Effect of Measured Three-Dimensional Tire–Pavement Contact Stress on Pavement Response at Asphalt Surface

Top-down cracking results from horizontal strains at the pavement surface that are caused by high wheel loads. When horizontal strains are calculated, the tire–pavement contact stress is assumed to be equal to the tire inflation pressure and to be distributed uniformly over a circular area. In reality, tire–pavement contact stress is distributed nonuniformly over a noncircular area. Actual contact stresses vary along the longitudinal and transverse directions. For precise assessment of the effect of actual three-dimensional (3-D) contact stress on pavement response, this study evaluates the horizontal strains at the surface of the asphalt layer produced by measured 3-D nonuniform stresses. The analysis evaluates five wheel loads, five tire inflation pressures, and 12 pavement structures. A multilayer linear elastic computer program, CIRCLY, was used to estimate horizontal strains in the longitudinal and transverse directions. CIR-CLY's ability to handle normal and shear stresses at the pavement surface makes it a preferred tool compared with finite element models, which are more data and computational demanding. Strain distributions due to uniform stress were also calculated for comparative purposes. The results show that horizontal strains at the pavement surface are compressive within the contact area and tensile at the edge of or outside the contact area. The vertical contact stress and transverse contact stress have significant effects on the longitudinal strains. The vertical stress dominates the developed transverse strains. Two models were developed to estimate the surface critical horizontal strains in the longitudinal and transverse directions. These equations could serve as a tool for determination of critical combinations of asphalt thickness, wheel load, and tire pressure that the uniform stress model would grossly misestimate.