A Preliminary Study On The Mechanical Properties Of Hollowed Box Concrete-encased CFST Columns Under Impact And Explosion Loads

Hollow box concrete-encased CFST columns(hereinafter referred to as box composite columns)have the advantages of light weight,high bearing capacity,good ductility and strong fire resistance,and in the large span and vertical loadbearing structure of(super)high-rise buildings are the most widely used.However,during its operation,there will inevitably be strong dynamic loads such as earthquakes,explosions and shocks,the structure once damaged,it will cause significant casualties and property damage.At present,the research on box composite components is mainly focused on static,fire resistance and earthquake resistance,and the research on impact resistance is relatively lagging.Therefore,in this paper,the mechanical properties of the box composite components under the impact and explosion load are studied.The main contents are as follows:(1)The lateral impact test of box composite columns was carried out on a self-developed drop hammer test machine.The influence of boundary conditions,impact height and axial compression ratio on impact time history,mid span displacement,embedded concrete filled steel tube strain time history and failure mode were mainly studied.Experimental results show that the box composite columns under impact load failure belong to the elastoplastic damage;with the increase of impact height,the time history curve of impact force is developed from two stages into three stages,the failure modes of the specimens showed damage of reinforced concrete deformation increases,external damage is serious,but no internal concrete filled steel tube local deformation;with the change of boundary condition,the impact performance of specimens with fixed ends is better than that supported simply at both ends;and the axial force applied is not significantly affected to the dynamic response.(2)Based on ANSYS/LS-DYNA software,a finite element model of a box composite column with two fixed ends under impact load and simply supported ends is established,respectively.By comparing with the experimental results,the calculated results of finite element models are in good agreement with the experimental results.(3)On the basis of validating the reliability of the finite element model,the force mechanism and the function of the encased concrete filled steel tube are mainly analyzed,and the internal energy distribution of each component of the test piece is also analyzed.In addition to the influence of some parameters of box columns under impact load mechanics performance were analyzed,The results show that similar to the other composite structures,the impact velocity has the greatest impact on the impact resistance of the box composite columns;for different points,the change of the single material has a weak impact on the impact performance,but the impact effect is obvious after the superposition of the concrete filled steel tube.(4)Based on the finite element software LS-DYNA,the finite element analysis model of the concrete filled steel tube column under the explosive load is established,and the reliability of the model is verified by the related literature.On this basis,the influence of explosive load on the surface pressure distribution of box composite columns,the internal energy distribution of each component and the yield strength of the main material under the explosion load are studied.