Research On Seismic Design Method Of Steel Frames Based On Constant Yield Displacement

The traditional constant-period seismic design method takes the elastic vibration period as the basic design parameter,and considers that the period remains the same when the structural strength is reduced,that is,the stiffness of the structure is independent of its strength.When using this method to design the structure,there are two defects:First,the method requires multiple iterations in the design process to achieve structural performance goals.Second,the low-strength(Strength reduction factor Ry is larger)structure designed by this method has unreasonable displacement ductility demands.Therefore,this paper studies a new displacement-based seismic design method,namely the constant yield displacement seismic design method.The method assumes that the yield displacement of the structure is constant and the structural stiffness is related to its strength.Based on this assumption,the average displacement ductility spectrum between structural ductility demand and yield displacement is studied,and the correlation between structural ductility demand and its strength is established.A seismic design method of constant yield displacement is proposed.Compared with the traditional method,the method can more realistically determine the displacement ductility demand value with the expected strength structure,and more accurately calculate the strength value required to meet the specific performance target.The main research work of this paper is as follows:(1)Research on stability of structural yield displacement and seismic design method of constant yield displacement..Pushover analysis of cantilever beam and plane steel frame by Sap2000 is carried out,and the yield displacement of cantilever beam members with different dimensions is calculated.The stability of yield displacement values of plane steel frames with different strengths,different spans and different heights is analyzed;(2)Dynamic Response Analysis of Single Degree of Freedom Structure Based on Constant Yield Displacement.Two inelastic SDOF structures are designed by the constant-period method and the constant yield displacement method respectively,and the displacement ductility demand values of the two structures(Ry takes 2,3,4 respectively)under the same Ricker pulse are solved by Matlab;(3)Study on Displacement Ductility Spectrum of SDOF Structure.120 seismic waves and a series of SDOF structures with different yield displacement values were selected,and then the nonlinear dynamic analysis of the structure was performed using Sap2000 to obtain the displacement ductility spectrum;The effects of strength reduction factor,site category and post-yield stiffness coefficient on displacement ductility are discussed.The fitting formula R*-?-uy,s for nonlinear seismic design and the fitting formula ?-R*-uy,s for displacement ductility prediction are given;(4)Seismic design of multi-layer steel frame structure based on constant yield displacement.A 6-story steel frame structure was designed by the constant yield displacement seismic design method,and the structure was evaluated and analyzed to verify the feasibility and rationality of the method.Research indicates:The structural yield displacement is independent of the strength and span,and has a stable relationship with the height of the structure.In the design process,it is more reasonable to use the yield displacement as the basic design parameter;When Ry is large,the displacement ductility demand value of the inelastic structure by the constant-period method is very large and unreasonable.In contrast,the result of the structure by the constant yield displacement method is reasonable;The displacement ductility value calculated by?-R*-uy,s relation in this paper is not much different from that obtained by Sap2000 analysis.Therefore,it is feasible to calculate the structural displacement ductility demand value by using ?-R*-uy,s relation;The design process of the constant yield displacement method is simple and easy to implement,without any multiple iterations,and the structure designed by this method can effectively control the top peak displacement and the maximum interstory lateral drift ratio.