Identification of Vehicular Axle Weights with a Bridge Weigh-in-Motion System Considering Transverse Distribution of Wheel Loads

A modified 2-D Moses algorithm for acquiring the field-calibrated influence line (IL) of an existing bridge is presented, based on strain data acquired continuously at a high scanning rate with calibration vehicles of known axle weights and axle spacings crossing an instrumented bridge. Considering the transverse distribution of the wheel loads on each girder due to two-dimensional (2-D) behavior of slab-girder bridge, the ILs of each of the girders can be calculated, which does not require the girders to possess the identical material and geometrical properties. By using the calculated ILs of each girder as references, a modified 2-D Moses algorithm was derived to identify axle weights of moving vehicles, taking into consideration the transverse distribution of the wheel loads on each girder. Mathematical equations to calculate ILs and axle weights were derived, and the proposed algorithms were implemented by a computer program written in MATLAB. The accuracy of the ILs calculation and axle weight identification was verified through a field test of a bridge on highway US-78 in Alabama. The identified axle weights showed agreement with the static measurements from weighing pads and with results from the bending-plate weigh-in-motion (BPWIM) system near the instrumented bridge.