An investigation of a prefabricated steel truss girder bridge with a composite concrete deck

Abstract

Steel truss girder bridges are an efficient and aesthetic option for highway crossings. Their relatively light weight compared with steel plate girder systems make them a desirable alternative for both material savings and constructability. A prototype of a welded steel truss girder constructed with an integral concrete deck has been proposed as a potential alternative for accelerated bridge construction (ABC) projects in Montana. This system consists of a prefabricated welded steel truss girder topped with a concrete deck that can be cast at the fabrication facility (for ABC projects) or in the field after erection (for conventional projects). To investigate possible solutions to the fatigue limitations of certain welded member connections in these steel truss girders, bolted connections between the diagonal tension members and the top and bottom chords of the steel truss girders were evaluated. A 3D finite element model was used to more accurately represent the distribution of lane and truckloads to the individual steel truss girders. This distribution was compared to an approximate factor calculated using an equivalent moment of inertia with expressions for steel plate girders from AASHTO. A 2D analytical model was used to investigate the fatigue strength of the bolted and welded connections for both a conventional cast in place deck system and an accelerated bridge deck system (cast integral with the steel truss girder). Truss members and connections for both construction alternatives were designed using loads from AASHTO Strength I, Fatigue I, Fatigue II, and Service II load combinations. A comparison was made between the two steel truss girder configurations and 205 ft. steel plate girder used in a previously designed bridge over the Swan River. Material and fabrication estimates suggest the cost of the conventional and accelerated construction methods is 10% and 26% less, respectively, than the steel plate girder designed for the Swan River crossing.