Researches On Seismic Performance Of Knee Braced Steel Frames

Knee braced steel frame (KBSF) is a new braced structure style. The feature of KBSF is one of the knee ends connects to the beam, the other one connects to the column, and not less than one end of the brace connects to the knee. The knee in the braced system is designed as a dissipating member, so it can dissipate energy by plastic distortion and yield in shear in advance to avoid the main members destroyed under infrequency earthquake. KBSF combines the stiffness of the concentrically braced steel frame (CBSF) and the inelastic behavior of moment-resistant frame (MRF), and overcomes the disadvantage of the eccentrically braced steel frame (EBSF) dissipating energy by immolating the main member. So it is an effective lateral load-resisting braced structure style which can apply in high intensity area. The series researches have been developing abroad, but the theories of KBSF have not been carried out. The researches at home are just begun. As the aseismic fortification is required in most area in China, in order to utilize the advantage of the KBSF and explore the application of KBSF, the researches on the aseismic performances of the KBSF are not only significant in theory, but also important in practice.A 1:2 steel KBSF specimen is tested by low cycle loading in this paper. The lateral load-resisting capability of the KBSF is studied, the stiffness between the KBSF and corresponding MRF is compared, and the dissipation capability between the KBSF, MRF, and EBSF is compared. The results indicate the KBSF has excellent aseismic performances such as great elastic stiffness, satiable hysteretic loop, slowly stiffness deterioration, and yielding localized in knee.A new method of finite element model set is brought up to analysis the dissipation capability of the KBSF, the method combines analysis precision and calculation efficiency. The three-dimensional beam element (Beam188) in ANSYS program is selected to simulate the beam, column, brace that are in elastic state, and the spatial shell element (Shell181) is selected to simulate the knee that will distort plastic. The method is proved reasonable by compared to the completed test results. The KBSF model is set up by the above method, the results of cyclic loading simulation is similar to the test results in the paper.To analyze aseismic effect factors such as eccentrically distance, knee web depth, web thickness, flange width, flange thickness, web hole setting, web stiffeners setting and so on, there are series KBSF model set up derived from the test specimen. The lateral load-resisting capabilities of these KBSF are studied by low cycle loading. The effect rules of these factors are expressed with elastic stiffness, dissipation energy, and stiffness deterioration. Some...