Finite element analysis of a concrete slab under various non-uniform support conditions

A two-dimensional finite element program was utilised to study the effects of a non-uniform subgrade support on the tensile stresses in a concrete slab. A total of 12 subgrade support conditions were created including uniform and non-uniform support. The modulus of subgrade reaction (k-value) for different support areas was arbitrarily assigned either a soft (50 psi/in., 13.5 MPa/m) or stiff (500 psi/in., 135 MPa/m) value. Three axle types (single, tandem and steer-drive), three linear temperature differentials (none, negative and positive), two loading paths (edge and wheel path) and multiple longitudinal wheel positions were considered in the analysis. The theoretical analyses showed that several non-uniform subgrade support cases had a profound impact on the peak tensile stresses in a slab. In particular, a stiff subgrade with soft edges and a subgrade with randomly assigned soft and stiff locations significantly increased the peak tensile stresses relative to a uniformly soft support condition by at least 30%.