Construction Loading Lecture by Dr. McCullouch

Construction Loadings
Bob McCullouch P.E. Ph.D.

Construction Loadings
• Construction Perspective
• Design Perspective – Important but not
covered
9/28/2010 Slide 3 of 34

Maryland Bridge
9/28/2010
“The collapse in August 1989 of
the Route 198 bridge over the
Baltimore-Washington Parkway
was caused by poorly constructed
scaffolding that was built with
rusty, deteriorating metal and
unapproved parts and materials,
federal highway officials said
yesterday.”
“The approved plans called for
screw-shaped jacks capable of
handling a load of 25,000 pounds,
McCormick said. However, federal
investigators found the contractors
had used smaller screw jacks with
only a 10,000-pound capacity.”
-Veronica Jennings, The
Washington Post
Slide 4 of 34

Hawaii Bridge
9/28/2010 Slide 5 of 34

Colorado Bridge
9/28/2010
May 2004
Family of three killed.
Slide 6 of 34

Causes
• Girder out-of-plumb
– 4.26o at south abutment
– 2.33o at center bridge pier
• Temporary bracing, a failure
– Expansion bolts separated from bridge deck
• Bolt hole dia. 0.90”
• Bolt dia. 0.75”
• Bolts required to be embedded into concrete minimum 3.25”
• All but 1 bolt embedded into concrete at depths of 1.25” to 2.50”
• Finite element analysis determined cyclic vibrations
caused by lateral vibrations and wind loads caused
failure
9/28/2010 Slide 7 of 34

Arizona Bridge
9/28/2010
Occurred in August 2007
Slide 8 of 34

Causes
• Collapse was due to lateral instability.
• Lateral instability was due to several factors:
– Bearing eccentricity, initial sweep, thermal sweep, creep
sweep, wind load.
• Providing Lateral bracings at the ends of each
girder after erection, including cross bracing
and diagonal bracing anchored to the caps,
would have prevented lateral instabilities and
the collapse.
9/28/2010 Slide 9 of 34

Illinois Bridge - -80/I-294 Bishop
Ford Expressway
9/28/2010 Slide 10 of 34

Causes
Lateral braces were used to directly inter-
connect the bridge girders, but there was no
apparent horizontal cross bracing members to
resist possible lateral deformations.
Unfortunately, the worker in the reach-all
shown in the bottom of the photograph was
killed in the accident.
9/28/2010 Slide 11 of 34

Maryland Requirements
• Section 420
• Working Drawing Approval. Submit detail, form, falsework, and centering
plans and design loads for approval as specified in Section 499. Working
drawings for forms shall include all members proposed for use as well as form
ties and bracing. Do not submit details for form ties separately; incorporate
them in the general working drawings submittal. The rate of placing concrete
shall be noted on the working drawings. Approval of the working drawings
does not relieve the Contractor of responsibility as specified in TC-4.01. The
provisions of 430.03.28 also apply when working drawings are submitted for
falsework and centering
• Form Scaffolds and Platforms. Build form scaffolds and platforms along the
outside of bridge deck fascias during construction of forms for bridge decks.
Design and construct them as integral parts of the form supports. Furnish
separate design calculations with the working drawing submission.
9/28/2010 Slide 12 of 34

Maryland Requirements
• 430.03.27 Erection Plan. Submit an erection plan for approval outlining erection
procedure of the main members. Submit the erection plan as specified in Section 499
and to the Director, Office of Bridge Development, at least 30 days prior to beginning
erection. Include the numbers and types of equipment to be used including crane
capacity, location of crane for lifting, falsework when required, and main member
erection sequence and weight.
• 430.03.28 Falsework. Comply with the provisions specified in TC-4.01 and Section 499.
Build and maintain the falsework in accordance with the approved falsework plans. Any
changes subsequent to initial approval shall be proposed through the Contractor’s
professional engineer and be as approved. Before permitting any loads to be placed on
falsework, the Engineer shall receive written certification by the Contractor’s
professional engineer that the falsework system has been assembled in conformance
with the approved falsework drawings. This certification shall be accompanied by a
Certificate of Compliance stating that all manufactured materials and assemblies fully
comply with the falsework design and plans. The Engineer may either accept the
certificate or invoke any provision of GP-5.08. Perform all tests required at no additional
cost to the Administration.
9/28/2010 Slide 13 of 34

South Carolina
702.05 Falsework. Detailed plans shall be submitted for review to the Bridge Construction Engineer with a
copy to the Engineer. The detailed plans shall be for items of work involving cofferdams, falsework over
highways or railroads, falsework for caps adjacent to railroads or highways, sheeting, retaining walls and
other items as designated in the plans or special provisions. The plans submitted shall be sealed by a
South Carolina licensed Professional Engineer and comply with Subsection 702.10. Review of plans shall
not relieve the Contractor of responsibility for results obtained by use of these plans.
Design. Falsework/form systems shall be designed to handle all vertical and horizontal loading that may be
placed upon it and shall be designed with sufficient redundancy to prevent failure of the system as a result
of the failure of any individual element. Falsework shall be designed for the sum of vertical dead and live
loads and an assumed horizontal load. Dead loads shall include the weight of concrete, reinforcing steel,
forms and falsework. The weight of concrete shall be taken as not less than 150 pounds per cubic foot for
normal concrete and not less than 120 pounds per cubic foot for lightweight concrete. Live loads shall be
the actual weight of any equipment to be supported by falsework applied as concentrated loads at the
points of contact and a uniform load of not less than 20 pounds per square foot applied over the area
supported, plus 75 pounds per linear foot applied at the outside edge of deck overhangs.
The assumed horizontal load shall be the sum of the actual horizontal loads due to equipment,
construction sequence or other causes plus not less than 50 pounds per square foot of horizontal surface
area for wind, but in no case shall the assumed horizontal load be less than two percent of the total dead
and live load.
9/28/2010 Slide 14 of 34

Colorado Changes to Specs & Contracting Practices
• Requires an erection plan and pre-erection conference for steel and concrete
girders. Requires a safety critical element conference.
• Requires the contractor to submit a bridge removal plan.
• Requires bridge contractor to retain a professional engineer that designs and
approves falsework , erection plans and a demolition plan if needed.
• Added language to section 601 – “For structural steel girders, temporary struts
and ties shall be provided as necessary to resist lateral loads applied to the
girder flanges and to prevent appreciable relative movement between the
edge of deck form and the adjacent steel girder. “
“For structural steel girders, temporary struts and ties shall be provided as
necessary to resist lateral loads applied to the girders and to prevent
movement between adjacent steel girders. Where the deck overhang exceeds
1/3 of the distance between steel girders, bracing shall be provided to prevent
rotation of the exterior girder due to the weight of the overhang falsework
and formwork and concrete placement operations. Struts and ties shall also be
provided between interior steel girders to prevent movement between
girders. Falsework drawings for bracing, struts, and ties shall be submitted and
conform to the requirements of subsection 601.11(a).”
9/28/2010 Slide 15 of 34

Colorado Changes
The Contractor shall submit, for record purposes only, an initial detailed
construction plan that addresses safe construction of each of the safety
critical elements. When the specifications already require an erection plan
or a bridge removal plan, it shall be included as a part of this plan. The
detailed construction plan shall be submitted two weeks prior to the
safety critical element conference described below. The construction plan
shall be stamped “Approved for Construction” and signed by the
Contractor. The construction plan will not be approved by the Engineer.
9/28/2010 Slide 16 of 34

Colorado Construction Plan Requirements
• Safety Critical Element for which the plan is being prepared and submitted.
• Contractor or subcontractor responsible for the plan preparation and the work.
• Schedule, procedures, equipment, and sequence of operations, that comply with the working hour limitations
• Temporary works required: falsework, bracing, shoring, etc.
• Additional actions that will be taken to ensure that the work will be performed safely.
• Names and qualifications of workers who will be in responsible charge of the work:
– Years of experience performing similar work
– Training taken in performing similar work
– Certifications earned in performing similar work
• Names and qualifications of workers operating cranes or other lifting equipment
• Years of experience performing similar work
• Training taken in performing similar work
• Certifications earned in performing similar work
• The construction plan shall address how the Contractor will handle contingencies such as:
• Unplanned events (storms, traffic accidents, etc.)
• Structural elements that don’t fit or line up
• Work that cannot be completed in time for the roadway to be reopened to traffic
• Replacement of workers who don’t perform the work safely
• Equipment failure
• Other potential difficulties inherent in the type of work being performed
• Name and qualifications of Contractor’s person designated to determine and notify the Engineer in writing when it
is safe to open a route to traffic after it has been closed for safety critical work.
• Erection plan or bridge removal plan when submitted as required elsewhere by the specifications. Plan
requirements that overlap with above requirements may be submitted only once.
9/28/2010 Slide 17 of 34

Arizona DOT Spec Changes
• 601-3.07 Section B Bridge Girder Erection
Girders shall be placed accurately on bearings to avoid creating eccentricities capable of initiating
imbalance.
Girders with shapes that exceed a height to width ratio of two shall be temporarily braced. The girder
width shall be determined from the outside dimension of the bottom flange.
The contractor shall secure such girders in position on the structure with temporary lateral bracing to
resist loads as specified in the AASHTO Guide Design Specifications for Bridge Temporary Works. Lateral
bracing shall be designed to allow for girder temperature movements. The bracing shall be placed prior to
the release of the erection equipment from each girder.
Prior to erection of any girders, the contractor shall provide a lateral bracing plan, prepared and sealed by
a professional engineer registered in the State of Arizona, for the Engineer’s review. Such bracing plan
shall be included with the working drawings specified in Subsection 105.03, and shall include supporting
calculations. A girder pre-erection meeting will be scheduled following the review and prior to erection of
any girders. All parties involved in the installation shall be represented, and no girders shall be placed
until the plan has been approved.
No traffic shall be allowed under each newly erected girder until the girder has been laterally braced.
Temporary bracing shall remain in place until after permanent concrete diaphragms are installed at the
bents, or the girder is integrated with a permanent feature that restricts the girder’s lateral movement.
9/28/2010 Slide 18 of 34

ASCE 37 –Platform Live Loads
9/28/2010 Slide 19 of 34

Issues to Consider
• Wind Loads
q is calculated from formula,
I, importance factor from ASCE 37-02, is 1.0. V is obtained from Fig 6-1 ASCE 7.
From ASCE 7 For Indiana , Vmax = 90 mph
Applying 37-02 section 6.2.1, V = 90(0.80) = 72 mph
Kz – Table 6-3 (ASCE 7)
Height = 30 ft. and exposure C condition. Exposure C is Open terrain which includes flat
open country.
Kz(30) = 0.98
Kzt = 1.0 – No topographic factor
q(30) = 0.00256 (0.98) (1.0) (72)2 (1.0) = 13 PSF
Basic pressure equation : p = qGCf
9/28/2010 Slide 20 of 34

Wind Loads
9/28/2010 Slide 21 of 34
Two cases: 1. Vertical forms(e.g. piers)- Horizontal 2. Horizontal Platforms - Vertical
1. Using Table 6-8, Assume Cf = 1.5
G = 1.00
Cf = 1.5
Pressure = 13 *1 * 1.5 = 20 psf
2. Using Table 6-6
G = 1.0
Cf = 0.75
Pressure = 13 *1*0.75 = 10 psf

Lateral Form Pressures
• ASCE 37-10 Sect 4.7.1 Proposed Form Pressures
Cc = wh
4.7.1.1 For concrete having a slump of 7 inches (175 mm) or less, and placed with
normal internal vibration to a depth of 4 feet (1.2m) or less, formwork may be
designed for a lateral pressure as follows;
For Columns:
CC = FCFW (150 + 9000 R/T)
For Walls with a rate of placement of less than 7 feet (2.1 meters) per hour and a
placement height not exceeding 14 ft (4.2 meters) per hour
CC = FCFW (150 + 9000 R/T) (4-3)
For Walls with a rate of placement of less than 7 feet (2.1 meters) per hour where
placement height exceeds 14 feet (4.2 meters) and for all walls with a placement rate
of 7 to 15 feet (2.1 to 4.5 meters) per hour
CC = FCFW [150 + 43,400/T + 2800 R/T]
Fc – Chemistry Factor Fw – Unit Weight Factor
9/28/2010 Slide 22 of 34

Slip Form Pressures
4.7.2 Slipform Pressure
For a slipform concreting operation, the lateral pressure of fresh concrete to be used
in designing the forms, bracing and wales shall be calculated as:
CC = c + 6000 R/T (4-5)
9/28/2010 Slide 23 of 34

Material Quality
• Lumber - Observe the physical
condition. Look for wear ,
knots, splits, straightness, and
moisture content. All of these
will affect strength
characteristics. Some
reduction in design table
stresses may have to be made.
• Steel – If the steel grade is
unknown then assume A36.
Inspect for imperfections and
the allowable may have to be
reduced.
9/28/2010 Slide 24 of 34

Material Quality
9/28/2010 Slide 25 of 34

Check Wedges
9/28/2010 Slide 26 of 34

Welds
• Visually inspect welds
9/28/2010 Slide 27 of 34

Foundations
• Proper support is critical.
• Review Geotechnical report for any possible recommendations
for shallow foundations. If information is not sufficient then
perform: In-situ testing, proof rolling for surface
soils(appropriate for 2’-4’) depths., or load testing of soils.
9/28/2010 Slide 28 of 34

Foundations
9/28/2010 Slide 29 of 34

Lateral Loads
ASCE 37-02 has provisions for lateral loads on working platforms.
• For wheeled vehicles transporting materials, 20% for a single vehicle or 10% for
two or more vehicles of the fully loaded vehicle weight. Said force shall be applied
in any direction of possible travel, at the running surface.
• For equipment reactions as described in Section 4.6., the calculated or rated
horizontal loads, whichever are the greater.
• 50 lbs per person (0.22kN/person), applied at the level of the platform in any
direction.
• 2% of the total vertical load. This load shall be applied in any direction and shall be
spatially distributed in proportion to the mass. This load need not be applied
concurrently with wind or seismic load.
This provision shall not be considered as a substitute for the analysis of
environmental loads.
9/28/2010 Slide 30 of 34

Thermal Distortions
ASCE 37-10 proposed language:
• “Some components can develop substantial flexural
distortions and/or forces due to solar radiations on a large
surface [15, 17, 18, 19, 20] during construction; this can be
detrimental for a component that is designed to be shielded
in the finished structure. “
• AASHTO LRFD Bridge Design Specifications Section 5.14.2.3.5
“Thermal effects that may occur during the construction of the
bridge shall be considered.”
9/28/2010 Slide 31 of 34

ODOT Language
ODOT 2010 Construction and Material Specifications, Section 501
(Structures) discusses designs in general. Designs must be completed
according to AASHTO Standard Specifications for Highway Bridges and
approved by a P.E. before being submitted to ODOT. It also states that
falsework must be designed according to the AASHTO Guide Design
Specifications for Bridge Temporary Works.
ITEM 508 – Falsework and Forms
Submit falsework plans for cast-in-place concrete slab superstructures
according to 501.05.
501.05 Design falsework in accordance with the latest AASHTO
Guide Design Specifications for Bridge Temporary Works, Section
2.
9/28/2010 Slide 32 of 34

Temporary Structures are Vulnerable
9/28/2010 Slide 33 of 34

Conclusions
• Are ODOT’s requirements sufficient to reduce
these types of risks?
• Should there be more definitive requirements?
• Temporary Lateral Bracing Requirements needed.
• A complete approach to construction loads is
needed.
– Designer Loads, construction loads types and
magnitudes, specs, contractor requirements, additional
costs.
9/28/2010 Slide 34 of 34

Construction Loading Lecture by Dr. McCullouch

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