LOAD EQUIVALENCY FACTORS OF TRIAXLE LOADING FOR FLEXIBLE PAVEMENTS

This paper presents the load equivalency factors of triaxle loading for flexible pavements. Two diffeent approaches were used to determine load equivalency factors--American Association of State Highway Officials' (AASHO) empirical and mechanistic approaches. AASHO's empirical approach was used first to determine the load equivalency factor of 338-kN (76-kip) triaxle loading. For this approach, experimental pavements were subjected to approximately 55,000 repetitions of 338-kN triaxle loading. The load equivalency factor determined was 2.60 for the range of structural numbers studied and for a terminal serviceability index of about 2.0. The mechanistic approach was used in order to include a broad range of triaxle loading intensity. For this approach, the maximum vertical compressive strain on the top of the subgrade was analyzed by using the bitumen-structures-analysis-in-roads (BISAR) computer program. The maximum subgrade compressive strains were related with load equivalency factors in logarithmic coordinates for single- and tandem-axle loadings. The relation for triaxle loading was established by first plotting the equivalency factor determined from the AASHO approach against the maximum subgrade strain. Then a line was drawn through this point parallel to the lines of single- and tandem-axle loads. The load equivalency factors of various triaxle loading intensities were then obtained by entering the maximum subgrade strain of each load intensity into the relation. (Author)