Bridge temporary works research program

Public Roads, Sept, 1991 by Sheila Rimal Duwadi

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