| In recent years,large span,high rise,heavy load has become a development direction of modern engineering structure.Composite structure has been widely used in engineering owning to its good adaptability to the development needs.As a new type of composite column,steel tube filled with steel-reinforced concrete tubular has broad development prospects due to its excellent bearing capacity and seismic performance.In the process of normal working,the structure will inevitably suffer from accidental loads,such as impact etc..To ensure the safety of the structure in its whole service life,it is essential to consider the effect of impact load on the structure.The previous research on steel tube filled with steel-reinforced concrete members is mainly focused on the mechanical properties under static load and seismic performance,while the research on the impact resistance of the components is still needs to be further studied.In this paper,the study on impact resistance of square steel tube filled with cross steel-reinforced concrete columns is carried out and the main research work is as follows:（1）The test of seven square steel tube filled with cross steel-reinforced concrete columns under lateral impact were carried out on the extra-heavy drop-test machine in Taiyuan University of Technology,taking impact velocity,wall thickness of steel tube and boundary condition as test parameters,in which the process of deformation development,final failure mode,impact force time curve,deformation time curve and axial compression time curve are obtained.The results show that square steel tube filled with cross steel-reinforced concrete columns performance a good impact resistance,and the square steel tube can provide significant protection for members.Among the influencing factors,the impact resistance columns can be effectively improved by increasing the wall thickness and adopting fixed-fixed boundary condition.（2）The refined numerical models of square steel tube filled with cross steel-reinforced concrete columns are established using the nonlinear finite element software ABAQUS,in which the strain rate effect of steel and concrete,the plastic damage of concrete and contact relationship between the different parts are considered.The influence of axial force is considered by combining method implicit analysis and explicit analysis.Then,the reliability of the modeling method is verified by the test data in this paper and other classic test results.（3）Based on the verified numerical model,the working mechanism of square steel tube filled with cross steel-reinforced concrete columns under lateral impact is analyzed,and the whole process of impact,deformation form,energy dissipation,interaction between steel and concrete as well as energy dissipation are deeply studied.The results show that slide bending deformation occurs during the impact process,and the external square steel tube is the main energy dissipation mechanism of the square steel tube filled with cross steel-reinforced concrete columns.The interaction between steel and concrete is mainly concentrated in the corner of steel tube and reinforced steel.When the axial compression ratio is 0.3,the axial compression has an adverse effect on the impact resistance of columns.With the increase of impact energy,the residual bearing capacity of the composite columns decreases.（4）A systemic study on the parameters which affect the mechanical properties of square steel tube filled with cross steel-reinforced concrete columns under lateral impact is carried out from four aspects of load parameters,material parameters,geometric parameters and boundary condition.The results show that the impact resistance of the members can be significantly improved by adopting the boundary conditions of fixed support at both ends and increasing the steel ratio;the impact resistance can also be improved by increasing the steel embedded index,whose effect is not as obvious as increasing the steel ratio;The dynamic responses of the members at different impact positions are different,and the middle of the span is the weakest part of the members;The impact velocity and impact mass have significant effects on the dynamic response of concrete-filled square steel tubular members with cross steel ribs.The material strength has a certain influence on the impact resistance of components,and the yield strength of steel tube has the most obvious influence... |
