Thin Iron Plates Collapse Bridge in Three Seconds

On August 1, 2007, a 1,907-foot highway bridge carrying I-35W over the Mississippi River in Minneapolis, Minnesota, collapsed into the water in roughly three seconds, as news.detik.com reported. The sudden structural failure dropped the main span 108 feet down into a 15-foot-deep river, trapping 111 vehicles on the crumbling deck at the exact moment of disaster. A total of 190 people were confirmed to be on or immediately near the structure when it gave way, leaving 13 individuals dead and numerous others injured.

Highway 35W Bridge Collapse Details and Timeline

The tragedy began as four lanes of the heavily traveled route were closed off to accommodate concrete resurfacing work. Construction crews and heavy materials—including large stockpiles of sand and gravel—were placed directly over the center span gusset plates in the two closed southbound lanes. Security cameras captured the initial structural failure taking place on the south side of the center span. Within three seconds, the entire midsection tore away from the rest of the framework and plunged into the river below.

I-35W bridge collapse: one thin gusset plate changed everything ⚠️ #structuralengineering #bridge

NTSB Investigation Findings on Gusset Plates

The National Transportation Safety Board concluded through its official investigation that the primary catalyst for the collapse was the inadequate load capacity of undersized gusset plates. Investigators found that the 0.5-inch-thick steel plates suffered from shear instability while bearing immense structural weight. The investigation pointed to a lack of adequate design reviews by Federal Highway Administration officials prior to the catastrophic failure.

Frequently Asked Questions About the 2007 Minneapolis Disaster

How fast did the I-35W bridge collapse?

The entire center span of the Minneapolis bridge separated and fell into the Mississippi River in approximately three seconds after the structural failure began.

The small plates in the I-35W bridge collapse

How many vehicles and people were on the bridge when it fell?

Official reports confirm that 111 vehicles were traveling across the collapsing section, with a total of 190 people on or near the bridge resulting in 13 fatalities.

What caused the steel plates to fail?

The National Transportation Safety Board determined that 0.5-inch gusset plates were simply too thin to handle the heavy load and experienced shear instability under the combined weight of traffic and construction materials.