Study On Seismic Performance And Design Method Of Y-type High Strength Steel Composite Eccentrically Braced Frames

In high strength steel composite eccentrically braced frames(HSS-EBFs),links use the stell with low yield point and good ductility(e.g.Q235 steel and Q345 steel),braces use Q345 steel and other structural members use high strength steel.The HSS-EBFs structure disspate the energy through the plastic deformation of links during the earthquake,beams and columns still at elastic stage or slightly entered plastic stage because of using high strength steel.For this approach can result in reduced steel consumption and increased economic efficiency.The HSS-EBFs can improve the popularization and application of high strength steel in seismic region.In order to research seismic performance of HSS-EBFs,this paper conducted the following study work:1)The shake table test of a 1:2 scale three-story Y-type HSS-EBFs(Y-HSS-EBFs)was carried out to research the seismic performance of the structure,which can be applied to seismic design and application in seismic area of Y-HSS-EBFs.The result indicated that the stiffness of the structure degenerated obviously during the rare earthquakes and no collapsing appeared.The maximum interstory drift of the structure during the frequent earthquakes and the maximum interstory drift during the rare earthquakes met the demands of interstory drift limitation in the seismic design code of buildings.Links entered plastic stage while others were stell in elastic stage during rare earthquakes.2)Based on the shake table test of Y-HSS-EBFs,nonlinear time history analyses were conducted to research the influence of link length,link web ratio of height to thickness and ratio of depth to span to inelastic performance of Y-HSS-EBFs.Results indicated that different link length,link web ratio of height to thickness and ratio of depth to span had different influence to the interstory displacement,load-carrying capacity of columns,base shear force and energy dissipation capacity.Some design recommendations were given based on the analyses and providing reference for engineering design.3)The restoring force model of Y-HSS-EBF is established based on the experimental results and theoretical analyses.A two-linear skeleton curve model with stiffness degradation which was defined through yield point and ultimate point was proposed.The formula to calculate the points are recommended through theoretical analyses.And nonlinear simplified seismic response analysis method for Y-HSS-EBFs were studied by using the hysteresis rules of multi-linear plastic Kinematic element in SAP2000.4)In order to investigate the lateral force distribution based on inelastic state of Y-HSS-EBF,several Y-HSS-EBF models with different stories and global yield mechanism were established.Also,the effects of story number,velocity pulse of near-fault motions and acceleration cumulative effect of far-fault motions were considered.Nonlinear time history analyses were conducted to obtain the lateral force distribution of the structures during the rare near-fault and far-fault earthquakes.The formula of lateral force distribution in inelastic state of Y-HSS-EBF was proposed based on equivalent base shear method in design code,and it was compared with other lateral force distribution.Results indicate that near-fault earthquakes with velocity pulse and far-fault earthquakes with acceleration cumulative had different effect to the lateral force distribution of structure,the lateral force distribution proposed in this paper was more accurate than other ones and it can be adopted for the performance-based plastic design(PBPD)method of Y-HSS-EBF.5)Performance-based plastic design(PBPD)method was used to design Y-HSS-EBFs in this paper.Target drift and ideal global failure model are adopted as the key to estimate and control the plastic behavior of the structure.Also the story drifts are uniform along the structural height and avoiding the appearance of weak layer in the structure.One ten-story Y-HSS-EBFs structure was designed based on PBPD method,nonlinear static pushover analysis and nonlinear dynamic analyses were used to study the seismic performance of the ten-story structureand the results indicated that the ten-story Y-HSS-EBFs designed by PBPD method had good seismic performance,and structure damaged followed the ideal failure model at the ultimate state.Also all links appeared plastic deformation to dissipate the energy and story drifts distributed uniformly along the structural height.