The I-35W bridge in Minneapolis, MN collapsed on August 1, 2007, as a result of an overstressed gusset plate. Following the collapse, state departments of transportation sought to confirm the adequacy of gusset plates in other bridges to ensure overstressed gusset plates were not present. However, the analytical tools to assess the adequacy of gusset plates depend on assumed loading based on the intended design configuration of the bridge. Actual stresses and loads in a gusset plate, which may be affected by unintended or unexpected load distributions, cannot be determined using conventional tools such as strain gages. This paper will report on research intended to develop a methodology for nondestructive assessment of actual stress levels in gusset plates, to support safety analysis. This research utilizes the acoustoelastic effect to evaluate actual stress levels by assessing the acoustic birefringence in the plate. The birefringence measurement evaluates normalized variations of polarized shear waves propagating through the plate thickness, which vary proportionally as a function of stress. This paper discusses exploratory testing to evaluate the potential of the approach as a tool for the condition assessment of gusset plates.

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