The I-35 Bridge over the Mississippi River in Minneapolis, Minnesota catastrophically failed during the evening rush hour on August 1, 2007, collapsing to the river and riverbanks beneath. In the years prior to the collapse, several reports cited problems with the bridge structure. This research analytically investigated the cause of the collapse using the Applied Element Method, which recently presented its capability to study the behavior of collapsing structures. The bridge was modeled using the original construction drawings, where all the structural details were taken into consideration (steel truss, gusset plates, concrete slabs, concrete piers, etc.). All the loads at the time of collapse were taken into consideration including traffic and construction loads. It was proven that AEM was capable of analyzing and investigating the cause of collapse of the I35-W bridge. The cause of collapse was found to be the failure of the gusset plates at connections L11 and U10, which well agreed with the field investigations of the collapsed bridge. The under-designed thickness of the plates, their corrosion, and the overloading due to traffic and construction loads at time of collapse were the reasons for the bridge collapse.
- The Applied Element Method (AEM) could analyze the I35-W bridge behavior till its complete collapse.
- The cause of collapse was obtained from the analysis and was found to be in very good agreement with the investigations of the collapsed bridge.
- The failure of the gusset plates at connections L11 and U10 was found to initiate the collapse of the bridge. Their failure was initiated by their buckling.
- The under-designed thickness of the plates, their corrosion, and the over loading were the reasons for the bridge collapse.
H.M. Salem, Cairo University, H.M. Helmy, Applied Science International, Giza, Egypt – Engineering Structures,PP 635-645, Vol.59, February 2014.