Research On Seismic Behaviors Of Spatial Connections With T-stub In Steel Frames

The traditional beam to column joints in steel frame structures which connected by weld had serious brittle fractures during strong earthquake in 1994 Northridge and 1995 Kobe.The bolted semi-rigid beam to column connections have a lot of advantages,such as high bearing capacity,good ductility and convenient construction,which are recognized as attractive alternative to welded connections.The multi-dimensionality of ground motions inevitably leads to the complicated stressing state of the beam to column joints in spatial steel frame structures.At present time,the research on seismic behavior of beam-to-column connections with T-stub are focused on plane joints,there are some differences between research results and the actual situation,so it could not be well promoted and applied in engineering.Therefore,it is very significant to research the seismic performance of this kind of spatial joints.The main contents of this paper are as follows:1.The quasi-static test methods and characteristics of spatial beam to column joints are studied.The test about the spatial joints were designed,in which load is applied to the column,and also loading scheme was designed.In order to analyze the influences of the minor axis plane of the spatial joints on the major axis plane,the test specimens of spatial joints and plane joints were designed which connected by T-stubs.Taken the connecting forms of minor axis plane as distinguishing features,two kinds of spatial beam to column joints were designed,and each kind of joint included middle column connection,side column connection and corner column connection,spatial load path was established for pseudo-static test of spatial joints2.The designed 1:1 full-scale joint specimens were tested by pseudo-static test.By analyzing the failure modes,hysteresis characteristics,moment bearing capacity,ductility,rotational stiffness and energy dissipation characteristics of the joints,the law of mechanical properties of major axis plane affected by the minor axis plane have been studied.The experimental results show that the mechanical properties of the major axis plane in joints are reduced,which is due to the stressing state of the minor axis plane.The stiffness of the connector and the connection form of the joints are the main factors affecting the mechanical characteristics of the joints.3.The finite element models of two kinds of spatial joints in this paper was established by taking the stiffness of T-stub as the change parameter,and the geometric nonlinearity,material nonlinearity and contact nonlinearity are considered for numerical analysis and calculation.According to the analysis of the bending moment bearing capacity,rotational stiffness,ductility and energy dissipation capacity of the joints,the influence of stiffness changes of the joints on the mechanical properties of the joints was obtained.At the same time,the change laws about the contact state of the component and the pre-tightening force of bolts in the joints were obtained.4.According to the mechanics behaviors of the joints obtained from the test and finite element analysis,the components mechanics model of the spatial joints were established by using the component method which recommended by Eurocode3.According to the components model,the yield moment bearing capacity and the initial rotation stiffness of the joints are analyzed.The joints studied in this paper were evaluated according to EC3 and AISC,and the main factors that influence the mechanical properties of major axial plane and minor axis plane are clarified.The ideal elastic-plastic moment-rotation relationship of the joints were established,and the main factors influencing the mechanical properties of the major and shallow axial planes of the joints were obtained.Finally,on the basis of comprehensively summarizing the research results,some problems that need to be further studied are proposed.