Failure Analysis of Minneapolis I-35W Bridge Gusset Plates

On August 1, 2007, the I-35W highway bridge over the Mississippi river in Minneapolis, MN collapsed. The sub-sequent National Transportation Safety Board (NTSB) investigation identified the U10W truss node as a likely initiation site for the failure. (Bridge main truss nodes were numbered from the south starting at 0. U indicates a node along the upper chord, and L indicates a node along the lower chord. E and W indicate a node on the east or west truss) [1, 2, 3].
Finite element analyses were performed to study the states of stress and strain in the gusset plates of the U10W joints, and to investigate potential instability in the bridge structure. A global-local approach was taken, in which a detailed three-dimensional U10W local model was embedded into the global bridge model provided by FHWA [1, 2, 3, 4].
As reported in [2], “the finite element computations indi-cated the bridge failure was initiated by a local structural instability before any localized material failure occurred. Additionally, the computations indicate that the structural instability that triggered the bridge collapse was a local bending instability in the U10W gusset plates.”
In this Technology Brief, the use of Abaqus in the investi-gation of the collapse of the I-35W bridge is outlined.