Federal investigators probing the collapse of the Interstate 35W bridge in Minneapolis said today that the Aug. 1, 2007, tragedy was the result of design errors and not aging infrastructure.
In the investigators' first public testimony, buttressed by shards of jagged metal and slow-motion video, a picture emerged of an underdesigned bridge that could not withstand the increasing loads added over a 40-year life, culminating in the catastrophic rush-hour collapse that took 13 lives and injured 145.
"The collapse was the result of a serious design error," said Mark Bagnard, the lead investigator for the National Transportation Safety Board, which is expected to issue its final accident report on Friday, at the end of two days of public hearings.
Even as the NTSB appears to be laying the blame on undersized gusset plates that were supposed to hold together the bridge's steel beams, some corrosion and preexisting cracks were found in other parts of the structure.
Although the corrosion did not contribute to the collapse, "it is a source of concern," said Jim Wildey, the NTSB engineer who presented a structural analysis of the bridge's last moments.
