Static And Seismic Performance Of Stirrups-stiffened Rectangle Concrete Filled Double-skin Steel Tube

The concrete-filled double-skin steel tube(CFDST)columns have been widely used in transmission line towers and marine platform support column structures,and have good prospects for application in cross-valley high bridge piers and super high-rise building structures.However,with large hollow ratio,CFDST column has weak restraint on the core concrete,and its axial pressure ratio is limited,so it is necessary to take internal restraint measures to improve the seismic performance of CFDST column.Based on the research of the group,this thesis proposes the structural form of stirrup-confined concrete-filled double-skin steel tube(SCFDST)column so that it can be applied to more complex engineering situations.In this thesis,based on the National Key Research and Development Program special project "Research on the seismic performance and design method of high-rise and large-span composite structure buildings"(2017YFC0703404),the static performance and seismic performance of SCFDST columns are investigated using a combination of experimental research and finite element analysis,and the main contents and results are as follows:(1)A total 8 concrete-filled double-skin normal/stirrup-confined steel tubular stub columns were tested under axial compression,to investigate how stirrup improve the ultimate bearing capacity,stiffness and ductility of CFDST short columns and different hollow ratio and stirrup ratio on axial compression performance.ABAQUS was used to establish the 3D finite element models for the calculation and analysis of 92 stub columns,And a practical formula for calculating the bearing capacity of SCFDST columns which considers the shape constraint coefficient of steel tube and the coefficient of reinforcement improves the constraint effect of steel tube was established.(2)The pure bending experiment of a total 6 SCFDST columns was carried out.Combined with finite element calculation and analysis,the slip,stress and neutral axis change law between core concrete and steel tube were further studied.The effects of stirrup ratio and hollow ratio on the pure bending performance of SCFDST columns due to 240 models are discussed.The formula for calculating pure bending specimen bearing capacity of SCFDST was established which considers the coefficient of section bending,bending stiffness reduction and reinforcement improvement and section bending stiffness.(3)By using ABAQUS,a total of 440 full-scale finite element model of SCFDST columns were established,the interaction relationship among core concrete,steel tube and stirrup was deeply analyzed,the cooperative working mechanism of stirrup,internal and external steel tube and concrete was revealed,and the theoretical problems of constraint and cooperative work calculation and analysis of SCFDST columns were solved.Finally,the calculation formula of the stability coefficient of axially compressed medium-and-long columns was compared and advised,the calculation method of the slenderness ratio of the elastic-plastic instability limit was proposed,and the compression bending bearing capacity formula of SCFDST columns considering the axial compression stability coefficient,compression bending stability coefficient,section shape bending coefficient and reinforcement constraint coefficient and the stiffness formula of concrete stiffness reduction considering the influence of stirrup on axial compressive ratio,concrete cracking and interface slip were established.(4)The hysteresis experiments of 13 SCFDST columns and a total of 60full-scale finite element models were carried out to investigate the influence of stirrup ratio,axial compressive ratio and loading direction on the skeleton curve,elastic stiffness,ultimate bearing capacity,ductility coefficient,hysteresis curve,stiffness degradation,cumulative energy dissipation,plastic energy dissipation and equivalent damping viscosity coefficient of SCFDST columns.The calculation results of finite element parametric analysis reveal the mechanism of plastic energy dissipation and the influence mechanism of stirrup under low circumferential reciprocal loading.