Thermo-hygro-mechanical modelling of self-induced stresses during the service life of RC structures

Abstract

Current practices of structural design in reinforced concrete (RC) structures usually account for stresses caused by phenomena such as heat of hydration and drying shrinkage in a quite simplified manner. The present paper aims to evaluate the consequences of explicitly considering self-induced stresses, which actually vary significantly within structural cross-sections, combined with stresses caused by external loads. The used numerical framework involves the explicit calculation of the temperature field in concrete, with proper account for the heat of hydration of cement. Simultaneously, the moisture field in concrete is computed in order to ascertain the relative humidity changes in the pore structure caused by drying, and the inherent shrinkage strains. Stress calculations are made with due consideration of the evolution of mechanical properties of concrete as a function of the equivalent age, as well as relevant phenomena like creep, concrete cracking and influence of reinforcement. Two separate groups of numerical applications are presented, checking influence of the self-induced stresses: a unrestrained concrete prism usually used for shrinkage measurement, and concrete slabs subjected to external loads. Particularly for the second set of applications, the obtained results (with explicit consideration of the differential effects of self-induced stresses) are compared, in terms of cracking loads and crack propagation, to those that would be obtained by using the simplified design approach based on considering uniform shrinkage fields in concrete. It is found that the behaviour of both formulations is quite similar after crack stabilization, but may be quite distinct in the crack propagation phase.