ACI SP-134

Abstract

<strong>Introduction</strong> <br>It has long been known that ultimate loads of concrete structures exhibit size effect. The classical explanation has been Weibull's weakest-link theory which takes into account the random nature of concrete strength [1,2,3,4,5]. However, for reasons given elsewhere [6] and briefly explained in the Appendix, it now appears that the statistical theory does not suffice to describe the essence of the size effect observed in brittle failures of reinforced concrete structures and plays only a secondary role. The main mechanism of the size effect in this type of failure is deterministic rather than statistical, and is due to the release of the stored energy of the structure into the front of the cracking zone or fracture. This phenomenon is properly described by fracture mechanics in its recently developed nonlinear formulation which takes into account the distributed nature of cracking at the fracture front. <br>The purpose of this review paper is to summarize the existing evidence and also present some recent experimental results obtained at Northwestern University.