Cumulative Damage Reasearch Under Improved Steel Connections Subjected To Cyclic Loading

Compared to the traditional steel connections, improved steel connections can achieve relocating the plastic hinge under cyclic loading, so as to protect end welds and enhance the ductility as well as energy dissipation capacity of connections. But numerical simulation results always overestimate the load carrinying capacity as well as energy dissipation capacity, and underestimate plastic deformation when cumulative damage is not considered. In this thesis, the ductility and damage evolution process under improved steel connections subjected to cyclic loading were firstly studied in depth. Then, nonliner finite element analysis on different connections to investigate hysteretic energy dissipation capacity as well as damage degradation behavior.The main work of this thesis consisted of three parts:(1) According to the referred connection tests result, the development of plastic hinge, stress distribution of plastic hinge and degradation properties have been compared by using numerical analysis method. Conclusion shows that three connections can achieve relocating the plastic hinge and the failure mode is in agreement with the tests results. The stress distribution in the plastic zone can reflect the strength degradation of the connections.(2) Damage index model based on plastic deformation and cumulative damage constitutive model based on cyclic process have been used in hysteresis curve, degradation properties and energy dissipation coefficient by consider damage and not.Then, the influence of hysteretic behavior of different flange width thickness ratio and web width thickness ratio under damage have been discussed,and damage degradation process of different connections by compared.(3) By establishing a four storey shell element steel frame model, the proposed model is carried out under strong earthquake. With time-history analytical method applied, the displacement of model top layer and layer displacement angle compared between model with damage and traditional, The influencing factors and impact degrees of damage were analyzed in depth on seismic behavior of steel frame.