I-35W Investigation and Expert Report

The I-35W Mississippi River Bridge (officially known as Bridge 9340) was an eight-lane, steel truss arch bridge that carried Interstate 35W across the Mississippi River in Minneapolis, MN. On the afternoon of August 1, 2007, it collapsed, killing 13 people and injuring 145.

The NTSB cited a design flaw as the likely cause of the collapse, and asserted that additional weight on the bridge at the time of the collapse contributed to the catastrophic failure. Attorneys representing 117 survivors and relatives of victims took legal action against URS Corp., the consulting firm hired by the Minnesota Department of Transportation to evaluate the bridge, and Progressive Contractors Inc. (PCI), the company that had put hundreds of tons of construction materials on the bridge, claiming the collapse was preventable. Further, attorneys representing URS Corp. and the State of Minnesota took legal action against Jacobs Engineering, who had acquired the firm that originally designed the bridge, Sverdrup and Parcel.

CTLGroup was retained to provide expert opinion as to the cause of the collapse of the I-35W Bridge. Our investigation included observations of the salvaged members of the bridge, document review, animation-based time sequences and structural analysis. Specifically, non-linear finite element analysis was performed to assess collapse initiation and sequence, considering physical characteristics and loading history. The findings of this project are confidential due to ongoing/pending litigation.

CTLGroup's involvement in this project represents our continued presence as leaders in the field of forensic engineering. Our expertise is continually sought out for work on our nation's highest profile disasters/failures.

Expert opinions were offered by Dr. W. Gene Corley. Dr. Danielle Kleinhans managed the project and Dr. Hamid Lotfi conducted the structural modeling.