Dynamic Response And Failure Mechanism Of Structural Tubular Steel Members Subjected To Transverse Impact

In recent years,the frequent occurrence of accidents and natural disasters and the increasing number of terrorist attacks represented by "911" have made the research of construction safety a hot topic.In addition to constant load,live load,wind load and temperature load,steel structures are also susceptible to accidental loads such as fire,explosion and aircraft impact.When the accidental load is large,it can destroy the building directly and bring huge economic loss and casualties.In the case of small occasional load,the local damage to the building structure can easily induce progressive collapse.Circular steel tubes have become the most commonly used structural steel section in steel structures such as grids,reticulated shells,tube trusses,and offshore platforms with their excellent mechanical properties and its simple and clear shape.Generally,it is subjected to normal working load and temperature load as axial force components,mostly in axial compression or axial tension.At present,there are few researches on the impact resistance of the circular steel tube,and the relevant regulations abroad are mostly aimed at the offshore platform structure.It can be seen that it is of great academic and engineering significance to carry out the research on the impact resistance of the circular steel tube.Due to the diversity of node forms,the steel tubes have variety of constraints in tubular structures.Moreover,the tubes are mostly in normal working conditions,that is,the tubes suffer from transverse impact when subjected to axial load.Most of the related research work has been based on the offshore platform structure of tubes or oil and gas pipelines as the research object,but there are obvious mechanical differences between them.In view of this,this paper takes the Q235 B circular steel tube of tubular structure as the research object,and has carried out the transverse impact test,the finite element analysis and the theoretical analysis.The specific research contents are as follows.(1)Experimental study of circular steel tubesThrough the large drop hammer impact test system,104 groups of tests were carried out on the transverse impact resistances of circular steel tubes.The test loading device and measuring device for different working conditions were designed,and the dynamic response process of the circular steel pipe is described in detail.The effects of the section size,span,impact energy,impact position,constraint form and axial force were mainly investigated.Finally,the dynamic response and the axial force mechanism of the circular steel tube under the transverse impact were obtained.(2)Study of finite element modeling method of transverse impact of steel tubesBased on ANSYS/LS-DYNA,the finite element analysis technology of steel tube under lateral impact load was studied.By conducting the material test,three commonly used Q235 B material dynamic constitutive models were fitted,and The applicability of the models were analysised.Based on the verification of the finite element model,the sensitivity analysis was carried out for the influence factors such as mesh size,constitutive model and impact simplification in the finite element modeling.Finally,the principle of finite element analysis modeling for the transverse impact of tubes was proposed.(3)Parametric analysis of transverse impact of tubeThe parametric analysis of the steel tubes subjected to impact was carried out through ANSYS/LS-DYNA.The finite element analysis was divided into two parts,the non-axial force tubes and the preloaded steel tubes.The influencing factors of the section size,restraint form,indenter form and axial force were investigated.The dynamic response process and failure modes of steel tube under different scenarios were obtained.(4)Study on thefailure mechanism and deformation forecast of circular steel tubeOn the basis of the test and the finite element analysis,the failure mechanism of the circular steel tube subjected to transverse impact was studied through the plastic theory.The plastic denting areas of the circular steel tube were described in detail.The empirical formula of the effective length of the plastic sag zone was obtained by fitting.By summing up the failure mode of circular steel tubes,the elementary failure criterion was proposed.Finally,the deformation formula of the transverse impact resistance of the circular steel tube was obtained,and the reliability of the proposed deformation formula was verified by comparative analysis.