EQUIVALENCY FACTOR DEVELOPMENT FOR MULTIPLE AXLE CONFIGURATIONS

Through the analysis of AASHO pavements a fundamental relationship is developed between subgrade compressive strain and equivalency factor. Other elements such as tensile strain in the surface and deflection were examined, but the best relationship evolved when the subgrade compressive strain was used. Once the basic relation of equivalency factor and strain is developed, the equivalency factors for axle configurations other than single and tandem can be computed over a wide range of loads. The elastic-layered theory was used for computing strain. The computed results were compared to extrapolations of the AASHO equations used to compute equivalency factors. These comparisons were good in some instances; in others, they were not. The equivalency-factor concept can be extended to new size and weight configurations of highway vehicles. Thus it will be possible to include these new loads in both new and rehabilitative pavement design procedures that use the concept of equivalent loadings. (Author)