23 Pages

Chapter11EnvironmentalEffects ( Temperature , Shrinkage , Corrosion )

This paper presents the first results of a research aimed at understanding the modifications of the behaviour of concrete structures due to shrinkage, most specially its influence on the structural strength. After defining the phenomenological framework and identifying the essential parameters, a simplified method to describe the eigenstress fields is presented and discussed and the numerical procedure, based on a cohesive crack model, is outlined. The effect of the shrinkage is numerically investigated for three point bent unnotched beams and three different softening curves. The results show that the effect of the shrinkage first increases as drying deepens, but then goes through a maximum and decreases again. This behaviour leads to the existence of upper bound and a lower bound curves for the strength. It is also shown that a Bazant size effect curve may describe very well the “average shrinkage” behaviour lying midway between the lower and upper bound curves. Finally, it is shown that the size effect curves for different softenings may be brought to lie on a “master” curve by defining an equivalent linear softening.