Behaviour of fracture process zones in concrete influenced by simultaneously applied normal and shear displacements

Detta är en avhandling från Division of Building Materials, LTH, Lund University

Sammanfattning: The thesis deals with the determination of the post peak behaviour of concrete in pure tension, and combined tension (compression) and shear. A test arrangement has been developed in order to determine the post peak behaviour of concrete expressed as stress - displacement curves. The theoretical basis of the thesis is in accordance with the "Fictitious Crack Model" which is a model based on the softening properties of concrete. The model was originally developed in order to describe the crack propagation in concrete when the direction of the principal stresses remains consiant during the entire fracture process. However, since the mid-eighties the applicability of the model has been further extended to cases where the direction of the principal stresses is changed during the fracture process. The applications of the model in these cases require material properties describing the behaviour of a fracture process zone initiated in pure tensile stress state and later subjected to the combined normal and shear stresses (displacements). The developed test arrangement is, with some limitations, able to provide the requisite material properties for analyses of crack propagation in concrete. The thesis describes the physical basis of the Fictitious Crack Model and, compares the concepts of the model with the concepts of Linear Elastic Fracture Mechanics. Furthermore, the thesis describes the test arrangement and discusses the instability phenomenon associated with the tensile tests. The combined normal and shear tests in this investigation were conducted in displacement control where the relation between the normal and shear displacements, also called displacement path, was prescribed. Basically two different paths have been utilized, namely linear and parabolic paths. The thesis presents the results of both paths, and discusses the cracking process and path dependent behaviour of the fracture process zone on the basis of the presented results. Furthermore, the thesis presents expressions which a¡e adopted to the test results describing relations between stresses and displacements within the fracture zone.