Study On Performance Of Circular Concrete-filled Steel Tubular (CFST) Members Under Low Velocity Transverse Impact

Concrete-filled steel tubular (CFST) structure has been widely used inhigh-rise buildings and bridge piers for its good performance under static andseismic loading. Structures might be crashed by vehicles or vessels and impactloads may bring permanent deformation to structural members or even destroythem, and hence should be considered in structural design. This research is tostudy the performance of CFST beams and columns under transverse impactloads. The main contents are as follows.Firstly, experimental work of CFST beams under transverse impact loadwas done with the drop hammer rig. The main parameters of the specimensinclude the impact height, the mass of the drop hammer and the boundarycondition. Hollow steel tubes were also tested under the same condition. Failuremodes, impact force curves, mid-span deflection curves and strain curves wererecorded in the tests. The test results showed that CFST beams have ductilefailure modes and good impact resistance.Then a finite element analysis (FEA) model was established to predict theimpact behaviour of CFST members, in which the strain rate effects of thematerials and the contact behaviour of different parts of the model wereconsidered. The effect of axial load and crack of steel tube were also simulatedin the FEA model. Test data from the author and other researchers were used toverify the accuracy of the FEA model and general good results were achieved.Thirdly, the FEA model were used to study the mechanical behaviour ofCFST members under transverse impact load, which includes the failure mode,impact force, stress and strain development, section moment and the energydissipation capacity. The influences of axial load level on the impact force,deflection, flexural capacity, critical failure energy and remaining resistance ofthe CFST column were also analysed.The influences of main parameters on the impact resistance of CFST beamswere studied, including the yield strength of steel, concrete strength, steel ration,slenderness, impact velocity, impact mass, position of impact and the plasticityof the impact et al. It was shown that the yield strength of steel, steel ration, section diameter and impact velocity are the key parameters that may influencethe dynamic increase factor of the flexural capacity of CFST section underimpact load.Based on the parameter study, a simplified calculation method was drawn onthe dynamic flexural capacity of CFST section which can be used in the designof CFST members under impact loads.