Capacity analysis of gusset plate connections using the Whitmore, block shear, global section shear, and finite element methods

The 2007 collapse of the I-35W Bridge in Minneapolis, Minnesota led to additional load rating requirements for gusset plates. The Federal Highway Administration provided the direct tension and block shear methods to assess tensile capacity for use in load rating, as well as a mechanics based method to assess shear capacity on critical planes. However, the three methods provide limited information about ultimate behavior for complex connections. Using finite elements, the authors modeled the connection from Whitmore’s 1952 study to evaluate the plate capacity and failure mechanism. The analysis showed that the direct tension method was conservative, but predicted neither capacity nor behavior. Model performance corresponded well with the critical block shear capacity load in the left diagonal, and shear capacity on the gross horizontal plane. Yielding on this plane began around critical bolt holes and spread to either side of the plate, forming the critical failure mechanism.