8.25/), k = 2.0
One end pinned, but the other end can drift
while fixed against rotation (see Fig.
8.25g), k = 2.0
The product of k and the actual column length is
called the effective length of the column. For the
conditions shown in Fig. 8.25, effective length
ranges fromhalf the actualcolumn length to double
the column length. Slenderness ratio, in general
then,is the ratio ofeffective length to least radiusof
gyration of the column cross section.
In columns with a slendernessratio belowa certain
limiting value, the elastic limit may be exceeded
before the column buckles. In such cases, E can no
longer be considered constant. It may be more
accurate to substitute for E in Eq. (8.22) a tangent
modulus, the slope of the stress-strain curve for the
material at a point corresponding to actual unit
strains in the column.
Column Curves
These are the lines obtained by plotting criticalunit
stress with respect to the corresponding slenderness
ratio.A typicalcolumn curve (see Fig.8.26)consists
of two parts: a curve showing the relationship
between Euler loads and slenderness ratios, which
applies for large slenderness ratios, and a curve
showing the relationship between tangent-modulus
critical loads and slenderness ratios, which applies
for smaller slenderness ratios.
The curve for the smaller slenderness ratios is
greatly influenced by the shape of the stressstrain
curve for the column material. Figure 8.2ÓỠ shows
the column curve fora material that does nothavea
sharply defined yield point; for instance, a material
with a stress-strain curve suchas that in Fig.8.6c, p.
214. For such material,the tangent-modulus critical
loads increase with decrease in slenderness ratio.
Figure 8.26Z? shows thecolumn curve fora material
with a stress-strain curve that approximates that
shown in Fig. 8.6Z?, with a sharply defined yield
point. For such material, the tangent-modulus
critical loads become nearly constant at small
slenderness ratios, because the tangent modulus of
the material is very small.
Forlarge slenderness ratios,column curves have a
steep slope. Consequently, critical loads are very
sensitive to end conditions, as measured by the
factor k. Thus, the effect of end conditions on the
stability ofa column is much largerforlong columns
than for short columns.
Local Buckling
The preceding discussion of column instability
considers only buckling of a column as a whole.
Instead, a column may fail because of buckling of
one of its components; forexample, a thin flange or
web. Hence, in determination of the
Slenderness Ratio - L/r
(a)
Fig. 8.26. Column curves for materials, (a} Without a sharply defined yield point. (Ô) With a sharply defined
yield point.
Slenderness Ratio - L/r
(b)

(824) = (8.28)
strength of a column, the stability of components
should be investigated as well as that of the whole
column. To decrease the possibility of local
buckling, design standards generally limit the ratio
of unsupported length or width to thickness of
components in compression.
Behavior of Actual Columns
Equation (8.22) for column strength is derived from
theoretical considerations. Columns in structures,
however, behave differently from the idealized
column on which the equation is based. Actual
column behavior is affected by many factors,
including the effects of nonhomogeneity of
materials, initial stresses, initial crookedness and
eccentricity of load. Also, effects of end conditions
may be difficult to evaluate accurately.
Consequently,columns generally are designed with
the aid of empirical formulas. Different equations
are used for different materials and for short,
intermediate and long columns.
Structural-Steel Column Formulas
For axially loaded structural steel columns, the
allowable compressive stress on the gross cross
section is given by formulas selected in accordance
with the range in which the slendernessratio kL/rof
the columns lies. One formula is used for short
columns; anotherformula is used forlong columns;
and still anotherformula is used forslender bracing
and secondarymembers.The divisionbetweenshort
and long columns is determined by the slenderness
ratio Cc corresponding to the maximum stress for
elastic buckling failure:
Cc = ZlTĩ2
EỊFy (8.23)
where
E = the modulus of elasticity of the steel
= 29,000 ksi
Fy = the specified minimum yield stress,ksi, of the
steel
For kLỊr<CCì the allowable compressive stress,
ksi, is
r 5 t 3kL/r ịkLỊrý-
■ ■ 3 8Cc 8Cc
2
F.s. is a safety factor.It varies from1.67 when kL/r
= 0 to 1.92 when kL/r = Cc.
When kLỊr>CCì the allowable
compressive stress, ksi, is given by Eq.
(8.22), with a safety factor of 1.92 and E taken as
29,000 ksi:
Since Fy does not appear in this formula, the
allowable stress is the same forall structural steels.
For bracing and secondary members with
Zz/r>120, the allowable compressive stress, ksi, is
This formula permits higherstresses than Eq. (8.26)
and allows k to be takenas unity.The higherstresses
are warranted by the relative unimportance of the
members and the likelihood of restraint at their end
connections.
Tables ofallowable stresses are given in the AISC
Steel Construction Manual.
Wood Column Formulas
For wood columns of structural lumber with
rectangular cross sections, allowable column
compressionstress (F')is determined by one ofthree
formulas.Use ofa particularformula,is basedonthe
value of the slenderness ratio, which is determined
as Lid forthe rectangularsectioncolumn, d beingthe
dimension of the side of the section in the direction
of buckling (the least dimension of the column if it
is freestanding).The formulas and the limits for Lid
are as follows:
Zone 1: 0 < Lid < 11
F' = Fc
where Fc = allowable maximum compression
parallel to grain.
Zone 2: 11 < Lid < K
(8.25)
149,000
a = Wfý (8.26)
as
1.6-Z,/200r (8.27)

where K — 0.671 IEIFC and E = modulus of
elasticity ofthe particularspeciesandgrade ofwood
Zone 3: K < Lid < 50
_ 0.3 E ___
F'c = 77772 (8.29)
c
(L/d)2
The value of 50 for Lid is the maximum permitted
for a solid wood column.
Adjustments are made to the formulas for
columns with other cross sections, such as round
columns.
Reinforced Concrete Columns
Ultimate-strength design, with factored loads, is
used for reinforced concrete columns. The material
is treated as a composite. Axial load capacity is
taken as the sumof the capacity ofthe concreteand
the capacity of the reinforcing steel. The ACI
Building Code, however, applies a capacity
reduction factor 0 = 0.75 for columns with spiral
reinforcement around the longitudinal bars and 0 =
0.70 for other types of columns.
The capacity ofthe longitudinalreinforcement of
an axially loaded column can be taken as the steel
area A's times the steelyield stress Fy.The capacity
of the concrete can be taken as the concrete area
times 85% of the 28-day compressive strength fc of
the standard test cylinder. The ACI Building Code,
however,requires thatallcolumns be designed fora
minimum eccentricity of load of 1 in. but not less
than 0.1 Oh for tied columns and 0.05/z for spiral-
reinforced columns, where h is the overall column
thickness in the direction ofbending.Design tables
for columns are given in the ACIDesignHandbook,
SP 17.
8.9. TRUSSES
In structural frameworks, loads from roofs and
upper floors are transmitted to the ground through
columns. Structural members, therefore, must be
provided to carry loads fromthe roofs and floors to
the columns. When the column spacing is large,
trusses often are an economical choice for those
structuralmembers.For economy,however,trusses
usually have to be deep and consequently they can
be used only ifthere willbe sufficientspace forthem
and adequate headroom under them. (Openweb
joists, which are actually shallow trusses, are used
on close spacing, about 24 in. center- to-center and
for shorter spans or lighter loads than ordinary
trusses. While open-web joists can be designed in
the same way as ordinary trusses, the joists are
excluded from the discussion in this section.)
Because of the space requirements, the principal
application of trusses in buildings is for supporting
roofs.
Basically, a truss is a stable configuration of
interconnected tension and compression members.
The connections between members are assumed in
truss design to be pinned, free to rotate, although
actually the types of connections used may apply
some restraint against rotation of truss joints.
To preclude bending of the truss members,
location of loads applied to trusses should be
restricted to the truss joints. Also, at each joint, the
centroidal axes of all members at the joint and the
load at the joint must pass through a single point,
called the panel point.
Three members pinned togetherto forma triangle
comprise the simplest typeoftruss.Ifsmallchanges
in the length ofthemembers underload are ignored,
the relative position of the joints cannot change.
Hence, the configuration is stable. More
complicated trusses are formed by adding members
in a continuous sequence of triangles.
Ordinary trusses are coplanar; that is, all the
component triangles lie in a single plane. Typical
roof trusses shown in Fig. 8.27 are of this type.
Trusses, however, also may be three dimensional.
Such trusses usually are called space trusses or
space frames.
As indicated in Fig. 8.27, the top members of a
truss are known as the upper, or top, chord.
Similarly, the bottommembers are called the lower,
or bottom,chord. Vertical members may simply be
called verticals, or posts when they are undergoing
compression, or hangers when they are undergoing
tension. Inclined members incorporated between
chords are called diagonals.Verticals and diagonals
are collectively referred to as web members.

Load Vertical
(a) King Post
(b) Howe (e) Howe
(c) Pratt (f) Pratt
(d) Bowstring
Fig. 8.27. Types of roof trusses.
(g) Uarren
Truss Joints
Figure 8.28 shows howconnections are often made
in steel and wood trusses with fasteners.
Figure 8.28« shows a bolted joint at the topchord
of a steel Warren truss in which the members are
composed of pairs of angles. The connection is
made through a steel gusset plate inserted between
each pair of angles at the joint. In the case
illustrated,the gage lines ofthe fasteners closest to
the outstandinglegs ofthe angles meet at the panel
point. The applied load would be centered directly
above the panel point.
Connections in steeltrusses alsomay be made by
welding.In that case,ifthe web members are single
or double angles, the connections can be made
without gusset plates by using for the
Fig. 8.28. Forms of truss connections, (a) At top chord of a steel truss with bolted joints and gusset plate. (6) At
top chord of steel truss with welded joints, (c) In a light wood truss.

top and bottomchordsWT shapes,made by cutting
a wide-flange shape longitudinally along the web,
and then inserting theWT web between eachpairof
angles (see Fig. 8.28Z?).
Fig. 8.28c shows halfofa symmetricalwood truss
with top chord inclined on a slope of 4 on 12. This
truss is ofa type that might be used tosupport lightly
loaded roofs on spans from20 to 30 ft, for example,
for houses. The connection at the support, or heel,
and connectionswhere more thantwo members meet
are made with machine bolts and split rings,as is the
bottom-chord splice at midspan. Elsewhere, the
connections are nailed and made through a piece of
lumber, called a scab. In more heavily loaded
trusses,members may be composed oftwo or more
pieces of lumber instead of the single component
shown in Fig. 8.28c.
Stresses in Trusses
The reactions of a truss usually can be calculated
from the laws of equilibrium [see Eqs. (8.1) and
(8.2)]. (For wind loads, the horizontal components
of the reactions often are assumed equally divided
between the two supports,to simplify calculations.)
Afterthe reactionshavebeen determined forspecific
loads,the stressesin the trussmembers canbe deter-
mined by vector analysis, either analytically or
graphically,except for unusualtrusses.The stresses
can be found simply by applying the laws of static
equilibrium. These laws require that, if a section is
cut in any mannerthrough a truss,the vectorsumof
internal and external forces must be zero on either
side of the section, and the sumof the moments of
the forces about any point must be zero.
A commonly used sectionis onetakencompletely
around a single joint,to isolateit from the rest ofthe
truss.The forcesactingthenare the load at thepanel
point and the stressesat thecut endsofthe members
of the joint. The stress in each member is directed
along the centroidalaxis ofthe member. Because all
the forces intersect at the panel point, the moments
of the forces about that point is zero. To satisfy Eq.
(8.1), the sumof the horizontalcomponentsand the
sumof the verticalcomponentsofallthe forces also
must be zero.
Fig. 8.29. Stresses in truss members, (a) Forces acting
at truss heel (support), (b) Force vector triangle
indicating equilibrium at the joint.
As an example,considertheheelofthewoodtruss
in Fig. 8.28c. A circularsection may be taken around
the joint, as indicated by section 1-1 in Fig. 8.29tf.
This sectioncuts throughthe supportandthe top and
bottomchords, which are represented in Fig. 8.30tf
by their centroidal axes. The forces acting on the
isolated portion of the truss then are the reaction R,
the stress c in the top chord, assumed to be
compression, and the stress T in the bottomchord,
assumed to be tension. Note that R is vertical, and
the top chord is the only member at the joint with a
vertical component. Hence, the vertical component
of c, by Eq. (8.1), must be equalto R but oppositely
directed. As indicated in Fig. 8.29Z?, if Ớ is the
angle the top chord makes with the horizontal, c
must be equalto R/sin 0.This value ofc can nowbe
used to determine the stresses in the next topchord
joint.The value ofTcan alsobe found by application
of Eq. (8.1) to the isolated joint. The law requires
that the sumof the horizontal forces be zero. As a
result,T must be equalto the horizontalcomponent
of c but oppositely directed.As shownin Fig.8.29b,
T = R cot 0. This value of T can now be used to
determine the stresses in the next bottom-chord joint.
Fig. 8.30. Stressesin a truss with parallel chords.

A section commonly usedfortrusseswith parallel
chords is one taken vertically between panelpoints.
Consider, for example, the part of the Pratt truss in
Fig. 8.30 isolated by cuttingthe trusswith section2-
2. The forces acting are the reaction 7?; loads p at
two panel points; stress c in the cut top chord,
assumed to be compression; stress T in the cut
bottomchord,assumed to be tension,and stress sin
the cut diagonal, assumed to be tension. All the
stresses may be calculated by application of Eq.
(8.2), which requires that the sumofthe moments of
all forces be zero. To find T, moments should be
taken about the panelpointwhere c and s intersect:
2Rp - Pp- Th = 0
where p is the panel length. In this case, with R =
2.5P, T-^PpỊh, where h is the depth of the truss. To
find c, moments should be taken about the panel
point where T and s intersect:
3Rp - 2Pp - Pp - Ch = 0
In this case,c = 4.57^/71. (If the directions of c and
Thad been incorrectly assumed,the solutionswould
have appeared with negative signs, indicating that
the directions should be reversed.)
The stress s in the diagonal can be determined in
either of two ways.
One method is as follows: For the truss with
parallel chords shown in Fig. 8.30, the diagonal is
the only membercut by section2-2that has a vertical
component. This vertical component is the only
force available at the section for resisting the
imbalance ofthe verticalcomponents ofthe external
forces.This vertical shear equals R — IP = 2.5P —
2P = 0.5P. Hence,the verticalcomponent of s must
equal0.5P, and s = Ồ.5P sec 0 = 0.5Pl/h,where Iis
the length of the diagonal.
The second methodis usefulwhen the trusschords
are not parallel,as is the case with bowstringtrusses
(see Fig. 8.27d). In this method, s is first resolved
into a vertical component V and a horizontal
component H,both locatedat the intersection ofthe
diagonal and the bottomchord. Then, moments are
taken about the bottom-chord panelpoint justinside
section 2-2 and set equal to zero:
2Rp - Pp - Ch + Vp = Q
from which, since c has already been computed, V
can be determined.
Bracing of Trusses
Because the components of ordinary trusses are
coplanar,suchtrusses offerlittle resistance to forces
normal to their plane or to buckling of the
compression chord unless adequate bracing is
(c) Partial Plan of Roof Framing
Fig. 8.31. Roof framing for an industrial building, symmetrical about both centerlines.

provided.Rooforfloorframing can be used tobrace
the top chord. Usually, however, additional
horizontal and vertical bracing are necessary,
because the bottomchord, although in tension, is
long and slender.
Figure 8.31b showsa Pratt trussfora roofwith just
enough slope in two directions to provide good
drainage ofrainwater.The roofis supportedoneight
such trusses,each truss supported at its two endson
columns. The roof framing is symmetrical in two
directions.Hence,Fig.8.31c shows only five of the
eight trusses. Also, the upper half of the plan view
shows only the framing for the upper chords,
whereas the lower half of the drawing shows only
the framing for the lower chords. Similarly, Fig.
8.31a shows only half of the cross section through
the roofnormalto the trusses.In allcases,thehalves
not shown are identical to the halves shown.
Figure 8.31a shows that three pairs of trusses are
braced laterally by cross frames containing two
diagonals in a vertical plane. Purlins supporting the
roof and carried by the trusses brace all the top
chords.Struts lying in the same plane as the purlins
and the cross frames brace the bottomchord.
Figure 8.31c indicates that,in addition,horizontal
diagonal bracing is placed in the plane of the top
chords.This bracing should be designed to transmit
wind loads on the building to bracing in vertical
planes along the sides and ends of the building, for
transmission to the foundations.
Economics of Trusses
Trussesofferthe advantage oflighterweight forthe
long spansorheavyloadsforwhich they are usually
used thanthat forbeams.Also,the openingsbetween
truss members often are usefulforpassage ofpipes,
ducts and wiring.
Costs of trusses, however, are not necessarily
lower than costsofbeams,despite the lesseramount
of material in trusses.Fabrication anderectioncosts
for trusses and their bracing must be taken into
consideration.Also,use oftrussesmay be restricted
to types of buildings in which fire protection of the
trusses is not required orto locations in which costs
of fire protection are sufficiently low.
SECTIONS 8.7-8.9
References
J. McCormac, Structural Analysis, 4th ed., Harper & Row,
New York, 1984.
ed., McGraw'-Hill, New York, 1982.
Words and Terms
Axial load
Buckling
Effective length (column)
Equilibrium: stable, unstable
Euler load
Moment of inertia
Net section
Radius of gyration
Slenderness: column, ratio
Truss parts: chords, heel, panel points, gusset plate
Axial loadin linear members.
Net section in tension members.
Column actions: buckling, failurestress relatedtoslenderness,
end conditions and effective length.
Stresses (internal forces) in trusses.
Bracingof truss systems.
8.10. BEAMS
Like trusses,beams are usedto support floors,roofs,
walls, machinery and otherloads overspaces below.
Unlike trusses, however, beams are solid between
their top and bottom surfaces. Consequently, they
are subjected to both bending and shear stresses.
Beams generally are more economical than trusses
for short spans and light loads and are necessary
where space for structural members is limited or
headroombelow is restricted.
The term beam is applied in general to structural
members subjected principally to bending stresses.
In specific applications, beams may be called by
other names. For example, joists are light
floorbeams; stringers support stairs; headers frame
openings in floors and roofs; purlins are light,
horizontalroofbeams; rafters are light,inclined roof
beams; girts are light members that span between
columns to support curtain walls; lintels are light
members that cany walls at floorlevels in multistory
buildings oroverwindowor dooropenings; girders
are heavily loaded beams orbeams supportingother
beams; spandrels support exterior walls and floor
edges in multistory buildings; grade beams are

shallowwalls at ground leveland extending slightly
below to enclose the bottomof a building.
Typesof Beams
Beams may be supported in various ways.One type
of support is applied at the end of a beam and
restricts translation but permits free rotation. This
condition is representedbythe symbolshownin Fig.
8.32a or by the forces in Fig. 8.32b. A support
instead may restrict translation but permit a member
that is continuous over it to rotate freely. This
condition is representedbythe symbolshownin Fig.
8.32c and by the forces, including moments
represented by curved arrows, in Fig. 8.32J. The
symbolshown in Fig. 8.32e indicates a support that
restricts only vertical movement. Only a vertical
reaction is present(see Fig.8.32/).Alternatively,the
end of a beammay be fixed, or com-
(b) (d) (f) (h)
Fig. 8.32. Beam supports, (a) Hinge, or pin. (b) Forces
acting on beam at hinge, (c) Continuous, {d} Forces
acting in continuous beam at support, (e) Hinge support
that permits horizontal movement. ( f} Force acting on
beam at support shown in (e). (g) Fixed (clamped) end.
(h} Forces acting on beam at a fixed end.
pletely restricted against movement.The symbolfor
this condition is shown in Fig. 8.32g and the forces
are shown in Fig. 8.32b.
Beams may be classified in accordance with the
methods of support. A beam free to rotate at both
ends is called a simply supported, or simple beam
(see Fig. 8.33a). The beam in Fig. 8.33b is a
cantilever.The beamin Fig. 8.33c is a simple beam
with overhangs. The overhangs are also called
cantilevers. Hung-span, or suspended-span,
construction results when a beam is connected
between the overhangs oftwo otherbeams (seeFig.
8.33J). Figure 8.33e shows a fixed-end beam.Figure
8.33/shows a beamwith one-end fixed and one end
free to rotate and move horizontally. A three-span
continuous beam is illustrated in Fig. 8.33g.
Reactions for the beams in Fig. 8.33a to d can be
computed fromthe laws of equilibrium [Eqs. (8.1)
and (8.2)]. When the reactions have been
determined,internalforces in the beams also can be
calculated from the laws of equilibrium, as will be
demonstrated later.Such beams are called statically
determinate beams.
The equations of equilibrium, however, are not
sufficient for determination of the reactions or
internal forces for the beams of Fig. 8.33e to g.
Additional information is needed. This may be
obtained froma knowledge of beamdeformations,
which permits development ofadditionalequations.
For example, the knowledge that no rotation or
translation of a beam end can occur at a fixed end
permits development of equations for obtaining the
reactions of the beams in Fig. 8.33e and/. Beams
such as those in Fig. 8.33e to g are called statically
indeterminate beams.
Internal Forces
The externalloads on a beamimpose stresses within
the beam.Consider,forexample, the simple beamin
Fig. 8.34a. Section 1-1 is cut vertically through the
beamto the right of the first load p. The part of the
beam to the left of section 1-1 nevertheless must
remain in equilibrium. Consequently, as shown in
Fig. 8.34b, the loads must be counterbalanced by a
shearing force K| and a moment Mị, to satisfy the
laws of equilibrium. If the left reaction RL is

known,Vị and Mỵ can be computed.FromEq. (8.1),
vỵ = -RL + p. From Eq. (8.2), Mj = -RLXX + P(xx -
a).
The moment Mỵ that counterbalancesthemoment
about section 1-1of RL and p is provided within the
beam by a couple consisting of a force c acting on
the top part ofthe beamand an equalbut oppositely
directed force T acting on the bottom part of the
beam(see Fig.8.34c). c at section 1-1is the resultant
of unit compressive stresses acting over the upper
part of the beam. T at section 1-1 is the resultant of
unit tensile stressesacting overthe lowerpart ofthe
beam.
The surface at which theunit stresseschangefrom
compressiontotensionandat whichthe stressis zero
is called the neutral surface.
Shear
The unbalanced forces on either side of any section
taken normal to the neutral surface of a beam is
called the shearat the section.Forthe portion ofthe
beamon the left ofthe section,forcesthat actupward
are considered positive andthose thatact downward
are considered negative.Forthe portion ofthe beam
on the right of the section, the signs should be
reversed.
Bending Moment
The unbalanced moment ofthe forces on eitherside
of any sectiontaken normalto the neutralsurface of
a beamis called the bending moment at the section.
Forthe portion ofthe beamon theleft ofthe section,
clockwise bending moments are consideredpositive
and counterclockwise bending moments are
considered negative. When the bending moment is
positive,thebottomofthe beamis in tension,the top
in compression. For the portion of the beamon the
right of the section, the signs should be reversed.
When thebendingmoment andshearare known at
any section, the bending moment and shear at any
other section through the beam can be computed
from the laws of equilibrium. For example, for the
beamin Fig. 8.34ứ, the bending moment at section
2-2 can be determined
Fig. 8.33. Types of beams, (a) Simple beam, (b} Cantilever, (c) Simple beam with overhangs, (d) Hung- span, or
suspended-span, construction, (e) Fixed-end beam. ( f} Beam with one fixed end, one simply supported. (g}
Three-span continuous beam.
Fig. 8.34. Bending stresses in a beam, (a) Simple beam with concentrated loads. (6) Bending moment and shear
at section 1-1. (c) Bending moment replaced byan equivalent force couple, c and T, at Section 1-1. (Ờ) Bending
moments and shears at sections 1-1 and 2-2.

from the bending moment and shear at section 1-1.
Figure 8.34J shows the shearand bending moments
acting at sections 1-1 and 2-2. From Eq. (8.2), the
sumofthe moments aboutsection 2-2forthe portion
of the beam between section 1-1 and 2-2 must be
zero. Hence,
Ml + vx2 - Pb - M2 = 0
from which
M2 + ViX2 - Pb
This result can be generalized as follows:
The bending moment at any section of a beam
equals the bending moment at any other section on
the left, plus the shear at that section times the
distance between sections, minus the moments of
intervening loads. If the section with known shear
and moment is on the right,the moment ofthe shear
and the moment of intervening loadsshould bothbe
subtractedfromthe knownbending moment because
of the reversal of the sign convention. w, however,
the shear curve is a straight line sloping downward
from left to right. The slope ofthe line equals — w;
that is,at any distance X fromthe startofthe line,the
verticaldrop ofthe line equals wx,which is the total
uniformload within the distance X.
Figure 8.35 shows some sheardiagrams forsimple
beams with fromone to three concentratedloads and
a uniform load. Note, for example, that the shear
diagram for the single concentrated load in Fig.
8.35ơ can be drawn bystartingonthe left byplotting
to a selected scale the magnitude ofthe left reaction
ofthe beambP/Lupward.Fromthe left reaction over
to the load p, the shearcurve is a horizontalstraight
line, as drawn in Fig. 8.35/?. At the locationofp,the
shearcurve drops vertically a distance p (to the same
scale at which the reaction is plotted).Fromp to the
right reaction, the shear curve is again a horizontal
straight line.At the location ofthe right reaction,its
magnitude aP/L is plotted upward, to complete the
diagram.
Shear diagrams for a combination of different
Shear Variation along a Beam
A beammust be capable ofresisting the designshear
at every normal section along the neutral surface.
The design shear at a section is the maximum that
can be produced there by any possible combination
of dead, live and other loads.
For a specific set of loads, it is convenient for
design purposes to plot graphically the variation of
shearalong thespan.Usually,the sheardiagramcan
be speedily drawn by application of simple
principles.
For instance, from the definition of shear, if a
beam is horizontal and the loads are vertical, the
shearat anysection is the algebraic sumofthe forces
that lie on either side of the section. Consequently,
if only concentrated loads are applied to the beam,
the shearcurve is a straight,horizontalline between
the loads. Furthermore, at a concentrated load, the
shear curve moves in the direction of the load
abruptly vertically a distance,in accordancewith the
scale selected for the diagram, equal to the mag-
nitude of that load.
For a uniformly distributed downward load
(d) Shear Diagram
Fig. 8.35. Shear diagrams for various types of loads
on a simple beam.

loading conditionscanbe plotted by superpositionof
the diagram for each condition. For example, the
shear diagram for the loads in Fig. 8.35e and a
uniformly distributed load w can be plotted by
adding the ordinates of the shear diagram in Fig.
8.35/to the ordinates of the shear diagram in Fig.
8.35/ỉ, when these diagrams are drawn to the same
scale.
Moment Variation along a Beam
A beammust also be capable ofresisting the design
bending moment at every normal section along the
neutralaxis.The designbendingmoment at a section
is the maximum that can be produced there by any
possible combinationofdead,live and other loads.
For a specific set of loads, it is convenient for
design purposes to plot graphically the variation of
bending moment along the span. Usually, the
bending-moment diagramcan be speedily drawn by
application of simple principles.
For instance, from the definition of bending
moment, at any section the bending moment is the
algebraic sumofthe moments ofthe forceson either
side of the section. Consequently, for a specific set
of concentrated loads, bending moment varies
linearly with distancefromthe loads.Asa result,the
bending-moment curve between any two
concentrated loads, for a beam subjected only to
concentrated loads, is a straight line. For a uniform
load, however, the curve is parabolic. Bending
moment for a uniform load varies as the square of
distance, inasmuch as the total load increases with
distance.
For any set of loads, the maximum bending
moment occurs where the shear curve passes
through zero shear.
Figure 8.36 shows some bending-moment
diagrams for a simple beamwith from one to three
concentrated loads and for a uniformly distributed
load. Note, for example, that the bending-moment
diagram for the single concentrated load p in Fig.
8.36a can be started at either the left or the right
beam end. In either case, the bending moment at a
distance X from either reaction equals the reaction
times X. The bending-moment curve,therefore,is a
straight line on both sidesof p,with a slope bP/Lon
the left of p and a slope —aP/L on the right of
p (Fig. 8.36Z?). The maximum bending moment
occurs at the location of p, where the two lines
intersect, and is equal to Pab/L.
The bending-moment diagrams for the loading
conditions in Fig. 8.36c and e can be drawn by
computing the bending moments at each
concentrated load, plotting the moments to scale at
the location of the corresponding loads and then
connecting the plotted points with straight lines.
The bending-moment diagram for the uniform
load w in Fig. 8.36g is a parabola symmetricalabout
midspan. Its equation can be formulated by
determining the bending moment at a point X from
the left reaction. The reaction equals wLI2, and its
moment is wLx/2. The load totals wx, its moment
arm is x/2, and its moment therefore is wx2
/2. Con-
sequently, the bending moment for a uniformly
loaded simple beamis
w T w ? w
M = j Lx - j X2
= I x(L - x) (8.30)
This is the equation for the parabola shown in Fig.
8.36/1. The maximum bending moment occurs at
midspan and equals wL2
/8.
Bending-moment diagrams for combinations of
different loading conditions can be plotted by
superpositionofthe diagramforeach condition.For
(f)
Fig. 8.36. Bending moment diagrams for various types
of loads on a simple beam.

example, the bending-moment diagramforthe loads
in Fig. 8.36e and a uniformload w can be plotted by
adding the ordinates of the bending-moment
diagramin Fig. 8.36/ to the ordinates ofthe bending-
moment diagram in Fig. 8.36/1, when these
diagrams are drawn to the same scale.
Fixed-End Beams
A fixed-end beam has both ends completely fixed
against translation and rotation. It is statically
indeterminate, because its reactions, bending
moments and shears cannot be determined fromthe
laws ofequilibrium. Forverticalloads,each reaction
consists of a vertical force and a moment, which
prevent vertical movement and end rotation. These
reactions can be computed by adding to Eqs. (8.1)
and (8.2) equations that indicate that the end rota-
tions are zero.
Figure 8.37 shows for a fixed-end beam of
constantcrosssectiontheshearandbendingmoment
diagrams for a single concentrated load p and a
uniform load w. The shear diagramfor the uniform
load (see Fig. 8.37e), because of the symmetry of
loading and beamgeometry,
Fig. 8.37. Shear and bending moment diagrams for a
single concentrated load and a uniformly distributed
load on a fixed-end beam.
is the same as for a simple beam (see Fig. 8.37/ỉ).
The shear diagramfor the single concentrated load
(see Fig. 8.37Z?) is the sheardiagramforthe simple
beamin Fig. 8.37tf displaced vertically, because of
the presence of equal but oppositely directed forces
at each end ofthe beam,to counterbalancethe fixed-
end moments.
The bending-moment diagram for the single
concentrated load (see Fig. 8.37c) is the bending-
moment diagram for the simple beamin Fig. 8.37tf
displaced vertically, because of the occurrence of
negative moments at each end of the beam. The
maximum positive bending moment still occurs at
the location of the concentrated load. Similarly, the
bending-moment diagramfor the uniformload (see
Fig. 8.37/) is the bending-moment diagramfor the
simple beamin Fig. 8.37/1 displaced vertically, be-
cause of the occurrence of negative end moments.
The maximum positive bending moment stilloccurs
at midspan. For the uniform load, however, the
maximum negative moment is larger than the
maximum positive bending moment. For fixed-end
beams,in general,maximum bending moments may
occurat eitherbeamend orat one oftheloads onthe
span.
Note that in a simple beam(see Fig.8.37) bending
moments vary from zero at the beam ends to a
maximum in the interior of the beam, usually near
midspan. As a result, much of a simple beam is
subjected to low bending stresses. In a fixed-end
beam(see Fig. 8.37), in contrast,the ends as wellas
the centerofthe beamare subjectedto large bending
stresses. Consequently, a greater portion of a fixed-
end beamthan ofa simple beamis usefulin carrying
loads.
With a uniformly loaded fixed-end beam, it may
be economical to use a light section for the center
portion and deeper sections, or haunches, at the
beam ends, to resist the larger bending moments at
the ends.
The bending moments and shears in a fixed- end
beam are influenced by the cross-sectional
dimensions throughout the beam. In contrast, the
bending moments and shears in a simple beam are
independent of the beam cross- sectional
dimensions. The effects of the cross

sectional dimensions of a fixed-end beam are
introducedby the equationsdevelopedby settingthe
end rotations equal to zero. As a consequence of
these equations, deepening the ends of an initially
prismatic fixed-end beam increases the negative
bending moments at the ends.At the same time, the
positive bending moments decrease. Hence, the
effect of haunches on the prismatic beamis similar
to that of a decrease in span.
Continuous Beams
The variation of bending moments and shears in a
loaded span of a continuous beamis similar to that
of a fixed-end beam. If the loads on a horizontal
continuous-beamspanare vertical,the reaction at an
interior support or at an end that is not simply
supported consists of a vertical force and a bending
moment. The beam is statically indeterminate,
because the reactions, shears and bending moments
cannot be determined fromthe laws of equilibrium.
Additional equations are needed to account for the
continuityofthe beamovereachinteriorsupport and
for restraints, if any, on rotations at the ends of the
beam. The equations can be developed from the
continuity requirement that the rotation ofthe beam
at a support must be the same on both sides of the
support. As a consequence of these equations,
verticalloads on a spaninduce negative endbending
moments, and the bendingmoment diagram
resembles those in Fig. 8.37 for fixed-end beams.
Figure 8.38tf shows one loaded span of a
continuousbeam.Fora single concentratedload,the
bending-moment diagram for that span (see Fig.
8.38c) looks very much like the bending-moment
diagramin Fig. 8.37c for a fixed-end beamwith the
same loading.The continuous spanalsohas negative
bending moments at its supports,and the maximum
positive bending moment is smaller than that in a
simple beam.
The bending-moment diagrams in Figs.8.37c and
8.38c can be obtained by superposition of the
bending-moment diagrams for each of the span’s
external forces considered acting on a simple beam
of the same span. For example, the loaded span in
Fig. 8.38tf may be taken as equivalent to the sumof
the loaded simple beam in Fig. 8.38b, the simple
beam with negative end moment ML at the left
support and the simple beam with negative end
moment MR at the right support. The bending-
moment diagram in Fig. 8.38c then is equivalent to
the sum of the corresponding bending-moment
diagrams for those load conditions, as indicated in
Fig. 8.38/ to h.
As for a fixed-end beam, bending moments and
shears are influenced by the cross-sectional
dimensions throughout a continuous beam. The
effects of the cross-sectional dimensions are in-
troducedby the equations developedby equatingthe
end rotations of spans continuous at a support.
Note also that for a continuous beam the laws of
equilibrium require that at every support the
algebraic sum of the end bending moments must be
zero.
Fig. 8.38. Bending moment diagram for a span of a continuous beam resolved into component moment
diagrams for a simple beam with the same span.

Bending Stresses in a Beam
The bending moments imposed on beams by loads
are resisted at every section normal to the neutral
surface by unit compressive and tensile stresses
parallel to the neutral surface. The product of the
average compressivestressabovetheneutralsurface
and the section area in compression equals the toal
compressive force Cat the section (see Fig. 8.34c).
Similarly, the product of the average tensile stress
below the neutral surface and the section area in
tension equals the totaltensile force T at the section
(see Fig. 8.34c). Determination of the unit stresses
requires that assumptions concerning beam
geometry, loads and strain distribution be made.
To insure that bending is not accompanied by
twisting, the beam cross-section should be sym-
metrical about a plane perpendicular to the neutral
surface.Also,theloadsshould lie in that plane.As a
result, the line of action of the loads will pass
through the centroidal axis of the beam.
Because many structuralmaterials behavelike the
idealized structural material with a stress-strain
curve as shown in Fig. 8.39Z?, beams will be
assumed to be made of this material. Accordingly,
within the proportional limit, unit stress equals the
product of the modulus of elasticity of the material
E and the unit strain.Also,the modulus ofelasticity
in tension is the same as that in compression.
Tests and experience indicate that it is reasonable
to assume furthermore that, in a beam subjected to
pure bending, cross sections that are plane before
bending occurs remain plane during bending. As a
result, both total and unit strains vary linearly with
distance fromthe neutral surface.
Elastic Range. Consider, for example, a
vertical section through a loaded horizontal beam,
(a) Load Diagram (b) Stress-Strain Curve
(c) (d)
Strain Distribution
Stress Distributions Corresponding to strain Distributions Above
Fig. 8.39. Bending stresses in the elastic and plastic ranges.

such as section1-1in Fig. 8.39«. The material ofthe
beam is assumed to have the stress-strain curve
shown in Fig. 8.39/?, with stress proportional to
strain up to the yield stress fy and correspondingunit
strain ev. For larger strains, stress remains constant
at/v.
Under service loads, unit strains at section 1-1
vary linearly with distance fromthe neutralsurface,
where unit stresses are zero. The maximum unit
strain is e, and the plane of the cross section rotates
through an angle Ộ(see Fig. 8.39c). At a distancey
from the neutral surface then, the unit strain equals
ey/c,where c is the distance fromthe neutralsurface
to the outer surface at the section. From Hooke’s
law, the maximum unit stressis f = Ee, and the unit
stress at a distance y fromthe neutralsurface equals
fy/c. The force exerted on section 1-1 by the stress
equals the product of the stress and the very small
area A A of a strip parallelto the neutralsurface.The
moment of this force about the neutral surface then
is fy2
AA/c.
The bending moment M on section1-1is equalin
magnitude to the total resisting moment of the
stresses. Thus,
M=Vfy2
AAlc (8.31)
where the summation is taken over the whole cross
section of the beam. By definition, Sy2
AX is the
moment of inertia / of the cross section about the
neutral axis. Substitution in Eq. (8.31) yields
M = - (8.32a)
c
from which the maximum unit stress is
r=y (8.32b)
Equation (8.32) is known as the flexure formula.
The ratio He in Eq. (8.32) is called the section
modulus. For a rectangular section with depth d
normal to the neutral surface and width
b,
/ = y- (8.33)
and the section modulus is
5 = 7 = y- (8.34)
The AISC Steel ConstructionManuallists moments
of inertia and section moduli for structural-steel
shapes.
PlasticRange. Suppose the loadp onthesimple
beam in Fig. 8.39« were increased until the
maximum unit stress at section1-1became the yield
stress fy and thecorrespondingunit stress became ev.
The interior of the section would remain in the
elastic range. The strain distribution would be the
same as that shown in Fig. 8.39J and the stress
distribution the same as that shown in Fig. 8.39/ỉ,
both still linear.
Suppose now the load were increased until the
maximum unit strain was several times larger than
ev, say kty. The cross section would remain plane
(see Fig. 8.39c). But the stress distributionwould no
longer be linear. The part of the cross section with
strains greaterthan ev would be stressed to fy.In the
rest of the section, the unit stresses would decrease
linearly to zero at the neutralsurface(seeFig.8.390-
With further increases in load, the unit strains
would increase rapidly (see Fig. 8.39/). The unit
stresses would become a constant fy throughout the
whole section, which then would be totally plastic
(see Fig. 8.39j).
During the process of load increase, the cross
section would rotate froman angle Ộat service loads
(see Fig. 8.39c) to <Ị)y when the yield stress is
reached initially (see Fig. 8.39c/). Under larger
loads, the section will rotate freely, like a hinge,
without change in bending moment. The section is
said to have become a plastic hinge.
Before a plastic hinge could format section 1-1,
however, the beam would fail, because a plastic
hinge would form first at the section where
maximum bending moment occurs, under the load.
The beamwould then have three hinges-one at each
end and one under the

load—and it would act like a mechanism, rotating
freely with little or no increase in load.
The capacity,orultimate strength,ofa beamcan
be measured by the resisting moment for the stress
distribution in Fig. 8.39/ The capacity can be
expressed by the plastic moment:
Mp=Zfy (8.35)
where
z = plastic section modulus
FromFig. 8.39/ fora rectangularbeamwith depth
d and width b, the plastic section modulus is
z = ÈỂ (8.36)
4
(The AISC Steel Construction Manual lists plastic
section moduli for structural-steel shapes.)
Comparison of Eq. (8.36) with Eq.
(8.34) and letting / =fy in Eq. (8.32a) indicates that
a rectangular beam can resist 50% more moment
after the yield stress is first reached at the outer
surfaces.
Recall now that in a uniformly loaded fixed- end
beam, the negative end moments are much larger
than the positive moments. Suppose the uniform
load were increased beyond the service load.Plastic
hinges would formfirst at the beamends,where the
bending moment is maximum. At this stage, the
beam would start to act as if it were simply
supported. Load then could be further increased
without failure occurring,untila third hinge formed
at midspan,the point ofmaximum positive bending
moment. At this stage, the bending moment at each
hinge is the same and equals WpL2
/}6, where Wp is
the uniformload at which the third hinge forms and
L is the span. Assume now that the beam has a
constant cross section with plastic section modulus
z. Substitution in Eq.
(8.35) yields
Wp = f>fyZ!L2
(8.37)
From Fig. 8.37/, the bending moment at which the
first hinges formis WVL2
/12, where wy is the load at
that stage. Then, by Eq. (8.35),
Wy = UfyZlL2
(8.38)
Consequently, the capacity of the beam is 33%
greaterwhen failure occurs than at formation of the
first hinge, as indicated by comparison with Eq.
(8.37). For a simple beam, the moment at which the
third hinge forms is w’pL2
/8, as indicated in Fig.
8.36/1, and by Eq. (8.35),
Wp = 8ẠZ/Ả2
(8.39)
Hence, by comparison with Eq. (8.37), a fixed- end
beamwith the same spanandcross sectioncan carry
twice as much uniformload as a simple beam.
Behavior of a uniformly loaded continuous beam
is similar to that of a fixed-end beam. Thus, a span
of a continuous beamcan carry much larger loads
than a simple beam of the same length and cross
section.This indicates that it is advantageous to use
continuous beams instead ofsimple beams whenever
conditions permit.
Combined Bending and Axial Stresses
Some structural members may be subjected to both
bending and tensile axial loads. The resulting unit
stress at any point is equalto the sumofthe bending
stress and the tensile stress at that point.Thus,ifthe
assumptions of the flexure formula hold, the
maximum stress at anyverticalsection is tensile and
equal to
(8.40)
where
p = axial load
A = cross-sectional area of the member
M = bending moment at the section
c = distancefromneutralsurfaceto surface where
maximum unit stress occurs
I = moment of inertia of the cross section about
the neutral surface
The bending moment need not be caused by
transverse loads but instead by the eccentricity e of
the axis. In stress is
p Pec p / ec
— + -7- = — 1 +
A I A r2
load with respect to thecentroidalthat
case,M~Pe and the maximum
(8.41)

where r= radius ofgyrationofthe crosssection[see
Eq. (8.20)].
When the axial load is compressive, it has an
eccentricity nevertheless, because of the beam
deflection due to bending.The bendingmoment PA
due to the deflection A should be added to the
bending moment M.Fora beamwith relatively small
bending deflections, however, the maximum stress
is compressive and given closely by Eq. (8.40).
Unit Shear Stresses in Beams
The shear on a section of a beam normal to the
neutral surface is resisted by nonuniformly dis-
tributed unit shearstresses.Accordingto Eq. (8.10),
the horizontal unit shear stress at any point in the
section equals the vertical unit shear stress at that
point. So when the horizontal unit shear stress has
been determined,theverticalunit shearstressis also
known.
Consider the loaded beamin Fig. 8.40ứ. Vertical
sections 1-1 and 2-2 are taken very close together.
The bendingmoment atsection 2-2is largerthanthat
at section 1-1.Consequently,theunit compressiveor
tensile stress at any distance y from the neutral
surface is greateron section 2-2 than on section 1-1
(see Fig.8.40c). Forequilibrium, the unbalancemust
be resisted by a horizontalshear.This force,in turn,
induces horizontal unit shear stresses fv on the
surface at the distance y fromthe neutralsurface(see
Fig. 8.40J). The corresponding vertical unit shear
stresses on section 2-2, X in Fig. 8.41c, combine to
resist the totalshearon section 2-2.The relationship
between this shear and the change in bending mo-
ment between sections 1-1 and 2-2, and use of the
flexure formula [see Eq. (8.32)], leads to the
following formula for unit shear stress at any point
of section 2-2:
VQ
fv = -^ (8.42)
where
V = shearon the section
I = moment of inertia ofthe beamcross section
b = width of the beamat the point
Q = moment, about theneutralsurface,ofthe
cross-sectionalarea ofthe beamincluded
between the nearest surface free ofshear
(outersurface,forexample) and a line,
parallel to the neutralsurface,drawn through
the point
Fig. 8.40. Unit shear in a beam, (a) Simple beam with concentrated load, (b) Beam cross section, (c) Bending unit
stresses at sections 1-1 and 2-2. (Ờ) Distribution of unit shear stresses at section 2-2. (e) Vertical unit shear
stresses at section 2-2.

For a rectangular cross section (see Fig. 8.40Z?),
for determination of the unit shear at a distance y
from the neutral axis,
Q = b(c - y) (y + yy
(8.43)
The moment of
inertia I of the rectangular cross section equals
bd3
112. Hence, the unit shear stress at any point is,
by Eq. (8.42), where A = cross-sectionalarea of the
beam.
This equationindicatesthatfora rectangularcross
section the unit shear stress varies para- bolically
over the depth of the beam (see Fig. 8.40J). The
maximum shear stress occurs at middepth, where y
= 0. The maximum shear on a rectangular section
then is
. V
Á=1.5-J (8.45)
A
Thus, the maximum shear is 50% larger than the
average shear V/A.
In structural design, however, it is common
practice to compute the average shear stress and
compare it with an adjusted allowable unit stress.
Beam Deflections
When a horizontal beam is loaded by vertical
downward-acting loads in its vertical plane of
symmetry, the unsupported portion of the beam
moves downward, that is, bends. The new, curved
position of its originally straight, longitudinal
centroidalaxis is called the elasticcurve ofthe beam.
The vertical distance between the initial and final
position ofa pointon thecentroidalaxis is called the
deflection of the beamat that point.
Beam deflections are determined for several
reasons. One of the most important reasons is that
Jv
8bd C2
J
be2
bd2
8
(8.44)

the effect of beamdeflection on supported objects,
especially those that may be damaged by large
movements, needs to be known. Another important
reason is that large deflections are unsightly. In
addition,deflectionsmay beneeded in determination
of reactions, shears and moments of statically
indeterminate beams, as discussed previously.
Beam deflections may be calculated by any of
severalmethods,all based on the same assumptions
as the flexure formula [see Eq. (8.32)]. Of principal
concern in most cases is the maximum deflection of
a beam. For a simple span, symmetrically loaded
beam, this will occur at the midspan point. For a
cantileverbeam,it will occurat the unsupported end.
Derived by various theories,formulas for maximum
deflection take the general form,
ym = c (8.46) turn,traps more
water,as a result ofwhich the beams may fail.
One method of limiting beam deflections is to
require the maximum deflection to be less than a
specific fraction ofthe span.Forexample,fora beam
supporting plasterceilings,maximum deflection for
live loads may be restricted to not more than Z/360,
where L is the beamspan.
Another method is to set limits on the ratio of
beamdepth to span.Forexample, fora beamof A36
steel subjected to normal loading, the beam depth
should not be less than Ả/22.
Camber. A sagging beam is not aesthetically
appealing and may induce in observers a lack of
confidence in the safety of the structure. Con-
sequently, heavily loaded or long-span beams and
trusses oftenare cambered,that is,given an upward
deflection equal to the deflection anticipated under
dead load.Then,when the structureis completed,the
beamortruss becomes straight underthe dead load.
where
ym = maximum vertical deflection
w = beamload (in pounds, kips, etc.)
E = elastic modulus of the beammaterial
I = moment of inertia of the beamsection about
the bending axis
Figure 8.41 shows several common loadings for
beams and the corresponding formulas for
maximum deflection. Note that for the uniformly
loaded beams,with unit linear load of w, the load is
expressed in total force units; thus w = w(L). For
beams with concentrated loads, the load is
traditionally expressed as p, as shown in the
formulas in Fig. 8.41.
Limits on Deflections. Design standards generally
set limits on the maximum deflections of beams.
This is done to preventdamage to objectssupported
on the beams and to controlvibrations ofbeams.In
addition,the deflectionofroofbeams supportingflat
roofs must be restricted to prevent ponding ofwater
on the roof. The weight of water trapped on a
saggingroofcausesadditionaldeflections,which,in
Buckling of Beams
Because parts of a beam are in compression, the
beam may buckle, just as a column may buckle
under a critical load. For example, a narrow,
rectangularbeammay deflect normalto the plane of
the loads as wellas in the direction ofthe loads.This
buckling can be prevented byuse ofa lowallowable
compressive stress,lowratio of span to beamwidth
or short unsupported length of compression flange.
The unsupported length can be decreased by place-
ment of intermittent bracing at sufficiently close
intervals or reduced to zero by a continuous
diaphragm,such as plywoodsheathingora concrete
floor orroofslab,firmly securedto the compression
flange.
Local buckling of a compression flange or of a
beamweb undera concentratedload also may occur.
This may be prevented by use of a low allowable
compressive stress orlow ratio of width or depth of
beam components to their thickness. For cold-
formed steel beams, it is common practice to
consider only part of the cross-sectional area
effective in resisting compression,depending onthe
width-thickness ratio of components. Thin webs of
deep structural steel beams are often reinforced at
concentrated loads with stiffeners. These may be
plates set perpendicularto the web and welded to it
or angles with one leg bolted or riveted to the web
and the otherleg setnormalto the web.Compression
flanges of cold- formed steel beams often are
reinforced with a lip,or edge of flange bent parallel
to the web (see Fig. 8.12).
Design standards for the various structural

materials contain requirements aimed at prevention
of beambuckling.
Reinforced Concrete Beams
While structural steel, cold-formed steel and wood
behave structurally much like the idealized
structural material for which the flexural formula
was derived,especially in the elastic range,concrete
does not. As pointed out in Sec. 8.5, concrete has a
much lower tensile strength than compressive
strength.Ifplain concretewere usedforbeams,they
would fail due to tension well before the ultimate
compressive strength is attained.
To make use of concrete more economical for
beams and to avoid sudden, brittle failures, one
method employs steelreinforcement,usually rebars,
to resist the tensile bending stresses. The bars are
most effective forthis purpose whenplacedas close
to the outer surface that is in tension as proper
concrete cover for fire and corrosion protection
permits.
Design Assumptions. Computation of bending
strains, stresses and load-carrying capacity is based
on the following assumption:
Unit strain in the concrete andreinforcing steelis
the same. Hence,
fs = nfc (SAI)
where
fs = unit stress in reinforcing steel
fc = unit stress in concrete
n = modular ratio = Es/Ec
Es = modulus of elasticity of the steel
Ec = modulus ofelasticity ofthe concrete (secant
modulus)
Sections that are plane before bending remain
plane during bending. Hence, total and unit strains
are proportionalto distance fromthe neutralsurface.
The maximum usable unit strain at the outer
concrete surfacein compressionequals0.003 in. per
in.
Steel unit stress less than the specified yield
strength fy equals Eses, where es is the steel unit
strain.Forunit strainslargerthanfyỊEs,the steelunit
stress is independent of unit strain and equals fy.
Unless unit tensile stresses are very low, tensile
strength of concrete is zero, because of cracks.
Behavior under Service Loads. Cast-in-place
concrete beams are usually cast at the same time as
floor or roofslabs.As a result,the beams and slabs
are monolithic.While the part ofthe beambelowthe
slab may be rectangular in cross section, the beam
that is effective in resisting bending is actually T-
shaped, because the slab works together with the
concrete and steel protruding below. Precast
concrete beams, however, often are rectangular in
cross section, but other shapes, including tees and
double tees, also are commonly used. In the
following discussion of the behavior of concrete
beams,however,a rectangularcross section is used
for illustrative purposes. The principles presented
nevertheless are also applicable to othershapes and
to beams reinforced in both tension and
compression.
Figure SA2a shows a simply supported,reinforced
concrete beam, with width b and depth h.
Reinforcing steelis placed at a distance d belowthe
outersurface in compression (see Fig.8.42c and d).
Totalsteelarea provided is As. If fs is the unit stress
in the steel, then the force available for resisting
tension is
T = Asfs (8.48)
Under service loads p, cracks are formed on the
tension side of the beam(see Fig. SA2a). (Because
the reinforcing steel resists opening of the cracks,
they may not be visible.)Section1-1is taken normal
to the neutralsurface between cracks and section2-
2 is taken at a crack. Figure 8.42b shows theportion
of the beambe-

tween the two sections.A compressive force CỊ acts
on the upper part of the beamat section 1-1, while
tensile force TS1 acts on the steel and tensile force
TcX acts on the concrete bottom portion. For
equilibrium, C| = Tsỵ + Tcl. Simultaneously, a
compressive force c2 acts on the upper part of the
beam at section 2-2, while tensile force ?2 acts on
the steel. Because of the crack, the concrete is
assumed to offer no resistance to the tension (see
Fig. 8.42d). For equilibrium, c2 = r2.
The unit strains at section 1-1 vary linearly (see
Fig. 8.42e). Also, the unit stresses in the concrete
vary linearly overthe whole depth ofthe beam(see
Fig. 8.42/z). Conditions,however,are much severer
at section 2-2.
Since cracks may occur at any place along the
tension surface of a reinforced concrete beam,
design must be predicated on the assumption that
conditions similar to those at section 2-2 may
develop at anysectionconsidered.The magnitude of
the stresses andstrains,however,will depend onthe
bending moment at the section.
At section 2-2, unit strains are proportionalto the
distance from the neutral surface (see Fig. 8.42/).
Consequently, the steel unit strain is related to the
concrete unit strain by
^2 = eC2 (8.49)
k where kd is the depth ofthe portionofthe beam
in compression.The compressive unit stresses also
vary linearly (see Fig.8.420- Hence,the total
compressive force is
Concrete
(a) (b) (c) (Ờ)
Strain Distribution
Fig. 8.42. Bending stresses in a reinforced concrete beam, as load increasesfrom serviceload to ultimate load.

c2 = ±fckbd (8.50)
where
fc = maximum compressive unit stress in the
concrete
With the use of Eq. (8.47), Eq. (8.49) can be
converted to the useful relationship:
Í - hi <->
where
fs = unit stress in the steel
Equating c2 as given by Eq. (8.50) and T2 as given
by Eq. (8.48) yields
fckbd = Asfs = pbdfs (8.52)
where
p = As/bd orratio ofreinforcingsteelarea to concrete
area
Simultaneous solution of Eqs. (8.51) and (8.52) for
k yields
k = yjlnp + (np)2
— np (8.53)
The bending moment at section 2-2 is resisted by
the couple c2 and T2, which have a moment arm jd
(see Fig. 8.42/?). Because of the linear variation of
concrete stress, c2 acts at a distance kd/3 from the
outerbeamsurface in compression.Hence, jd = d —
kd/3 and
k
j = 1
- I (8.54)
The resisting moment of the beam in compression
can be found by taking moments about the centroid
of the reinforcing steel:
Mc = ị fckjbd2
(8.55)
Similarly, the resisting moment of the beam in
tension can be found by taking moments about the
centroid of the compression area:
M, = f'A'jd = fspjbd2
(8.56)
When allowable unit stresses are used in design,
Eqs. (8.51) through (8.56) provide sufficient
information for design ofreinforced concrete beams
for resistance to bendingmoments.In such cases,it
is desirable thatMc be greaterthan Ms so that failure
will occur in tension. Yielding of the steel,
permitting wide cracks to form, will give warning
that failure is imminent.
Bending Strength. If the loads p on the beam
in Fig. 8.42a are gradually increased,the cracks will
lengthen, the neutral surface will move upward and
eventually the reinforcingsteelwill be stressedto its
yield point fy.With furtherincrease in load,the steel
will carry no greater tensile force than Asfy. (It is
assumed here that the beamis so proportioned that
failure by crushing of the concrete will not occur
before the steelreaches its yield point.)At this stage,
unit strains are stillproportionalto distancefromthe
neutralsurface (see Fig.8.42g); but the compressive
stress in the concrete no longeris proportionalto the
unit strain. The stress distribution is likely to
resemble that shown in Fig.8.42J. The ratio a ofthe
average compressive stress to the 28-day
compressive strength of the concrete/' is 0.72 for f'c
up to 4 ksi, but decreases by 0.04for each ksi above
4 ksi. The resultant compressive forcec2 at thisstage
acts at a distance jSc below the outer concrete
surface in compression, where c is the depth of the
part of the beamin compression (see Fig. 8.42j). /3
= 0.425 forf’c up to 4 ksi, but decreases by0.025 for
every ksi above 4 ksi.
While the strength of the beamcan be computed
from the preceding information, it is common
practice to assume a simpler but equivalent
distribution of compressive stresses. Usually, the
unit compressive stress when the steel reaches its
yield point fy is assumed constant at 0.85 f’c. The
depth ofthis rectangularstress distribution(see Fig.
8.42fc) is taken as

a = /3ỊC, where 31 = 0.85 for/c up to 4 ksi, but
decreases by 0.05 for every ksi above 4 ksi. These
assumptionsmake the rectangularstress distribution
equivalent in computations of moment-resisting
capacity to the stress distribution shown in Fig.
8.42j.
The depth c of the compression area in Fig. 8.42j
can be obtainedbyequatingthetotalcompression c2
= af'cbc to the tensile force T2 = Asfy = pbdfy. The
result is
(8.57)
The resisting moment in tension then equals
Mu = AJyjd = Asfy (d - 0
Asfy I d 2 Asfyd 11 2otff
p/
(8.58)
The steel ratio p should be chosen small enough
that the unit strain in the concrete does not reach
0.003 in. per in. to avoid failure by crushing of the
concrete.
The ACI Code requires that a capacity reduction
factorỘ = 0.90 be applied to the strength ofa beam
[see Eq. (8.58)] to provide for small adverse
variations in materials, workmanship and
dimensions.
Shear Strength. Longitudinal reinforcement
placed close to the tension surface of a reinforced
concrete beamresiststension due to bending.There
are also, however, tensile unit stresses associated
with shear unit stresses. As pointed out previously,
maximum unit shear stress occurs away from the
beam outer surfaces and at or near the neutral
surface. Consequently, tensile stresses due to shear
are also at a maximum near the neutral surface.
These stresses are inclined at an angle of 45° with
the verticalsectionon which theshearacts.At some
distance fromthe neutralsurface,thetensile stresses
due to shear,which decrease with distance fromthe
neutral surface, occur at a section where there is
appreciable horizontal, tensile bending stresses,
which increase with distance from the neutral
surface. The vector sum of the shear and bending
tensile stresses act at an angle to the horizontal and
is known as diagonal tension. Usually, it is
necessaryto providesteelreinforcement in concrete
beams to resist this diagonal tension, which can
cause flexuralcracks to curve toward midspan,as in-
dicated in Fig. 8.43ứ and c.
If the shear strength at a vertical section of a
horizontal beamis VU9 lb, the nominal shear stress,
psi, at the section is given by where
bw = width ofa rectangularbeamorof the web of
a T beam, in.
d = depth from outer compression surface to
centroid ofreinforcement fortensile bending
stresses
0 = capacity reduction factor = 0.85
Because the associated tension acts on a diagonal,
the section formaximum shear vu may be taken at a
distance d from the face of each support in simple
beams, unless the beams are very deep.
Stirrups
Rebars
Fig. 8.43. Shear reinforcement for a reinforced concrete
beam, (a) and (b} Stirrups, (c) and (d) Bent- up
longitudinal rebars.
If the concrete will not crack at the stress
computed fromEq.(8.59), no shearreinforcement is
needed to resist the diagonal tension. Tests indicate
that the shear unit stress vc that causes cracking in
normabweight concrete lies between 2 /fl and 3.5
'Jfl, whereis the 28day compressive strength of the
concrete, psi. The actual value of vc depends on the
J; _ Vụ Vu
ộbwd
(8.59)

ratio of shearto moment at the section and the ratio
of longitudinalsteelarea to the area of the concrete
web. The lower value of vc can be used for
conservative calculations.
If vu > vc,steelreinforcement mustbe provided to
resist the tensile stresses due to vu - VC9 but the ACI
Code requires that vu — vc not exceed 8
Stirrups are commonly used as shear rein-
forcement in reinforced concrete beams. A stirrup
has barlegs lying in a vertical plane and close tothe
outer, vertical beam surfaces. The legs are hooked
around the longitudinal steel reinforcement or have
plain hooks of 90° or more (see Fig. 8.43b). The
cross-sectional area Av of the legs provides the
required resistance to diagonaltension.Stirrupsmay
be set vertically as in Fig. 8.43a or at an angle. In
eithercase,theyshould be setclosely enoughsothat
at least one stirrup will pass through every possible
location ofa 45° crack.Also the ends,orhooks,ofa
stirrup should be anchored in a compressionzone of
the beam. The area, sq in., required in the legs of a
vertical stirrup is
. vu — vr ,
Av = — ---------bws (8.60)
Jy
where
fy = yield strength of the shear reinforcement, psi
s = spacing, in., of the stirrups
For inclined stirrups, the right-hand side of Eq.
(8.60) should be decreased by dividing by sin a 4-
cos a, where a is the angle of inclination of the
stirrups with the horizontal.
An alternative method of providing shear re-
inforcement is to bend up reinforcing bars at an
angle of 30° or more, as indicated in Fig. 8.43c and
d. Bending moments producing tension at the
bottom of a beam generally are maximum near
midspan and decrease rapidly with distance toward
the supports. Hence, fewer reinforcing bars are
needed as the supports are approached. Those bars
not needed may be bent up to serve as shear
reinforcement.The area required for a single baror
a single group ofparallel bars all bent at an angle a
at the same distance from the support can be
computed by dividing the right-hand side of Eq.
(8.60) by sin a.
The ACI Code requires, however, that at least
some shear reinforcement be incorporated in all
beams with total depth greater than 10 in., or more
than 2| times the flange (slab) thickness, or
exceeding halfthe web thickness,except where vu is
less than ị vc. The area of this minimum shear
reinforcement should be at least
A„ - (8.61)
Jy
Prestressed Concrete Beams
The concept ofprestressedconcreteis presented and
the advantages of prestressing are discussed in Sec.
8.5. In the following, the application ofprestressing
to beams is discussed.
Consider as an example the prestressed concrete
beam in Fig. 8.44a. Assume that it is simply
supportedandthat it will carry uniformly distributed
dead and live loads.The bending moment due tothe
total load then will vary par- abolically from a
maximum Mị at section 1-1, at midspan, to M2 at
section 2-2,and then tozero at the supports.Suppose
now that tendons are placed in the beam in a
parabolic shape,sagging close tothe tensionsurface
at midspan andanchoring closeto the centroidalaxis
of the beam cross section at the supports. A total
force Ps is applied to tensionthe tendons.(The angle
of inclination ofthis force at the supports is actually
so small that the horizontal component of this
prestress may also be taken equal to Ps.)
At any section of the beam, the prestress applies
an axial compressive stress Ps/Ac, where Ac is the
cross-sectional area of the beam. The prestress also
imposes bending unit stresses whose magnitude
depends on the eccentricity, at the section, of the
tendons. For example, at
(b) Total Prestress at Section 1-1

Fig. 8.44. (a) Prestressed concrete beam with draped
tendons, (b) Axial compression adds to bending
stresses induced bytendons to impose linearlyvarying
prestress at section 1-1. (c) Bending stresses due to
load imposed on prestress at section 1-1 results in net
stresses with no tension, (d) At section 2-2, bending
stresses due to load imposed on prestress results in
compression over the whole section.
section 1-1,the maximum bending stressis Pseỵc/ỉg,
where is the eccentricity of the tendons (see Fig.
8.44ỡ), c is the distance fromthe outerbeamsurfaces
to the centroidalaxis and Ig is the moment of inertia
of the beamcross section about the centroidal axis.
Note that the prestressbendingcausestensionat the
upper beam surface and compression at the lower
beam surface. The total prestress is given by Eq.
(8.41), as indicated in Fig. 8.44b.
At section 1-1, the vertical load on the beam
causes maximum bending stresses M{c/Iv with
compression at the upper beamsurface and tension
at the lower beam surface. These stresses are
superimposed onthe prestressalready presentin the
beam. The result is a linear stress variation, which,
for the case shown in Fig.8.44c, varies from zero at
the bottomof the beamto a compressive unit stress
at the top.Hence,underservice loads,the sectionis
completely in compression.
At section 2-2, the eccentricity of the tendons is
smaller and produces smaller bending stresses than
those at section 1-1. The resulting prestress
consequently exerts less compression at the bottom
of the beamthan that at section 1-1,but the bending
moment at section 2-2 is also proportionately less
than that at section 1-1.Hence,when the prestressis
superimposedon thebendingstressdue to theloads,
the net stresses are compressive (see Fig. 8.44J).
If a straight tendon with constant eccentricityhad
been used,sectionsnearthesupportswould have net
tensile stresses at the upper surface of the beam,
because of the near-zero bending stresses imposed
near the supports by the loads. An advantage of
curving the tendons to decrease the eccentricity as
they approach the supports is that the whole beam
cross section can be kept in compression.Designof
the beamcan then be based on Eq. (8.41), with the
whole cross sectionofthebeameffective in resisting
bending.
Specifications for the design of prestressed
concrete beams are contained in the ACI Code.
Composite Steel-Concrete Beams
In the preceding discussions of reinforced concrete
and prestressed concrete beams, methods are
presented for use of steel to increase the load-
carrying capacity of concrete in beams. In the
following,methods are described foruse ofconcrete
to increase the load-carrying capacity of structural
steelin beams.Specifications forthe design ofsuch
steel-concrete composite beams are containedin the
AISC Specification for the Design, Fabrication and
Erection of Structural Steel for Buildings.
Structural steel beams are often used to support
reinforced concrete floor or roof slabs. The slabs
may be designed to support their own weight and
other dead and live loads over the

spacesbetween thesteelbeams.The beams,in turn,
may be designedto supporttheirown weight and the
load from the slab.Because the slab hasa relatively
large cross-sectional area and the compressive
strength of this area is not fully utilized, an
opportunityexists formore economicaldesignofthe
beams and slab. If the slab is secured to the
compression flanges of the beams, the reserve
compressive strength of the slab can be utilized to
assistthe beams in carrying theirloadsoverthe span
between beamsupports.
Interaction betweentheconcreteslab and thesteel
beams by natural bond can be obtained by fully
encasing the beams in reinforced concrete (see Fig.
8.45ứ). For this purpose,the top ofthe compression
flange of each beammust be at least 2 in. above the
slab bottomand, for fire protection, at least 1| in.
belowthe slab top.Also,there must be at least 2 in.
of concreteon the sidesofthe soffit.This methodof
construction,however,has thedisadvantagethatthe
encasement adds considerable weight to the loads
the beams have to support and to the loads
transmitted to the columns and foundations.
An alternative method of insuring interaction
between slab and beams is to use shear connectors
between them. The shear connectors must prevent
separation of the beam flange and slab and must
transfer horizontal shear between the steel and
concrete. For this purpose, steel studs (see Fig.
8.45/?), steel channels set with web vertical and
perpendicularto the beamweb, or steelwire spirals
may be welded to the topofthe compression flanges
of the steel beams.
The beams should be designed to support their
own weight and that of the concrete and formwork
imposed on them during construction. Shores,
however, may be used until the concrete has
hardened, to assist the beams if the steel would be
overstressed.
After the concrete slab has attained sufficient
strength to supportloads,the compositesectionmay
be assumed to support the total load on the beam
spans. The flexure formula [see Eq. (8.32)] may be
used to design the composite beams.In this formula,
the section modulus He for the transformed section
should be used.The transformed section consists of
the actual steel area plus the concrete area divided
by the modular ratio n = Es/Ec (equivalent steel
area). The concrete area equals the slab thickness
times the effective width (see Fig. 8.45/?).
Number of Connectors. Shearconnectors may be
spaced uniformly overthe compressionflanges ofthe
steelbeams.(Two ormore welded studs may be placed
in line at any cross sectionofa beam.) The totalnumber
of shearconnectors required equals the totalshear vh to
be transmitted between steeland concrete divided bythe
allowable shearload on a single connector q.This load
q depends on the type andsize ofshearconnectorand
the strength fc ofthe concrete.The shear V'h is the
smaller of the values given by Eqs.(8.62) and (8.63).
Fig. 8.45. Composite construction with steel beams and
concrete slabs, (a) Steel beam completely encased in
concrete, {b} Steel beams attached to concrete slab with
shear connectors.
where
fc = 28-day compressive strengthofthe concrete
Ac = actual area of effective concrete slab
As = cross-sectional area of steel beam
Fy = specified yield stress of the steel
The AISCSpecification also sets a minimum for the
number of shear connectors when a concentrated
load occurs between the points of maximum and
zero bending moment.
References
THEORY:
Shear
Connector
•a
Structural
Steel Beam
(b)
0.85/'/lc
2
(8.62)
(8.63)
Concrete
Slab
1 1/2" Min.
(a)
Ef f ectiv e
Width .
b < 1
/4 Span
Ef f ectiv e Width

H. Parker andJ. Ambrose, SimplifiedMechanics andStrength
H. Laursen, Structural Analysis, 3rd ed., McGraw-Hill, New
York, 1988.
New York, 1984.
DESIGN:
F. Merritt, Building DesignandConstructionHandbook, 4th
H. Parker and J. Ambrose, Simplified Engineering for Ar-
chitects and Builders, 7th ed., Wiley, New York, 1989.
J. Ambrose, Building Structures, Wiley, New York, 1988. s.
Crawley and R. Dillon, Steel Buildings: Analysis and
Design, 3rd ed., Wiley, New York, 1984.
Manual of Steel Construction, 8th ed., American Institute of
Steel Construction, Chicago, 1980.
p. Rice, et al., Structural Design Guide to the AC I Building
Code, 3rded., Van NostrandReinhold, New York, 1985.
Building Code Requirements for Reinforced Concrete, ACI
318-83, American Concrete Institute, Detroit, 1983.
CRSI Handbook, 4th ed.,ConcreteReinforcingSteel Institute,
Schaumburg, IL, 1982.
D. Breyer, Designof WoodStructures,2nded., McGraw- Hill,
New York, 1986.
Timber Construction Manual, 3rd ed., American Institute of
Timber Construction, Wiley, New York, 1985.
Words and Terms
Beam
Beam buckling
Beam stresses: bending (flexure), shear
Bending moment
Composite beam
Deflection
Diagonal tension
Neutral surface
Prestressedbeam
Shear (force)
Stirrups
Special purpose beams: joists, stringers, headers, purlins,
rafters, girts, lintels, girders, spandrels.
Types of beams: simple, continuous, cantilever, fixed-end,
statically indeterminate.
Beam loadings: distributed, concentrated.
Interrelation of shear and bending moment.
Plastic behavior of a steel beam.
Service load behavior versus ultimate-strength behavior of a
reinforced concrete beam.
8.11. ARCHES AND RIGID FRAMES
An arch is a structural member with its centroidal
axis lying in a plane and curved so that loads are
carried between supports principally by
compression (see Fig. 8.46).
Bending moments and shears canbekept smallby
propershapingofthe axis.Supports thatare capable
of resisting the reactions of the arch without
translation, however, must be provided. Arch
supports are subjected to forces inclined to the line
of action of loads applied to the arch.
The distance between arch supports is called the
span. The distance between the line between
supports and a point on the centroidal axis farthest
from the line, measured along a normal to the line,
is called the rise. The smaller the ratio of rise to
span, the flatter the arch and the larger the bending
moments and shear are likely to be.
Usually, an arch axis is set in a vertical plane in
buildings, and loads are applied in that plane. The
arch supports may or may not be at the same level.
The thickness, or depth, of arches is generally very
small compared with the span and may be varied
along the span forefficient resistance to stresses.In
this section, however, only symmetrical arches of
variable cross section, with supports at the same
level—an arrangement generally used—are
discussed.
Arches are more efficient than beams and can
eliminate the need for columns by carrying loads
directly to foundations; however, the arch shape is
not always desirable in a building and the space
required for the large ratio of rise to span for
efficient arch action is not always available.
Consequently, the most frequent ap-

Fig. 8.46. Arches, (a) Two-hinged, (b) Arch reaction
resolved into horizontal and verteal components. (c)
Resolution of thrust at point in arch above base, id}
Two-hinged arch with tie. (e) Three-hinged arch. ( f}
Fixed-end arch and names of arch components.
plication of arches in buildings is support of roofs,
especially when long spans are desired. The added
cost of fabricating curved members usually makes
beams ortrussesmore economical for short spans.
Types of Arches
Arches are classified astwo-hinged,three-hingedor
fixed, in accordance with conditions provided at
supports and in the interior.
Two-hinged arches are shown in Fig. 8.46ứ
and d. Only rotation is permitted at the supports of
the arch shown in Fig. 8.46ứ. The reactions have
both horizontal and vertical components (see Fig.
8.46Z?). The arch must be supported on abutments
that prevent both horizontal and vertical
movements.
For the arch shown in Fig. 8.46d, the horizontal
components of the reactions are resisted by a tie
between supports.Small horizontalmovements can
occur at the supports because of elastic elongation
of the tie on application ofwind,snoworlive loads.
Two-hinged arches are statically indeterminate.
The laws of equilibrium do not provide sufficient
equations for determination of the two horizontal
and two vertical reaction components.
A three-hinged arch is shownin Fig. 8.46e. In
practice, hinges are placed at the two supports and
at the crown,orhighestpoint ofthearch.Conditions
at supports are similar to those for two-hinged
arches.Three-hingedarches,however,are statically
determinate. Free rotation of the two halves of the
arch at the crown hinge provides information for
adding another equilibrium equation to those
available for two- hinged arches.
A fixed arch is shown in Fig. 8.46/. No
translation orrotationis permitted at eithersupport.
Consequently, the reaction at each support has a
bending moment as well as horizontal and vertical
components. The arch is statically indeterminate.
Determination of the reactions requires two more
equations than that needed for a two-hinged arch.
Fixed arches are not often used for buildings.
Conditions for prevention of rotation at supports
may not exist on a building site ormay be expensive
to provide. Furthermore, if an arch should be
designed as fixed and the assumption of fixity
should prove to be unwarrantedby field conditions,
portions of the arch may be dangerously
overstressed.
Figure 8.46/also indicates the names commonly
used for parts of an arch. The extrados is the upper
surface, or back, of the arch. The intrados is the
under surface, or soffit, of the arch. Thickness, or

depth, of the arch is the distance, measured in a
plane normal to the axis, between the intrados and
extrados. A deepened portion of the arch near each
support is called a haunch. The intersection of the
abutment and a side of the arch is known as a
skewback, and the intersection of the abutment and
the arch soffit is called a springing line.
Arch Curvature
For any type of arch, minimization of bending,and
hence more efficient arch action, depends on the
shape ofthe arch and characteristicsofthe loads.If
service loads did not change,it would be possible to
shape an arch to eliminate bending moments
completely. For example, consider conditions at
point A in Fig. 8.46a. If there is no bendingmoment
orshear,only a thrustN anda load p are present (see
Fig. 8.46c). These combine vectorially to impose a
thrust Ton an adjoining point on the arch axis. If T
does not cause bending moment at the adjoining
point, T must pass through that point. Hence, to
eliminate bending moment, the arch axis should be
tangent to the line of action of T. For bending
moment to be eliminated throughout the arch, the
axis should be so curvedthat the line ofactionofthe
thrust at every point coincides with the axis.
For a vertical load uniformly distributed overthe
horizontalprojectionofan arch,the axis would have
to be parabolic if the arch is to be subjected only to
compression. Similarly, the axis would have to be
shaped as an inverted catenary for a vertical load
uniformly distributed along the arch axis, as would
be the case for the weight alone of an arch with
constant cross section.
These loading conditions rarely are attainable in
building applications. Like other structural
members, arches should be designed to resist at
every sectionthe maximum stressesthat may occur.
Such stresses may be imposed when live, snow or
wind loads are applied over only part of the arch.
Also,archesmay be subjectedtoconcentrated loads.
Consequently, at best it is practical to shape arches
so that the thrust nearly coincides with the axis at
every point. This, however, may not always be
possible,becauseoflimitations placedon the rise by
otherdesign requirements.Costs ofroofing,for ex-
ample, increase with increase in rise,asdoesthe cost
of heating thespace underthe arch,because volume
increases with increase in rise.
Hundreds ofyears ago,when arches were made of
stone,thematchingofthe arch profile to the loading
was critical,due to the tensionstress limitation ofthe
material. With modem construction, use of steel,
reinforced concrete, or glued-laminated timber
makes this less significant.
Arch Cross Sections
Thickness,ordepth,ofarches,often is varied along
the axis as stresses change. In this way, with cross
sections subjected mainly to uniform compression,
arches use the materials of which they are made
much more efficiently than beams do.
Arches may have solid cross sections of almost
any shape. Wood or concrete arches usually have
rectangular cross sections. Steel arches may be
formed with wide-flange rolled shapes orbuilt-up of
plates in similar shapes. Steel boxor circular tubes
are also used.
Alternatively,wood orsteelarches may be built-
up like trusses.In suchcases, ifthe loads are applied
only at panel points, the chords and web members
are subjected only to axial forces, usually
compressive.
Reactions of Three-Hinged Arches
The horizontal and vertical components of the
reactions of a three-hinged arch can be determined
with the laws of equilibrium. Four equations are
available for determination of the four unknowns:
1. The sumof the horizontal components of the
loads and both reactions must be zero.
2. The sumofthe moments abouttheleft reaction
of all the forces acting on the arch must be
zero.
3. The sum of the moments about the right
reaction of all the forces acting on the arch
must be zero.
4. The bending moment at the crown hinge must
be zero. (The sum of the moments about that
hinge of all forces acting on the arch also is
zero, but this condition does not yield an
independent equation.)
As a check,the sumofthe verticalcomponents of
the loads and both reactions must be zero. This
condition, too, does not yield an independent
equation.

The reactions of a three-hinged arch can also be
determined graphically. Consider, for example, the
arch shown in Fig. 8.47ứ. It carries a load p, which
may be a concentrated load or the resultant of a
distributed load. There are no loads between the
crown hinge and the rightreaction.Since there is no
bending moment at the crown, the line of action of
the right reaction RB must pass through the hinge.
The line intersects the line ofaction of p at point X.
Because p and the two reactions are in equilibrium,
the line of action of the left reaction RA must also
pass through X. Then RA and RB can be determined
graphically, as indicated in Fig. 8.47Z?. First, p is
drawn as an arrow with length proportional to its
magnitude.Fromboth extremities ofthearrow,lines
are drawn parallel to AX and BX,the lines ofactions
ofthe reactions,to forma parallelogramofforces.If
p is the equilibrant,the othertwo forces comprising
Fig. 8.47. Determinations of reactions for a three-
hinged arch.
the sides of the parallelogram are, to scale, the
reactions RA and RB.
Three-hinged arches do not use material as ef-
fectively as two-hinged arches,because ofthe large
bending moments midway between crown and
supports.Also,insertion ofa hinge at the crowncan
in some cases add to construction costs.
Maintenance costs also may be increased, because
care should be taken that dirt or corrosion products
do not cause the hingeto freeze and prevent rotation
of the arch,thus making designassumptionsinvalid
and causing overstressing of parts of the arch.
One advantage of the three-hinged arch is the
elimination ofthermal stresses,inasmuch asrotation
at the crown permits dimensional changes to occur
freely. Another advantage rises for three-hinged
arches of modest span and is the possibility for
fabrication of the arch in two pieces that can be
relatively simply erected and connected in the field.
The latter advantage is often significant for
buildings requiring short to moderate spans (50 to
150 ft).
Supports for Arches
Arches generally are supported on concrete
abutments set in the ground.Ifthe soilis sufficiently
strong, for example, sound stable rock to resist the
arch thrust, a tie between supports is not needed.
When the soilis incapable ofwithstanding the arch
thrust, the supports must be tied. In such cases, the
tie is often placed under the ground floor. It is
sometimes desirable,however,to installthe tie at a
higherlevel,forexample, between two points on the
arch.This tie may be a deep girderalso usedto sup-
port a floor.If the girderspan is long,thegirdermay
also be suspended at intervals fromthe arch.
Sometimes, it is desirable ornecessary to support
an arch above ground,on walls orcolumns.In such
cases,provisionforresisting thethrust,suchas a tie
between supports, must be made.
Arch Bracing
The maximum unit stress in an arch,the sumof the
axial thrust and bending stresses, is compressive.
Consequently, arches should be

braced to prevent buckling. In addition, arches
should also be braced to prevent overturning in the
direction normal to the plane of the centroidalaxis.
Bracing may have to be put in place during erection
of an arch.
Transition from Arch to Rigid Frame
As mentioned previously, arches with a suitable
shape forthe loadstobe supportedcan be shaped so
that little or no bendingmomentsare imposed.Such
arches, though, require a large ratio of rise to span.
A high rise, however,may be undesirable formany
reasons,primarily economic,fora specific structure.
A flat arch springing fromthe ground may be used
instead, but in that case the space near the supports
often cannot be used,because ofthe smallclearance
between floor and arch. One alternative to this
undesirable condition is to make a portion of the
arch in the vicinity of the supports vertical, like
columns. The result is an arched bent (see Fig.
8.48iz).
Such a bent has many of the characteristics of an
arch. It may be two- or three-hinged or fixed.
Reactions and stresses may be determined in the
same way as for an arch.An arched bent,however,
is subject to much larger bending moments and
Fig. 8.48. Types of bents, (a) Arched bent, {b} Tudor arch, or gable frame, (c) Rigid frame. {</) Continuous rigid
frame.

shears than an arch with the same span and rise.
Nevertheless,the arched bent is more efficient than
a simple beam of the same span supported on two
columns.
Curving structural members to a shape, such as
DCE in Fig. 8.48«, adds to fabrication costs.
Consequently,two straight rafters DC and CE often
are substituted for the arched portion of the bent.
The result is a Tudorarch, orgable frame (see Fig.
8.58/?).
This bent, too, has many of the characteristics of
an arch, but like an arched bent, a gable frame has
much larger bending moments and shears than an
arch of the same span and rise. In particular, large
stressesoccurat the knees,theintersections Dand E
of the rafters DC and EC with the columns AD and
BE (see Fig. 8.48/?). Consequently, a smooth,
curved transition is usually provided at the knees.
The rafters may be haunched near the knees or
tapered fromthe depth at the kneesto a lesserdepth
at the crown c (see dashed lines in Fig. 8.48/?).
Similarly, the columns may be tapered from the
depth at the knees to a lesserdepthat theirsupports.
Also,a rigid connection is provided at the knees,to
insure that the column and rafter ends at each knee
have the same rotation underloads.As a result,the
structural efficiency of a gable frame is lower than
that of an arch, but the gable frame permits more
efficient utilization of space and may be more
economicalto fabricate,especially forshort spans.
When a flat roof is preferred or a floor has to be
supported, the upper portion of the bent must be
made straight.The result is the rigid frame shown in
Fig. 8.48c, with horizontal beam DE and columns
AD and BE. This bent has fewer characteristics of
arches than the preceding bents. Nevertheless,
reactions and stresses can be computed in the same
way as for an arch.
As for a gable frame, rigid connections are
provided at thekneesatDand E.The beamtherefore
should be treated as a continuous beam. It is
subjected to negative end moments at D and E,
which make the positive moments near midspan
much smaller than those in a simple beam. For
greater economy, DE may be deepened where
bending moments are largest,forexample, at D and
E. Because of continuity, the columns AD and BE
are subjected to axial compression and bending
moments and may be haunched or tapered to vary
the cross section with change in stresses, as
indicated by the dashed lines in Fig. 8.48c.
Bents such as that in Fig. 8.48c can be placed in
line in a vertical plane to form a continuous rigid
frame (see Fig.8.48J). Where columns are permitted
at wide spacings within a building,this type ofbent
is advantageous forsupportingfloors orflat roofs of
considerable length. Beam FGHIJ may be made
continuous forallor part ofits length,dependingon
the economics of fabrication and erection of long
lengths and shipping limitations on length.
The spaces between columns in a bent are known
as bays.Figure 8.48J shows a one-storyrigid frame,
four-bays wide.
Rigid frames may also be stacked one above the
other in a vertical plane, to form a multistory,
continuous rigid frame. Figure 8.49c shows a two-
story, single-bay rigid frame.
Applications of Rigid Frames
Rigid frames are widely used forskeleton frames of
buildings for many reasons.
One important reason is that the verticalcolumns
and horizontalbeams ofsuch frames are compatible
with the rectangular spaces generally desired in
building interiors. (Rigid frames, however, can be
constructedwith inclined columns andbeams,when
it is desirable.) In buildings in which it is required
that structural framing be hidden from view, it is
simple to concealthe verticalcolumns in walls and
the horizontal beams between floors and ceilings.
Another important reason for the popularity of
rigid frames is that they often cost less than other
types of construction for the spans frequently used
in buildings. The economic advantage of rigid
frames stems from the utilization of continuity of
beams and columns. Continuity reduces bending
moments from those in simple beams and permits
more efficient utilization ofthe materialin structural
members. Also, the rigid connections between
beams and columns enables rigid frames to resist
lateral, or horizontal, forces, such as wind and
earthquake loads. Often, such frames are

capable of withstanding lateral loads without
assistance from bracing or walls in their vertical
planes.Elimination of bracing often is desirable for
architectural reasons, because bracing with truss
diagonals, X-bracing, or shear walls may interfere
with doororwindowlocationsorotheruse ofspace.
Stresses in Rigid Frames
Continuousrigid frames are statically indeterminate
to a high degree. Special techniques had to be
developed to permit determination ofthe numerous
reaction components and stresses. Tedious
calculations, though, are often required for
multibay,multistory buildings.Computerprograms,
however, are available for rapid analysis with
electronic computers.
A complicating factor in analysis of continuous
frames is that, because of continuity, the structural
properties of each member affects the response of
every other member to loads. To illustrate, Fig.
8.49« shows a single-bay, one- story rigid frame
subjected to a vertical load p at midspan of beam
DE. The deflected positionofthe centroidalaxes of
the beamand columns is indicated by a dashed line.
Note that the sagging of the beam compels the
columns AD and BE to bow outward, because the
rigid connections at D and E make the beam and
column ends rotate through the same angle. Note
also that the reactioncomponents forthe bent under
the verticalload p are the same in direction as those
for an arch.
Stresses in the rigid frame, however, differ from
those in an arch because of the presence of large
bending moments and shears. The columns under
Fig. 8.49. Deflection and bending moment diagrams for single-bayrigid frames, one- and two-stories high, under
vertical and horizontal loads.

load p are subjected to an axial compression, as in
an arch,but are also subjected to a bendingmoment
that increaseslinearly with distance fromthe support
(see Fig. 8.49/?). For example, the bendingmoment
in column AD at any point at a distance y fromthe
support equals HAy, where HA is the horizontal
componentofthe reactionat A.Forequilibrium, the
bending moment in the beam at D equals the
bending moment in the column at D. Consequently,
as shown in Fig. 8.49/?, the beam is subjected to
negative end moments that reduce the positive
moment at midspan from what it would be in a
simple beam. (In Fig. 8.49/?, bending moments are
plotted on the tension side of the centroidal axis of
each member.)
Considernowthe same rigid frame subjectedto a
horizontalload w at the levelofDE (see Fig. 8.49c).
As indicated by the dashed line representing the
centroidal axes of beam and columns, the bent
sways, or drifts, in the direction of w, restrained by
the rigid connections at D and E. This restraint
curves the beam and columns. The beam, in
particular, has an inflection point, or point where
curvature reverses, at or near its midpoint.
The reaction components at A are reversed in
direction from those at A in Fig. 8.49tz. The
horizontal component HA at A must be directed to
add to the horizontalcomponentHB at B to equalw.
The vertical components VA and VB must form a
couple to resistthe moment of w aboutthe supports.
Hence,VA must be directed downward,while VB acts
upward. Consequently, in tall, narrow buildings
with light gravity loads, the net axial unit stress in
windward columns may be tensile.Also,thesupport
must be anchored against uplift to prevent
overturning.
Bending moments in the columns vary linearly
with distance fromthe support (see Fig.8.49J). The
bending moments in the beamat D and E are equal
respectively to those in the columns at D and E.
Because DE is not loaded in this case, the bending
moment in the beamvaries linearly,passingthrough
zero at the inflection point.
Conditions in a two-stoiy rigid frame (see
Fig. 8.49e) are not greatly different from that in a
one-stoiy bent. One important difference is the
presence of a bending moment at the base of each
second-story column (see Fig. 8.49/). This induces
reverse curvature in these columns and reduces the
moment at the top of the columns from that for a
simple support at the base.Forequilibrium,the sum
of the column moments at D must equal the beam
end moment at D. Similarly, the sumof the column
moments at E must equal the beamend moment at
E.
8.12. SHELLS AND FOLDED PLATES
Section 8.11 discusses the efficiency of arches,
which is due to theircurvature.Arches,in effect,are
linear structural members, generally lying in a
vertical plane.They transmit to the ground orother
supports loads carried by otherstructuralmembers.
Greater structural efficiency, however, can be
achieved byutilizing curvature ofthree-dimensional
structuralmembers,suchas shells andfoldedplates.
A shell is a curved structure capable of trans-
mitting loads in more than two directions to
supports.A thin shellis a shellwith thickness which
is relatively small compared with its other
dimensions (see Fig. 8.50). Such a shell is highly
efficient when it is so shaped, proportioned and
supportedthat it transmits loads onit to the supports
without bending or twisting.
Shells are defined by the shapes of their middle
surfaces, halfway between the extrados, or outer
surface,and intrados,orinnersurface.Thickness of
a shellis the distance,normalto the middle surface,
between extrados and intrados. Shapes commonly
used for thin shells are the dome, often a
hemisphere; barrelarch,often a circular cylindrical
shell; and hyperbolic paraboloid, a saddle-shaped
shell.
Because oftheircurvature,shells generally have a
high rise relative to theirspans,as doarches.Hence,
like arches,shells are often used forroofs.Theyare
especially efficient for long spans and light loads.
They receive loads directly for transmission to the
ground or other supports, thus eliminating the need
for otherstructuralmembers to carry loads to them.
Be-

cause of the curvature of the middle surface, shells
usually are subjected only to tensile, compressive
and shear stresses, called membrane stresses.
Consequently, the full cross section is effective in
resisting internal forces.
Shell Construction
Because of the structural efficiency of shells, they
may be built of almost any rigid material— cold-
formed steel, wood, reinforced concrete, plastics.
An egg is an appropriate example. It may have a
ratio of radius of curvature to thickness of 50 or
more.
Thin shells often have a solid cross section, like
an egg.Because they are subjected to compression,
however,precautions must be taken,in many cases,
to prevent buckling or a failure due to punching
shear, where concentrated loads have to be
supported.Reinforced concrete shells,for example,
are usually made just thick enough to provide the
minimum cover required for steel reinforcement.
Buckling may be preventedby bracinga shellwith
deepened sections, called ribs. In such cases, the
ability ofribs to carry loads to supports may also be
utilized to supplementthe load-carrying capacityof
the shell. Sometimes, however, shells are made
corrugated or sharply folded to increase their
resistance to buckling.
An alternative method of constructing shells is
with skeleton framing and a lightweight enclosure
supportedby that framing.The framing may lie in a
curved surface or it may be a curved, three-
dimensional truss or space frame.
Cylindrical Shells
One way to develop a shell conceptually is to start
with a roof framed with arches spaced at equal
intervals.For generality,assume that the arches are
supported on columns, with ties between column
tops to resist the arch thrusts. To eliminate the roof
framing carrying loads to the arches,each arch may
be made so wide that it extends tothe adjoiningarch
on eitherside.When this is done,the arches may as
well be joined to each otherto become a unit.While
Fig. 8.50. Thin cylindrical shells, {a} Barrel arch on columns with ties, {bi Ribbed shell, (c) Multiple shells. {d}
Continuous shells.

the arches are widened, they can also be made
shallower,because theroofloadsare nowspreadout
overthe whole surfaceinstead ofbeing concentrated
on a linear arch. The resulting structure is a thin
cylindrical shell spanning between the original
columns (see Fig.8.50a).It is also known as a barrel
arch.
In the preceding concept ofthe development ofa
cylindrical shellfrom an arch, it is not necessary to
considerallofeach arch to be spreadout.Part ofthe
material may be left in place as an arch rib, to brace
the shell against buckling. Figure 8.50b shows a
ribbed cylindrical arch. In the case shown, the ribs
support the shell and transmit roof loads to the
ground.
Different arrangements of barrel arches may be
used.Figure 8.50a shows a single shell.Figure 8.50c
shows a roofcomposed ofmultiple shells,orbarrel
arches placed side by side with edges joined. With
this type of roof, consideration must be given to
drainage of the valleys between the shells and the
probable load fromsnowcollecting in thevalleys.In
the case shown,the shells are supportedand tied by
solid diaphragms,which are supported by columns.
Shells also may be constructedto be continuousover
one ormore interiorsupports(seeFig.8.50J). In the
case shown, the supports are arched bents.
Figure 8.50 illustrates only some of the ways in
which shells may be supported.Othermethods also
may be used.Forexample, shells may be carried to
the ground and supported on spread footings.
Membrane Stresses in Cylindrical Shells
Shells are highly statically indeterminate. In the
interior of thin shells, however, bending moments
and shears normalto the middle surface usually are
small and may be ignored. When this is done, the
shell becomes statically determinate.
Cylindrical arches,such as the one shown in Fig.
8.50a, may be treated as a beamwith a curved cross
section. Longitudinal tensile and compressive
stresses then may be computed from the flexure
formula [see Eq. (8.32)]. Shear stresses may be
determined with Eq.(8.42). Tangentialcompression
may be computed by applying the laws of
equilibriumto the other stresses.
For circular barrel arches, beam theory yields
acceptable accuracy when the ratio of the radius of
the shell to the span in the longitudinal direction is
less than about0.25.For largerratios,more accurate
stress analysis is necessary.
Folded Plates
Curved surfaces generally are more expensive to
construct than flat surfaces. Consequently, it is
sometimes economical to use planar surfaces to
approximate the shape of a cylindrical shell. The
result may be a folded-plate roof (Fig. 8.51a).
In the case shown in Fig. 8.51a, the roof is
composed offive plates.They are shown supported
near their ends on solid diaphragms, in turn seated
on columns. As in the case of cylindrical shells,
however, many arrangements are possible, such as
multiple folded plates and continuous foldedplates.
Also,there may be more or less than the five plates
in the example.
Behavior of folded plates resembles that of
cylindrical shells. Folded plates, however, are
subjected to significant bending moments in both
the longitudinal and transverse directions.
Consequently, stresses are generally determined by
a different method fromthat used for thin shells.
A common procedure for folded plates is to
analyze a transverse strip of unit width (see Fig.
8.51a). This strip is temporarily considered
supportedat eachfold by verticalreactions supplied
by the plates (see Fig. 8.51b). The strip is then
treated as a continuous beamfor determination of
transverse bending moments and shears normal to
the planes of the plates. The reactions for this
condition may be resolved into components in the
planes oftheplates at eachfold.Each plateso loaded
now may be treated as a beam spanning between
supports in the longitudinal direction, for de-
termination of longitudinal bending moments and
shears in the planes of the plates (see Fig. 8.51c).
Some modification of the resulting

stresses generally is necessary to adjust for the
assumptions made in this simplified analysis.
Domes
As indicatedpreviously,a shellmay be generated by
widening arches. Alternatively, a cylindrical shell
may be considered generated by translation of the
centroidalaxis ofan arch normal to the plane of the
arch. With the use of this concept, a dome may be
considered generated by rotation of the arch
centroidalaxis 180° about the axis ofsymmetry (see
Fig. 8.52«). Such shells are also called shellsofrev-
olution.
Domes have double curvature; that is, they are
curved in both horizontal and vertical planes. The
double curvature improves the structural efficiency
of a thin shell over that of the singly curved
cylindrical shell.Use of domes,however,is limited
to applications where circular spaces andhigh roofs
are acceptable.
As indicated bythe dashedlines in Fig.8.52«, the
intersection of the dome middle surface with a
vertical plane is called a meridian and the
intersection with a horizontal plane is called a
parallel. The highest point on a dome is called the
crown.
Membrane Stresses in Domes
To determine the membrane stresses in a dome, a
tiny element at an interior point p is selected for
analysis. For convenience, a set of three-
dimensional, rectangular coordinate axes is es-
tablished atp (seeFig.8.52/?).The z-axis is oriented
in the direction of the normal to the middle surface
at p. The y-axis is tangent to the parallel throughp.
The x-axis is tangent to the meridian through p. A
Fig. 8.51. (a} Folded plate roof, (b} Loaded transverse strip of unit width, (c) Loaded longitudinal girder.
Fig. 8.52. (a) Thin-shell dome. (/>) Coordinate system and load at a point, (c) Unit forces at a point.

load vv on the element then may be resolved into
components in the X, y and z directions.
The internalforces perunit oflength actingon the
element at p are shown in Fig. 8.52c. For
simplification, only the forces on two edges of the
element are represented by symbols. These unit
forces are shears T,meridional thrust NQ and hoop
stress Nộ.They may be resolved into componentsin
the X, y and z directions.
All the forces on the element must be in equi-
librium. This condition applied to components
parallel to each coordinate axis yields three
equations, from which T,Ne and Nộ can be de-
termined. As for cylindrical shells, one equation is
algebraic and two equations are differential
equations. They may be readily evaluated only for
simple shapes and loads.
One simple case is that of a thin shell with
constant curvature, or spherical shell, subjected to
uniform vertical loading w per unit area over the
horizontal projection of the shell. For this case:
T=o (8.64)
Ne = -y (8.65)
Nộ = cos 20 (8.66)
where
r = the radius of the shell
Ớ = angle between the normalto the surface at p
and the shell axis
The solution given for NQ, with a negative sign,
indicates that there is a constant meridional thrust
throughout the shell. The hoop forces Nộ are
compressivein the upperportion ofthe shell,where
0 is less than 45°, and tensile in the lower portion.
At the base of the shell, reactions must be
provided to counteractNe andNộ.Usually,a dome is
terminated at the base, along a parallel, in a wide,
deep structuralmember, called a ring girder,which
is designed to resist the hoop tension. The ring
girder, in turn, may be seated on a circular wall or
on columns capable of resisting the meridional
thrust.
When a sphericaldome is subjected to a uniform
vertical load w over the area of the shell:
T=o (8.67)
Ne = - (8.68)
1 + cos 0
Nộ = wr ( 1
- cos ớ) (8.69)
1 + cos 0 /
This type ofloading may be imposed by the weight
of a shell of constant thickness. In this case, the
meridional compression NQ increases with 0 and
therefore is larger at the crown than at the base of
the dome.The hoop forces convert fromcompresion
in the upper portion to tension in the lower portion
at 0 = 51°51'. Again, a ring girder is desirable to
resist the hoop tension at the base of the dome.
Design Considerations for Shells
Shells can readily accommodate openings for
natural lighting and ventilation. For example, a
round openingmay be providedat the topofa dome.
Similarly, openings may be left at the base of a
cylindrical shell for use as entrances or windows.
These openings, however, are discontinuities in the
shell.Provision must be made for resisting the shell
forces at the discontinuities or else the membrane
theory will not be applicable in those regions ofthe
shells.
The membrane theory does not apply where
boundary or discontinuity conditions are in-
compatible with the requirements of equilibriumor
shell geometry, including shell deformations under
load, temperature change, shrinkage or creep.
Generally, the effects on membrane action of
geometric incompatibility at boundaries or
discontinuities are significant only in a narrow
region about each source of disturbance. Often, the
resulting higher stresses can be taken care of by
thickening the shell in the effected region or by
adding a reinforcing beam.But much largerstresses
result fromincompatibility with the requirements of
equilibrium. Consequently, it is important that
reactions along boundaries and discontinuities are
equalin magnitude and direction to the shellforces
indicated by the membrane theoryforthose edges.
The ring girderused at thebaseofa dome to resist
hoop tension there is a good example of the
reinforcement of a shell to resist reactions at a
boundary. Similarly, a stiffening beam is often
desirable along the bottom edges of cylindrical

shells to resisttheshears andtangentialthruststhere.
If an opening is provided around the crown of a
dome,a stiffening ring may be necessary toresistthe
hoop compression around the discontinuity.
In all these cases,the stiffeningmemberwould be
much thickerthan the shell.The deformationsofthe
stiffening member then would be geometrically
incompatible with those of the shell. To reduce the
effects of this incompatibility, the shell should be
gradually thickened to provide a transitionfromthe
typical shell thickness to the thick stiffening
member. In general, abrupt changes in shape and
dimensions should be avoided in shells.
Disturbances due to equilibrium or geometric
incompatibility arise fromthe imposition ofbending
and torsional stresses. When shell design cannot
eliminate these,provisionmust be made fortheshell
to resist them.
Bending theory may be employed for the cal-
culation ofsuch stresses,butthe method is complex
and tedious. The presence of bending and torsional
stresses makes a thin shell highly statically
indeterminate.A knowledge ofshelldeformationsis
needed to supplement equilibrium conditions in
development of differential equations for
determination ofthe unknown forces andmoments.
Even for simple cases, these equations usually are
difficult and timeconsuming to solve. Therefore,
designersgenerally try to satisfy the assumptionsof
the membrane theory to the extent possible and
minimize disturbances due to equilibrium or
geometric incompatibility.
In computation of stresses in shells for the
membrane theory, it is common practice to assume
that forces are uniformly distributed over the
thickness t of the shells. The unit forces derived
from the membrane theory are forces per unit of
length. Hence, the unit stresses in a shell are
calculated by dividing the unit forces by the shell
thickness t.
References
E. Gaylordandc. Gaylord, Structural Engineering Handbook,
2nd ed., McGraw-Hill, New York, 1982.
R. White and c. Salmon, Building Structural Design
Handbook, Wiley, New York, 1987.
c. Wilby and I. Khwaja, Concrete Shell Roofs, Wiley, New
York, 1977.
Words and Terms
Arch: barrel, fixed, three-hinged, Tudor,two-hingedDome
Foldedplate
Membrane stresses
Rigid frame
Ring girder
Shell
Rise-to-span ratio of arches related to stress in the arch and
thrust at supports.
Hinged conditions in arches related to structural behavior.
Bracing of arch systems.
Rigid-frame behavior versus pinned-frame behavior.
Beam, arch andmembrane actions in shells andfoldedplates.
Meridional thrust andhoopstresses in domes.
8.13. CABLE-SUPPORTED ROOFS
For structural purposes, a cable is a structural
member with high resistance to tensile stresses and
no resistance to compression or bending.
Consequently, cables are used to sustain tensile
loads.Because steelhas hightensile strength,cables
usually are made of steel, as discussed in Sec. 8.5.
Common applications of cables in buildings
include use as hangers,to support gravity loads; ties,
to prevent separation of building components, such
as the bases of arches or rigid frames; and roof
supports. This section deals only with the last type
of application.

Types of Cable Structures
Cable-supported roofsmay be classified basically as
cable-supported, or cable-stayed, framing or cable-
suspended roofs.
In a cable-stayed structure, the roof is supported
directly on purlins and girders. One or more cables
are used to assist each girder in carrying the roof
loads.
Figure 8.53a showsoneway to obtain a long span
that has often been used for airplane hangars. The
construction is much like that for a cantilevertruss.
The major difference is that in the cable-stayed roof
the bottomchord is a girder subjected to bending
moments and axial compression, whereas in the
truss, the bottom chord carries only axial
compression.The girderis supported at one end on
a column and near the other end by a cable, which
extends on an incline from a mast seated atop the
column.The cable usually is continuedpastthemast
to an anchor. In Fig. 8.53a, the cable extension, or
cable stay, is anchored to a rear column. This
column must be capable of resisting the uplift
imposed by the cable. The tension in the cable
makes it nearly straight.(There may be a slight sag
due to the weight of the cable.) For long girder
spans, or for heavy loads, another cable may be
extended from the mast to support the girder at a
second point.
The cable-stayed girders usually are placed
parallel to each otherat intervals alongthe lengthof
the building. Roof loads are transmitted to themby
purlins.In a hangar,a sliding dooris installed under
the end of the cantilever.
Figure 8.53Z? shows a cross section through a
building with similar cable-stayed girders. In this
case, however, the girders cantilever on both sides
of a pair of columns.The cross sectionis typicalof
two cases. One case, like the construction in Fig.
8.53tz, applies to girders set parallel to each other.
The second case applies to a circular roof. The
columns are set around an inner ring. The girders
and their cables are placed radially.
In this type ofconstruction,verticalloads impose
bending moments in the girders. The vertical
reactions ofthe girders are supplied by the columns
and the inclined cables. One vertical reaction
therefore equals the verticalcomponent ofthe cable
Fig. 8.53. Cable-stayed structures.

stress.The girder,in turn,hastoresist the horizontal
component of the cable stress and transmit it to the
column. The horizontal force may then be
counteracted by the horizontal component of the
cable stay and by bracing orrigid-frame action with
the second column. Maximum unit stresses in the
girder may be computed fromEq. (8.40).
In a cable-suspended structure, roofloadsusually
are supported directly on one or more cables. The
cables may lie in a single ordouble surface,in either
case with single ordouble curvature.The cablesmay
be used singly,setin parallelornear parallelvertical
planes or placed radially between concentric rings.
Or the cables may form a net,crossingeach otherat
intervals.
Figure 8.54a shows one way ofsupporting a roof
with cables used singly. The cable extends on a
curve between two masts. The roof may consist of
panels set directly on the cables or suspended from
them. If the cables are set in parallel vertical planes
with supportsat the same level,the resulting surface
has single curvature.
In Fig. 8.54/?, single cables extend radially
between an inner tension ring and an outer
compression ring.The latteris shown supported on
columns. The tension ring is a device for
interconnecting the radialcables at the centerofthe
roof, to avoid a common intersection for numerous
cables, which would be massive and clumsy. In
effect, the tension ring floats in space. The
compression ring provides the necessary reactions
around the circumference of the roof. The
compression is imposed by the inward pull of the
cables underthe roofgravity loads.The roof,being
dish-shaped, has double curvature.
A pair of cables forming part of a doublesurfaced
roofis shown in Fig.8.54c. If the cable pairs are set
in parallel vertical planes with supportsat the same
level, the surface hassingle curvature.The upper,or
primary cable, of each pair is the main load-
supportingmember.It is kept at fixed distancesfrom
the secondary cable by compression rods, or struts.
These are shown verticalin Fig. 8.54c, but they also
may be inclined, as in a Warren truss. The purpose
of this type of construction is to make the roof
construction more resistant tovibrationsthansingle-
surface roofs.
A cable used singly is very flexible. Under
dynamic loads, it can develop large or rapid
vibrations, which may damage the roof. Such
vibrations are unlikely to occur, however, if the
cable were to be forced to move in unison with a
second cable that has a different natural period of
vibration.This is the principalreason forthe use of
double-surface cable roofs.
Figure 8.54J shows a double-surface roof with
radial cables. This roof has double curvature.
Figure 8.54e shows a single-surface, cable- net
roof with double curvature. This type of
construction alsohas greaterresistance tovibrations
than cables used singly. In the structure illustrated,
the primary cables are strung between arches at
opposite ends ofthe roof.Cross cables are curvedin
the opposite direction to that of the primary cables.
The resulting surface is saddle shaped. The
secondary cables are anchored to boundary cables,
also strung between the end arches.
Cable Reactions and Stresses
The basic principles of cable action may be il-
lustrated with the simple example of a cable strung
between two supports at the same level and
subjected to vertical loads.
The cable offers no resistance to bending.
Consequently, its shape is determined by the loads
imposed.Figure 8.55a to c showthe shape takenby
a weightless cable as a concentrated loadp is shifted
in succession fromone quarter point of the span to
the next one on the right. Figure 8.55d shows the
curve adopted by a cable under distributed vertical
loading.
The reactions at supports A andB in Fig.8.55J are
inclined.For equilibrium, the horizontalcomponent
H at A must be equalin magnitude to the horizontal
componentat B but oppositely directed.Thevertical
component VA at A can be determined by taking
moments about B of all the loads and setting the
moments equal to zero. The moment of H is zero,
because its

(b)
Fig. 8.54. Cable-suspended structures, (a) Single-surface cable roof with single curvature, (b) Single-surface roof with
double curvature, (c) Cross section through double-surface cableroof. (Ờ) Double-surface cable roof with double curvature,
(e) Single-surface, saddle-shaped roof.

line of action passes through B. The vertical
component VB can be obtained by setting moments
about A equal to zero.
H can be determined from the condition that the
bending moment in the cable is zero at every point.
At the lowest point c of the cable, the cable stress
equals H(see Fig.8.56). This stressandthereaction
component Hform a couple Hf, where/is the sag of
the cable below the supports. Since the bending
moment is zero at c, Hf = Mc, where Mc is the
bending moment due tothe verticalforces. (Mcis the
same bending moment that would be present at the
coưesponding location in a simple beam with the
same span Las the cable andwith thesame loading.)
Hence,
Mr
H = (8.70)
Forexample, fora load w uniformly distributedover
the horizontal projection of the cable, Mc = wZ?/8
and
«’77 (87!)
Because all the loads are downward-acting
vertical forces, the maximum stress in the cable
occurs at the supports and equals the reaction:
R = 'JH
1
+ V2
A (8.72)
Cable Shapes. The shape of the cable can be
determined by setting equal to zero the bending
moment at any point D on the cable at a horizontal
distance X andverticaldistancey fromthe lowpoint
c. Because there are only verticalloads on thecable,
the horizontal component of the cable stress equals
H throughout.AtZ),this component forms with the
horizontal component of the reaction a couple H(f-
y). For the bending moment at D in the cable to be
zero, = MDi where MD is the bending
moment due to the vertical forces. is the same
bending moment that would be present at the
corresponding location in a simple beam with the
same span as the cable and with the same loading.)
Solution for/- y yields
= (8
-73)
Since H is a constant, the vertical coordinates of
the cable with respect tothe line betweensupports is
proportional to the simple-beambending moments.
Consequently, a cable subjected to loads assumes
the same shape as the bending-moment diagramfor
the same loads acting on a simple beamofthe same
span as the cable. It follows from this conclusion
that the lowpoint of the cable occurs at the pointof
maximum bending moment and thereforealso at the
point where the shear is zero.
Substitution in Eq. (8.73) for H from Eq. (8.70)
and solution for y gives
(8.74)
Equations for cables with various types of loading
can be determined fromthis equation.Forexample,
for a load w uniformly distributed over the
horizontalprojection ofthe cable, MD = (L2
/4— X2
)
w/2 and Mc = wL2
/8. The cable then is a parabola:
Fig. 8.55. Cable shape varies with load location and distribution.
Fig. 8.56. Half-span of a cable.

y = 4fa2
/L2
(8.75)
For a load w uniformly distributed along the
length of the cable, as is the case for cable weight,
the shape is a catenary-.
„ H i. H-x
y = — cosh -II , w H / (8.76)
... 2 ...3„4 wx w X
=
TH +
24 H3 +
” ’
In Eq. (8.76), y is expressed in the alternative form
obtained by substituting an infinite series of terms
equivalent to the hyperbolic cosine.Terms after the
first in the infinite series in Eq. (8.76) are usually
very small. If those terms are ignored, the cable
shape approximates a parabola. Because it is
difficult to compute cable stresses for the load
uniformly distributed along the cable length froma
catenary equation, because of the hyperbolic
functions, a parabola may be conveniently
substituted for the catenary, generally with little
error.
More complicated cable structures often require
that changesin cable shape andsagwith additionof
live and other loads to dead loads be taken into
account. Also, the possibility of damaging
vibrations under variations in load must be
investigated.
8.14. PNEUMATIC STRUCTURES
Section 8.12 points out that shells are highly
efficient structurally and canbe made thin because:
1. Loads are spread out over large areas.
2. Curvature enablestheentire crosssectiontobe
effective in resisting stresses,in the absence of
bending and twisting.
One way that the efficiency of shells can be
improved,however,is to reduce theloadstheyhave
to carry. The weight of a shell is a high percentage
of the total load imposed. It follows, therefore, that
if a shellcan be constructedofa very light material,
such as fabric, the load to be supported would be
reduced substantially so that the shell can be made
very thin, virtually a true membrane.
Shells, however, must be capable of resisting
compression.Ifthey are made very thin,theywould
buckle and collapse. Hence, for a membrane to
become structurally useful, compressive stresses
must be eliminated from it. One way to achieve this
objective is to let a membrane hang freely from
supports around its edges,like a dish-shaped,single-
surface cable net. Then, all the stresses would be
tensile. This principle has been widely used for
tents. Another method that appears to have greater
potential for economical, long-span enclosures for
buildings is use of prestress.
Prestressed Membranes
The application of prestress was discussed pre-
viously for concrete. For that material, prestress is
used to overcome the weakness of concrete in
tension. Prestress, however, can also be used to
counteract the inability of a membrane to sustain
compression. If a pretension were applied larger
than any compressive stressthat loads are likely to
impose, then compressive forces would merely
reduce the tensile stresses and buckling could not
occur.
In practice, membrane roofs have been pre-
stressed by pressurization. The construction is
controlled and stabilized by application of pressure
differentials achieved by the uniform loading
actions of air or other gases, liquids or granular
solids. An air-stabilized, roof, in effect, is a
membrane bag held in place by small pressure
differentials applied by environmental energy.
Materials for Structural Membranes
A prime structural requisite for a structural
membrane is that it should have high tensile and
shear strength, so that it will be tearresistant. It
should have a high modulus of elasticity, to avoid
excessive deformations; yet,

it should be flexibile. It should have high fatigue
resistance. In addition, for structural efficiency, it
should have a large strength-toweight ratio.
To prevent leakage ofair that createsthe pressure
differentials acting on the membrane, the material
should be airtight.Jointsthat may be necessary also
should be airtight and at least as strong as the basic
material.
In addition,a membrane should possessproperties
that are required of other roof materials. For
example, a membrane should be durable,waterand
chemical-resistant and incombustible. It should
provide good thermal insulation. Furthermore, its
properties should be stable despite climatic changes
and passage of time.
Four basic types of material have been used for
membranes: coated fabrics, plastic films, woven
metallic fabrics and metalfoils. Coated fabrics have
been usedmostfrequently.Theyare generally made
of synthetic fibers, such as nylon and Dacron.
Coatings,which may be applied to one ortwo sides
of the fabric, usually are relatively impervious
materials, such as vinyl, butyl, neoprene and
Hypalon. Weight generally ranges between 0.1 and
0.5 lb per sq ft.
When considerationis being givento use ofanair-
stabilized roof, the potential service life of
membrane materials should be investigated. Some
of the materials have a considerably shorterservice
life than many of the materials ordinarily used for
roofs, and replacement costs, including installation
and facility shutdown costs, may be high.
Types of Pneumatic Construction
Shapes of air-stabilized roofs often resemble those
frequently used for thin-shell construction.
Sphericaland hemisphericaldomes (see Fig. 8.57a)
are quite common. Semicircular cylinders with
quarter-sphere ends also are often used (see Fig.
8.57Z?). But a wide variety ofshapes have beenand
can be used.Figure 8.57c illustrates a more complex
configuration.
Air-stabilized roofs may be classified as air-
inflated, air-supported or hybrid structures.
In an air-inflated structure, the membrane
completely encloses pressurized air. There are two
main types.
Inflated-rib structures are one type. They consist
of a framework of pressurized tubes that support a
membrane in tension. The tubes serve much like
arch ribs in thin-shellconstruction.The principle of
their action is demonstrated by a water hose.When
the hose is empty, it will collapse under its own
weight on short spans orunderlight loads normalto
its length; but when it is filled with water, the hose
becomes stiff.The water pressure tensions thehose
walls, significantly improving theirability to sustain
compression.
Inflated dual-walledstructures are the second type
of air-inflated construction. These structures
comprise two membranes tensioned by the air
pressure between them (see Fig. 8.58a). The
membranes are tied together by drop threads and
diaphragms. Because of the large volume of air
compressed into dualwalled structures, they can
economically span larger distances than can
inflated-rib structures.
Even though the membranes used for airinflated
structures are fairly impervious, provision must be
made for replenishment of air. Some leakage is
likely to occur, particularly at joints. Also, air
pressure changes with variations in temperature
inside and outside the building. Consequently, air
must be vented to
Fig. 8.57. Some shapes for air-supported structures.

relieve excessive pressures, to prevent overten-
sioning of the membrane, and air must be added to
restore pressure when reductions occur, to prevent
collapse.
An air-supported structure consists of a
single membrane that is supported by the excess of
the internal pressure in a building over exterior
atmospheric pressure (see Fig. 8.58Z?). The
pressure differential produces tension in the
membrane and pushesit upward.To resist the uplift,
the air-supported structure must be securely
anchored to the ground.Also,to prevent leakage of
air, the membrane must be completely sealed all
around its perimeter.
Note that if loads, including membrane weight,
were uniform and completely balanced by the
internal pressure, there would be no pressure
differential. There would be no tension in the
membrane and no uplift forces requiring anchorage.
The membrane would just be a medium serving
merely to separate the building interior from the
outside environment.In that case,the air-supported
structure theoretically could span overan enormous
space. Actually, however, loads are never uniform
over the whole area of a large membrane. Hence,
pressure differentials large enough to prevent
compressive stresses in the membrane must be
applied to the membrane.
In practice, small pressure differentials are used.
Often,they are in the range of 0.02 to 0.04 psi(3 to
5 psf) above atmospheric pressure.
While there may be some air leakage throughthe
membrane,a more important source ofairloss is the
entrancesandexits to the building.Theselossescan
be minimized with the use ofairlocks and revolving
doors. Nevertheless, provision must be made for
continuous replenishment of the air supply with
blowers to maintain the pressure differential.
Bubble Analogy
A soap film is a naturalanalogy to an air-supported
structure. Surface-tension forces determine the
shape ofa bubble.The membrane is stressedequally
in all directions at every point.As a result, the film
forms shapes with minimum surface area, often
spherical.Because ofthe stresspatternin soapfilms,
any shapethatcan be obtainedwith themis feasible
for an airsupported structure. Figure 8.57c shows a
configuration formed by a group of bubbles as an
illustration ofa shape that can be adopted foran air-
supported structure.
Membrane Stresses
When a spherical membrane with radius R, in., is
subjected to constant radial internal pressure p, psi,
the unit tensile force, lb per in., is given by
pR
=
2 (8.77)
In a cylindrical membrane, the unit tensile force
in the circumferential direction is
T = pR (8.78)
where R is the radius, in., of the cylinder. The
longitudinal membrane stress depends on the
conditions atthecylinderends.With immovable end
abutments, for example, the longitudinal stress
would be small. If the abutments were not fixed to
the ground,however,a tension abouthalfthat given
by Eq. (8.78) would be imposed in the longitudinal
direction in the membrane.
Hybrid Structures
The necessity of providing a continuous air supply
and access to a building against a pressure
differential is a significant disadvantage of pure
pneumatic construction. An economical alternative
is to use light metal framing, such as cables orcable
nets,to support and tensiona membrane underlight
loads. Pressurization may then be employed to
supplementthe framing underheavywind and snow
loads.
Membrane
Membrane
Anchor
and Seal
Membrane
Anchor
and Seal
p
Fig. 8.58. (a) Inflated dual-walled structure, (b) Air-
supported structure.

Fig. 8.59. Pneumaticallystabilized membrane surface
with restraining cables.
Cable-Restrained Membranes
Use of air-supported membranes often results in
buildings with a high profile and a general bulbous
look. A method for holding down the high arching
profile ofa pneumatically stabilized membrane is to
employ a net of restraining cables,as shown in Fig.
8.59. In this case a perimeter structure—usually a
form of compression ring—is used to anchor the
edges of an inflated membrane, and is also used to
anchor a set of cables that are tensioned by the
inflation forces; thusrestrainingthemembrane from
developing its natural inflated profile. Major spans
with a relatively low profile have been achieved
with this system.
References
H. Irvine, Cable Structures, MIT Press, Cambridge, MA,
198L
p. Drew, Tensile Architecture, Granada, St. Albans, England,
1979.
R. Dent, Principles of Pneumatic Architecture, Architectural
Press, London, 1971.
M. Salvador!, Structure in Architecture, Prentice-Hall, New
York 1986.
Words and Terms
Cable
Cable structures, types: cable-stayed, cable-suspended, cable
net, cable-restrained
Pneumatic structures, types: air-inflated(ribbed, dualwalled),
air-supported
Structural use of tensionforspanningstructures: cables, cable
nets, draped and stretched membranes, pneumatically
stabilized membranes.
Support and anchoring systems for tensile structures.
8.15. HORIZONTAL FRAMING SYSTEMS
Structural roofs and floors are systems, but are
subsystems offloor-ceiling or roof-ceiling systems,
which, in turn, are part of the building system.
Consequently, design of structural roofs and floors
must take into accounttheireffects onothersystems
and the effects of other systems on them.
An enormous numberofdifferent structuralfloor
and roofsystems have been and stillare in use.It is
not feasible, therefore, to describe and compare
more than a few commonly used systems in this
section which deals only with substantially
horizontal, flat floor and roof systems. Steeply
sloped and curved roof systems, however, are
discussed in Sec. 8.9 and Secs. 8.11 to 8.14.
Decks
Prime components of a floor or roof are materials
that serve as a wearing or weathering surface, or
both, and a supporting, or structural, material. A
structuralmaterial is necessary because the wearing
or weathering material can be very thin. In some
cases, the structural material may also be the
wearing or weathering material. The structural
material is often referred to as a deckor, in the case
of concrete, a slab.
Being horizontal and flat, a deck is subjected to
verticaldead and live loads,which tend to bend and
twist it. (A deck may also serve as a horizontal
diaphragm as part of the lateral-loadresisting
structural system.) The bending and twisting limit
the distance that the deck can span between
supports.Spacingofsupports depends mainly on the
loads to be carried and the structuralcharacteristics
of the deck. Heavy loads or a weak or thin deck
generally require closely spaced supports.
Decks may be made of any of a wide variety of
materials. They are discussed in Chaps. 15 and 16.
For this section, it is desirable to note that flat roof
decks generally consist of a waterproof membrane
fastened to a structural material, such as concrete,
plywood,cold-formed steelorgypsum.Floordecks
usually consist of a wearing surface, such as
carpeting, concrete, wood, linoleum or asphalt,

plastic or ceramic tile, and a structural material like
those listed for roof decks.
Types of Horizontal Framing
In load-bearing construction, the prime vertical
supportsare walls.These mustbe spacedfarenough
apart to meet the architectural or functional
requirements of the building. Sometimes, wall
spacing falls within a range where it is economical
to employ a deck that can span between the walls.
Often, however, the most economical construction
consists of a thin deck placed on beams that span
between the walls. Spacing of the beams can be
made appropriate to the loads to be carried and the
structural characteristics of the deck.
Similarly, in skeleton framing, columns must be
spaced farenoughapart to meet the architecturalor
functional requirements of the building. This
spacing may lie within a range where it is
economicalto employ a deckthat can span,without
additionalsupports,betweenthe columns.But often
it is more economicalto use a thin deckand support
it on beams.The beams,in turn, may span between
columns, but usually only the edge beams of a
structural bay do so, while the interior beams are
supported on transverse girders that span between
the columns.
In any case, it is convenient to classify decks as
one way ortwo way.One-way decksdevelop,under
verticalloads,curvature in only one directiondueto
bending. Loads are transmitted by such decks only
in the plane ofcurvature to the decksupports.Two-
way decks develop, under vertical loads, curvature
in two perpendicular directions due to bending.
Loads therefore are transmitted by such decks in
more than one plane to the deck supports.
Factors in Selection of Horizontal Framing
Many things must be considered in selection of the
structural floor or roof system for a building.
Spacing of supports and magnitude of loads are
major factors, as are architectural and functional
considerations. Interaction of the structural system
with othersystems also must be taken into account.
Cost of the system, erected, is important, too. Bear
in mind, though, that the lowest-cost structural
system may not always yield the lowest-cost
building.
Other factors that should be considered include
fire resistance, depth of structural system and
weight. Often, the deeper the horizontal structural
system,the higherthe buildingmust be.The greater
the height,the more costlybecome thewalls and,for
high-rise buildings, the piping, air-conditioning
ducts and electricalrisers.Also,the heavierthe floor
framing, the more costly the columns and
foundations become.
Two-Way Concrete Slabs
When conditions are propitious for their use, flat-
plate floors and roofs (see Fig. 8.60tf) offer many
advantages overothertypes offraming.This type of
construction generally employs cast-in-place,
reinforced concrete. Sometimes, however,
prestressed concrete or precast concrete is used to
achieve greater economy. The concrete may be
made with ordinary stone aggregate, to obtain high
strength for long spans or heavy loads, or with
lightweight aggregate, for lower weight.
The flat plate is usually supported on columns
arranged to formrectangularbays,butothercolumn
layouts are feasible. Thickness of the plate is kept
uniformthroughout each bay (see Fig.8.60tf). This
simplifies the formwork for the concrete and helps
keep construction costs low. Without beams,
lighting, from windows or ceiling fixtures, is
unobstructed. Often, the underside of the flat plate
can be plastered and painted, or simply painted, to
serve as a ceiling.Piping and electricalconduit may
be incorporated in theplate byinstalling themon the
formwork before concrete is cast (see Fig. 8.61).
Underverticalloads,a flat plate,developing two-
directional curvature, assumes a dish shape. When
column spacing is not equal in the perpendicular
directions or when loads are unsym- metrically
placed in a bay, twisting occurs at

(c)
Fig. 8.60. Horizontal concrete framing systems, (a) Flat plate, (b} Flat slab, (c) Two-wayslab supported by edge
beams, (d) One-wayslab supported by parallel beams; beams supported bycolumn-line girders.
Fig. 8.61. Rebars and electrical conduit set on formwork, ready to receive concrete for a flat slab. (Cour tesy
Symons Manufacturing Co.)

the corners. Hence, the plate transmits loads to the
columns through a combination of bending and
torsion.
The structural action makes flat plates highly
efficient for loads and spans such as those
encountered in residential buildings. Consequently,
for short spans and light loads, thickness of
reinforced concrete flat plates may be as small as 5
in. Thus,because ofthe smalldepthofthehorizontal
framing, flat-plate construction is advantageous for
high-rise buildings. Some of this advantage is lost,
however,when lighting fixtures are set on the floor
underside or air-conditioning ducts are run
horizontally under the floor and especially when
they have to be hidden above a ceiling.
Because of continuity, bending moments are
larger at the columns than at the centerofeach bay.
(The moments nearcolumnsare negative,producing
tension at the top of the slab, thus requiring
reinforcing steelto be placedcloseto the top.)Also,
maximum shear occurs at the columns. To increase
the capacity of flat plates, it becomes necessary in
some cases to provide a column capital, an
enlargement ofa small length ofcolumn nearits top
(see Fig. 8.60/?). For longerspans orheavierloads,
flat plates, in addition, may be thickened in the
region aroundthe columns.Thistypeofconstruction
is called flat slab.
Flat slabs are flat plateswith anabruptthickening,
called a drop panel, nearcolumns(seeFig.8.60Z?).
The ACI Code requires that a drop panelbe at least
25% thickerthan the slab thicknesselsewhere.Sides
of the panel should have a length at least one-third
ofthe column spacing.Designofflat slabsis similar
to that for flat plates.
Note that in the center portions of flat plates and
flat slabs,bending momentsare positive,producing
tension at the bottomof the slabs, thus requiring
steel to be placed near the bottom. This steel is
usually uniformly spaced in two perpendicular
directions.
More efficient use may be made of the concrete,
however, if larger but fewer bars are used at much
larger spacing and the concrete in tension between
the bars is omitted. The remaining concrete then
forms a thin slab with ribs in two perpendicular
directions incorporatingthe rebars.Theundersideof
the slab has the appearance of a waffle.
Waffle flat slabs therefore consist, in the middle
portion, of a thin, two-way top slab spanning
between a grid of concrete joists in perpendicular
directions.Thejoists terminate atdroppanels,which
may have a thickness equal to or greater than the
depth of the joists. Waffle slabs are generally
constructed by casting concrete over square dome
forms with lips around the perimeter, so that
concrete placed between the domes becomes the
joists.Formwork may be more expensive forwaffle
slabs than for flat slabs, but for a given volume of
concrete, waffle slabs can carry heavier loads or
span longer distances than can flat slabs.
Anotherway to improve the capacity offlat slabs
and flat plates is to make them thick but hollow.
Hollow,orcellular,slabs, in effect,consist ofa top
and bottomslab connected by ribs.
Two-way slabs provide still another way of
improving the capacity offlat plates.In this type of
construction, a slab with constant thickness is
supported on beams that span between the columns
(see Fig. 8.60c). The design procedure is similar to
that for flat slabs and flat plates, except that the
structuralcharacteristics of the beams are taken into
account.As an alternative,walls may be substituted
for the beams and columns.
One-Way Decks
The structural behavior of the framing changes
significantly ifone ormore beams are placed within
a bay in eitherorboth directions normalto the beams
in Fig. 8.60c.
A grid of beams placed in perpendicular di-
rections is often economical for very large column
spacing. (For roof construction, trusses often are
used instead of beams in such cases.)
For more usual column spacings, it is often
economicalto place intermediate beams in only one
direction (see Fig. 8.60d). Ends of these beams are
supportedon girders spanningbetween thecolumns
or on load-bearing walls.
With the type of construction illustrated in Fig.
8.60J, the span of the deck is much shorter in the
direction normal to the beams than the span in the
direction parallelto the beams.Consequently,under
vertical loads, the deck may be classified as one

way, because there is very little curvature due to
bending in the direction parallelto the beams.Load
may be considered transmitted only in the direction
normal to the beams. One-way slabs therefore may
be designed by treating a unit-width strip as a beam
spanning in the short direction.
Spacing ofbeams and hence thenumberofbeams
per bay depend on the width ofbay and the type of
deck selected. Often, for economic reasons, the
spacing is chosen close to the maximum span with
the minimum thickness permitted for the deck
material. For example, if the deck is made of
reinforced concrete and the local building code
requires that a one-way concrete slab have a
thicknessofat least4in.,the most economicalbeam
spacing usually is the maximum distance that the 4-
in. slab can spanwith the designloads.This spacing
may be about 8ft for lightweight concretein a high-
rise office building.If the deckis plywood,joists or
rafters may be spaced 16 to 48 in. center-to-center,
depending on the strength and thickness of the
plywood (see Fig. 8.62). This type of construction
often is used in one- and two-story houses.
The added depthofframing when beams are used
is not a complete disadvantage. The space between
beams can often be utilized for useful
Fig. 8.62. Plywood deck is nailed to rafters spaced
24-in. center-to-center for a roof. (Courtesy American
Plywood Association)
purposes. For example, the space between rafters
can be filled with insulation,forwhich space would
be needed in any case. Often, airconditioning ducts
can be run in the spaces between beams and can be
hidden behind a ceiling extending between the
bottomflanges ofthe beams.Figure 8.63 illustrates
horizontal framing with a cold-formed steel deck
supportedonsteelbeams,with a ductparalleling the
beamon the right.(Note thata fire-resistantmaterial
has been sprayed on the steel beams and deck,
whereas the steel columns have been fire protected
with concrete enclosure.) If ducts have to be run
transverse to the beams, however, holes have to be
cut for passage of the ducts. The holes usually are
made in the beam webs, because the web bending
stresses are lowerthanthosein the flanges.Also,the
holes shouldbe formed where bending moments are
small, to minimize the loss ofstrength fromremoval
ofmaterial. The perimeterofthe hole often has to be
reinforced to compensate for the loss of material.
When open-web joists ortrusses are used instead of
beams,however,they offerthe advantagethat ducts
and piping canbepassed throughthespaces between
web members.
Connections in Horizontal Framing
A chain is no stronger than its weakest link. The
weakest links in the chain of structural members
transmitting loads from points of application to
foundations are likely to be the joints, or con-
nections. These must be capable of transmitting
between connected members the largest loads the
members may impose on each other. Also, the
connections must be made without causing
undesirable changes in the strengthorstiffness ofthe
members joined.In addition,at joints,deformations
of the ends of members must be geometrically
compatible and should conform closely to
assumptions made in design of the structural
framing. Forexample, connections between the ends
of simple beams and supporting members should be
capable of transmitting the reaction, resisting end
shears andallowing thebeamend to rotatefreely.In
contrast, where continuity of a beam is desired, a
rigid connection should be provided, to insure that

all connected members will rotate through the same
angle.
Wood Connections. The type ofconnectionsused
for wood framing depends, in addition to the
preceding conditions, on the size of members to be
joined. Thin pieces, for example, may be nailed,
screwed orgluedto othermembers.Thickorheavily
loaded members should be joined with more
substantial fasteners. A few of the many fastening
methods for such joints, in addition to those
described in Section8.5, Wood, are illustrated in Fig.
8.64.
One method ofsupportinga wood beamon a wall
is shown in Fig.8.64ứ. The beamis held in position
by a bolt througha pairofclip angles.Each angle in
turn is secured to the wall with an anchor bolt,
embedded in the masonry. A steel bearing plate
underthe beamend distributes the beamreaction to
the masonry and may be set in mortar, if necessary,
to bring the beamend to the required level.
Figure 8.64Z? illustrates the use of a steel bent-
strap hangerto support the endofa purlin at a wood
beam. A steel tie strap is nailed to the tops of the
purlin and beamand to a purlin on the opposite side
of the beam.
For a heavily loaded wood beam framed into a
wood girder,the connectionmay bemade with a pair
of steel angles bolted to both members (see Fig.
8.64c). A bolted connection with one or two steel
angles also may be used forpurlins orbeams seated
atop a girder (see Fig. 8.64d). Bolted angles also
may be employed for connecting beams or girders
below the tops of columns.
Fig. 8.63. Cold-formed steel deck supported on steel beams, with sprayed-on fireproofing. (Courtesy H. H.
Robertson Co.)

Figure 8.64^ and f show two methods for seating
wood beams atop columns.In Fig.8.64^, two beams
are bolted to the wood-column topthrougha pairof
steelT plates.In Fig. 8.64/, a steelu strap is welded
to the top of a steel pipe column. The wood beams
are seated in and bolted to the u strap.
Steel Connections. Steel members usually are
connectedto eachotherwith boltsorwelds.(In older
buildings, rivets were generally used, but now
riveted joints are more expensive.) For reasons of
economy and quality control, steel parts are often
welded in the fabricating shop and assembled with
bolts in the field. Sometimes, however, both shop
and field welding are economical,and field welding
offers such advantages as savings in connection
material and quieter operations. Bolts are tightened
with impact wrenches, which are noisy.
Steelbeams supportedon walls usually are seated
on a bearing plate,like the wood beamin Fig. 8.64a.
The plate distributes the beam reaction to the
masonry to prevent crushing.
Simple-beam connections betweensteelmembers
may be classified as framed or seated.
Figure 8.65a illustrates one type of framed
connection made with bolts.In the caseshown, each
beamis delivered to the building site with a pair of
steel angles bolted to the web at the end to be
connected to the girder.The outstanding legs ofthe
angles are field bolted to the girder.Also,in the case
shown,the beams frame into the girder with tops of
all members at the same level. To prevent the top
flanges of the beams and girders from interfering
with the connection, the beams are notched, or
coped,to remove enoughofthe flanges andwebs to
clear the girder flange. Framed connections
generally require less steelthan seated connections.
Examples ofseated connections are shown in Fig.
8.65Z? and c. Seated connections often are used
where there is insufficient clearance for framed
connections. For example, seated connections are
used for connections of girders to column webs to
make erection of the girders between the column
flanges easier. Seated connections, in general,
however, are helpful in erection. They provide
support formembers to be connected while holesfor
field bolts are aligned and while bolts are installed
or welds made.
(a)
(d)
Fig. 8.64. Connections for wood beams.
(f)

Fig. 8.65. Connections for steel beams.
A stiffened seat (see Fig. 8.65b) may be used
when loads tobe carried exceedthe capacitiesofthe
outstanding legs of standard unstiffened seats (see
Fig. 8.65c). An unstiffened seat consistsonly ofan
angle with one leg shop bolted to the supporting
member and the outstanding leg horizontal,forfield
bolting to the seated member. The seat is designed
to carry the full beam reaction. A top or side lug
angle is also bolted to the connecting members to
provide lateralsupport (see Fig.8.65Z? and c). In a
stiffened connection,additionalsupport is provided
to the outstandingleg ofthe seat angle.This may be
done by bolting a pair of angles ora WT (W shape
split by a cut through the web) to the supporting
member so that the seat bears against the
outstandinglegsofthe stiffeninganglesorWT web
(see Fig. 8.65Z?).
Framed connections also may be welded. Figure
8.65d shows a case where the framing angles are
shop welded to a beamand field bolted to a column
flange.Figure 8.65c illustrates a framed connection
that is both shop and field welded.A fewtemporary
field bolts are used to secure the framing angles to
the column flange untilthe field welds can be made
between that flange and the angles.
Similarly, seated connections may be welded.
Figure 8.65/ illustrates an unstiffened welded seat
connection and Fig. 8.65g, a stiffened welded seat
connection.The supporting memberis delivered to
the site with the seat angle welded to it. The top or
side lug is welded to the connecting members in the
field to prevent interference with erection of the
seated member.
7/8 " ộ A325 Bolts
(Shop)
W18
Holes f or
Field Bolts
W18
Beam
W24
Girder
13/4"
Shop
Bolts
1 3/8 " Minimum Tightening
Clearance f or
T~ Impact Wrench g0Ịt
Section 1-1
2 Angles
(a)
Top or
Column Web or
Flange or
Girder Web
Seat
Fitted
Top or
Side Lug
Column Web X
or Flange or
Girder Web
One or Two Stif fener Angles
(b)
Top or Side Lug
3/4
"
Beam
Seat
Angle
Weld
Angle
Column
Weld
Beam
Beam
Angle
Number and Ty peof
Fasteners for Reaction
of Beam
(c)
(d) (e)
or Girder Web
Column
(/>)
Weld
Stif fener
Stif fener
Weld
Weld
Beam
Backup
Strip Weld
2 Angles f or Shear
Column
Plate, Narrower
,than Beam Flange
Plate, Wider
e
than Beam Flange
Erection Seat (useas
backing strip)

Two types ofrigid connections, oftenused when
continuity of beams or rigid-frame action to resist
lateralforces is desired,are shown in Fig.8.65/zand
i. The connections illustrated are welded. In Fig.
8.65/i, the beam is supported on an erection seat
during welding. The seat also serves as a backup
strip for the weld between the beambottomflange
and the column flange. Both beam flanges are
welded directly to the column flange, to resist the
end bending moment in the beam, while the beam
web is welded to the column flange to resist the end
shear. The type of connection shown in Fig. 8.65/
may be used forlargerbendingmomentsandshears.
Plates are welded to the top and bottom beam
flanges and to the column flange, to resist the
bending moment, while a pair of steel angles is
welded to the beamweb and column flange,to resist
the end shear. In both types of connection,
horizontal steel plates are welded between the
column flanges at the level of the beam flanges to
brace the column flangesagainsttheforcesimposed
by beambending.
Concrete Connections. In any consideration of
concrete connections, a distinction must be made
between joints between cast-in-place members and
those between precast members. In cast-in-place
construction,concrete formembers at a joint can be
cast continuously so that the members are
monolithic,or integrated.Reinforcementfromeach
member is extended through a joint into the other
members, to tie them together with steel (see Fig.
8.66). Often,the deckand beams for a floor or roof
are cast simultaneously with the columns of the
story below. Reinforcement for those columns are
extended vertically above the deck to dowel the
columns for the next story (see Fig. 8.66).
Precast-concrete joints require careful design.
The members to be connected are discrete, as are
wood and steel beams. Two techniques are in
general use. One method extends reinforcement
from the members to be connected and embeds the
overlapping steel in cast-in-place concrete. The
othermethod anchors steelplates to the concrete at
the surfaces to be connected, and the plates of
adjoining members are field welded.An alternative
sometimes used is to connect members with steel
tendons, which apply prestress.
8.16. VERTICAL STRUCTURAL SYSTEMS
A verticalstructuralsystemis that subsystemofthe
structural systemof a building that transmits loads
from the level at which they occur to the
foundations. The vertical systemmay be hidden or
exposed for aesthetic purposes. It may be used in
addition to structural purposes, as air-conditioning
ducts orto enclose piping,but its prime function is
load transmission.
The loads on the vertical systemmay be re
Fig. 8.66. Framing of concrete beams.

solved into vertical components, which usually are
gravity loads, and horizontal components, which
generally consist of such lateral forces as wind or
earthquake loads. Causing sidesway or drift of the
building,the horizontalcomponentstendtorackand
overturn the structure.Theverticalstructuralsystem
must prevent this and keep drift, including
oscillations,within acceptable limits. Gravity loads
often are helpful in preventing uplift under the
overturningloads,but only dead loads canbe relied
on in design to offset uplift forces.
Lateral loads usually are of short duration.
Furthermore, the probability of simultaneous
occurrence of maximum lateral and maximum
gravity loads is small.Hence,building codespermit
a smaller safety factor to be used in the design of
structural components for combinations of lateral
and gravity loads than foreithertype ofload alone.
As a result,sometimes little orno increase in size of
structural members over that required for gravity
loads alone is needed for the combination loading.
Systems design ofstructuralframing should seekto
take advantage of such conditions.
Vertical structural systems may consist of
components designed to resist the combination
loading or of components designed to sustain only
gravity loads while assisted by othercomponentsin
resisting lateral loads. Selection of either type
depends on the height-width ratio of the building,
loads, column spacing and structural materials.
Load-Bearing Walls
Floors, beams, girders and trusses may be seated
conveniently on walls that transmit the loads
directly to the foundations. Such walls are ad-
vantageousin thatthey may alsoserve asenclosures
of rooms or the building exterior. They have the
disadvantage, however, that they have to be made
thicker in the lower portion as height is increased
and occupy considerable space in very tall
buildings. Also, walls usually take longer to build
than skeleton framing.
For small, lightly loaded buildings, it is often
economical to construct load-bearing walls of
closely spaced columns,called studs,with nonload-
bearing facings. In houses, studs usually
are spaced 16 or 24 in. center-to-center. They
generally are about one story high.Theyare seated
at the bottomon a sole plate and are capped at the
top by a top plate, which supports
Fig. 8.67. Erection of a prefabricated wood-stud wall.
(Courtesy Western Woods Products Association)
Fig. 8.68. Plywood sheathing isnailed to studs of a load
bearing wall. (Courtesy Western Woods Products
Association)

Fig. 8.69. Load-bearing construction for a two-story
building with basement.
horizontal framing members or roof trusses at that
level. Figure 8.67 shows a wood wall, with studs
spaced 24 in. center-to-center, being erected. Studs
may be diagonally braced or have a diaphragm
securely attached to themto preventracking.Figure
8.68 shows plywood sheathingnailed to wood studs
for that purpose.
For taller buildings, load-bearing walls may be
built of unit masonry, reinforced unit masonry or
reinforced concrete. Figure 8.69 illustrates load-
bearing construction for a two-story building with
basement. Similar construction may be used for a
high-rise building but with thickerwalls at the base.
Reinforced concrete walls may be cast in place,
usually one story at a time, or precast. Figure 8.70
shows construction of a multistory building with
one-story, precast wall panels and precast, hollow
floor deck.
Skeleton Framing
When skeleton framing is used, columns are the
main components of the vertical structural system.
(Their structural behavior is described in Sec. 8.8.)
They may be required to carry only gravity loads or
both lateral and gravity loads. In either case,
columns need lateral support from other framing
members to keep their slenderness ratios within
acceptable limits, to prevent buckling. Stiff floors,
Fig. 8.70. Multistorybuilding with precast load-bearing wallsand floors.

roofs, beams, girders or trusses connected to shear
walls, rigid frames or bracing may serve this
purpose.
Wood andcast-in-placeconcrete columnsusually
are erected in lengths one story high. The concrete
columns generally are cast at the same time as the
floor or roofthey will support.Precast concreteand
structuralsteelcolumns often are erected in lengths
two or three stories high in multistory buildings.
Steelcolumns usually are spliced 2or3ft above a
floor, for convenience, when extension upward is
necessary. Stresses are transferred from column
section to column sectionby bearing.Consequently,
splice plates used to join the sections need be only
of nominal size, sufficient for structural safety
during erection. When the sizes of sections to be
spliced are significantly different,stressesshould be
transmitted fromthe upperto the lowersectionwith
the aid of bearing flange plates on the uppersection
orby placing a horizontalbuttplate between the two
sectionsto distribute the load to the lower section.
A bearing plate is desirable under wood or steel
columns seated on masonry oron concrete footings.
The plate distributes the column load to prevent
crushing ofthe masonry orconcrete.Also,the plate
may be set in mortar so that it will be level and the
bottom of the column will be at the required
elevation. In addition, column bases should be
secured with anchorboltsembeddedin the masonry
or concrete.
Gravity and lateral loads are transmitted to
columns by floors, beams, girders, walls or trusses.
The columns require lateralbracing forbothtypesof
loads not only because horizontalcomponentsofthe
loads must be transmittedto thefoundationsbut also
because the horizontal framing may impose
eccentric vertical loading and bending moments.
Even in low buildings, the vertical structural
systemmust provideresistance to racking,sway and
overturning.Figure 8.71a illustrates howtrussesand
X bracing may be employed in the framing fora one-
story industrial building. Inclined trusses are
incorporated in the planes of the roof to transmit
wind loads to the ends of the building. X-braced
bays at each end carry the wind loads to the
foundations.Diagonalbraces in the end walls resist
wind loads acting on the sides of the building.
Multistory Framing
Resistanceto lateralloads in high-rise buildings may
be provided in a variety of different ways. Some
commonly used methods are indicated in Fig. 8.7b
through m. Sometimes, combinations of these
methods are used.
Shear Walls. The primary function ofa shearwall
is to resist horizontal forces parallel to the plane of
the wall. The lateralforces may be transmittedto the
wall by other walls, floors or horizontal framing.
Under these loads, the shear wall acts as a vertical
cantilever. Shear walls also may be used as load-
bearing walls for gravity loads and as enclosures for
elevator shafts, stairways or closets or as large
hollow columns. The walls usually are constructed
of reinforced concrete or reinforced unit masonry.
Figure 8.71/illustrates the use of shear walls for
resisting thecomponent oflateralloads acting in the
narrow direction of a building. The lateral loads in
the perpendicular direction are carried by rigid-
frame action of girders and columns.
Shear walls have little resistance to loads per-
pendicularto theirplane.Consequently,shearwalls
often are constructed in perpendicular planes (see
Fig. 8.71g) to resist lateralloads thatmay come from
any direction. Figure 8.71/z illustrates the use of
shear walls as enclosures for elevator shafts and
stairways.
Wind Bents. As indicated in Fig. 8.71c, lateral
loads may be distributed to specific bents,
combinations ofgirders,columns andoften diagonal
bracing lying in a verticalplane,which are designed
to transmit the loads to the foundations. Because a
bent is a planar structure, it has little resistance to
loads perpendicular to its plane. Consequently, the
specialbents,often called wind bents,are placed in
two perpendicular directions to resist lateral loads
that may come fromany direction.

The proportion of the component of the lateral
loads in the direction of a bent that is distributed to
the bent dependson the relative stiffness ofthe bent
compared with the stiffness of all the bents parallel
to it. Stiffness is measured by the relationship of
sidesway, or drift, of a bent to the load causing the
drift. Load distribution also is dependent onstiffness
of the floors and horizontal framing.
Figure 8.71/ through m illustrates some of the
commonly used types ofconstruction usedforwind
bents. Figure 8.717 shows part of a wind bent with
two X-braced panels per story in a building four-
Fig. 8.71. Lateral bracing systems for buildings, (a) One-Story industrial building with trussed bracing, (b} Core
shear wall, (c) Selected vertical planar bents as rigid frames. (Ờ) Framed tube, (e) Tube-in-tube. ( f} Exterior
(peripheral) shear walls, (g) interior shear walls, (h) Core shear walls. (7) X-braced bents. (/) K-bracing. (Aj
Inverted V-bracing. (I) Knee bracing, (zn) Moment-resistive connections for beams to columns.

bays wide. The bracing forms a pair of vertical
cantilever trusses. This type of bracing has the
disadvantage of obstructing the center of the panel
formed by the girders and columns,so that doorsor
windows cannot be placed in such panels. An
alternative formof bracing,Kbracing shown in Fig.
8.7lj, has a similar disadvantage. The action of the
two types of bracing differs in that one of the di-
agonals in each panelofK bracing must be capable
ofcarrying compression,whereasthe diagonals ofX
bracing may be designed only for tension.
Another alternative is the inverted V bracing
shown in Fig. 8.7k. This type leaves the center of
the panel open. Hence, windows or doors can be
placed in the panel. The bracing has the
disadvantage,however,that it is subjectedto gravity
loads fromthe girders.
Still another alternative method for developing
resistance to lateral loads is through rigid- frame
action. One way of doing this is to place knee
bracing, short diagonals, near the intersection of
girders and columns (see Fig. 8.71/). This type of
bracing has the disadvantage that it must be placed
in every panel and may not be architecturally
desirable because the bracing may protrude beyond
partitions and ceilings into rooms, or may interfere
with window placement.
Rigid-frame action developed with rigid con-
nections between girders and columns (see Fig.
8.7 lra) generally is more compatible with ar-
chitectural objectives. Haunched girders, as shown
in Fig. 8.7lra, often are acceptable for wind bents
along a building exterior. The haunches, however,
are usually eliminated from interior bents so that
structural framing can be hidden in partitions or
above ceilings.
Framed Tubes. If the floors and roofofa building
are made stiff enough to act as horizontal
diaphragms, wind bents can be placed along the
exterior only. Under the action of lateral loads, the
bents will act togetheras a vertical cantilever tube.
Such a framed tube was used for the 100-story
John Hancock Building in Chicago (see Fig. 8.72).
The exterior bents are exposed for ar-
Fig. 8.72. John Hancock Building, Chicago. 100 stories
high, with X-braced, framed-tube construction.
chitectural effect. In these bents, lateral loads are
resisted by X braces placed across the full width of
the bents.
A different type of framed tube was used for the
110-story twin towers ofthe World Trade Centerin
New York City (see Fig. 8.73). The bents along the
exterior develop resistance to lateral loads through
rigid-frame action. In this type of construction, the
exterior columns can be placed closertogetherthan
in the building interiorbecause they do not interfere
with the use ofinterior space.Spacing may be 10 ft
or less. The short spacing permits use of much
smaller columns than would be required for the

larger spacing usually used.Underlateralloads,the
structural system acts like a vertical cantilever
perforated tube.
Similar construction was used for the 110- story
Sears Towerin Chicago (see Fig.8.74). In this case,
however, several narrow tubes are combined, or
bundled. More tubes are provided in the lower
portion of the building, where greater lateral-load
resistance is needed, than in the upper portion.
Another variation of tubular construction is the
tube-in-tube illustratedin Fig.8.71e. Wind bentsare
placed around the exterior of the building, but, in
addition, a tube is also constructed around the core
of the building. The interior tube is usually formed
with shear walls, which may be load-bearing and
which also may enclose elevator shafts and
stairways. The exterior and interior tubes act
together in resisting lateral loads.
SECTIONS 8.15 and 8.16
References
w. Scheuller, Horizontal-Span Building Structures, Wiley,
New York, 1983.
w. Scheuller, High-Rise Building Structures, Wiley, New
York, 1977.
Fig. 8.73. Twin, 110-storytowers of World Trade Center, New York City, with perforated-tube construction.
(Courtesy Port Authority of New York and New Jersey.)

Fig. 8.74. Sears Tower, Chicago, 110 stories high, with
bundled tube construction.
Words and Terms
Connections
Deck (structural)
Lateral bracingsystems: shear wall, lateral bents, framedtubes
Load-bearingwalls
Skeleton framing
Spanningsystems: one-way, two-way, continuous
Issues
Horizontal system development: choice of type; relation to
vertical supports; selection of deck; integration with
roofing, flooring, ceilings, building services.
Vertical system development: planning; lateral bracing;
coordination with horizontal system design; relations to
architectural planandspatial development; integration with
doors, windows, stairs, elevators, building services.
8.17. SYSTEMS-DESIGN APPROACH
TO STRUCTURAL SYSTEMS
Many of the innumerable variables in systems
design of structural systems develop from the
interaction ofstructuralsystems with otherbuilding
systems.Asa result,structuraldesigngenerally is an
iterative process. In each step of the process,
potentialstructuralsystems are generated,evaluated
and compared. As design proceeds, the framing
being developed must be checked to insure
compatibility with othersystems as wellas to verify
that othersystems willbe properly supported.Often,
structuralsystems have to be modified in all design
stages,frompreparation ofschematics through final
design, to meet architectural, mechanical, electrical
or other building needs. A good building team,
however,will insure that only minorchanges willbe
necessary in the later design stages.
Because ofthe interaction ofthe various building
systems with each other,selection ofthelowest-cost
structural systemdoes not necessarily result in an
optimumbuilding.Such a system,for example, may
be a dome with such a large volume of space
enclosed that heating costs would be excessively
high; or the system may require closely spaced
columns that would interfere with activities planned
for the building and make production costs
unacceptably high; or the beams may obstruct
passage ofducts andpiping orincrease the building
height with consequent increases in costs of walls,
ducts and piping. Instead, design of the structural
systemmust be consistent with the objective of an
optimumbuilding.
Design ofa structuralsystemgenerally starts after
a schematic architectural floor plan has been
prepared. This floor plan should be based on
conditions at the building site. At this stage also an
estimate should beavailable ofthenumberofstories
the building is to contain. Little mechanical or
electrical information may be available at this time
because design of the mechanical and electrical
systems too may be just starting. The structural
engineertherefore canonly rely on his judgment and
experience and select potentialstructuralsystems for
investigation. These systems must be fitted to the
proposed floor plan and made compatible with
design of an optimum site-foundation system. The
systems-designsteps illustratedin Fig.3.4should be
applied to all structural systems considered.
Data Collection and Problem Formulation
Basic information for structural design comes from
site studies,architecturalfloorplans,elevations and
cross sections, and the owner’s program of
requirements. Additional information that will be
needed should be obtained fromlocal building and
zoning codes, from design standards for various

structural materials and from studies of local
construction practices, including the type of work
handled by the local construction trades or unions
and union restrictions.
The floor plans and type of occupancy often
determine the live loads that will be imposed on the
structuralsystem.The localbuilding code,however,
may set minimum loads on which design must be
based, rather than the actual service loads. In
addition,provision mustbe made forfuture changes
in type of occupancy or floor plans.
The zoning code generally will set a limit on the
height of the building. This limit, in turn, may
restrict the depth of the horizontal framing, if the
building is to contain the specified numberofstories
and also provide acceptable headroomor floor-to-
ceiling heights. Also, the zoning code may require
the building to have setbacks as height increases.
The setbacks,in turn, alter the structuralframing in
upper and lower portions of the building.
In the laterdesign stages,furtherinformation will
come from electrical and mechanical engineers and
other consultants. This information should provide
details on equipment to be supported, ducts, pipes
and wiring to be installed and accessto be provided
to all these building components. In addition, more
details should become available on walls and
partitions, elevator shafts and stairways. The new
information may make necessary substantial
modifications in the structural system or even a
complete change.
The goal may be stated as: To design, as a
component of an optimum building, a structural
systemthat will enable the building to sustain all
anticipated loads under ordinary and emergency
conditionswith noriskofinjury to personsin ornear
the building, or of damage to any building
components, or of motions causing human
discomfort, except under very extreme conditions,
such as cyclones or earthquakes, in which case the
risk will be small.
Objectives
Most buildings have many objectives in common.
Foremost among these objectives is the aim of
selecting from among all the possible structural
systems that can achieve the goal the one that will
have the lowestlife-cycle cost.Thiscostincludesthe
cost of material, fire protection, fabrication,
shipping, erection, maintenance and repairs.
Anotherobjective is toprovidea structuralsystem
that is compatible with architectural requirements
and with mechanical, electrical and other systems
needed for the building.
Still another objective is to design a structural
systemofmaterials that can be obtained quickly and
then can be fabricated and erected speedily.
Specific buildings may require unusual objec-
tives.Forexample, for various reasons,an objective
may be to have far fewer columns orwalls, or even
no walls,in the first storythan may be usedat higher
levels; or an objective may be to have a very long-
span roof, for example, for an airplane hangar or a
stadium; or sometimes, the objective may be to
design a systemthat can be easily dismantled, to
permit easy alterations orformovement to and reas-
sembly on a different site.
Constraints
Numerous constraints may be imposed even for a
simple building (see Sec.8.6). Design live loads are
among the most important. These depend on the
purpose for which the building is to be used. The
loads vary with the number of persons permitted to
occupy a space, the equipment to be installed, and
materials or vehicles to be stored. Geographic
location and foundation conditions, however, may
be equally important. The location of the building
site and the shape of the building determine wind
and seismic loads that the structuralsystemmust be
capable of resisting. Foundation conditions may
restrict the weight of the structural system and
influence the spacing of columns or loadbearing
walls.
Building and zoning codes, in addition, impose
many constraints. Building codes may set limits on
dimensions of materials, specify allowable unit
stresses orloads and dictate design andconstruction
methods,including safe workingconditions and safe
use of equipment. Building codes also incorporate
requirements for fire protection of structural
systems.Zoning codes generally constrain structural
systems through limits on building height and
requirements for setbacks from lot lines with
increase in height.
Constructionlaboralsoimposes some constraints.
Wages paid some trades,forexample,may be higher

than those paid others,especially when productivity
is taken into account, so that structural systems
requiring employment ofthe higher-paid tradesmay
be uneconomic.In some regions,masonsmay be so
expensive that skeletonframing should be chosenin
preference to load-bearing walls, whereas in other
regions, the reverse may be true. As another
example, union work rules may prohibit some types
of construction. In some regions, construction
workers may refuse to handle components
prefabricated off the site, whereas in other regions,
prefabrication is an accepted practice. In some
regions also, a union may require employment of a
workerfull time, although the workermay be needed
only to start a machine in the morning andshutit off
in the afternoon.Theselaborconstraintsmay have a
significant influence on selection of structural
systems.
Synthesis and Analysis
In the schematics stage,the structuralsystemshould
be laid out to be compatible with foundation
conditions and the architectural floor plans,
elevations and cross sections. Analysis of the
proposed design should verify that the goal,
objectives and constraints established for the
structural systemhave been met.
In the preliminary design stage, with much more
information available from the owner, architect,
mechanical and electrical engineers and other
consultants, preliminary designs of alternative
structuralsystemsshould be prepared.Thesedesigns
should be checked for compatibility with other
systems of the building. Cost estimates for the
systems should then be made.
Value Analysis and Appraisal
The benefits and costs of the alternative structural
systems should be compared.In general,evaluation
and selection of an optimumstructural system will
be difficult. Many criteria must be satisfied.Cost,as
usual,is important,but there are likely to be several
others about as important, such as those concerned
with compatibility with other systems and speed of
erection.The final decision on which systemto use
may have to be subjective,basedon opinionsofthe
members of the building teamand how the benefits
and costs are weighted in an evaluation.
In the final design stage, design of the chosen
structuralsystemmay be refined.Value engineering
may be helpful in reducing both weight and cost of
the systemand finding ways to speed construction.
During the early design stages, ways should be
investigated to cut costs by making the structural
systemserve severalpurposes,forexample,to serve
also as walls or partitions or as ducts or as conduit
for wires. Costs also can be cut through
standardization of components and operations.
Repetition usually reduces fabrication costs and
speeds erection, because workers become familiar
with the procedures. For this reason, in multistory
buildings, the roof systemoften is made similar to
the more heavily loaded floorsystem,thus avoiding
a change from a repeated procedure at the lower
levels to a new procedure at the top.
When repetitionis feasible,prefabricationoflarge
sections of the structural systemoften saves money
and speeds construction. Figure 8.67 illustrates
erection ofa preassembled,load-bearing,wood stud
wall. Figure 8.70 shows the construction of a
multistory building with precast concrete, load-
bearing walls and floors. Figure 8.75 shows
placement of a one- story-high section of a precast
concrete wall for an elevator shaft. Often, it is
economicalto prefabricateformworkforconcrete in
large sections,make it easily demountable andmov-

able,and reuse it many times during constructionof
a building (see Fig. 8.21c). (Prefabrication of small
units, such as domes for waffle slabs or pans for
ribbed floors, is common practice.)
A novel example of the use of repetition is
illustrated in Fig. 8.76. The construction system
shown utilizes one-story-high beams or trusses
repeatedly. Extending the width of the building,
these structural members may be uniformly spaced
at each level, but their locations
Fig. 8.76. Staggered girder, or truss, construction.
are staggered in adjoining stories. Each floor is
supportedat the base ofone beamortrussandat the
top ofthe adjoining beams ortrusses.Consequently,
the spanofthe flooris only halfthe spacingbetween
the structural members. Hence, even with a thin
floor deck, structural members can be widely
spaced, with the result that fewer beams or trusses
and columns are needed than for conventional
construction. In addition, with the beams or trusses
being as deep as one story, they can span long
distances economically and hence it is feasible to
eliminate interior columns in many cases.Openings
for doors and corridors can be provided in the
members.
references relating to individualchaptersections are
Fig. 8.75. Story-high, precast concrete unit for an elevator shaft. (CourtesyHigh Concrete Structures of New
Jersey)

Structural Theory
AmericanStandardMinimum DesignLoads for Buildings and
Other Structures, American National Standards Institute,
1982.
H. Parker andJ. Ambrose,SimplifiedMechanics andStrength
R. Gutkowski, Structures: Fundamental Theory andBehavior,
2nd ed., Van Nostrand Reinhold, New York, 1987.
E. Gaylordandc. Gaylord, Structural EngineeringHandbook,
2nd ed., McGraw-Hill, New York, 1979.
H. Laursen, Structural Analysis, 3rd. ed., McGraw-Hill, New
York, 1988.
New York, 1984.
Structural Materials
H. Rosen, ConstructionMaterials for Architects, Wiley, New
York, 1985.
F. Wilson, Building Materials Evaluation Handbook, Van
R. Smith, Materials of Construction, 3rd ed., McGraw- Hill,
New York, 1988.
Structural Design
H. Parker and J. Ambrose, Simplified Engineering for Ar-
chitects and Builders, 7th ed., Wiley, New York, 1989.
R. White and c. Salmon, Building Structural Design
Handbook, Wiley, New York, 1987.
D. Breyer, Design of WoodStructures, 2nded., McGraw- Hill,
New York, 1986.
Timber Construction Manual, 3rd ed., American Institute of
Timber Construction, Wiley, New York, 1985.
s. Crawley and R. Dillon, Steel Buildings: Analysis and
Design, 3rd ed., Wiley, New York, 1984.
B. Johnson and F. Lin, Basic Steel Design, 3rd ed., Prentice-
Hall, New York, 1986.
Manual of Steel Construction, American Institute of Steel
Construction, Chicago, 1986.
p. Rice, et al., Structural Design Guide to the ACI Building
Code, Van Nostrand Reinhold, New York, 1985.
M. Fintel, Handbook of Concrete Engineering, 2nd ed., Van
Building Code Requirements for Reinforced Concrete, (ACI
318-83), American Concrete Institute, Detroit, 1983.
PCI Design Handbook—Precast and Prestressed Concrete,
Prestressed Concrete Institute, Chicago, 1985.
J. Amrhein, Masonry Design Manual, 3rd ed., Masonry
Institute of America, Los Angeles, 1979.
Construction Methods
D.Watson, Construction Materials and Practices, 3rd ed.,
E.Allen, Fundamentals of Building Construction: Materials
and Methods, Wiley, New York, 1985.
American Plywood Association Design/Construction Guide:
Residential and Commercial, American Plywood
Association, Tacoma, WA.
ACI, Manual of Concrete Practice, American Concrete In-
stitute, Detroit, MI, 1988.
EXERCISES
for review ofthe individualsections ofthe chapter.
Section 8.1
1. What is the prime function of the structural
systemof a building?
2. What is the relationship between applied
loads and reactions?
3. How does a load differ, by definition, from
stress?
4. What is the difference between dead loads
and live loads?
5. What types ofdeformations do the following
loads cause in a structural member?
(a) Tensile forces?
(b) Compressive forces?
(c) Shearing forces?
6. Howmany unknowns can bedetermined with
the laws of equilibrium for a set of
nonconcurrent coplanar forces acting on a
rigid body?
7. The 10-kip load on beam AB in Fig. 8.2 is
replaced by a uniformly distributed load of
0.5 kip perft. Determine the reactions forthe
beam.
8. The 10-kip load on beamAB in Fig. 8.2 is
replaced by joists at 5-ft intervals. Each joist
imposes a 2-kip load on the beam. Determine the
reactions for the beam.
9. The 10-kip load on beam AB in Fig. 8.2 is
replaced by a uniformly distributed load of
0.25 kip per ft and joists at 2.5-ft intervals.
Each joist imposes an 0.8-kip load on the
beam. Determine the beamreactions.
10. A simple beam with a span of 20 ft is loaded

from one end to midspan with a uniformly
distributed load of 0.5 kip per ft.
(a) What are the magnitudesofthereactions?
(b) What is the maximumshear?
(c) Where does the maximum bending
moment occur?
(J) What is the value of the maximum
moment?
11. A load of 30 kip is applied 2 in. from the
centroidal axis of a thick column. What is the
value of the bending moment imposed on the
column?
12. A steel hanger 120-in. long with a cross-
sectional area of 1.25 sq in. is subjected to an
axial tension load of 20 kip.
(a) What is the value oftheunit tensile stress,
ksi?
(b) If the elongation is 0.006 in., what is the
value ofthe unit tensile strain,in.perin.?
13. A steelhanger84 in. long is subjected to a 16-
kip axial tensile load.
(a) If the steel is permitted to carry a unit
stress of 24 ksi, what is the minimum
cross-sectional area required for the
hanger?
(b) If the unit tensile strain is 0.00008 in. per
in., how much will the hanger lengthen?
14. A steel hanger 96 in. long has a crosssectional
area of 2 sq in.If the steelis permitted to carry
a unit stress of 24 ksi, what is the maximum
tensile load allowed on the hanger?
15. A short concrete bracket, part of a concrete
column, is subjected to a 14-kip vertical
reaction froma beam. At the intersection with
the column,the bracket is 12in.deep and 6in.
wide. What is the value of the unit shearing
stress at the face of the column?
16. One end ofa beamrests on a steelbearingplate
seated on a concrete pier. The purpose of the
bearing plate is to distribute the beamreaction
of 8 kip to the top of the pier. The concrete is
allowed to carry a bearing stress of 0.4 ksi.
What is the minimum area required for the
bearing plate?
17. What distinguishes the structural behavior of a
slender column from that of a short
compression member?
Section 8.4
18. Why is a ductile structural material desirable?
19. What condition determines whether a material
is elastic?
20. Define proportional limit.
21. What is thesignificanceofyield point and yield
strength?
22. A material is elongated 0.00004 in. per in. by a
tensile load.If Poisson’s ratio forthe material
is 0.25, what change takes place normalto the
direction of the load?
23. What is Hooke’s law?
24. A 300-in.-long steelbarhangerwith a modulus
ofelasticity of30,000 ksi and a Poisson’s ratio
of0.3 is subjectedtoa 96-kip tensile load.The
cross section of the bar is 2 sq in.
(a) What is the unit tensile stress in the bar?
(b) If the proportional limit is not exceeded,
how much does the bar elongate?
(c) How much does the width of the bar
decrease?
25. What is the distinguishing characteristic of:
(a) A homogeneous material?
(Z?) An isotropic material?
(c) A tough material?
(d) A plastic (responsive) material?
26. A steel beam is subjected to a shearing unit
stress of11.5 ksi. The material has a modulus
of elasticity of 30 ksi and Poisson’s ratio of
0.3.
(a) What is the value of the modulus of
rigidity of the beam?
(/?)What is the magnitude ofthe shearingunit
strain?
27. A structural steel member has a yield point of
36 ksi. If the safety factoris 1.67, what is the
allowable unit stress in tension?
28. Why are yield point and yield strength
important in structural design?
29. What characteristic ofa material is determined
by:
(a) Modulus of elasticity?
(b) Modulus of rigidity?

Section 8.5
30. What are the advantages in structural ap-
plications of:
(a) Structural steels?
(b) Wood?
31. What type of material is indicated by A572,
Grade 45 steel?
32. What is designated by w 14 X 84?
33. What are the basic chemicals in structural
steels?
34. How does the structural behavior of the
following materials compare with that of the
idealized material with the stressstrain curve
shown in Fig. 8.7?
(a) Steel.
(/?) Wood.
(c) Concrete.
35. Howdo structuralsteels andcold-formed steels
compare in thickness?
36. Describe at least three ways of protecting
structural steels against corrosion.
37. How does bridge rope differ from bridge
strand?
38. How does the strength ofsteelcables compare
with that of carbon steels?
39. What are the advantages of connecting steel
pieces with welds?
40. What is the purpose of lips on cold- formed
shapes?
41. In what direction is wood strongest in tension
and compression?
42. What is the purpose ofthe grading of lumber?
43. What is meant by dimension lumber?
44. A piece of lumber has a compressive strength
parallel to the grain of4ksi, and crossgrain of
0.8 ksi.What is the compressive strengthat an
angle of 45° with the grain?
45. Which has greaterwithdrawalresistance under
load for the same length of embedment in
wood, a nail or a wood screw?
46. Explain why fewer bolts are required in a
connection between wood members if split-
ring connectors are used.
47. Why does each ply in plywood have its grain
perpendicularto the grain in adjoining plies?
48. What materials are generally used to make:
(a) Portland cement?
(/?) Normal weight concrete?
(c) Lightweight concrete?
(J) Heavyweight concrete?
49. Why is reinforcing or prestressing needed for

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