Significance of Eigenstresses and Curling Stresses for Total Thermal Stresses in a Concrete Slab, as a Function of Subgrade Stiffness

Abstract

Thermally induced stresses of a concrete slab are quantified based on in situ temperature measurements. PT100A sensors recorded the temperature at four specific depths during 23 days in autumn. Best-fit quadratic polynomials are used to extrapolate the measured temperatures to the top and the bottom of the slab. The obtained surface temperature histories are used as boundary conditions for the solution of the transient heat conduction problem in thickness direction. Postprocessing the thermal eigenstrains provides access to the eigencurvatures of the plate and to the eigendistortions of the plate-generators. Stresses resulting from the constrained eigencurvatures of the plate are computed numerically, for values of the modulus of subgrade reaction amounting to 50, 100, 200, and 300 MPa/m. Self-equilibrated eigenstresses resulting from the prevented eigendistortions of the plate-generators are quantified analytically. Daily maxima of tensile stresses in corner regions at the top of the slab, and in the central region at its bottom, are found in the early morning and in the early afternoon, respectively. Disregarding the eigenstresses leads to an underestimation of tensile stresses in corner regions by at least (Formula presented.) and an overestimation in the central region by at least (Formula presented.). The misestimations increase with decreasing modulus of subgrade reaction.