This Bridge Was Flagged for 17 Years. The Real Flaw Wasn't

In 1990, the I-35W bridge over the Mississippi River in Minneapolis was rated structurally deficient. For the next 17 years, inspectors, university researchers and consultants studied it closely, mostly looking for fatigue cracks. On August 1, 2007, the bridge collapsed during evening rush hour. 13 people died and 145 were injured. The NTSB later traced the cause to something none of those reports had checked: steel gusset plates at the U10 joints, only half an inch thick, undersized since the original 1960s design. Retired infrastructure inspector Walter Briggs walks through the public record: what was found, when it was written down, and why the real flaw was never on the list. Sources: NTSB Highway Accident Report NTSB/HAR-08/03, Collapse of I-35W Highway Bridge (2008) https://www.ntsb.gov/investigations/A... University of Minnesota, Fatigue Evaluation of the Deck Truss of Bridge 9340 (MnDOT Report 2001-10) https://www.lrrb.org/pdf/200110.pdf FHWA TechBrief FHWA-HRT-12-071, Application of Radiographic Testing to Multilayered Gusset Plate Inspection https://www.fhwa.dot.gov/publications... Numerical investigation of collapse of the Minnesota I-35W bridge, Engineering Structures (2013) https://www.sciencedirect.com/science... FHWA Technical Advisory T 5140.29, Load-Carrying Capacity Considerations of Gusset Plates (2008) https://www.fhwa.dot.gov/bridge/t5140...