Evaluating the Effect of Concrete Slab Curling on Joint Load Transfer Responses

Abstract

Past and current rigid pavement thickness design procedures used by the FAA use single-slab free-edge loading stress analysis as the basis of design. The FAA's rigid pavement design methods have assumed a 25% reduction in free-edge bending stress to account for the ability of properly designed joints to transfer load from slab to slab and reduce bending stress from heavy wheel loads. This percentage of reduction is actually changing continuously as a function of slab temperature, joint type, pavement age, and traffic. A systematic procedure is used to evaluate the joint load transfer percentage of stress reduction factor in greater detail with falling weight deflectometer (FWD) measurements, slab curvature measurements, and finite element method (FEM) structural analysis. Field measurements of joint stiffness and slab curling are presented and compared with FEM simulations calibrated to reproduce field measurements. With the use of calibrated FEM models, the full range of expected load transfer percentages is demonstrated for single-wheel loads, two-wheel gears, and four-wheel gears for a wide range of possible joint stiffness values. Top-down and bottom-up slab cracking stresses are compared. Slab curling measured from test sites is compared with slab curling calculated from FEM models. The calibration of an FEM model to reproduce detailed site measurements of joint stiffness, load transfer efficiency, and slab curvature combined is demonstrated.