Tweet
Link.....
Potential Flaw Is Found in Design of Fallen Bridge
By MONICA DAVEY and MATTHEW L. WALD
MINNEAPOLIS, Aug. 8 — Investigators have found what may be a design flaw in the bridge that collapsed here a week ago, in the steel parts that connect girders, raising safety concerns for other bridges around the country, federal officials said today.
The Federal Highway Administration swiftly responded by urging all states to take extra care with how much weight they place on bridges when sending construction crews to work on bridges. Crews were doing work on the deck of the Interstate 35W bridge when it gave way, hurling rush-hour traffic into the Mississippi River and killing at least five people.
The National Transportation Safety Board’s investigation is months from completion, and officials in Washington said they were still working to confirm the design flaw in the so-called gusset plates and what, if any, role it had in the collapse.
Still, in making public their suspicion about a flaw, the investigators were signaling they consider it a potentially crucial discovery and also a safety concern for other bridges around the country. Gusset plates are used in the construction of many bridges, not just those with a similar design to the one here.
“Given the questions being raised by the N.T.S.B., it is vital that states remain mindful of the extra weight construction projects place on bridges,†Secretary of Transportation Mary E. Peters said in a statement issued late today.
Concerns about the plates emerged not from the waters of the Mississippi River here, where workers have only begun to remove cars and the wreckage with cranes, but from scrutiny of the vast design records related to the steel truss-type bridge.
>
State authorities here said the plates were made of steel, and were, in most such bridges, shaped like squares, 5 feet by 5 feet, and a half-inch thick. Such plates are common in bridge construction as a way to attach several girders together, said Jan Achenbach, an expert in testing metals at the Northwestern University Center for Quality Engineering and Failure Prevention.
A consultant hired by the state of Minnesota in the days after the collapse to conduct an investigation of what had gone wrong, even as the national safety board did its work, first discovered the potential flaw, the board said. Representatives at Wiss, Janney, Elstner Associates Inc., the consulting firm, could not be reached late today.
Federal authorities indicated that one added stress on the gusset plates may have been the weight of construction equipment and nearly 100 tons of gravel on the bridge, where maintenance work was proceeding when the collapse occurred. A construction crew had removed part of the deck with 45-pound jack hammers, in preparation for replacing the 2-inch top layer, and that may also have altered the stresses on the bridge, some experts said.
>
If there was a design error in the 1960s, failure to identify it before the bridge collapse indicates a problem with the federal inspection program, said Thomas M. Downs, who was the associate administrator of the Federal Highway Administration from 1978 to 1980.
>
Mr. Peterson said that concerns about gusset plates might normally focus on questions of corrosion over time, but that he had never heard of a dispute over the original design or metal make up of a plate here. Had ultrasonic testing of the plates shown signs of corrosion, that would be a concern, he said. But in the case of the Interstate 35W bridge, Mr. Peterson said he recalled “no gusset plate issues at all.â€
When the bridge was built, in the 1960s, its hundreds of gusset plates were attached with rivets, though bridge designers here switched to bolts, a stronger option, in the 1970s. “Bolts are better,†Mr. Peterson said, “but we wouldn’t consider anything wrong with rivets.â€
By MONICA DAVEY and MATTHEW L. WALD
MINNEAPOLIS, Aug. 8 — Investigators have found what may be a design flaw in the bridge that collapsed here a week ago, in the steel parts that connect girders, raising safety concerns for other bridges around the country, federal officials said today.
The Federal Highway Administration swiftly responded by urging all states to take extra care with how much weight they place on bridges when sending construction crews to work on bridges. Crews were doing work on the deck of the Interstate 35W bridge when it gave way, hurling rush-hour traffic into the Mississippi River and killing at least five people.
The National Transportation Safety Board’s investigation is months from completion, and officials in Washington said they were still working to confirm the design flaw in the so-called gusset plates and what, if any, role it had in the collapse.
Still, in making public their suspicion about a flaw, the investigators were signaling they consider it a potentially crucial discovery and also a safety concern for other bridges around the country. Gusset plates are used in the construction of many bridges, not just those with a similar design to the one here.
“Given the questions being raised by the N.T.S.B., it is vital that states remain mindful of the extra weight construction projects place on bridges,†Secretary of Transportation Mary E. Peters said in a statement issued late today.
Concerns about the plates emerged not from the waters of the Mississippi River here, where workers have only begun to remove cars and the wreckage with cranes, but from scrutiny of the vast design records related to the steel truss-type bridge.
>
State authorities here said the plates were made of steel, and were, in most such bridges, shaped like squares, 5 feet by 5 feet, and a half-inch thick. Such plates are common in bridge construction as a way to attach several girders together, said Jan Achenbach, an expert in testing metals at the Northwestern University Center for Quality Engineering and Failure Prevention.
A consultant hired by the state of Minnesota in the days after the collapse to conduct an investigation of what had gone wrong, even as the national safety board did its work, first discovered the potential flaw, the board said. Representatives at Wiss, Janney, Elstner Associates Inc., the consulting firm, could not be reached late today.
Federal authorities indicated that one added stress on the gusset plates may have been the weight of construction equipment and nearly 100 tons of gravel on the bridge, where maintenance work was proceeding when the collapse occurred. A construction crew had removed part of the deck with 45-pound jack hammers, in preparation for replacing the 2-inch top layer, and that may also have altered the stresses on the bridge, some experts said.
>
If there was a design error in the 1960s, failure to identify it before the bridge collapse indicates a problem with the federal inspection program, said Thomas M. Downs, who was the associate administrator of the Federal Highway Administration from 1978 to 1980.
>
Mr. Peterson said that concerns about gusset plates might normally focus on questions of corrosion over time, but that he had never heard of a dispute over the original design or metal make up of a plate here. Had ultrasonic testing of the plates shown signs of corrosion, that would be a concern, he said. But in the case of the Interstate 35W bridge, Mr. Peterson said he recalled “no gusset plate issues at all.â€
When the bridge was built, in the 1960s, its hundreds of gusset plates were attached with rivets, though bridge designers here switched to bolts, a stronger option, in the 1970s. “Bolts are better,†Mr. Peterson said, “but we wouldn’t consider anything wrong with rivets.â€