Fracture mechanics models for fatigue in concrete structures

Sammanfattning: This thesis deals with the application of fracture mechanics to model monotonic and cyclic loading of reinforced concrete structures. The main features of the work are:  constitutive modelling based on fracture mechanics numerical studies of the models in various applications experimental studies to check the models and to determine material parameters The fracture mechanics models are formulated on a constitutive level. The models are based on energy considerations. Physically, the energy consumed in the fracture zones corresponds to microcracking of the material. The models apply directly to the description of two simple failure types in reinforced concrete: the tensile failure of plain concrete and the bond failure between steel and concrete. The fracture mechanics models are implemented in a finite element program (FEMP), and numerical studies are performed. As the constitutive relationships are non-linear, an incremental-iterative solution procedure is used. Three main examples are studied: the splitting of a concrete cube, the bending of a concrete bearn, and the pull-out of a smooth steel bar. Comparative experiments were conducted for all the three examples. Most of the constitutive material parameters can be obtained from standard tests. Two new parameters are introduced in order to model crackopening and crack-closing during cyclic loading. It is found that the presented theory can satisfactorily describe experimentally observed phenomena. Several phenomena, familiar to traditional fatique research, can also be recognized in the results of the numerical studies.