Seismic Performance Of Multi-story And High-Rise Y-Shaped Eccentrically Braced Frames Fabricated With High-Strength Steel

Eccentrically braced frames fabricated with high-strength steel(HSS-EBFs)have the advantages of both high-strength steel(HSS)(e.g.high strength,resource saving)and eccentrically braced frames(EBFs)(e.g.good energy dissipation).HSS-EBFs can incorporate high-strength steel for beams and columns,and conventional steel with medium yield strength for links.Under earthquake loads,the column and beam members of HSS-EBFs are designed to remain in the elastic stage or show slight plasticity while the links enter the plastic stage completely.The beam–column frame can be considered to be a reserve defence for earthquake resistance.The link and brace members can be arranged in an inverse Y shape,with the link perpendicular to the beam.This arrangement allows the length and section designs of the links are flexible enough to meet the required strength without requiring the uniform cross-section of the beam members.This arrangement also allows links damaged after a massive earthquake to be changed easily,with minimum impact to beams.The research on seismic performance of Yshaped HSS-EBFs(Y-HSS-EBFs)would help increase the usage of HSS in seismic areas.The main research work and conclusions of this dissertation are as the followings:(1)One half-scale three-storey one-bay by one-bay building with Y-HSS-EBFs was subjected cyclic reversed triangular lateral load to examine the seismic performance.The bearing capacity,stiffness degradation,ductility,energy dissipation capacity,rotation capacity of links and the structural failure process of the Y-HSS-EBFs were investigated.The research result shows that the Y-HSS-EBF structure has good load-carrying capacity,ductility capacity and energy dissipation capacity.The links fabricated with conventional steel with medium yield strength entered plastic stage firstly,and dissipate a lot of energy,while the non-designated yield members fabricated with high strength steel remain in elastic stage,to insure the structural integrity.(2)Based on rationality finite element model(FEM)validation,the refined FEMs of the 3-storey structure prototype of the specimen and 10-storey and 15-storey Y-HSS-EBFs were established.A series FEMs of Y-HSS-EBFs were designed with different link length.By comparing the mechanical properties of the models under cyclic reversed triangular lateral load,the reasonable value range of the link length were suggested,and the values are between 0.9M_P/V_P and 1.2M_P/V_P.By defining different web height-width ratio and flange width-thickness ratio,considering the influence of the link length at the same time,different series parameter models were designed.The limited values of web height-width ratio and flange width-thickness ratio were suggested,by comparing the cyclic behaviour of the parameter models.The web height-width ratio should be restricted by no more than72 235/f_y and flange width-thickness ratio should be restricted by no more than13 235/fy.(3)A simplified model of Y-HSS-EBFs was established.Shell elements(S4R)were used for links and the floor deck,and beam elements(B31)were used for beam,column,and brace members.It is verified that the simplified model is effective and applicable by the comparison of stiffness,strength,plastic development,the failure model and ductility of the specimen between the test results and the finite element model results.The research provides a basis for the following investigation,and the simplified model is simply and easy for practical use.(4)Based on the reasonable value range of link length and link section,10-storey,15-storey and 20-storey Y-HSS-EBFs global structures were established using the simplified model.The global structures models were subjected cyclic reversed triangular lateral load to examine the cyclic behaviour.The story shear distribution of each frame in Y-HSS-EBF structures in elastic stage,noticeable yield stage,plastic stage were obtained.The share of the beam–column frames story shear in the whole base shear at elastic stage,noticeable yield stage,plastic stage were analysed.Comparative studies show that there are important differences between the story shear distribution in elastic phase and elastic-plastic phase.The structural design could not simply use the elastic design method,and the elastic-plastic behaviour of the structure cannot be ignored.