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Failure: Truss Collapse

Year: 2007

Location: Minneapolis, MN

During rush hour traffic one early August evening, a bridge along Interstate 35 westbound across the Mississippi River, also known as Bridge 9340, experienced a structural failure resulting in a collapse into the river approximately 100 feet below [2]. A motion-activated camera nearby was able to capture a portion of the collapse, and can be viewed here. There were some casualties involved: according to the Minneapolis StarTribune, 13 people were killed and 145 were injured [3].

The bridge was originally built in the 1960’s and had undergone maintenance several times. At the time of the failure, the bridge was undergoing some renovations: four of its eight lanes were closed, diverting all traffic between the remaining four lanes. According to the official accident report, several pieces of heavy machinery/equipment and tons of concrete materials were on the bridge [4].There was additionally heavy traffic on the four lanes that were open.

After investigating the incident, several reasons for the failure were cited. First, the gusset plates used for the joints of the trusses were extremely thin and did not strengthen the bridge as much as it was intended to.

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Additionally, two extra inches of concrete had been added to the road surface over the years, increasing the bridge’s total dead load by 20%. The failure could have been avoided had there been a more thorough inspection of the gussets and underlying structure, as well as had the bridge been appropriately reinforced when it became out of code over the years.