Research On Seismic Performance Of Eccentrically Braced Steel Frame Applied 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 keepsatisfactoryhysteretic behaviorafter the plastic state,dissipating a great deal of energy during the elastic-plastic hysteresis deformation.When earthquake hits,energy-dissipating components made of LYP steel will yield and enter plastic stateearlier than any other components,absorbing seismic energy by hysteretic behaviors,which keeps main body structure and main bearing components away from heavy damage.Eccentrically braced steel frame is equipped with the advantage of concentrically braced steel frame and unbraced steel frame both.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,theexcellentductility of eccentrically braced steel frame keeps structure away from collapse.Eccentrically braced steel framedissipates a great deal of seismic energy by the shear yielding or bending yieldof link beam.Only link beam yield,when rare earthquake hits the eccentrically braced steel frame.As the characteristics of LYP steel can meet the requirement of the link beam in eccentrically braced steel frame well,so link beam made of LYP steel should be workable and worth studying.Eccentrically braced steel frameapplied withLYP link beam is characterized byexcellent seismic performance and possesses very broad prospect in engineering practice.In this paper,seismic performance of eccentrically braced steel frameapplied with LYP link beam is systematically studied.The main studying works and conclusion are as follows:(1)Expressions for axial force of brace and shear of link beam in K-type eccentrically braced steel frame(KEBF)under lateral force is proposedbased on the structural mechanics.The lateral displacement of KEBF could be split into 4 parts as follows: lateral displacement from the axial deformation of brace;lateral displacement from the axial deformation of girde;lateral displacement from the shear deformation of link beam;lateral displacement from the bending deformation of link beam.Elastic lateral rigidity of KEBF is proposed based on the small deformation assumption and Hooke’s law.And,approximatecalculation formula of axial force in brace is proposed based on the internal force analysis of brace.(2)Seismic design method of KEBF based on yield mechanism and energy method is studied,which is according to the reasonableoverallfailure mode,inter-storey shear distribution state and base shear of KEBF.The design and calculation of components in KEBF are proposed based on this seismic design method.(3)Finite element models of KEBF is established by ANSYS,and these models are analyzed by monotonic loading and cyclic loading.The influence of 5 different parameters on the seismic performance for eccentrically braced steel frameapplied withLYP link beam is studied systematically.The 5 parameters are as follows: length of LYP link beam;web thickness of LYP link beam;flange thickness of LYP link beam;stiffener thickness of LYP link beam;stiffener spacingof LYP link beam.Some suggestion about the design of eccentrically braced steel frame applied with LYP link beam is put forwardconcerning the analysis result.(4)The shear plastic hinge is studied combined withcorrelated studies both at home and abroad.The correction coefficients of load-displacement relationship for shear plastic hinge in SAP2000 are put forward.The setting and calculation of plastic hinge in girder,column and brace is analyzedaccording tocorrelated codes both at home and abroad.(5)Steel frame(SF),K-type eccentrically braced steel frame(KEBF)and K-type eccentrically braced steel frameapplied with LYP link beam(LKEBF)are designed based on the same design overview and seismic force.To study the seismic performance of these three structures,Pushover analysis under uniform load and inverted triangle load is analyzed.The analysis result shows that,when rare earthquake hits LKEBF,LYP link beams could yield and other components in the LKEBF keep elastic state at the same time,meanwhile,LYP link beamsfully develop their actions on energy dissipation.In addition,the seismic performance of LKEBF is better,because the inter-storey displacement of LKEBF is smaller than SF and KEBF when rare earthquake hits.