As a result of the structural failure of the I-35W bridge in Minneapolis in 2007, FHWA issued guidelines for the load rating of gusset plates and recommended that the capacity of these plates on non-load-path-redundant steel truss bridges be verified. The intent of the guidelines is to be simple, i.e., amenable to hand calculations, and safe. The compressive strength of a gusset plate, according to the guidelines, is obtained from column strength curves in the inelastic range, which assume an initial out-of-straightness of L/1500, applied to an equivalent column whose width is approximated by the Whitmore width and whose length is the average of three distances to the plate edges or the nearest rivet or bolt groups. The purpose of this paper is to examine the buckling behavior of steel gusset plates in greater detail, accounting for parameters that were not explicitly included in the guidelines, such as initial deformations of the gusset plate, stiffness of the framing members, load distribution from the framing members to the plate and load eccentricity. For this purpose, a finite-element model of a gusset plate was developed and verified against experimental measurements. Results show that the FHWA guidelines for load rating are conservative and safe for larger initial out-of-plane deformations, up to one plate thickness. This is true for in-plane compressive loads with no moment and no eccentricity.
July 11-15, 2010
Fifth International Conference on Bridge Maintenance, Safety and Management