A three-dimensional (3-D) finite element (FE) model was developed to predict pavement responses to vehicular loading. The model incorporates measured tire-pavement contact stresses, continuous moving wheel loading, and hot-mix asphalt (HMA) viscoelastic characteristics. The model was fine-tuned using implicit-dynamic analysis and validated using pavement response from accelerated loading. Two tire configurations (dual-tire assembly and wide-base 455 tire) and three full-depth flexible pavement designs (HMA 152 mm, 254 mm, and 420 mm) were used in both FE modeling and accelerated loading tests. The predicted and calculated strain responses at the bottom of HMA were in agreement. Most important, the study shows that vertical shear strain in the upper 76 to 100 mm of the pavement surface is critical for thick pavement and is influenced by the 3-D tire-pavement contact stresses under each tire rib. However, the tensile strain at the bottom of HMA is affected mainly by the total wheel load. The vertical shear strain is responsible for near-surface fatigue cracking as well as HMA primary rutting. Top-down cracking could result from the local vertical shear strain in the upper 25 mm of the HMA where the effect of tire-pavement tangential stresses are the highest. In addition, the study concluded that wide-base tires cause higher longitudinal tensile strain at the bottom of HMA and compressive strain at the top of subgrade, where those responses are highly affected by the total wheel load. However, wide-base tires were found to cause less vertical shear strains near the surface than dual-tire assembly loading regardless of HMA thicknesses.

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A three-dimensional (3D) finite element (FE) parametric study was conducted to quantify the viscoelastic pavement responses due to different tire configurations: dual and wide-base tires, at three temperatures (5, 25 and 408C) and two speeds (8 and 72 km/h). Three factors affecting pavement responses were investigated: type of moving wheel loading amplitude (continuous, trapezoidal), interface layer condition (simple-friction and elastic-stick models) and lateral surface forces. It was found that the continuous loading amplitude, which has an asymmetric stress magnitude and considers the difference between the entrance and exit of the tire, can simulate pavement responses to moving wheel vehicular loading more accurately than the currently used trapezoidal loading amplitude. The elastic-stick model resulted in a sensible improvement for predicting pavement responses to dual tire, while the simple-friction model is more comparable to field measurements in the case of the wide-base tire. The shear force was found to positively improve the prediction of the calculated strain at the bottom of the wearing surface and to a lesser degree at the bottom of the hot mix asphalt (HMA) base layer. This study concludes that using continuous loading amplitude and non-uniform pressure distribution to simulate a moving wheel, surface shear forces and appropriate layer interface friction may significantly improve the capability of FE models to predict pavement response to vehicular loading. Results have been successfully validated against field measurements.

The effect of transient dynamic loading on flexible pavements was estimated. Transient dynamic loads within a tire-to-pavement contact area are characterized by continuously increasing or decreasing local dynamic contact stresses, depending on vehicle speed. A transient dynamic load model was successfully incorporated into a three-dimensional finite element model. Dynamic flexible pavement responses to one pass of a heavy vehicular load through a dual-tire assembly were calculated. Results of this study indicate that the flexible pavement response at different pavement temperatures varies depending on whether the analysis was quasi-static or dynamic, where the mass inertia and damping forces by the transient local dynamic loads are considered in the equation of motion. Results also show that the time-dependent history of the calculated pavement responses in the dynamic analysis is more comparable to measurements in the field. The transverse and longitudinal tensile strains at the bottom of the hot-mix asphalt and the compressive stress at the top of the subgrade are underestimated when the mass inertia and damping forces exerted by the transient local dynamic load are ignored.

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