Study On Seismic Behavior Of Short Yield Buckling Restrained Braced Steel Frames

Considering the excellent hysteretic behavior of buckling restrained braces(BRB),BRB are used in many existing or new buildings to replace the bracing members in traditional steel frame structures with central braces,which greatly improves the seismic performance of steel frames.However,some studies have shown that when the buckling restrained braced steel frame encounters rare earthquakes,the residual deformation of the structure is large,which makes it difficult to replace the bracings,or even impossible to replace them at all.This is contrary to the original intention that buckling restrained braces can be used as "fuses" of structures for easy replacement.In this paper,the buckling restrained bracings with short yield section are proposed and the steel frame is studied from the following aspects.(1)The mechanical properties of buckling restrained braces with different length of yield section are calculated and analyzed,including initial axial stiffness,axial stiffness after yield,energy dissipation coefficient,equivalent viscous damping ratio and hysteretic model.(2)The general finite element software ABAQUS is used to meticulously model the buckling restrained brace members,and the initial defects are added to the core plate.The main parameters affecting the support performance are analyzed.The results show that the constraint ratio is sensitive to the change of the length of the yield section,and the amplification factor of the constraint ratio is given when the length of the yield section is reduced.(3)Using OpenSEES software,the time history analysis of short yield section buckling restrained braced steel frame designed by lateral stiffness ratio method under the action of frequent,fortification and rare earthquake is carried out.The results show that all the frames and supports are in the elastic stage under the frequent earthquakes.Under the fortification earthquakes,the frames are still in the elastic stage,and the braces begin to enter the plastic energy consumption state.Under the rare earthquake,all frames and supports are plastic.This is in accordance with the theory of buckling restrained braced steel frame system,which shows the rationality of using this method to design short yield section buckling restrained braced steel frame.(4)The time history analysis of short yield section buckling restrained braced steel frame and common buckling restrained braced steel frame under rare earthquake is completed.Taking the maximum story drift ratio,the residual story drift ratio and the horizontal shear force borne by each member as the index,the seismic performance of short yield section buckling restrained brace and common buckling restrained brace steel frame is compared and analyzed.The results show that the maximum interlaminar displacement angle of the structure can be reduced by about 10% and the residual interlaminar displacement angle of the structure can be reduced by more than 30% by using the short yield buckling restrained brace.While ensuring the safety of the structure,it greatly improves the repairability of the structure after the earthquake and the safety when encountering the second earthquake.And with the increase of the structural stiffness,the additional seismic load is almost borne by the buckling restrained brace,which will not increase the load on the frame.