Research On Mechanical Behavior Of Concrete-filled Double Skin Steel Tube Members Under Combined Compression,Bending And Torsion Loads

Concrete-filled double skin steel tube(CFDST)members are composite members formed by pouring concrete between two concentric steel tubes,and the inner steel tubeouter steel tube and sandwiched concrete jointly bear the loads.CFDST member is a new type of structural member developed from concrete-filled steel tube(CFST)members and centrifugal hollow concrete-filled steel tubular members.Compared with solid concretefilled steel tube members and centrifugal hollow concrete-filled steel tubular members,CFDST members have the advantages of light weight,large stiffness,and difficult spalling of sandwich concrete.At present,the research on the mechanical properties of CFDST members mainly focused on the static performance of CFDST members under axial compression,pure torsion,combined compression and torsion,bending and combined compression and bending.There is little research on the hysteretic performance of concrete-filled double skin steel tube members subjected to pure torsion,compressiontorsion,bending-torsion,and compression-bending-torsion.In this thesis,both experimental research,finite element analysis,and theoretical analysis are used to study the energy dissipation,ductility,and bearing capacity of CFSDT members under cyclic torsion,compression-cyclic torsion,cyclic bending-torsion,and cyclic compressionbending-torsion.The section types of concrete-filled double skin steel tube members are circular section,rectangular section,and square section.The main contents are as follows:(1)Pseudo-static tests of two circular CFDST members,two rectangular CFDST members,and two square CFDST members under pure torsion were carried out,and the parameters include hollow ratio and section type.Based on the experimental results,the hysteretic energy dissipation performance,stiffness degradation,bearing capacity degradation,ductility,and failure mode of circular,rectangular,and square concrete-filled steel double skin steel tubular members under cyclic torque were analyzed.(2)The quasi-static loading tests of four circular CFDST members,four rectangular CFDST members,and four square CFDST members under compression-torsion were carried out,and the parameters include hollow ratio,section types,and axial compression ratio.The stiffness and bearing capacity degradation,energy dissipation performance,and failure mode of CFDST members under compression-torsion were analyzed.(3)Pseudo-static tests of concrete-filled double skin steel tube members with the circular,rectangular,and square section under bending-torsion and compression-bendingtorsion were carried out.Based on the test results,the hysteretic behavior,failure mode,stiffness degradation,and bearing capacity degradation of concrete-filled double skin steel tube members were analyzed.(4)A finite element model of concrete-filled double skin steel tube members subjected to pure torsion was established by using ABAQUS software.The finite element analysis results were in good agreement with the experimental results.Based on the finite element model,the parametric analysis was carried out to investigate the influence of concrete strength,yield strength and steel consumption of inner steel tube,yield strength and steel consumption of outer steel tube and hollow ratio on the torsional bearing capacity of CFDST members with circular section,rectangular section,and square section.Based on the mechanism analysis results,design formulas were proposed to predict the torsional bearing capacity of concrete-filled double skin steel tube members with circular sections,rectangular sections,and square sections.(5)A finite element model of concrete-filled double skin steel tube members subjected to compression and torsion was established by using ABAQUS software.The results of the finite element model were compared with test results.Based on the finite element model,the parametric analysis was carried out to investigate the influence of concrete strength,yield strength and steel consumption of inner steel tube,yield strength and steel consumption of outer steel tube,and hollow ratio on the compression and torsion bearing capacity and correlation of concrete-filled double skin steel tube members with circular sections,rectangular sections,and square sections.Formulas to predict the compression-torsion correlation of concrete-filled double skin steel tube members with circular sections,rectangular sections,and square sections were proposed.The influence of the loading paths on the compression-torsion correlation of CFDST members was investigated.Base on mechanism and stress analysis results,formulas were proposed to calculate the torsion bearing capacity of concrete-filled double skin steel tube members under compression and torsion.(6)Finite element models of concrete-filled double skin steel tube members subjected to bending and torsion or compression,bending and torsion were established by using ABAQUS software.The influence of the loading paths on the bending-torsion correlation of CFDST members was analyzed.Parametric analysis was carried out to investigate the influence of concrete strength,yield strength and steel consumption of inner steel tube,yield strength and steel consumption of outer steel tube,and hollow ratio on the bending and torsion bearing capacity and correlation of concrete-filled double skin steel tube members with circular sections,rectangular sections,and square sections.Formulas are proposed to predict compression,bending and torsion correlation of CFDST members.