Fracture Analysis And Crack Propagation Research Of Beam-column Joints Based On XFEM

With the development of science and technology and economic conditions as well as the dramatic increase in population, steel structure has become the main structural form of high-rise and super high-rise buildings. Nevertheless, since the Northridge earthquake in United States and the Kobe earthquake in Japan, a large number of steel beam-column joints have encountered with the problems of brittle failure. Based on the Extended Finite Element Method(XFEM), the thesis aims to carry out a fracture analysis and crack propagation analysis of beam-column joints. Via ABAQUS finite element software, the author conducts an simulation analysis and completes the following assignments:(1) The stress intensity factor of plane-edge crack model subject to uniaxial tensile stress is calculated. This issue needs to be further discussed the influence of load, the initial crack length, and geometrical parameters of the member on stress intensity factors of the crack tip.Thus, the results of numerical analysis and the theoretical solution error are less than 5%, which conforms to the requirements of the precision. And according to the stress historical curves of crack tip element, the crack extension process in one unit has been known.(2) Extended Finite Element Method(XFEM) was applied to all welded steel framework beam-column joints in the engineering practice are numerically simulated. Linear elastic analysis indicates that the distribution of the stress intensity factor of node welds is roughly a “W” shape, along the width direction of beam-flange edge. The longer the initial crack length, the greater the values of stress intensity factors. Moreover, as the bending tensile stress increases, the stress intensity factors at the center of beam-flange edge also increase, roughly in a linear relationship, which is genuinely in accordance with the basic theory of fracture mechanics.(3) Formula of stress intensity factors of weld is in regression. Besides, the author puts forward a simple and effective practical formula that can calculate maximum value of stress intensity factor of all-welded beam column nodes in a similar structure of steel frame, so as to obtain significant engineering value.(4) The author analyzes two factors, viz. initial crack location and mesh size, that influence crack propagation path. Results show that although the position of initial weld crack is different, its crack propagation path is roughly the same, with different extension lengths. And mesh size has little impact on the crack propagation path.