The Revisions for the Gusset Plate Load Rating Approach: A Comparative Case Study

In 2009, the Federal Highway Administration (FHWA) published the “Load Rating Guidance and Examples for Bolted and Riveted Gusset Plates in Truss Bridges”. According to this document, main truss member gusset plates were required to be examined for five limit states based on either the Load Factor Rating (LFR) or the Load and Resistance Factor Rating (LRFR) approaches. However, further investigations showed that this methodology generally resulted in conservative gusset plate ratings. The National Cooperative Highway Research Program (NCHRP) was sponsored to address these concerns by investigating the shear, tensile and compressive strength resistance of gusset plates at the strength limit state. The findings of this program resulted in a set of propositions for revisions to the American Association of State Highway and Transportation Officials (AASHTO) Manual for Bridge Evaluation to be implemented in 2014. It is observed that these new provisions for the LFR and the LRFR methods result in significant variation in rating results for the different limit states. In this paper, a comparative study is completed on a gusset plate from the Charles M. Braga Jr. Memorial Bridge, which is located in Fall River/Somerset, MA, U.S.A., to investigate the dissimilarities between the load rating results obtained based on both the 2009 and the 2014 provisions for the LFR approach. The primary aim of this work is to provide a better understanding on the proposed changes for the gusset plate load rating approach described in the Manual for Bridge Evaluation, 2nd Edition, 2014 Interim Revisions.