Effects of Moving Dynamic Tyre Loads on Tyre-Pavement Contact Stresses

The purpose of this paper is to indicate the effect that moving dynamic tyre loads has on the tyre-pavement contact stresses used in pavement analysis. Traditionally tyre loads (in pavement analysis) are modelled as constant loads applied through circular uniform contact patches to a pavement surface. However, actual tyre loads are dynamic in nature and the contact stresses between the tyre and pavement are non-uniform and non-circular. Recent developments in the field of tyre-pavement contact stresses at CSIR Transportek permitted measurement of the 3-dimensional contact-stress patterns under slow-moving tyres. Research conducted on moving dynamic tyre loads indicated that the population for specific conditions could be modelled using a normal distribution. Combination of these data sets can be used to indicate the actual tyre-pavement contact stress distribution for traffic. This new distribution can be used to select more realistic tyre loading conditions for use in mechanistic analysis of pavement response to real traffic. Initial results of applying the distribution of moving dynamic tyre loads to a pavement analysis situation indicated that higher nominal tyre loads can be expected than traditionally used, mainly due to the dynamic nature of the tyre load distribution. Results from the tyre-pavement contact stress measurements indicated that different tyre contact-stress patterns develop when the tyre load changes and the tyre inflation pressure is a constant. Combination of these effects may shed light on pavement surface behaviour under real traffic loading. In this paper it was found that traditional assumptions regarding the constant nature of tyre loads and uniform, circular nature of tyre-pavement contact-stresses are not valid and that innovative use of available information can assist the pavement engineer to perform more realistic pavement analyses. Pavement response analyses using these new tyre loads are explicitly excluded, as it is covered in a companion paper by De Beer et al. (2002). For the covering abstract see ITRD E118503.