EVALUATION OF THE JOINT EFFECT OF WHEEL LOAD AND TIRE PRESSURE ON PAVEMENT PERFORMANCE

Most pavement design and analysis procedures predict performance based on the expected damage of the pavement structure under the traffic loads expected during the entire design life. Some failure criteria are primarily dependent on wheel loads and almost independent of contact stresses. Other failure criteria, however, are primarily dependent on normal and shear stresses, not on the load magnitude. The effect of contact stresses is currently indirectly accounted by using wheel load as a proxy for tire pressure. In most pavement design methods, the tire-pavement contact stress is assumed to be equal to the tire inflation pressure and uniformly distributed over a circular area. A methodology that explicitly accounts for the effect of tire inflation pressure and the corresponding contact stresses on pavement response and performance is currently lacking. This research evaluates the pavement responses of typical pavement structures under the combined actions of variable wheel loads and tire pressure. A multi-layer linear-elastic computer program, CIRCLY, was used to estimate the pavement responses under uniform constant stress and actual contact stress distributions. Three critical pavement responses were evaluated, including longitudinal and transverse tensile strains and compressive strains on the top of the subgrade. The differences of the strains estimated by the two models were statistically analyzed to quantify the effect of the assumption of uniform stress over a circular shape in most traditional pavement design approaches. The traditional model proved to be reliable for estimating the compressive strains on the top of the subgrade. The tensile strains at the bottom of the asphalt layer under actual contact stress, however, are quite different from those under uniform constant stress. Contrary to initial expectation, for the cases evaluated in this research, the assumption of uniform stresses is a conservative approach.