Experimental Study On Seismic Behavior Of Seicmic-damaged Lateral Joints In Composite Frame Consisting Of CFSST Columns And Steel Beams

With the rapid development of the national economy and increasing levels of urbanization, the city’s building gradually develop to high-rise and super high-rise buildings. To meet this demand, concrete filled steel tube(CFST) structure with its simple, good mechanical seismic performance and good repair after the earthquake, widely used in structural engineering.Based on the research status of seismic performance of CFST reinforced,the authors conducted a mechanical test of Concrete-Filled Square Steel Tubes(CFSST) strengthened with enclosed Reinforced Concrete(RC) at the frame lateral joint. A new composite strengthening method of seismic-damaged lateral joints in composite frame consisting of CFSST columns and steel beams strengthened with enclosed RC at the ends of columns and welding steel plate at the ends of beams was presented. Specific studies are as follows:1) Based on the current design specifications, one half scaled models of 4 lateral joints in composite frame consisting of CFSST columns and steel beams were designed and manufactured. One model was original control specimen, one was strengthened by enclosed RC, and the others were strengthened after pre-damage. The destruction tests under lateral cyclic load on the models were carried. Test phenomenon was analyzed in detail.2) By analyzing the experimental phenomena and test data nodes hysteretic curves, skeleton curves, regional strain, shear deformation, ductility factor, energy consumption indicators, ultimate load, ultimate displacement, strength and stiffness degradation and other indicators of parameters studied. The effectiveness of seismic-damaged joints strengthened with enclosed RC and the reinforcement effect on different levels of seismic damage were studied.3) Based on the experimental phenomena and analysis of relevant literature, the stress characteristics and bearing capacity theories of the node studied and bearing capacity of reinforced nodes formula proposed.The test results show that seismic-damaged joints in composite frame consisting of CFSST columns and steel beams strengthened with enclosed RC meets the strong column-weak beam joints requirement of seismic design, and the failure modes are of all joints are the bending failure of steel beam. The reinforcement with enclosed RC has a significant on increasing the ultimate capacity and the seismic behaviors of joints. The study indicated the rehabilitated joints recover the level of their original seismic performances before seismic damage in a certain extent damage level. Based on the test data, namely the ultimate capacity, limit displacement, ductility, the energy consumption coefficient, limit displacementthe strengthening method of seismic-damaged joints by strengthened with enclosed RC is an effective method for seismic strengthening. Based on the test results, considering the forces of reinforcing part, capacity calculation formula of lateral joints in composite frame consisting of CFSST strengthened with enclosed RC was established.