Restoring Force Model Of Concrete-Filled Stainless Steel Tubular Members

Concrete-filled stainless steel tube(CFSST),which is formed by filling a stainless steel tube with concrete,is a new kind of composite member.As CFSST has the advantages of both traditional concrete-filled steel tube(CFST)and stainless steel,it has a broad application prospect in engineering structures with high durability requirements,such as coastal and offshore buildings,offshore platforms,cross-sea bridges,etc.Scholars at home and abroad have done a lot of research on the static performance and design method of CFSST members;however,the research on the seismic behavior of CFSST members is not deep enough.In order to ensure the safety of engineering structures with CFSST in earthquake zone,it is necessary to systematically study the hysteretic behavior of CFSST members and put forward their restoring force model,which can provide the basis for seismic analysis and design of CFSST structures.Based on the established nonlinear finite element(FE)model,an in-depth study on the hysteretic performance and restoring force model of CFSST members is conducted.The main research work in this paper focuses on the following aspects:(1)Based on the determination of the parameters for the combined hardening model of stainless steel and carbon steel,together with the plastic damage model and the characterization method for crack surface effect of core concrete,the finite element(FE)model for simulating the behavior of CFSST members subject to cyclic loads was established by using the general software ABAQUS.The simulated hysteretic behavior using the FE model is in good agreement with the experimental results of CFSST members,concrete-filled outer stainless steel tube/inner carbon steel tube superposed members and concrete-filled double-skin stainless steel tube members,which verifies the accuracy and effectiveness of the FE model.(2)The verified FE model is utilized to comprehensively investigate the effect of cross-sectional steel ratio(as),yield strength of stainless steel(σ0.2),cubic compressive strength of concrete(fcu),axial compression ratio(n)and slenderness ratio(λ)on the moment(M)versus curvature(Φ)and horizontal load(P)versus horizontal displacement(Δ)skeleton curves.(3)Considering the influence of various parameters on the M-Φ and P-Δ skeleton curves and loading/unloading paths,the restoring force model for the CFSST members is put forward.The calculated results of the restoring force model are generally in good agreement with the experimental and FE simulation results,and thus the restoring force model suggested in this paper can be used for reference in the analysis of the elastoplastic seismic response of the CFSST structures.