Effect of Track Configuration and Loading Conditions on Vertical Wheel Load Measurements Using the Differential Shear Approach

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Measurement of vertical wheel loads on railroad tracks using strain gauges mounted on the rail web is common practice. This measurement approach makes use of the differential shear concept that the difference in shear force between two points along a beam equals the magnitude of the vertical load applied between those two locations. Although the applicability of this concept is easy to verify for simple beams, its validity for field applications under different track configurations including support and loading conditions is relatively unexplored. Findings are presented from an ongoing research effort that has utilized numerical models to assess the effects of different track and loading configurations on vertical wheel load measurements using the differential shear approach. The underlying theory behind this measurement approach is first introduced, and different scenarios are compared using a simple one-dimensional model. This is followed by detailed analysis of the effects of different vertical, lateral, and axial loading combinations on the measured shear strain values. Finally, a three-dimensional finite element model is used to study the dependence of the measured wheel loads and calibration approaches on track support conditions. Findings from the analyses clearly establish the applicability of this measurement approach across different scenarios observed in railroad tracks.