Effect of Transverse Shear on Edge Stresses in Rigid Pavements

Abstract

The classical Westergaard idealization of the rigid pavement system assumes that the slab-on-grade can be modeled as a thin elastic plate on a bed of springs. Implicit in this assumption is the Kirchhoff (or thin) plate theory, which ignores transverse shear stresses. This same assumption has been carried over into the development of a number of two-dimensional finite-element models developed for rigid pavements. In this paper, modern isoparametric two-dimensional and three-dimensional finite-element formulations are employed to show that the Kirchhoff assumptions are not strictly valid for the edge loading case in rigid pavements. For slabs where the span-to-depth ratio is less than 100, classical Kirchhoff assumptions, adopted by Westergaard, lead to errors in predicting edge stresses. The maximum edge stress is, in fact, less than that predicted by Westergaard. Furthermore, the maximum edge stress does not occur at the edge of the slab, but at some finite distance from the edge. For most practical rigid pavement systems, the maximum edge stress will occur at a finite distance away from the edge of the slab and will be approximately 10% less than that predicted by the Westergaard theory.