Heat-Force Coupling Action Of Reinforcing Steel Tubular T-Joints By Welding Collar Plates Under Load

Steel-tube through welding joints have been widely adopted in various infrastructural steel-tube construction projects like bus stations,airports and bridges in recent years,depending on their simple structure,easy connection and strong bearing capacity.The said constructions are crucial lifeline facilities and their partial joint damage after long service will seriously impact the structural safety,so renovation and reinforcement are inevitable.One common strengthening method is to weld collar plate at the joint area,but the safety of welding plate reinforcement under loading is still unclear.This paper took T-shaped joint as the research object and,with the method of combining tests and finite element theory analysis,it studied the influence of welding plate reinforcement under loading on the carrying capacity of joints,revealed the change rules of joint temperature and load-carrying property during and after welding plate reinforcement and the coupling rule between high welding temperature and joint load,and proposed the joint strength reduction formula concerning weld and loading effect,providing theoretical references for welding plate reinforcement under loading of steel-tube joints.First of all,it completed physical tests of the T-shaped steel-tube joints with 2 not reinforced and the other 6 reinforced with collar plates,which respectively surveyed the impacts of such factors as support conditions,load grades and high welding temperature.The result shows:(1)collar plates enjoy obvious reinforcement effect,which,regardless of the welding heat,can increase the carrying capacity of joints by 37.4%even when the loading grade of main tubes reaches 0.4.(2)The compressive bearing capacity of the joints reinforced by collar plates reduces as the loading grade of main tubes increases,while the load of relatively small side tubes has slight impact on the joints’bearing capacity.(3)In the process of collar plate welding,the strain measure points of the up surface area of the main tubes near the collar plate appear relatively obvious change,with the compressive strain also increased;the displacement in welding process is not evident;the compressive strain on the up surface area of main tubes near the collar plates starts to fall as collar plates are involved in force bearing,after the weld cools down;there is obvious displacement before and after weld cooling,with side tubes moving down and main tubes pressing inside.(4)Welding heat appears unapparent coupling effect with main tube load.Afterwards,ANSYS finite element analytical model for test joints was established,which adopted birth-death element technology to simulate the process before and after weld,indirect heat-structure coupling analytical method to simulate the coupling between the temperature field and stress-strain field,birth-death element welding heat input to simulate welding heat.And considering the changes of steel material property along with the changes of temperature.Documentary reference and welding test prove relatively high accuracy of the finite element model.And then,parameter analysis in group 308 model was finished by changing major influential factors like the main-tube load grade n,main and side-tube diameter ratio β,main tube radius-thickness ratio 2γ,collar plate length ζ1,collar plate width ζ2,collar plate thickness τc and welding heat.The result shows:(1)there are two typical failure modes for collar plate reinforcing joints,I main tube section ovalization and Ⅱmain tube portrait press bending,of which model Ⅱ usually happens when n≤-0.5.(2)The bearing capacity weakening law of the collar plate reinforcing joints caused by main tube load is similar to that of the unreinforced joints,but the weakening rate of the reinforced joints is higher.(3)The key factors that impact the compressive bearing capacity of the collar plate reinforced joints include n,β and 2γ,while the impact of welding heat and dimension parameters of the collar plate ζ1,ζ2 and τc on the compressive bearing capacity of the joints is relatively small.(4)Welding heat does not change the failure mode of the reinforced joints and appears unapparent coupling effect with main tube load.The compressive bearing capacity of the welding plate reinforced joints under loading is mainly impacted by the main tube load.Finally,this paper analyzed the bearing mechanism of welding collar plates under loading to reinforce T-shaped joints based on tests and parameter analysis,and the regression analysis proposed the reinforced joint compressive bearing capacity reduction formula concerning the load effect.The calculation results with the formula are generally identical with those of tests,parameter analysis and orthographic verification.This paper includes 76 figures,24 tables and 119 references.