FRACTURE IN CONCRETE AND REINFORCED CONCRETE.

Although cracking represents a salient feature of the behavior of concrete structures, not only under ultimate loads but also at service states, fracture mechanics has not been used in practical analysis of structures. Structural engineers had a good reason; the linear fracture mechanics was found to be inapplicable to typical concrete structures, and the premises of ductile fracture mechanics did not match material behavior. However, in various recent investigations, it has been shown that fracture mechanics can be applied to concrete structures provided that one takes into account the effect of a large micro-cracking zone or fracture process zone that always exists at the fracture front. The objective of the present paper is to review the results of the investigations at Northwestern University, many of them carried out under a cooperative agreement with Politecnico di Milano, and also to presented some new results on a continuum model for strain-softening and on R-curve analysis.