- Date:
- August 1, 2007
Minneapolis I-35W bridge collapse
Minneapolis I-35W bridge collapse, collapse of an interstate highway bridge spanning the Mississippi River in Minneapolis, Minnesota, U.S., on August 1, 2007. The disaster killed 13 people and injured 145.
The bridge, part of the Interstate Highway System, was an eight-lane steel truss arch bridge across the Mississippi River in the heart of Minneapolis. It was designed in 1961. Construction began in 1964, and it was completed in 1967. Though it consisted of 14 spans, the central span, crossing the river, was a single span 450 feet (150 m) long, with its supports on each river bank. The entire length of the bridge was 1,907 feet (581 m). For nearly 40 years it was one of the busiest bridges in the city, with some 141,000 vehicles crossing it daily.
Beginning in 1990, inspections of the bridge found that it was “structurally deficient” and noted cracking in the cross girders. By 2005 it had reached a level of deficiency that suggested that replacement might be warranted. Indeed, the day after the collapse, Minnesota Governor Tim Pawlenty indicated that discussions had taken place about replacing the bridge in 2020. A plan to reinforce the bridge in 2006 was canceled as being too dangerous. Construction was taking place at the time of the collapse, but that largely entailed resurfacing and replacing guard rails and lighting.
At 6:05 PM on August 1, 2007, during the evening rush hour, with four of the eight lanes closed for resurfacing, the central span of the bridge crumpled into the river, followed by the spans on either side of it, with 111 vehicles and several construction workers caught in the destruction. Only a few vehicles fell into the river, with most of those involved being trapped on the collapsed bridge. Rescue came quickly, with those stranded on the bridge being extricated within three hours.
A 15-month investigation into the cause of the disaster found that some of the gusset plates on the main trusses that had been incorporated into the I-35 bridge’s design and original construction were only .5 inch (13 mm) thick, far too small for the expected load. In addition, resurfacing projects over the years had increased the weight of the bridge by some 20 percent, with perhaps the last straw being the 262 tons of construction equipment on the bridge when it collapsed. Because of the importance of the bridge to residents and to national truck freight, a replacement bridge, the I-35 Saint Anthony Falls Bridge, was built rapidly and opened on September 18, 2008.