Quantification of Vertical and Lateral Loads Using Strain Gauges: Eliminating the Wheatstone Bridge

Real-time measurement of vertical wheel loads applied to the rail is commonly carried out using strain gauges. One standard approach involves measurement of shear strains at the rail neutral axis, and use of the differential shear concept. Strain gauges are typically mounted on the rail neutral axis between two adjacent ties (over the crib section). A set of four strain measurements (two each, pointed at 45 degrees up and down from the horizontal) are carried out at each end of the crib section, and the measured strains are used to calculate the shear strain magnitudes; this shear strain is in turn used to calculate the applied load. In practice, the four individual strain measurements on each end of the crib (on either face of the rail) are arranged in a single Wheatstone bridge circuit. The purpose for using this common strain measurement configuration lies in the circuits’ ability to eliminate crosstalk, or strain unrelated to the load being measured, e.g. bending strain, or strain due to lateral loading, etc. This paper will propose a new measurement approach whereby eliminating this Wheatstone bridge configuration and measuring eight independent strain signals will enable direct quantification of the vertical as well as lateral load magnitudes. Instead of having to install additional strain gauges on the rail base to measure the lateral loads, the same strain gauges mounted on the rail neutral axis can be used to measure both vertical as well as lateral loads. This proposed technique will simplify the process of vertical and horizontal wheel load detection, and may increase the applicability of these circuits to detect loads in curved sections of track as well as near special track work.