Test Research And Numerical Simulation Of Steel Column Impacted By Drop Hammer At High Temperature

In recent years,steel structures have been widely used in civil engineering due to their advantages such as light weight,high strength and good seismic performance,which has also promoted the development of related academic theories.During the design service life,important or densely populated buildings should have ability to resist accidental loads in addition to conventional design loads.After 9/11,research on fire and impact resistance of steel structure has become a hot spot.As the main bearing member,steel column’s ability to resist fire and impact must be fully considered.In this paper,the response behavior of restrained steel column subjected to transverse impact under fire environment is studied.Main contents are as follows:(1)The transverse impact test of the steel column subjected to drop hammer at high temperature was designed and carried out and axial force changes during impact process under different axial forces-temperature combinations were recorded.Also,cross-middle deflection and lateral displacement were measured.It is found that out-of-plane bending-torsional deformation will occur,and it will be aggravated by heating up or increasing axial force.(2)Using the general finite element software ANSYS and the explicit nonlinear dynamic analysis software LS-DYNA,specimens of the experimental conditions are simulated and validity of the model is verified.The constitutive model,thermal-structural coupling analysis and implicit-explicit joint analysis processes used in the modeling process provide references for other scholars to carry out relevant researches.(3)Based on finite element software,a large number of parameters are analyzed and the influences of boundary conditions,drop hammer and temperature are investigated.Relationship formula between axial constrained stiffness and critical buckling temperature of steel column is deduced,and it is found that the same axial compression ratio has different influence on deflection of steel column when it is impacted at different temperature where column is more sensitive to axial pressure ratio at high temperature.Temperature has a significant effect on torsion of steel column which is easy to bend and twist out of plane at high temperature.Friction has obvious effect on out-of-plane torsion of steel column under impact of drop hammer.On the premise of the same kinetic energy of the drop hammer,low-speed and high-mass hammer has a greater influence on the dynamic response of the components.(4)Based on the important background of structural progressive collapse and robustness analysis,this paper studies the response of restrained steel column subjected to fire and subsequent vehicle impact.Through nonlinear finite element analysis,residual load bearing capacity of columns is evaluated under several typical ideal constraints,and the elastic constraint effect at the end is discussed.Results show that the residual load bearing capacity of steel columns is closely related to temperature,impact velocity and boundary conditions.Temperature effect originates from the degradation of material’s mechanical properties,while the thermal expansion has less influence on residual load bearing capacity.Residual load bearing capacity of steel column decreases with the increase of vehicle impact speed,and they’re not a monotonic linear relationship for deformation pattern transforming.Rotational constraint of column base can greatly increase the residual load bearing capacity and it can be regarded as rigid connection when rotational stiffness reaches a certain value.The European Code for the regulation of key elements under accidental loads only considers some of the conditions and the scope of its coverage decreases with the reduction of constraint.