Lecture1_Structures_WU_MASE101.ppt

Introduction to Structural
Engineering
Tony Freidman

Background
• Graduate of University of Missouri – Rolla
– B.S. in Civil Engineering
– B.S. in Architectural Engineering
– Research in Architectural specialties
– Research on V-T-M diagram development for
reinforced concrete column design
• Currently enrolled as a Ph.D. student at
Washington University – St. Louis
– Research on MR Damper performance
– Research on Structural Health Monitoring

• http://www.youtube.com/watch?v=uKeENd
yIluI&feature=related
• http://www.youtube.com/watch?v=AsCBK-
fRNRk&feature=related
• http://www.youtube.com/watch?v=YCfgfcc
pHpc&feature=related
• http://em-ntserver.unl.edu/Mechanics-
Pages/Group1/sld001.htm

Structural Engineering is used so
that the events in the preceding
videos never take place.
“Engineers shall hold paramount the safety, health and welfare of the
public and shall strive to comply with the principles of sustainable
development in the performance of their professional duties. “
- 1st Fundamental Engineering Canon

Structural Engineering Overview
• What is a Structural Engineer?
• What do they do?
• What do they design?

What is a Structural Engineer?
• Engineer
– Mathematics of design
• Architect/Artist
– Vision
– Aesthetics of design
• Mediator
– Liason between parties
on a project
• Salesman
– Must sell your idea,
yourself

Structural Engineering Overview
• What is a Structural Engineer?
• What do Structural Engineers do?
• What do they design?

What do SE’s do?
• Designer
– Consultant
• Take a design, and fit a structural system to that
• Expert witnesses in lawsuits
– Inspector
• Fieldwork, Job site inspections
• Oversee the materials (concrete, steel, etc.)
• Inspect the building – pre- and post-construction
– Demolitions
• Building deconstruction
• Structural Retro-fits

SE’s design/analyze Structures
• What is a structure?
– A system designed to resist or support loading
and dissipate energy
• Building Structures
– Houses
– Skyscrapers
– Anything designed for continuous human occupation
• Non-building Structures
– Bridges
– Tunnels
– Dams

Forces
• Influence on an object that causes a change in a
physical quantity
• Considered “vectors” – magnitude and direction
• Static Force
– Unchanging with time
• Walls
• Floors
• Dynamic Force
– Changing with time
• People
• Furniture

Forces
• Axial Forces
– Acting along one axis, directly on a point or surface
• Momential (Bending) Force
– Acting along an axis, at a certain distance from a
point, causes a folding motion
– M = F*d
F

Forces
• Tensile Force
– Pulling on an object – stretching it
– Steel shows “necking” when too much tensile
force is applied
• Compressive Force
– Pushing on an object – collapsing it
– Concrete crushes when too much
compressive force is applied

Forces
• Strain
– Tensile-related property
– Deformation / Length
• Stress
– Compression-related
property
– Force / Area
• Compare using stress-
strain graph

What constitutes loading?
• Loading is a force being enacted on the
structure
– Many sources of load
• Gravity/Weight
• Wind
• Snow
• Earthquake
• Man-made
– Two Types of Structural Loading
• Dead Loads – static, ever-present (i.e. Walls, Floors, etc)
• Live Loads – dynamic, changing (i.e. People, Desk, etc)

What should we build our
structures out of??
• Common Structural Materials
– Timber
– Masonry
– Concrete
– Steel
– Composites

How do we judge the materials?
• Common Material Properties
– Strength – Tensile/Compressive
– Density
– Hardness
– Ductility / Brittleness
– Elasticity
– Toughness

Strength
• Ability of a material to withstand loading
– Tensile strength – ability of a material to withstand a
pulling force
• Steel is good at this, but concrete performs very poorly.
• http://www.youtube.com/watch?v=YdqvGGFIbfc
– Compressive strength – ability of a material to
withstand a pushing force
• Wood, concrete, steel, and masonry perform well
• http://www.youtube.com/watch?v=WC6AgX2N1Go&feature=r
elated
• http://www.youtube.com/watch?v=i5qwvtEqC5o&fe
ature=related

Density
• Mass per unit volume of a material
– Units – mass/vol - kg/m3 or lb-m/ft3
– Typically, materials with a high density are
very strong and offer great protection.
– However, a high density means that they are
heavy and difficult to work with $$$$$

Hardness
• Ability of a material to resist permanent
deformation under a sharp load
– Relates to the elasticity of a material
– Diamond is a very hard substance. If we built
a wall out of diamond, we could be sure that
very few things would scratch it.
– However, Diamond is incredibly expensive
and not as tough as other engineering metals.
It wouldn’t stand up as well in impact loading
versus other materials.

Ductility / Brittleness
• Ability of a material to deform without
fracture
– We want materials with high ductility, because
they will indicate structural failure without a
sudden collapse.
– http://www.youtube.com/watch?v=BXpqW9B0
eT4&feature=related – “Brittle failure”

Elasticity
• Ability of a material to deform and return to
it’s original shape.
– Important quantity
• Young’s Modulus
• Ratio of stress to strain
– Stress = Force / Area (lbs./in2 or N/m2)
– Strain = Deformation / Length (unitless)
• Generates a stress-strain graph
• Related to the ductility of a material

Toughness
• Ability of a material to resist fracture when
stressed (amount of energy absorbed per
unit volume)
– Units – J/m3 or Lb-f/ft3
– Area under the stress-strain curve, evaluated
from 0 to the desired strain.

So, we know what properties are
important in structural materials.
How do the common materials
stack up against each other?

Timber
• Advantages
– Cheap, renewable resource
– Good in Tension – ~40 MPa
• Disadvantages
– Susceptible to fire, nature
– Not very hard
– Not very strong
– Limits on shape, size

Masonry
• Concrete blocks, clay bricks
– Advantages
• Large compressive strength
• Cheap
• Good thermal properties – holds heat
well
– Disadvantages
• Not a cohesive material. The strength
could depend on the mortar, other
factors
• Poor tensile strength, unless reinforced
• Heavy material, requires skilled
laborers to use $$$$$
• Height restriction
• Susceptible to the weather

Concrete
• Combination of water, cement, small
aggregate, and large aggregate.
• Advantages
– Very versatile – can be modified with
admixtures for different effects
– High compressive strength (4~7 ksi)
– Fire resistant
– Many diverse sizes and shapes - formwork

Concrete
• Disadvantages
– Long curing time
– Low tension
strength (~0.4
ksi)
– Fails in shear,
unless reinforced
– Fairly heavy
material to work
with

Steel
• Advantages
– High tensile and compressive strength (A36
Steel ~ 60 ksi)
– Many varieties, depending on your need
• Carbon steel
• Stainless steel
• Galvanized steel
– Elastic material
– Ductile material
– Many shapes, sizes

Steel
• Disadvantages
– Expensive – limited quantities / competition
– Susceptible to fire, rust, impurities

Put them together and…
• Reinforced Concrete
– Concrete with steel reinforcement
• Concrete handles compression
• Steel takes the tension
– Can handle nearly 4 times the loading that
concrete alone can handle
– More expensive material
– http://www.youtube.com/watch?v=dGbrp7Mfp
2w

Composites
• Engineered compounds that have different
physical or chemical properties
– FRP – Fiber reinforced polymers
– CFRP – Carbon-fiber reinforced polymers
– Plastics
– Categories of Glass
– Categories of Wood

So, now we know what material
will best suit our needs..
What should we build with it?

Structural Shapes
• Rectangle / Square
• Triangle
– Interested in stability
• Truss
• Geodesic Dome

Shape Stability Exercise
• Split into teams of 5
• Build a triangle and square
• See which shape is the most stable
– Can the unstable shapes be made stable?
– How?

Rectangle
• Advantages
– Proficient in
resisting
vertical load.
• Disadvantages
– No lateral
support

Triangle
• Advantages
– Able to withstand
lateral & vertical
loading
– Many triangular
shapes available
• Disadvantage
– Wide base = $$$$

Rectangle
• Advantages
– Proficient in
resisting
vertical load.
• Disadvantages
– No lateral
(horizontal)
load support
Need another
bar for lateral
support!
--BRACING--

Truss
• Combination of square and triangle

Truss
Squares

Truss
Triangles

Truss
– Both vertical and lateral support

Domes
• Advantages
– Very strong shape, gets strong as the dome
size increases
– Perfect load distribution
– No need for structural supports
– Great aerodynamic performance

Structural Components
• Beams
• Girders
• Columns
• Floors
• Foundations
Column Girder
Beam

Load Path
• Floor
• Beams
• Girders
• Columns
• Foundation
• Soil/Bedrock

Foundations
• Support the building
– Typically attached to columns
• Types
– Shallow
• Spread footing – concrete strip/pad below the frost line
• Slab-on-grade – concrete pad on the surface
– Deep
• Drilled Shafts
• Piles

Lecture1_Structures_WU_MASE101.ppt

Columns
• Carry the load from floors to the foundation
– Never want the columns to fail COLLAPSE
– Typically reinforced concrete or steel
– Many sizes and shapes

Girders
• Attached column-
to-column
– Take the load from
the beams
– Transfer it to the
columns
– Generally shaped
as an I-Beam

Beams
• Attached between
the girders
– Take load from the
flooring system
– Transfer it to the
girders
– Generally solid
squares, I-beams

Flooring
• Composed of a subfloor and floor covering
– Usually leave space for ductwork, wiring, etc.
– Floor covering ranges from application to
application

Picture Credits
• Geodesic Dome
– http://www.ecophotoexplorers.com/images/antarctica/Dome.jpg
• Truss
– http://www.classictruss.com/art/wodd_truss_types_examples.gif
• Truss 2
– http://www.wwta.ab.ca/images/pic%201.jpg
• Truss 3
– http://www.garrettsbridges.com/images/pratt-truss-bridge.jpg
• Stress-Strain
– http://www.mittalsteel.com/NR/rdonlyres/8E6DAA96-67F0-4C32-8702-
FB02211647D9/0/InlandAutoApps_MildCS_ssGraph.gif
• Crushing Concrete
– http://images.google.com/imgres?imgurl=http://cee.engr.ucdavis.edu/faculty/chai/Research/P
lanar%2520Wall%2520Stability/Wallcolumn5.jpg&imgrefurl=http://cee.engr.ucdavis.edu/facul
ty/chai/Research/Planar%2520Wall%2520Stability/struct-
walls.htm&h=432&w=293&sz=38&hl=en&start=10&sig2=u3TW2TnwJ_IRSpfaQhJuUQ&tbnid
=7g-
JN0VhU59wxM:&tbnh=126&tbnw=85&ei=qUTYR56oL6jmigGFuaiFAg&prev=/images%3Fq%
3Dconcrete%2Bcrushing%2Bcompression%26gbv%3D2%26hl%3Den

• Pile Machine
– http://upload.wikimedia.org/wikipedia/commons/5/54/DFmachine.JPG
• Pile Machine 2
– http://upload.wikimedia.org/wikipedia/commons/8/8b/PileDriving.jpg
• Foundation Type
– http://upload.wikimedia.org/wikipedia/en/6/66/Found-House-Apt.png
• Rebar Cage
– http://i.pbase.com/u29/camera0bug/upload/17213579.P5070031.JPGco
py
• Circular Columns
– http://web.mit.edu/istgroup/ist/images/research_images/microwave/figur
e1.gif

• Timber
– http://www.certified-teak.com/images/timber_india.jpg
– http://www.timberframeworks.com/images/File0001.jpg
• Steel
– http://www.lakewoodconferences.com/direct/dbimage/50261363/Stainle
ss_Steel_Seamless_Tubes.jpg
– http://ocw.mit.edu/NR/rdonlyres/Global/6/695E8EC6-5161-4B05-B6F1-
8BE09DC40F68/0/chp_steel_struct.jpg
• Concrete
– http://www.lakewoodconferences.com/direct/dbimage/50261363/Stainle
ss_Steel_Seamless_Tubes.jpg
– http://www.imagico.de/pov/pict/concrete.jpg
• Masonry
– http://www.gomedia.us/arsenal/images/texturepacks/masonry-prev1.jpg
– http://www.cca.org.nz/images/masonry.jpg

• Structural Engineer
– http://vaengineer.com/images/mr__snell_0462.jpg
• Building
– http://www.brasfieldgorrie.com/_images/portfolio/84/2.jpg
• Girder
– http://www.popartuk.com/g/l/lgfp0432+men-on-a-girder-having-lunch-
new-york-city-collection-poster.jpg
– http://oldcooperriverbridge.org/small/oct_31_1927_pearman_resting_gir
der.jpg
• Beam
– http://www.cedar-log-homes.com/log-homes-images2/beams-glulam-
6.gif
• Flooring
– http://www.domoteck.org/domoteck_com_images/floor_cross_section.jp
g

Lecture1_Structures_WU_MASE101.ppt

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