Algorithms to determine wheel loads and speed of trains using strains measured on bridge girders

This paper reports a bridge weigh-in-motion system, for railways, when dynamic analysis is not required to determine the displacement response of the structure with reasonable accuracy. It is also assumed that the mechanism of resisting the axle loads is through bending action and the loads transferred to the bridge girder can be assumed to be point loads, as in the case of bridge without ballast. Because, the electric locomotive wheel load would be nearly constant and different from the wagon wheel load, except in case of a fully loaded freight train, the location of the locomotive and wagon can be identified from the time history of the measured shear strains. Further, whether a passing train is freight or passenger can be determined using the fact that the passenger trains arrive at close to scheduled times. Thus, using this information on the type of train and the arrangement of locomotive and wagons the distance between the wheel loads is determined. Estimate of the wheel speed and the load is done using two mechanics based algorithms. One of the algorithms is based on only the shear strain. Another algorithm uses shear strain to estimate the wheel speed and the axial strain to estimate the wheel load. The theoretical advantages and disadvantages of these algorithms are presented. Then, both the algorithms are bench marked with field data and their merits and demerits with respect to field implementation also documented.