Research On Dynamic Behavior Of Axially Pre-loaded Cold-formed Square Steel Tubular Strengthen T-joints Under Impact Load

In recent years,terrorist attacks,fires,explosions and other extreme disasters caused severe structural damage or collapse accident have occurred frequently.Structures are facing increasingly serious threat during service.In these extreme disasters the impact load is often the important reason for severe structural damage.There is an increasing focus on the impact resistance of structural engineering assessment and design issues.Steel structure is widely used in of buildings,bridges,offshore platforms and other types of structural engineering.For steel structure,the security of joints is essential.Once a joint fails,the levers connected to will lose some or all of the carrying function.This may cause the force transmission path changes,partial destruction of the structure,or even the serious consequences of the continuity failure of the whole structure.In addition,the shape of steel structure is complex,intersecting parts are changed and discontinuous and there are some defects in the welds.The impact resistance of tubular structure depends largely on the impact resistance of joint.The researches have done are focused on hot-rolled steel.With the widely use of cold-formed steel,impact resistance of cold-formed tubular structures also need research.In this paper,impact test on cold-formed T-joint square tube is carried out through a high-performance drop hammer machine.The finite elements models for steel tubular T-joints under axially pre-loaded was established by software ABAQUS in this paper.The research work is summarized as follows:(1)Impact test on cold-formed square section ordinary and strengthened T-joint is carried out.On the base of analyzing the effect of strengthen type to impact failure mode,the development of deformation,local and global deformations and energy dissipation,the failure mechanism of axially pre-loaded is determined(2)The numerical models for steel tubular T-joints under axially pre-loaded was based on software ABAQUS/Explicit.Mechanism for tubular T-joint under impact loading were analyzed.Based on the analysis of joint parameters,research of the impact mechanism under axial pre-load is conducted.The factors of its carrying capacity under impact is clear.(3)The assessment of impact carrying capacity is obtained by the equivalent impact force gained from energy theory and plastic hinge line method.The coupling relationship between global and local deformation is preliminary analyzed.By using the conversion of energy dissipation and kinetic and joint deformation formula,the evaluation method of impact resistance of strengthen joint under axial pre-load impact resistance is proposed.