EFFECT OF VARIOUS TRUCK AXLE - TIRE CONFIGURATION ON THE BEARING CAPACITY OF ROADS IN WASHINGTON

Many changes in allowable loading and operating procedure for trucks are under consideration in Washington. The main objective of this study is to analyse the relative damage caused by single "flotation" tires versus dual tires on flexible and rigid pavements. Several sites were selected around the state which would represent varying climatic and traffic conditions. From the construction data, pavement thickness and material properties were determined. A survey of truck tire sizes and pressures was conducted to see the range of tires sizes being used presently by the trucking industry. A considerable amount of literature search was conducted to develop fatigue and rutting criteria for use in the analysis. A BISAR computer program was used to calculate stresses, strains and displacements in the flexible pavement system and ILLISLAB, a finite element program, was used to analyse rigid pavements. The results so far in the study showed that for the same magnitude of axle load single flotation tires cause more damage than dual tires on both flexible and rigid pavement. (Author/TRRL)