Model for Tension Stiffening Effect of Concrete for Thermal and Shrinkage Loading Typically Founding Tropical Environmental Conditions

Abstract

There are increasing concern over the impact of thermal and shrinkage effect on the structural behaviour of concrete and specially, its influence on the serviceability prediction of cracking and deformation of concrete structures. The effect is considered significant in tropical and arid environmental conditions where extreme heat, wind and relative humidity conditions can set up challenging shrinkage and thermal conditions. As concrete strength properties build up gradually over time, effect of extreme environmental conditions expected to be significant in concrete than any other composite materials. However, none of the existing codes consider thermal and shrinkage behaviour for serviceability limit state performance. As a result most of the structures we live especially in the tropical climates run the risk of being deformed and cracked differently to what is predicted by code formulas. Accounting the concrete contribution, in tension, is the key for accurate modelling of serviceability performance of concrete structures and the tension stiffening effect is widely adopted in modelling tension behaviour of concrete. This paper looks at the possibilities of capturing the influence of thermal and shrinkage effect on the tension stiffening behaviour of concrete as a means of improving serviceability performance of reinforced concrete subjected to harsh environmental conditions. In order to simulate thermal and shrinkage effect, 42 Nos. of test specimens subjected to different shrinkage regimes varying; +2200 pe(expansion) -500 pe(shrinking) were studied. Results confirm that effect of shrinkage and expansion conditions are consistently reflected on the tension stiffening behaviour of concrete. From the results it is clear that the tension stiffening is invaluable means to incorporating thermal and shrinkage effect on serviceability prediction of reinforced concrete. However, the current method for accounting shrinkage base on free shrinkage/expansion is found over estimate expansion and shrinkage effect of simulated test specimens. Based on test results a comprehensive method to account tension stiffening effect of concrete found based on interaction of concrete and reinforcement and free shrinkage/expansion measurements is currently underway.