Research On Performance-based Seismic Design Method Of The Eccentrically Braced Steel Frame With Low-yield-point Link Beam

It is showed that low-yield-point(LYP)steel is characterized by its stable low yield strength,low yield ratio,high elongation and excellent low cycle fatigue property.LYP steel has strong plastic deformation ability,which makes it keep satisfactory hysteretic behavior after the plastic state,dissipating a great deal of energy during the elastic-plastic hysteresis deformation.Under frequent earthquake,the elastic stiffness of eccentrically braced steel frame is enough high that can meet the limit of inter-storey drift.And,under rare earthquake,the excellent ductility of eccentrically braced steel frame keeps structure away from collapse.Eccentrically braced steel frame dissipates a great deal of seismic energy by the shear yielding or bending yield of link beam,therefore,the safety of frame structure can be effectively protected.In this paper,the eccentrically braced steel frame applied with LYP link beam is studied by referring to relevant literatures.The main results are as follows:(1)Through the tensile test of materials,material constitutive relation of low-yield-point steel and the related mechanical properties can be obtained.By referring to relevant literatures and our research on the seismic performance of the eccentrically braced steel frame applied with LYP link beam,and combined with the reference example of inter-story drift for seismic performance requirement of structural members given in Appendix M of the Seismic Design of Buildings in China,the performance indexes of this eccentrically braced steel frame applied with LYP link beam are quantized based on the larger numbers of model tests.(2)Performance-based seismic design method based on displacement of the eccentrically braced steel frame applied with LYP link beam considering the high vibration mode is given.Firstly,the free vibration of structure is analyzed by SAP2000 software,and the elastic natural vibration period and the corresponding vibration mode value of the first three order vibration modes are obtained.Then,according to the natural vibration period of each mode,the equivalent displacement of single-degree-of-freedom system is derived from the standard acceleration response spectrum,and the elastic displacement of each vibration mode of this structure is derived from the equivalent principle,the displacement curve of the structure is obtained after the combination of vibration modes.So,the target displacement of each vibration mode of this structure is determined by the inter-story drift angle of the structure corresponding to the performance level,and through analysis and calculation,theshear at each story is obtained by mode combination.Finally,performance-based seismic design method based on displacement of the eccentrically braced steel frame applied with LYP link beam considering the high vibration mode is achieved.(3)The shear plastic hinge is studied by combining with the correlated literatures both at home and abroad.The correction coefficients of load-displacement relationship for shear plastic hinge in SAP2000 are put forward.Based on the parametric analysis of the LYP link beam,the LYP link beam is designed.(4)Through the performance-based seismic design method based on displacement of the eccentrically braced steel frame applied with LYP link beam considering the high vibration mode,15-storey eccentrically braced steel frame applied with LYP link beam are designed under four different performance levels and the design process is given in detail.The performance of structure is evaluated by capability spectrum and dynamic time history analysis.Under the performance 1,the structural safety requirements are the highest,and the structures are in elastic phase at three seismic levels.Under the performance 2,the structure is in the elastic stage under the small and middle earthquakes,and the low-yield-point link beam is in the yield stage to consume energy under the large earthquake.Under the performance 3 and 4,the structure is in the elastic stage subjected to the small earthquake,but with the increase of earthquake level,the low-yield-point link beam continues to yield to consume energy under the middle and large earthquakes,while the steel frame is always in the elastic stage.Those show that the low-yield-point link beam provides a good capacity of energy dissipation under the action of earthquake,and the eccentric braced structure with low-yield-point link beam has good seismic performance.