Gusset Plate Analysis for the MD 291 Through Truss Bridge over Morgan Creek

On August 1, 2007 the I-35W Mississippi River Truss Bridge collapsed in Minneapolis, MN.  Over the next 18 months, the National Transportation Safety Board performed a comprehensive investigation into the cause of the failure. The final report can be found here.  It was found that the primary cause of collapse was undersized gusset plates.  At the time gusset plates were typically assumed to be more conservatively designed than other members and were typically not included in load ratings.  Today that is no longer the case.

As a result of the findings mentioned above, I was tasked with the analysis of gusset plates for a through truss bridge on MD 291 in Kent County, Maryland to ensure another collapse does not occur.  The 193' long structure has 24 joints connected by gusset plates.  This project provided a unique challenge since the analysis is done by hand and the size and geometry of the gusset plates varies significantly.  The gusset plates are analyzed for shear and axial force effects in accordance with Publication No. FHWA-IF-09-014 (or more recently the AASHTO Manual for Bridge Evaluation).  Member connections are analyzed for bolt/rivet capacity, block shear capacity and Whitmore section stresses.

The photos below show the detailed information typically required for a gusset plate analysis to be completed.  All photos show different information for the same gusset plate.