Research Of Dynamic Response And Damage Assessment Of Concrete Filled Steel Tube Columns Under Impacting

Concrete Filled Steel Tube(CFST)is a new composite structure composed of core concrete poured inside the steel pipe.The interaction between the steel pipe and concrete is not only complementary to each other's shortcomings.Moreover,they have maximized their respective superior performance.In addition,the high bearing capacity,good plasticity and toughness,convenient construction,superior seismic performance and obvious economic effects make the concrete filled steel tube more and more important in engineering applications.Although the concrete-filled steel tube structure has achieved great results,there are still many problems during the service.Like the other engineering materials,the concrete-filled steel tube can not be affected by accidental impacts during the in-service process.For example,natural disasters such as hurricanes damage the building.The ship crashed,the impact of the explosion on the building structure,and the collision of the car with the structure.With the increasing use of concrete filled steel tubes,the safe design of concrete filled steel tube members is necessary.The research on the mechanical properties of CFST members under lateral impact has become more mature.However,the research on the residual bearing capacity of the members after impact and the overall damage assessment methods need to be improved.So in this paper,theoretical analysis,numerical simulation and experimental verification are combined to evaluate the dynamic response of concrete-filled steel tubular columns under lateral impact loads,the residual bearing capacity of specimens subjected to impact and the damage degree after impact damage.Aspects have been studied.The main contents include the following aspects:(1)The mechanical model of the concrete-filled steel tubular column is analyzed,and the ultimate bearing capacity formula and bending strength of the concrete filled circular steel tubular specimen are obtained.The theoretical value of the ultimate bearing capacity of the specimen is calculated.The damage of the concrete-filled steel tubular column is proposed.The evaluation method is carried out,and the damage degree of the test piece is analyzed by a failure criterion based on the vertical residual bearing capacity of the structural column,and the evaluation method of the damage of the test piece is determined.(2)The lateral impact test was carried out on four concrete-filled circular steel tubular columns with fixed constraints on both ends by a drop hammer tester.By changing the height of the drop hammer,the specimen undergoes three stages of damage,such as elasticity,elastoplasticity and plasticity,and obtains the impact time history curve of the hammer head,the deformation of the mid-span position and the strain time-history curve of the steel pipe surface.Through the comparative analysis of the data,it is concluded that the concrete-filled steel tubular column has good plasticity and impact resistance.(3)The finite element solid model of CFST columns was established by LS-DYNA finite element simulation software,and compared with the drop hammer impact test data to verify the correctness of the finite element model and the degree of agreement with the data analysis.Through the analysis and comparison of the impact time of the hammer head,the deformation of the mid-span position and the damage form of the test piece.The results show that the LS-DYNA finite element simulation software can simulate the dynamic performance of concrete-filled steel tubular columns under impact loading.(4)The vertical axial compression test was carried out on one intact test piece and four concrete-filled steel tubular columns with different degrees of damage.The results of the ultimate residual bearing capacity of each test piece measured by the vertical axial compression test were compared with the theoretical calculation results.The feasibility of the theoretical calculation formula is analyzed,and the bearing capacity loss of the specimen after impact load is analyzed,and the damage degree of all specimens after impact is evaluated.