Influence Line Calculation of Existing Bridges in BWIM System

The commonly used commercial BWIM system takes the influence line (IL) as a reference to calculate axle weights and assumes the IL along the transversal direction is the same; while for slab- girder concrete bridge, the IL of each girder is not exactly the same. With the latest developed BWIM system installed on a concrete slab-girder bridge on highway I-78 in Alabama in the U.S., this paper proposes a modified algorithm for acquiring actual IL of different girders of existing slab- girder bridge. The transversal distribution of the wheel loads on each girder and the two- dimensional behaviour of the bridge are considered. The proposed algorithm of IL calculation is based on least square methods with minimization the differences between measured and modelled response at mid span when pre-weighed vehicles pass the bridge. The accuracy of the acquired ILs by the proposed algorithm is verified through the field test on the bridge on highway I-78.