Investigators have found a design flaw in a US highway bridge that collapsed into the Mississippi River in August, killing 13 people and injuring 145, the government said Tuesday.
Steel plates that held the bridge's beams together at eight of its 112 joints were too thin, the National Transportation Safety Board (NTSB) said. When the wreckage was recovered, investigators found that those plates had broken, the report said.
The agency urged highway authorities to check all major steel - truss highway bridges in the country, though it emphasised there was no evidence of a similar problem in other spans.
The August 1 bridge collapse on the I-35W highway severed a major traffic link between the twin cities of Minneapolis and St. Paul in Minnesota state and set off weeks of debate about the state of US infrastructure.
In all, 16 so-called gusset plates - two at each of the weakened bridge joints - were only about half as thick as required for safe operation of the bridge, the NTSB said.
"This review discovered that the original design process of the I- 35W bridge led to a serious error in sizing some of the gusset plates in the main truss," said the agency's head, Mark Rosenker.
While strongly suggesting that the gusset plates were to blame, the NTSB said it is still working on a final report on what caused the disaster. The report is expected some time in 2008. ( Dpa )