Simple Check for Yielding in Truss Bridge Gusset Plate Connections

The failure of a large steel truss bridge in Minnesota has been, in part, attributed to overstressed and buckled gusset plates. This catastrophic event signaled concerns of the potential for a similar overstressed state in gusset plates in steel truss bridges across the county. To provide guidance to bridge engineers, the Federal Highway Administration released FHWA Bridge Design Guidance No. 1 Load Rating Evaluation of Gusset Plates in Truss Bridges; however, the somewhat complex evaluation methods make rapid assessment costly for DOTs. A study supported by the Washington State Department of Transportation and FHWA has developed a procedure for rapid and reliable evaluation of the state of gusset plates, including the maximum stresses and likelihood of yielding. The development utilized a parametric study of several gusset plate configurations performed using advanced nonlinear finite element analysis. Parameters such as plate thickness, yield stress, and load distribution were considered for actual gusset plate connections from bridges primarily in Washington State. The selected gusset connections also had different geometries to ensure the resulting evaluation approach is sufficiently broad in applicability. The new approach should enable bridge engineers to more expediently evaluate the capacity of gusset plates, allowing gusset plates with near critical demand-to-capacity ratios to be identified for further, more refined analysis or retrofit. The paper and presentation will detail the analyses and resulting rapid gusset plate evaluation procedure.