Thoughts on third anniversary this month, of collapse of the 35W bridge over the Mississippi River crossing, Minneapolis: I respect the work of the NTSB but still feel two factors were given insufficient attention in the final findings.
The report focused on understrength gusset plates as built, and how repaving work had concentrated static loads on certain parts of the bridge. Also worthy of study: truck traffic on the bridge that afternoon as an initiating event, not necessarily because any trucks at the time were overweight. Pavement roughness has been known for decades to be a major stressor when heavy trucks are crossing a bridge, and that day there were a couple of sizable bumps that resulted from pavement not milled off near the expansion joints. My point: even a two-inch bump on the pavement can put a lot of stress on the bridge if traffic speeds are not held to a crawl.
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