The recent increase of the maximum legal axle load limit in South Africa, as well as the increase in overloading observed in rural roads, have renewed the interest into methods of quantifying traffic load associated damage on road pavements. For pavement engineers the main interest lies in the design and management of the network, while road authorities' interest lies in their desire to recover the cost of the damage. Since equivalent damage factors (EDFs) are used to convert the actual traffic spectrum into equivalent standard axles (ESAs), methods for calculating EDFs should be evaluated in terms of their ability to deal with all practical load and axle configurations of mixed traffic. Extensive research with the Heavy Vehicle Simulator (HVS) over the past 20 years has led to improved fundamental understanding of pavement response and performance and has permitted the development of effective EDFs for single-axle loads. A major limitation of this approach, however, is that it does not directly facilitate the calculation of EDFs for multiple axle configurations. This paper describes the procedure developed for extending the existing HVS-based method. The method is then applied to the assessment of the effects of: wheel load, contact stress, single and dual wheels, and single, tandem and tridem axles. As a result, the procedure enables determination of EDFs for accurate estimation of equivalent traffic for design purposes and performance analysis. This, in principle, may facilitate the development of guidelines on permissible axle loads and tyre pressures for different axle configurations. The basic principle pertinent to this approach is that equal response implies equal damage. The formulation is based on a rational mechanistic evaluation of pavement-traffic load interaction. In this approach, the dependence on empirical formulae is minimized. (A)
Samenvatting