Crack Band Based Model for FEM Analysis of Concrete Structures

Abstract

Over the last 20 years several finite element models for cracked concrete have emerged [e.g., Nilson (1982)]. In early models tensile behavior of concrete was described by a linear relationship. To improve realism and to account for the influence of reinforcement and post-peak softening of concrete in tension, a strain-softening branch in the relationship was introduced [e.g., Lin and Scordelis (1975)]. The adoption of an unloading branch while still using a tensile strength criterion to control crack propagation, created a problem of mesh sensitivity. It was recognized (Bazant and Cedolin 1979; Hillerborg et al, 1976) that the fracture mechanics criterion of constant energy dissipation in the process zone during crack propagation had to be maintained to achieve objectivity of the model. Several models based on this approach were proposed [e.g., Hillerborg et al. (1976) and Bazant and Oh (1983)]. The aim of this paper is to present a new formulation capable of handling strain-softening processes both in tension and compression as well as nonlinear, pre-peak behavior of concrete in compression. The model does not place restrictions on crack directions or number of cracks that can appear at a single integration point. Further, a method of including effects of local bond slip of reinforcement, compatible with the approach to fracture of concrete, is described.