J. Macht:
"Ein 2D Werkstoffmodell für Beton auf der Grundlage der Plastizitäts- und der Schädigungstheorie unter Berücksichtigung rissinduzierter Anisotropie";
Supervisor: H.A. Mang, G. Meschke, R. Lackner; Institut für Festigkeitslehre, 1998.
This master's thesis is concerned with a material model for biaxially loaded plain concrete within the framework of multisurface damage-plasticity theory. The proposed model accounts for fracture-induced anisotropic strength degradation of cracked concrete in addition to anisotropic stiffness degradation as well as for inelastic deformations.For the representation of the anisotropic strength characteristics in cracked concrete a gradual stress release according to a kinematic softening law is considered in the post-cracking regime. The anisotropic strength characteristic is taken into account by means of two independend internal variables defined within a fixed reference frame determined by the direction of the primary crack. Crack initiation is detected according to the maximum principle stress criterion. The ductile behavior of concrete subjected to predominantly compressive loading is described by means of an isotropic hardening/softening plasticity model.
The algorithmic formulation of the model is based on the return map scheme as usually employed in plasticity theory. Selected results of a splitting-cylinder test and of a simulation of a notched beam are also contained in this thesis. As far as the numerical modelling of cracks in plain concrete is concerned, local models lead to mesh dependent results. For the numerical simulations the fracture energy approach is employed.