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

Lateral resistance system is one of the key factors of structural configuration selection for high-rise buildings. The concentrical brace and eccentrical brace have been actually obtained in many applications, and the use of which the lateral stiffness of structure can be augmented. But that was at the cost of dissipating energy for the structures themselves. The seismic damage was aggravated for those braced systems due to repeated loading, especially in the 1994 Northridge earthquake and 1995 Kobe earthquake. In order to improve the buckling performance of ordinary brace, the buckling-restrained brace was proposed, in which the lateral buckling could be avoided in earthquake. The buckling-restrained brace can prevent the compression buckling by encasing ordinary brace over its length in a steel tube filled with concrete, but without limiting the freedom of flexibility. Actually it can reach and retain full section yielding under compression and tension. On basis of good energy dissipation capacity and ductility for the concrete filled steel tube-steel beam composite frame system with buckling-restrained brace, the applied fields for the new type of brace become more and more widely in the United States and Japan. As the study on its property is relatively less, it has been used for individual project in China.Incorporated with the application of buckling-restrained brace in frame, seismic performance of this type of the composite structure is studied in this thesis through the theoretical and finite element analysis.(1) From the composition of BRBs, overall and local stability analysis are carried out to determine the necessary stiffness and moment resisting capacity of the outer tube, as well as all requirements that every parts should be met. At the same time, through the kernel's deformation, a suitable space is derived. Methord of the BRBs is presented for engineering application.(2) Various factors are considered in the contact analysis by finite element method to simulate the loading progress of the rectangle section BRB and the Criss-cross section BRB. Several parameters on the performance of BRBs such as constraint ratio, width to thickness ratio of the core, initial imperfections, slenderness ratio, and width to thickness ratio of the connection and gap are investigated. And then reasonable values of the parameters are suggested.(3) Seismic behavior of buckling-restrained braced frame is performed. The period and vibration mode of the ordinary braced frameand the BRBF are analyzed by SAP2000. And then the dynamic behaviors and influence of buckling restrained brace to column axial forces of the two structural systems are contrasted by elastic-plastic time history analysis. Finally, the seismic capacity of structure is examined through a performance point obtained by Push-over analysis.