Seismic Behavior Of Concrete Filled Tubular Column-steel Beam Composite Frames With Braces

The frame structures have advantages of flexible spatial arrangement, light weight, material saving, etc., and are applicated broadly in high-rise building structures. However, due to its small lateral stiffness, large horizontal displacement could be generated by the strong earthquake and wind loads easily. This will lead to serious non-structural damage. So the braces are often added to the structures to increase its lateral stiffness. While the braced-frame structures, to a certain extent, solve the problem of lateral stiffness, the braces are easy to buckle under the strong seismic action because of the pressure, which is very likely to cause the failure of the braces itself and the connection. Simultaneously the braces are difficult to dissipate the seismic energy of structure because of the deterioration of hysteretic energy dissipation after buckling. Therefore a new type of braces called the Buckling-Restrained Braces(BRBs) have been developed by many scholars. Unlike the conventional braces,the BRBs would not buckle under pressure and yield in tension and compression which generate full hysteresis curve to dissipate a significant amount of hysteretic energy during earthquakes. The Buckling Restrained Brace Frames (BRBFs) combine the advantages of the composite steel-concrete structures and the BRBs, and are a new structure system that have great development and good prospects of application. In this paper, the anti-seismic performance of the BRBFs will be investigated through the numerical analysis and substructuring pseudo dynamic test. The main contents include:(1) From the composition principle, theoretical analysis and design methods of BRBs, 3 groups of BRBs were produced. The BRBs’rectangular core plate was covered by the concrete-filled square steel tube. According to a certain loading system, an experimental study on the hysteresis curve of the BRBs under the low reversed cyclic loading was carried out. Experimental results show that the BRBs have a full hysteretic curve, high ductility, good seismic performance.(2) According to china-related design standards and displacement-based design procedures, two BRBFs of 10-story and 3-story were designed respectively. The finite element software Sap2000 was used to model the BRBFs and the nonlinear time history analyses were conducted using an assemble of ground motions.The earthquake records were scaled to three different seismic input levels: frequent occurrence earthquake(FOE), design basis earthquake(DBE), and maximum considered earthquake(MCE). Acceptable BRBFs behavior was observed at different seismic input levels.(3) The substructure pseudo dynamic test technique was used to investigate the seismic performance of the BRBFs through a test platform NetSLab. The test structure was constructed at a reasonable scale factor based on laboratory space and loading capacity. Then the overall test structure is divided into two substructures with the inverted-V BRB of the first floor to be tested physically while the others to be simulated in the NetSLab.