Whole-body vibration: A comparison of different methods for the evaluation of mechanical shocks

Abstract Two studies were performed in order to compare different technical methods for assessing the effect of mechanical shocks on discomfort. The studies were carried out in the field with a forest machine and a harbour tractor. These were driven by professional drivers on test tracks consisting of different sections with obstacles producing shocks. The discomfort of each section was rated with magnitude estimation. Vibrations on the seat were recorded. Each vibration record was analysed with different technical assessment methods. These included acceleration peak values, time-mean values, dose values, impulse values, acceleration response and displacement response methods. Regression analyses were applied to the drivers' ratings and each of the assessment methods to find the strength of the relationship. The study showed that a dose value based on an Rms or Rmq calculation gave the best prediction of discomfort from the shocks. The intergration time should be long enough (several seconds) to let significant parts of the shock give contribution to the dose value. In many vehicles and working-machines shocks occur, which can be harmful to the driver. Knowledge of how to evaluate these shocks should therefore be of interest for manufacturers of vehicles and also for health service groups in industry.