The Minneapolis bridge that failed last summer, killing 13 people, had fatal design flaws, the NTSB announced today. Steel gusset plates that held together beams on the eight-lane bridge were half the thickness they should have been, investigators found. While the agency didn't say the gusset plates caused the collapse,16 fractured plates were discovered on the center span, which collapsed during the evening rush hour Aug. 1, AP reports.
The gussets were deemed to have been inadequate when the span was built in the 1960s; tons of weight added during construction projects, including one at the time of the collapse, exacerbated the weakness. Investigators did not find evidence that corrosion or wear played a role in the bridge's failure. “This is not a bridge-inspection thing,” one investigator told the New York Times. “It’s calculating loads and looking at designs.”