Finite Element Analysis of Fracture in Concrete Structures

Description

In this report, the state-of-the-art in finite element modeling of concrete is viewed from a fracture mechanics perspective. Although finite element methods for modeling fracture are undergoing considerable change, the reader is presented with asnapshot of current thinking and selected literature on the topic .As early as the turn of the 19th century, engineers realized that certain aspects of concrete behavior could not be described or predicted based upon classical strength of materials tech-niques. As the discipline of fracture mechanics has developed over the course of this century (and indeed, is still developing),it has become clear that a correct analysis of many concrete structures must include the ideas of fracture mechanics.

The need to apply fracture mechanics results from the fact that classical mechanics of materials techniques are inadequate tohandle cases in which severe discontinuities, such as cracks, existin a material. For example, in a tension field, the stress at the tipof a crack tends to infinity if the material is assumed to be elastic.Since no material can sustain infinite stress, a region of inelasticbehavior must therefore surround the crack tip. Classicaltechniques cannot, however, handle such complex phenomena.

The discipline of fracture mechanics was developed toprovide techniques for predicting crack propagation behavior.Westergaard (1934) appears to have been the first to apply theconcepts of fracture mechanics to concrete beams. With theadvent of computers in the 1940s, and the subsequent rapiddevelopment of the finite element method (FEM) in the 1950s,it did not take long before engineers attempted to analyzeconcrete structures using the FEM (Clough 1962, Ngo andScordelis 1967, Nilson 1968, Rashid 1968, Cervenka and Gerstle1971, Cervenka and Gerstle 1972). However, even with the powerof the FEM, engineers faced certain problems in trying to modelconcrete structures. It became apparent that concrete structuresusually do not behave in a way consistent with the assumptions ofclassical continuum mechanics (Bažant 1976).