Analysis Of Deformation Capacity And Seismic Performance Of Partially Encased Concrete-steel Composite Columns

With the rapid development of steel-concrete composite structures,their application in the field of multi-story buildings is becoming more and more widespread.Partially Encased Composite Structures(PECs)are mainly composed of open-section main steel members such as H-beams and filled concrete,which have the advantages of light self-weight,good seismic performance and easy construction of steel structures and good integrity and durability of concrete structures.In this paper,the theoretical equation of the displacement ductility coefficient of PEC column is derived to provide the theoretical basis for the relevant research.In addition,in view of the problems of excessive deformation and low stiffness and bearing capacity of traditional steel frame structure under the action of large earthquake,the seismic performance of PEC column composite frame structure is studied,and it is verified that the PEC column composite frame structure has superior seismic performance than traditional steel frame structure.The main research contents of this paper are as follows:(1)In this paper,an Abaqus finite element model is established based on the results of the existing PEC column compression-bending tests,and a constrained concrete principal structure model is used to compare the test results with the simulation results to verify their correctness.On this basis,a model is established for the variable parameter analysis of PEC column compression bending influencing factors,and the bending moment-turning angle skeleton curve of the simulation results is extracted considering the P-Δ second-order effect.The results show that: the profile flange width-thickness ratio has a significant effect on the compressive bending load capacity of PEC column in strong axial direction,and the two are negatively correlated;however,when the axial pressure ratio and the profile strength also increase,the effect of the flange width-thickness ratio on the specimen is weakened.The strength of the section steel has a greater influence on the compressive bending capacity in the strong axis direction of the PEC column.The increase of the profile strength will improve the load carrying capacity of the PEC column model,but the corresponding turning angle will be reduced and the ductility will become poor when the peak bending moment is reached.With the increase of axial compression ratio,the degradation rate of PEC column model skeleton curve is accelerated,the descending section becomes steeper,the plastic deformation is serious,and the bearing capacity is accelerated;and when the width-thickness ratio of section flange increases,the influence brought by the change of axial compression ratio will be weakened.(2)Based on the assumption of flat section,the derivation of PEC column section curvature is carried out,and then the theoretical derivation of PEC column displacement ductility coefficient calculation formula is carried out to obtain the PEC column displacement ductility coefficient calculation formula,and the accuracy of the formula proposed in this paper is verified by comparing with the existing test results.The relationship between the axial compression ratio n,section strength fa and shear-to-span ratio λ and displacement ductility coefficient of PEC columns is obtained by analyzing the numerical calculation results of the deformation capacity of PEC column sections.The range of the displacement ductility coefficient of PEC columns under different values of influencing factors is given.Based on the results,it is concluded that the displacement ductility of PEC columns can be improved by strictly controlling the axial compression ratio,the strength of the steel sections and improving the shear-to-span ratio.(3)Pushover static elastoplastic analysis and nonlinear dynamic time analysis and structural vulnerability analysis were carried out for the common steel frame structure and PEC column composite frame structure under actual engineering conditions using the finite element analysis software Open Sees.The results show that the PEC-column composite frame structure has higher bearing capacity and ductility than the conventional steel frame structure,and has better collapse resistance under rare earthquakes,which has a broad prospect for practical application in high seismic areas.