Reinforced concrete under thermal gradients

Abstract

Summary The significance and current knowledge of thermal effects in concrete and reinforced concrete are reviewed briefly. It is evident that there is a need for more basic data on the shrinkage and creep of concrete subjected to high temperatures. Tests designed to obtain some of these data are described; results for the shrinkage and creep of a particular concrete at temperatures up to l40°C are presented. Some of the specimens were sealed to prevent loss of moisture, to simulate the conditions in mass concrete. It is shown that the time-dependent strains are markedly temperature-dependent. The paper then describes tests on model reinforced concrete beams subjected to a thermal gradient while flexurally restrained but without longitudinal restraint. The behaviour of the unsealed beams showed a severe departure from the predictions of conventional elastic theory, even to the extent of indicating compression in the reinforcing steel, instead of the expected tension. This was due to shrinkage and creep under the high temperatures. The behaviour of the sealed reinforced concrete specimens approximated to the predictions of elastic theory with a low value of the elastic modulus. A numerical procedure for estimating approximately the effects of time- and temperature-dependent strains in flexurally restrained beams is outlined in an Appendix.