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Bridge temporary works research program.

Bridge Temporary Works Research Program

Introduction

On August 31, 1989, the Route 198 bridge over the Baltimore-Washington Parkway collapsed, injuring nine workmen and five commuters--one critically--when 400 tons (363 Mg) of steel and concrete fell on the parkway without warning (figure 1). The collapse was subsequently and independently investigated by the Federal Highway Administration's (FHWA's) Federal Lands Division and a private consultant. Upon completion of the investigation, the FHWA Administrator established an impartial board of review to study and evaluate all aspects of the two investigations, determine the basic cause for the failure, and provide recommendations to prevent future occurrences. The board members represented Federal and State governments and private industry.

Based on the reports submitted by the investigators, the board concluded that the failure probably ocurred because the shoring tower assemblies were not constructed in accordance with the falsework plans approved by the Federal Lands Division, [1](1) The board went on to recommend that, to prevent such occurrences in the future, falsework specifications should be revised to better define the responsibilities of material suppliers, contractors, and engineers.

This recommendation was signed into law by the Department of Transportation and Related Agencies Appropriations Bill of Fiscal Year 1991, which states in part that ". . . the Committee on Appropriations directs the Federal Highway Administration to undertake the research project recommended in the report entitled |Investigation of Construction Failure Maryland Route No. 198 Bridge Over the Baltimore-Washington Parkway'" [2]

The bill goes on to specify that the research project should produce approved guidelines, improved specifications, and a falsework construction handbook. The guidelines and specifications should apply both to construction projects under direct FHWA supervision and those carried out by the States with Federal-aid highway funds. [2]

Given the complexity of the work involved in developing a specification, the Committee has set a final due date of December 1992 for the research program's report. This article describes recent falsework failures since the Baltimore-Washington Parkway incident which emphasize the even greater need for better guidelines on bridge temporary works and progress to date in fulfilling the Committee's research program mandate.

Recent Falsework Failures

Several other collapses have occurred since the Baltimore-Washington incident. These recent failures have motivated the task group in their mission. They are described below:

* On April 24, 1990, falsework for the Lake

Street-Marshall Avenue bridge near St. Paul, Minnesota,

collapsed, killing one worker (figure 2). An

estimated 300 tons (272 Mg) of steel and 1,100 (998 Mg)

tons of concrete fell into the Mississippi River.

According to the State bridge engineer, the failure

was related to human design error. [3] * On June 18, 1990, the falsework supporting one

section of a 63-ft (19.15-m) welded plate tub girder

being erected at N 370 and U.S. 75 in Bellevue,

Nebraska, collapsed, dropping the girder. There

were no injuries. Investigation and analysis showed

that the collapse was initiated by lateral loads on the

false work caused by strong southwest winds. The

failure of the falsework was progressive, ending

with the collapse of the girder. [4] * On July 13, 1990, the U.S. 45 bridge under

construction over Spring Brook in Antigo, Wisconsin,

collapsed as placement of deck concrete was nearing

completion. The cause of the collapse is believed to

be shear failure of the 48 bolts connecting the deck

form supports to substructure abutment walls. This

initial failure led to subsequent shear failure of all

but one of the remaining bolts. [5] * On October 10, 1990, a section of the superstructure

falsework for an elevated connector ramp of the

I 880/SR 238 interchange in San Leandro, California,

collapsed (figures 3 and 4). Three workers were

injured but there were no fatalities. The accident

occurred during the erection of a falsework beam

over an existing ramp. The cause of the collapse is

being investigated by the California Department of

Transportation and the California Department of

Occupational Safety and Health. [6]

In March 1990, the FHWA established a multidisciplinary Scaffolding, Shoring, and Forming Task Group to develop and guide the mandated falsework research program. The task group includes representatives from the FHWA, the American Association of State Highway and Transportation Officials (AASHTO), the Associated General Contractors, the American Road and Transportation Builders Association, the Transportation Research Board, and the Scaffolding, Shoring, and forming Institute.

The first meeting of the task group was held on April 17, 1990. During this meeting the task group identified the following as priority activities:

* Survey existing specifications on bridge temporary

works, synthesize them, and identify any gaps. * Establish a standard construction specification

dealing with bridge temporary works. * Develop a comprehensive design manual on

temporary works for bridges. * Develop recommendations for industry guidelines

for a certification program on suppliers' products. * Develop a construction manual.

The scope of these activities and progress to date in each of these areas is delineated in the following sections and shown in figure 5.

Survey existing specifications

The first task of the research program is to survey and locate all existing information on temporary works for bridges. To perform this work the task group let a 4-month contract, administered by the FHWA and conducted from January to April 1991.

The study synthesizes all existing codes and specifications dealing with bridge temporary works in the United States and abroad; it also identifies gaps and inconsistencies in these specifications. This study forms the basis for other research program activities, such as the development of the design specification and the construction manual. [7]

Establish standard specification

The task group has developed a standard specification for bridge temporary works which will soon be issued by the FHWA. Among other issues, the specification sets out the following requirements and responsibilities:

* The contractor is responsible for designing and

constructing safe and adequate temporary work systems. * The contractor is responsible for selecting material

suitable for falsework, subject to the approval of the

owner's engineer. * Falsework design must conform to that specified in

the Design Manual on Temporary Works for Bridges,

which is now being developed. * The contractor shall prepare working drawings under

the guidance of a registered professional engineer. * The contractor shall certify that the manufactured

devices have been maintained in a condition to

carry their rated loads safely. * Each piece of the manufactured device shall be

clearly marked so that its rated capacity can be

readily determined at the jobsite.

Develop design manual

In recognition of the need for a clear, practical design specification based on the best current technology, the task group has developed an outline for a Design Manual on Temporary Works for Bridges. The manual will address design considerations regarding such temporary structures as scaffolding, shoring, forming, and cofferdams. The manual will include comprehensive commentary to identify the origin and clarify the intent of key provisions. The AASHTO Standard Specification for Highway Bridges, Division I, Design will be used as a model in developing the Temporary Works manual.

Develop recommendations for industry guidelines

The private industry members of the task group were asked to develop a set of criteria for a certification program on equipment used on bridge temporary works acceptable to the industry. They responded that a certification program was not needed, rather the codes of the American National Standards

Institute and the Occupational Safety and Health Administration would be acceptable standards for incorporation into our specifications. The task group has determined these codes are not applicable to bridge construction, since these were originally written for building construction.

The task group sees a definite need to develop a certification/quality control program for products supplied to job sites. This would include the manufacturer if the manufacturer is the supplier.

Develop construction manual

The last task to be performed under the research program is the development of a bridge temporary works construction manual. Because some States have comprehensive construction manuals, this task has been deferred until the task group can determine if it is necessary to develop an original manual or an existing State manual can be adopted for use.

Summary

The collapse of the falsework on the Route 198 overpass over the Baltimore-Washington Parkway precipitated an official recommendation that the FHWA develop better specifications and guidelines. Several subsequent falsework collapses--some design-related, others the result of poor construction practices--have underscored the need for such specifications and guidelines.

The end products of the FHWA program will be a synthesis of all codes and specifications dealing with the subject, a standard specification, and a design manual on bridge temporary works with comprehensive commentaries, and--if necessary--a construction manual. These products are being developed with input from representatives of AASHTO, private industry, and the FHWA. The work of the task group should be completed by December 1992.

Scaffolding, Shoring, and Forming Task Group

Federal Highway Administration Robert L. Nickerson Sheila Rimal Duwadi James Hoblitzell Donald W. Miller William S. Cross James F. Hare

Transportation Research Board Ian M. Friedland

American Association of State Highway and Transportation Officials James M. Stout Donald Flemming

Associated General Contractors Damian Hill Robert Desjardins

American Road and Transportation Builders Association Kent Starwalt Richard F. Hoffman

Scaffolding, Shoring, and Forming Institute Ramon Cook (1)Italic numbers in parentheses identify references on page 40.

PHOTO : Figure 1.--Collapsed Route 198 overpass on the Baltimore-Washington Parkway.

PHOTO : Figure 2.--Lake Street-Marshall Avenue bridge near St. Paul Minnesota.

PHOTO : Figure 3.--I 880 and SR 238 interchange before collapse.

PHOTO : Figure 4.--I 880 and SR 238 interchange after collapse.

PHOTO : Figure 5.--FHWA Bridge Temporary Works Research Program.

References

[1]FHWA Board of Review. Report of the Investigation into the Collapse of the Route 198 Baltimore-Washington Parkway Bridge, Publication No. PR-90-001, Federal Highway Administration, Washington, DC, December 1989. [2]"Investigation of Construction Failure Maryland Route No. 198 Bridge Over the Baltimore-Washington Parkway," Department of Transportation and Related Agencies Appropriations Bill, Senate Report No. 101-398, 101st Congress, 2nd Session, 1991. [3]"Falsework Design Takes Rap," Engineering News-Record, Vol. 225, No. 15, October 11, 1990, p. 13. [4]Bellevue Interchange, Phase 2, Investigation of Falsework Failure, Publication No. F-370-7(113), Wells Engineers, Inc., Omaha, NE, September 5, 1990. [5]The FHWA Weekly Report to the Secretary of the Department of Transportation, Federal Highway Administration, Washington, DC, July 20, 1990. [6]The FHWA Weekly Report to the Secretary of Department of Transportation, Federal Highway Administration, Washington, DC, October 12, 1990. [7]Synthesis of Falsework, Formwork, and Scaffolding for Highway Bridge Structures, Publication No. FHWA-RD-91-062, Federal Highway Administration, Washington, DC, September 1991.

Sheila Rimal Duwadi is a research structural engineer in the Structures Division, Office of Engineering and Highway Operations Research and Development, Federal Highway Administration (FHWA). Ms. Duwadi is a graduate of the FHWA Highway Engineer Training Program. She has a masters degree in civil engineering from Oregon State University and a bachelors degree from Washington State University. Her primary responsibilities are the Timber Bridge and Temporary Works research programs. She is a registered professional engineer in the State of Virginia.
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Title Annotation:bridge collapse
Author:Duwadi, Sheila Rimal
Publication:Public Roads
Date:Sep 1, 1991
Words:1810
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