Stresses in a curled concrete slab under central FWD loading and curling prediction from measured surface temperature histories

Abstract

Nineteen central Falling Weight Deflectometer (FWD) tests, which are conducted on a 27 cm-thick concrete slab containing embedded temperature sensors, are analysed. Structural analysis focuses on tensile stresses at the slab's underside centre. This includes stresses due to dead load and curling, thermal eigenstresses of concrete and stresses resulting from the FWD load. Finally, a half-space model is developed to limit the temperature data required for stress analysis to surface temperature histories. The experimental results indicate that FWD deflections increase linearly with the degree of downward curling of the slab. Structural analysis delivers tensile stresses at the underside centre of the slab, which show a loop-like daily evolution with stress maxima in the early afternoon and stress minima in the early morning. The half-space model delivers analytical series solutions for the evolution of the temperature profile across the thickness of the slab, its degree of curling and the thermal eigenstresses of concrete. For the analysed slab, these quantities can be predicted provided that the surface temperature history is recorded (e.g. by ice warning systems) at least every 15 minutes over 7 days preceding the time instant of interest.