The principal objective of this study is to determine the accuracy of calculating stresses in concrete pavements and unbonded overlays under different loading conditions. The computed stresses for the single layer pavements are obtained based on Westergaard theory, the finite-element model (ILLI-SLAB), and the elastic layered model (ELSYM5). For the two-layer unbonded systems, stresses are estimated based on the finite-element theory and the Portland Cement Association design method. The experimental results for the comparison were available from a series of tests done on model scale concrete pavements and unbonded overlays. The results of present investigation show that the computed stresses for the single layer pavement slab are in good agreement with the observed stresses selected for this study, when the slab is loaded at the interior. When the pavement slab is loaded at the edge, the analytical methods give lower stresses and further investigation is recommended. On the other hand, the unbonded overlay of concrete pavement is thoroughly explored. The stresses as given by the analytical methods are, in general, of smaller magnitude than the observed ones in the unbonded overlay. The difference in the magnitude of stresses is considered attributable to the manner in which the stresses are distributed in the slab through the contact area with the load. A revised equation for the determination of the equivalent contact area is suggested to bring the analytical stresses in line with the experimental values. This revised formula is further verified in its application to some of the experimental stresses obtained from other tests and is found to give satisfactory results.
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