The Study On Resistance Of Reinforced Beam-to-Column Connections With Cover-Plate Under Initial Loads In Steel Frame

Steel frame connections widely used in high-rise seismic frame structure, it is considered to be superior seismic performance of a form of connections However, since the U.S Northridge and Japan Kobe earthquake, it is found that the reason structure damage and collapse, because of the weld brittle failure in flange of the beam-column connections. It does not realize the engineers design concept of "strong connections, weak component". After this earthquake, the engineers around the world recongntions these beam-column connections again. Because of the steel structure building development telatively late in our country, many steel structure has not experience the test of earthquake, so, there are many steel structure need reinforced. In fact, lots of the buildings are reinforced under initial loads. But there are very little research related to reinforcement under initial loads in our country, only a few similar research by finite element analysis. In order to provide the basis of reinforcement project, it is necessary to do the experiments.(1) In this paper, through experiments and finite element analysis method, design of four specimens, The finite element analysis under cycling loading for four beam-to-column connections with different initial loading is carried out to study the failure modes, limited resistance, hysteretic behavior, ductility, energy dissipation capacity, stiffness degradation of the connections, and compares with unreinforced connections. The result shows that the reinforcement can effectively improve the limited resistance and ductility of the connections, plastic hinge shifts away a quarter of the beam height from the cover-plate end, the specimen of hysteretic performance is better, and have the good energy dissipation, effectively avoiding the damage at the weld location and achieving the purpose of the reinforcement, in addition to SP-1 connection. By comparing the new specimen, it is found that with the increase of the peressive load level, the bearing capacity of the connections is on the decline. The conclusion shows that cover-plate reinforcement can significantly improved seismic performance of the beam-to-column connections, the reinforcement is effective. The finite element analysis results is similar to the experiment results, it can be used analysis in similar field.(2) Through the finite element analysis, establish lots of finite element model,study the mechanical performance with different initial loads, different cover plate size, different cover plate shape. The conclusion shows that the normal stress between cover plate and beam flange has jumping phenomenon, The distribution proportion is only affected by the thickness, but not the length of the cover plate. When the connections is designed, the loads distribution relationship between the cover plate and the original should be consider carefully. At the same time, the initial loads should be limited strictly. When the reinforcement is carried out with the initial loads, the initial loads are resisted only by the original connections and the additional loads are shared by the original connections and the cover plate with the same proportion as the newly erected reinforced connections(in other words, it is mean the reinforced connections). When it closed to 30?60% yield capacity,the bearing capacity of the beam should be discount. The change tule of bearing capacity without any relationship between rectangular plate and the trapezoidal plate.However,the trapezoidal plate energy dissipation is superior to the rectangular plate.The results provide the basis for specification and reinforcement of the engineering.