Analytical Study of Gusset Plate Joints in Steel Truss Bridges and Development of Assessment Procedures

Thesis (Ph.D.)--University of Washington, 2013Gusset plate connections are commonly used to join members in steel truss bridges. Most gusset plate connections were designed to provide sufficient thickness to resist tensile and shear forces as well as compression buckling based on simple approximations. The 2007 collapse of the I-35W Bridge in Minnesota necessitated the safety assessment of gusset plates and prompted several studies of gusset plate behavior. The complex geometry and various loading profiles make it difficult to analyze and estimate maximum stress in gusset plates and its capacity. This research focuses on numerical simulation of steel truss bridge gusset plate connections. A simple but accurate finite element modeling methodology was developed to efficiently simulate gusset plate connection subassemblages. A rapid procedure for assessing gusset plate safety, namely Triage Evaluation Procedure (TEP), was developed to predict the onset of gusset plate yielding. This procedure considers the worst-case scenario for the interaction of stresses generated by connected truss members and conservatively identifies at risk gusset plates. A Refined Evaluation Procedure (REP) was then developed to predict stress distributions at critical sections using simple and idealized approximate stress distribution models. By using these stress distribution models at the critical sections, the location and magnitude of the maximum stress in the gusset plate connections can be estimated. The TEP and REP are two-step evaluation procedures to provide fast and accurate estimate for gusset plate yield capacity. In addition to the gusset plates, rivet shear resistance needs to be considered to evaluate the overall safety of gusset plate connections. Rivet shear strength, rivet ductility, connected member yielding, and the effect of connection length were identified as factors which affect joint strength. The current AASHTO bridge evaluation code does not consider all four factors and yields an overly-conservative estimate of joint shear resistance. A revised equation which considers ``Strong'' and ``Weak" connected elements and produces a more reasonable estimate of joint shear resistance is recommended