Vertical wheel force characteristics of a coal wagon determined by sideframe strain measurement

Measuring forces at the wheel-rail interface requires sophisticated and expensive technology such as instrumented wheelsets. The cost of such equipment restricts research into wheel rail forces. A less expensive method to determine the vertical wheel force is by measuring the strain in the sideframe. Limitations are placed on the vertical wheel forces found by this technique because of the inertia of the wheelsets and the influence of lateral wheelset forces. Vertical wheel force measurement using sideframe strain has the additional benefit over instrumented wheelsets as it can be used during braking. This paper describes how sideframe strain measurement was used to determine vertical wheel force in operational train tests involving 70 tonne wagons with constant friction damped three-piece bogies. Experimental results that are presented include vertical wheel force distributions for the whole haulage operation. These wheel force distributions enable a comparison of wagon performance and can be used to identify track sections that continually exhibit low vertical wheel forces. The vertical wheel force measurements also located many interesting wagon dynamics. These include hunting, wagon bounce, suspension lock, the effect of longitudinal force transients on wheel forces and the superposition of multiple dynamic events.