Dynamic Behaviors Of Concrete Filled Thin-walled Steel Tubular Composite Columns

Concrete filled thin-walled steel tubular composite(CFTSTC)columns can be used in bridges and high-rise buildings due to its excellent features,such as high strength,excel lent performances of seismic resistance,good fire resistant and fast construction speed.But the current research is mainly focused on static behavior,there are few reports on the dynamic behaviors of CFTWSTC beam-columns.Dynamic behaviors of CFTWSTC beam-columns subjected to cyclic loading were investigated in this paper.The following studies were carried out:(1)For laying the foundation for the subject,the author reviews the relevant referencesfirstly.(2)In this paper,the dynamic experiments of fifteen beam-columns are carried out,including six concrete-filled double-tubular thin-walled steel tubular(CFDTTST)beam-columns,six concrete-filled double-skin thin-walled steel tubular(CFDSTST)beam-columns and three concrete-filled thin-walled steel tubular(CFTST)beam-columns.The effects of axial load level,cross sectional shape,and diameter-to-width ratio on the failure mode,rigidity degeneration,strength,energy-absorbing capacity and ductility of CFTWSTC beam-columns were primarily researched.Researchs show that the specimens mainly failed by local buckling of the steel tube,concrete crushing and steel fracture.The axial load level has a great influence on the performance of beam-columns.With the increasing of the axial load level,the ductility and energy dissipation capacity decrease gradually.The order of energy dissipation capacity from high to low is:CFDTTST beam-columns,CFDSTST beam-columns,CFTST beam-columns.(3)The finite element(FE)soft ABAQUS was used to numerically modeling beam-columns.The simulation results are consistent with the experimental results.Based on this FE model,the mechanism analysis was conducted,including the longitudinal stress distribution of different components and the contact stress between the steel tube and concrete.The constraining of steel tube is mainly concentrated in the corner.Therefore,the concrete strength at the corner of the column has been improved significantly.(4)Parametric analysis for envelope curves of dynamic curves was conducted by using the FE model.The main parameters include the material strength,width-to-thickness ratio,diameter-to-width ratio,diameter-to-thickness ratio,axial load ratio and slenderness ratio.It is found that the bearing capacity becomes larger with the increase of concrete strength and steel tube strength.With the increase of the slenderness ratio,the bearing capacity decreases.With the increase of axial load ratio,the ductility is significantly reduces.For the CFDTTST and CFDSTS beam-columns,the bearing capacity decreases with the increase of diameter-to-thickness ratio.(5)Based on the mechanical and parametric analysis,the simplified models were proposed to predict envelope curves of three types of beam-columns.Meanwhile,simplified models of the dynamic curve for three types of beam-columns were also provided.