Study On The Dynamic Response And Damage Failure Of Concrete Filled Steel Tube Under Lateral Impact

CFST with high loading-carrying capacity,good toughness and convenient construction etc are used widely in engineering and technology in recently, which subject to accident impact load possibly in the process of usage.Impact load are characterized by short duration and high intensity.The deformation and motion of structures subject to impact load is extremely rapid,hence the inertia must be considered in the dynamic response analysis.So the dynamic response and failure of CFST is differ from the static ones,it has many difference regular and characteristics.But few studies on dynamic response and damage failure of CFST under impact has been made so far because of coupling many effect, which make the problem get much complex and difficult.The dynamic response and damage failure of CFST beam and column under lateral impact are studied systemically in this paper.The important results are summarized in the following several aspects:1,The static bending experiment of CFST with three different kinds of thickness of steel tube and different boundary conditions were completed on the 50 ton electro-hydraulic servo tension tester.The relationship curves of load and deflection of mid-span were recorded.The platform in a majority of curves show that the CFST's toughness is good.The failure is normal section bending failure. Based on this failure character,a calculate expressions of plastic limit moment for cross section were given,and this expressions can be used in the dynamic response analyses for CFST.2,The lateral impact experiments of CFST beams with different thickness of steel tube and boundary conditions were accomplished on the DHR9401 drop hammer impact tester firstly.The hammers' mass are 229.8kg and 203.5kg and the top impact velocity is 14m/s.The failure modes of the buckling of steel tube at impact location and fixed boundary,the plat of mid-span cross section, integral bending deformation and crack of steel tube and concrete were observed. The time history curves of impact load were divided into three phases:loading,platform and unloading.The duration of loading is about 15ms-30ms,and it will be longer with increase of impact energy.The duration of unloading is decided by crack state of steel tube.The effect of boundary conditions on critical impact energy is obvious.The critical impact energy under simply support and simply-fixed boundary condition is about 40%and 75%of it under fixed-fixed boundary condition respectively.3,In order to observe anti-impact capability of CFST column,lateral impact experiment were accomplished by a experimental tester made by ourselves loading axial load with disc springs.The time history curves of axial load and impact load were recorded,the effect of axial load on mid-span deflection was achieved.The top loss amount of axial load during lateral impact is 20%of initial load quantity.The time history curves of impact force have not platform phases because of the coupling effect of axial load and lateral impact.4,The simulation analyses were achieved by use of LS-DYNA considering constitutive relationship of concrete in triaxial stress state.The results of simulation are consistent with the results of experiments.Simulation results show that the strain rates effect of steel is unobvious,the concrete stress state at the mid- span cross section are in high press state during loading phase,the concrete stress stayed around the value of the compressive strength of concrete under unaxial tension state in the long platform phase,and the crack state of steel tube depend on the ultimate tensile strain of steel.The anti-impact capability of CFST column is increased when axial compressive force is less than 0.3N₀,the anti-impact capability of CFST column will decrease obviously when the axial load is greater than 0.3N₀,the stability of specimens is lose when the axial load is 0.3N₀ under critical impact energy.5,The dynamic response of CFST were theoretically analyzed using rigid-plastic model and plastic limit moment proposed in this paper considering the simplified yield function of the coupling effect of axial load and lateral impact.The results of calculation are identical in the results of experiments.6,E_cr=6.46+1.21ζ+0.39ζ² between critical impact energy and casing hoop steel coefficient of cross section under simply support,E_cr=3.93+8.68ζ-0.65ζ² under simplified-fixed boundary condition and E_cr=5.26+11.62ζ-0.87ζ² under fixed-fixed boundary condition are given.The influence of yield strength of steel tube on critical impact energy is greater than that of steel ratio in cross section.