Design Method For Columns In RC Frames With Buckling-restrained Braces

RC frames with buckling-restrained braces(RC-BRBF)is one kind of assembly system which has been widely used because of its excellent seismic performance.Previous studies have more focused on considering the improvements given to RC frames,rather than the negative impact on RC columns induced by buckling-restrained braces(BRBs)such as additional axial forces.However,since axial load level has significant influence on the lateral deformation capacity of RC columns,the rationality of the axial compression ratio factor should be discussed.The major contents of the present thesis are listed as follows:(1)Investigates the lateral loading pattern and axial loading condition of RC columns under varying axial load through elastic-plastic time-history analysis.Besides,investigates the effect of proportionally and non-proportionally fluctuating axial load on the seismic behavior of RC columns through numerical simulation.It is shown that for RC columns in conjunction with BRBs,the axial loading patterns are non-proportional(‘out of phase' or ‘different frequency')to the lateral forces.Numerical evidence revealed that ‘in phase' loading path decreased the lateral drift capacity,however,increasing the frequency of the axial load cycles with respect to one cycle of lateral displacement had almost little impact on it.(2)Investigates the lateral deformability for columns under different seismic grade.Besides,through the analysis of global deformation of RC frames,recommended ductility factor for RC columns based on structural ductility capacity was investigated.The calculation results present the ultimate drift capacity which should be reached according to the limitation of axial compression ratio factor.In order to analyze the rationality of axial compression ratio,the ductility factor for RC columns should be checked.(3)An improved design procedure for RC columns in conjunction with BRBs in RC-BRBF is developed.This method was developed for columns under variable axial loading utilizing the limit value of axial compression ratio,which is based on ultimate drift capacilty as expressed by equivalent axial compression ratio,and the ratio of nominal axial value under the equivalent of gravity and seismic action.The analysis results revealed that optimal RC column section dimensions were obtained by the proposed method and the RC-BRBF met the requirements of Chinese seismic design of buildings.Besides,the limit value could effectively account for the influence of variable axial loads on RC columns.