Possible design flaw found in fallen American bridge

MINNEAPOLIS: 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

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 at work on the deck of the

Interstate 35W bridge when it gave way, hurling rush-hour traffic into the Mississippi River.

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 signalling 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 in Minnesota.

Concerns about the plates emerged not from the waters of the Mississippi River, 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.

If those who designed the bridge in 1964 miscalculated the loads and used parts too weak for the job, it raises the possibility that the bridge was structurally deficient from the day it opened. It does not explain, however, why the bridge stood for 40 years before collapsing.

In an announcement, the safety board said its investigators were “verifying the loads and stresses” on the plates as well as checking what they were made of and how strong they were.

Wiss, Janney, Elstner Associates, Inc., a consulting firm hired by the state to investigate the collapse discovered the potential flaw.