| In recent years,our country's economy has made a rapid development,people's requirements for comfortable and high-quality residences have become increasingly high.Because of the advantages of environment,green and economy,more and more people are in favor of steel,steel frame structure become more and more.With the development of the research in steel frame structure,scholars found the rigidity of the pure steel structure is relatively small,it's not suitable for earthquake prone region and resistance to lateral force system is proposed in concentrically braced steel frame.The applications of K-bracing are strictly limited,the main reason is that the column may fail due to the unbalanced force.Because the external frame does not bear the weight of the main frame,the concept of moment resisting frames with K-type external braces is proposed to reduce the unbalanced force on the column,which has greater lateral stiffness compared with other center support.The layout of internal space can be well solved,and the aesthetic appearance of residential buildings will not be affected.At present,research in K-bracing is relatively little.Therefore,it is necessary to study the performance of K braced steel frame system.To study the lateral resistant performance of the different slenderness ratios(from 50 to 150)of K-type external steel braces,the length of the braces has been kept a constant(2121.3mm).The slenderness ratio is altered by varying the size of the brace section.According to the unbalanced force formula based on the code for seismic design of buildings(GB50011-2010),the performance on 1,1.5,2 times columns,and 0.4,0.6 and 0.8 times columns was studied.Lateral resistance and hysteretic behavior of BRB and common steel brace are analysed.Finally,the static nonlinear analysis is applied to three story,six story and nine story steel frame model.With the above finite element analysis,the results show that the lateral load and displacement curve of the K-bracing can be divided into elastic stage,the buckling of the compressive brace-yield of the tensile brace stage and plastic stage.Tensile brace will not yield or yield before column failure.The overall lateral resistance will decrease rapidly when compressive brace firstly buckles.Plastic hinges always appear at connecting part between K-bracing and column.The K-bracing has hardly overstrength,that is,the lateral buckling capacity is equal to the ultimate bearing capacity,the overall lateral resistance is not very ideal.The slenderness ratio of K-type external steel brace is recommended between 70 and 120(Suitable for low-rise and mid-rise buildings).The column section size is designed between one time unbalance force and two times unbalance force.A new strength reduction and overstrength coefficient formulas of the compressive brace are obtained.The buckling restrained brace can effectively reduce the unbalanced force between the K support and the column,it can also improve its overall lateral bearing capacity.But the cost of buckling restrained brace is relatively high compared with ordinary steel support.By analyzing lateral displacement angle,overstrength coefficient,destructive order and the overall lateral resistance performance of three framework models,K-type external brace steel frame has good seismic performance. |
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