Nonlinear analysis of thermal stresses in mass concrete castings

Abstract

Temperatures and stress transients due to hydration process in concrete casting for dam constructions and to thermal exchanges between concrete and its surrounding environment are analysed. The problem under investigation is highly nonlinear due to different reasons. Placing technique of concrete is carried out by means of large block castings which are superimposed at different times. Concrete surfaces may be cooled using water at ambient temperature or at a lesser temperature; thermal exchanges between concrete and external ambient are affected by the increasing extension of casting surface, by solar radiation and wind action. Thermal stresses due to the temperature transients are produced and cracks may appear in massive concrete. The numerical analysis of corresponding complex phenomena is carried out according to the following lines. Temperature field is calculated at each time step taking into account the above mentioned nonlinearities, then for each time step equilibrium is imposed for finding displacements and stresses using maturity dependent constitutive relationships. Time integration of the nonlinear equation of heat transport is carried out using a two-level scheme with variable step sizes. Thermal and mechanical fields are then found for the whole time transient.