Study On Seismic Behavior And Design Method Of K-type Eccentrically Braced Steel Frames Composited With High Strength Steel

In the structure of eccentrically braced steel frames composited with high strength steel(HSS-EBFs), link uses ordinary steel(Q345) rather than high strength steel(Q460) used in the non-energy dissipation members—beam and column. The design principle of eccentrically braced frames is elastic-plastic deformation mainly occur at links under rare earthquake, while non-energy dissipation members are still elastic, which could provide enough support to links. The high strength members could reduce cross section of the members effectively and improve the consumption of steel, The HSS-EBFs can improve the popularization and application of high strength steel in seismic region. In order to research seismic behavior of HSS-EBFs, this paper conducted the following study work:1) A 1:2 scale three-story K-type HSS-EBF(K-HSS-EBF) with shear links was carried out under cyclic load to research its seismic performance. The results indicated that the K-HSS-EBFs structure has good load-carrying capacity, ductility capacity and energy dissipation capacity. The web tore of the link in second story resulted in the degradation of the load-carrying capacity. The non-designated yield members remain in elastic stage while the link entered the plastic stage completely to dissipate the energy in K-HSS-EBFs. High strength steel members are still in elastic condition for post-seismic recovery of stuctures.2) Finite element fine model of test specimen is created by ANSYS software:Steel members use SHELL element,and concrete floor use SOLID element. The fine model analysis results are good fits of test results. A simplified calculation model is proposed by SAP2000 software based on links with nolinear shear hinge. The pushover analysis results compared with fine model analysis and test results. The results indicate that the simplified calculation mode is feasible.3) The formulas of elastic axial force of brace and shear force of link K-EBFs subjected to lateral loads have been proposed based on the fundamental assumption of structural mechanics. The drift of eccentrically braces steel frames is divided into four parts: drift due to axial deformation by braces; drift due to axial deformation by beams; drift due to shear deformation by links; drift due to bending deformation by links, and then the elastic lateral stiffness formulas of K-EBFs are proposed on the basis of the small deformation assumption and Hooke’s law. The approximate formulas for braces are obtained by internal force analysis of K-EBFs.4) The yield drift of eccentrically braced frames is related to material property of brace and column, brace angle and depth-span ratio of structures. The performance-based seismic design(PBSD) method of eccentrically braced steel frames is proposed based on failure modes of K-EBFs, story shear distribution and base shear under rare earthquake. Test prototype structure is designed by PBSD method.5) Four groups of eccentrically braced steel frames are designed by PBSD method, includes 5-story, 10-story, 15-story and 20-story. Each group includes ordinary EBFs(All material are Q345),Q460-EBFs(links and braces are Q345, others are Q460),Q690-EBFs(links and braces are Q345, others are Q690). Nonlinear pushover analyses and nonlinear dynamic analysis under rare earthquake are conducted to all designs and the loading capacity, lateral stiffness, ductility and interstorey drifts and failure mode under rare earthquake of the designs are compared. The results indicate that HSS-EBFs and EBFs have similar loading capacity under the same design condition, while the lateral stiffness and ductility of HSS-EBFs is lower than that of EBFs. HSS-EBFs and EBFs designed by PBSD method have the same failure mode and interstorey drift distribution under rare earthquake, the steel weight of HSS-EBFs is 15%-25% lower than the EBFs resulting in good economic efficiency.