Modeling of fracture in heavy steel welded beam-to-column connection submitted to cyclic loading by finite elements

During the earthquake in Japan and California in the 1990s, some weld beam-to-column connections had some cracks in heavy rigid frame steel building. Consequently it is required to assess the performance of the welded connection in term of rotation capacity and crack propagation strength. Some experimental tests have been performed. The weld connections were submitted to cyclic loading with increasing amplitude until macro crack event. However the crack phenomenon depends on many parameters: the geometry, the material, the welding process. For this reason, it is interesting to develop a finite element modeling of this connection to complete these experiments and perform a parametric study. The welded connection is modeled by three dimensional mixed solid elements. The constitutive law is elastoplastic with isotropic hardening identified for the base metal and the weld metal. The crack propagation is modeled by cohesive zone model. The parameters of the cohesive zone model have been identified by inverse method with the modeling of three point bend tests of a pre-cracked sample performed on the base and weld metal. The fatigue damage generated by the cyclic loading is computed by the fatigue continuum damage model of Lemaitre and Chaboche and it is coupled with the cohesive zone model. The damage and the crack propagation depend on the residual stresses generated by the welding process. They have been computed by a simulation of this process with a thermo mechanical finite element analysis. This thesis presents the used models and the results compared with the experimental tests.