A comparative overview of the methods used to calculate mechanistic load equivalence factors (lefs) is provided. In addition, an application of the rainflow/range-pair counting method (astm e1049-85) in calculating lefs from in-situ pavement strains is demonstrated. The experimental program involved two test vehicles, with a bb truck providing the reference axle load. Asphalt concrete (ac) interfacialstrains were measured at three vehicle speeds and three levels of axle load. Counting fatigue cycles according to the astm standard hasshown that (a) the calculated lefs decrease with vehicle speed, and(b) the lefs for entire vehicles are substantially higher than the sum of the lefs of their individual axle groups. This trend becomes more pronounced at higher vehicle speeds. The lefs obtained by the rainflow/range-pair counting method were compared with those obtainedby the roads and transportation association of canada method. The two sets of mechanistic lefs were also compared with the empirical lefs recommended by aashto. This comparison, however, was inconclusiveand could not verify that one of the two mechanistic lef methods best describes the fatigue cycles caused in ac by multiple axle loads.This paper appears in transportation research record no. 1307, pavement analysis, design, rehabilitation, and environmental factors 1991.
Abstract