Triage Evaluation of Gusset Plates in Steel Truss Bridges

摘要

Following research into the collapse of the I-35W steel truss bridge in Minneapolis, Minnesota, FHWA released recommendations for load rating the gusset plates of steel truss bridges. The recommendations include evaluation of several limit states, one of which requires the consideration of multiple load cases and possible lines failure, making the procedures somewhat difficult and time consuming to employ. Given the large inventory of steel truss bridges in Washington state and around the country, and the large number of unique joints and gusset plates on each bridge, a more expedient method for evaluating gusset plate resistance is highly desirable. The objective of this study is to develop a procedure to rapidly evaluate gusset plates in steel truss bridges. The procedure should be appropriately conservative and easy to apply and should be able to be implemented instead of the current FHWA recommendations. This study used analytical methods, originally developed for analysis of gusset plates in braced frames, to develop a rapid gusset plate assessment tool that meets that objective. To develop a rapid gusset plate assessment procedure, denoted the Triage Evaluation Procedure (TEP), specific gusset plate joints from Washington state bridges were analyzed in detail. The TEP contains three primary checks, namely, gusset plate yielding, gusset plate buckling, and fastener strength. Analysis showed that the TEP is conservative in relation to the FHWA recommendations for evaluating gusset plate strength and, when applied at service loads, identifies the same joint with a rating factor of less than 1.0 as the FHWA recommendations applied at strength loads. The researchers concluded that gusset plates on steel truss bridge may be safely and conservatively load rated by using the TEP. When applied at service loads, the TEP will result in a minimum number of joints falsely identified as yielding. Furthermore, the TEP was found to be considerably more efficient than the FHWA recommendations.