Aseismatic Performance Of Concentrically Buckling-restrained Braced Steel Frames With PEC Composite Columns

It is well known that the lateral stiffness of the Moment Resisting Frames(MRFs)is poor and the lateral displacement under earthquake is hard to meet the requirements.The concentrically braced frames(CBFs)have higher lateral stiffness under elastic condition,which makes the frame have better seismic performance under small earthquake.While,the brace is easy to buckle and instability under major earthquake,resulting in stiffness and capacity of energy dissipation decrease sharply.If the concentrically brace is designed without buckling under the action of major earthquake,it will cause the earthquake action is too large and the node connection design is difficult,so that the main structure is increased with the amount of steel and not economical.At the same time,the steel frame column can't provide effective anchorage for the brace due to its own stiffness is not enough,which leads to the damage of the brace under compression,the reduction of the bearing capacity and lateral stiffness of the structure,and even leads to the failure of the connection of beam-column joints and the damage of the steel column due to excessive deformation after being subjected to large vertical load and horizontal load from brace.Therefore,the partially encased composite columns are introduced to replace the common steel columns of the frame,and the braces are effectively anchored by the PEC columns,which have the characteristics of high bearing capacity and lateral stiffness.At the same time,the PEC columns ensure the full play of the role of the brace,and the advantages of filling concrete in panel zone are used to relieve the stress of the panel zone and improve the mechanical properties of the structure.In addition,the buckling-restrained braces(BRBs)are introduced to replace common braces to solve the problem that brace yield and increase the earthquake action seriously under major earthquake,finally,a new structure system of the concentrically buckling-restrained braced steel frame with PEC columns is formed.In order to study the seismic performance of the structure system,the numerical simulation and experimental study of 11 model structures and 3 model specimens of 1/4 scale under the unidirectional load and cyclic load respectively were carried out by using finite element analysis and experimental research methods.The stress distribution,deformation,load-displacement curve and hysteretic curve of the specimens were obtained and the mechanical properties of the specimens,such as bearing capacity,initial stiffness,energy dissipation performance,ductility and failure mode were analyzed.The main factors affecting the mechanical properties and seismic performance of the structure were investigated by controlling the parameter variables.Combined with the results of finite element numerical simulation and experimental analysis,the following research is carried out:1)The finite element model of the concentrically buckling-restrained braced steel frame with PEC columns is established.The mechanical properties of the specimens under unidirectional loading,such as bearing capacity,initial stiffness and ductility,are discussed under the influence of concrete grade of PEC column,section aspect ratio,width-thickness ratio of the flange and brace core pipe area.It is found that concentrically buckling-restrained braced steel frame with PEC columns has higher bearing capacity,lateral stiffness and ductility.2)The numerical simulation of the finite element model under cyclic loading is carried out.The main factors affecting the seismic performance of the concentrically bucklingrestrained braced steel frame with PEC column are studied.The rules that the section aspect ratio of PEC columns section and the area of supporting core tube affect the seismic performance of the structure are obtained.3)The hysteretic curves,skeleton curves,stiffness degradation curves,stress distribution and deformation of the three concentrically buckling-restrained braced steel frame with PEC columns under cyclic loading were obtained.It is found that concentrically buckling-restrained braced steel frame with PEC columns have full hysteretic curves,stable hysteretic performance and good seismic performance.4)Comparing the experimental results with the numerical simulation results,it is found that the hysteresis curves are similar.The development trend of stress distribution and deformation of the test specimen is also consistent with the results of finite element simulation,both of them have reasonable yield mechanism and the same failure mode.