Fire Resistance Of Reinforced Tubular T/Y-joints Under The P Ost-earthquake Fire

In the design of steel tube structure,the strength checking calculation of the joint is often not satisfied.In order to improve the bearing capacity of the joint,the reinforcement methods such as the pad plate strengthening and the stiffening rib strengthening are usually adopted.At present,many scholars at home and abroad have done a lot of research on the mechanical properties of T/Y joints under various loading conditions.However,most of the research focuses on the mechanical properties and failure mechanism of unreinforced T/Y joints at room temperature and high temperature,the research on the mechanical properties and failure mechanism of reinforced T/Y-joints with initial defect or damage under fire is still at the initial stage.Therefore,the study on the reaction process and failure mechanism of reinforced T/Y joints under post-earthquake fire has important theoretical and practical significance for the fire prevention and earthquake emergency response of long-span space structures.Based on the experimental verification and parameter research,this paper mainly analyzes the different reinforced joints,the main contents are as follows:(1)According to the domestic code for fire resistance design of steel members,the reinforced T/Y-joints are designed,the material constitutive model of joints at high temperature is established,the fire resistance capacity of joint models is checked,and the critical point of joint models is calculated,based on this temperature,the finite element software simulates the high temperature critical point and failure conditions of the joints.(2)In this paper,the calculation model of unstrengthened and single-ring-strengthened T-shaped tubular joints is verified by existing tests,and the damage variable under earthquake loads is introduced,the effects of diameter ratio β,diameter thickness ratio γ,wall thickness ratio α,ring thickness and main pipe thickness ratio η on the whole process response,failure mode,failure mechanism and stress distribution of tubular T-joints strengthened with two rings in post-earthquake fire are studied.(3)The calculation model of three-inner-ring reinforced tubular T-shaped joints is verified by existing tests,the loading system is formulated,the damage variable caused by earthquake is introduced accurately,and the restarting analysis is used,then the influence diameter ratioβ,diameter thickness ratio Y,wall thickness ratio α,ring thickness and main pipe thickness ratio η on the failure mechanism,failure mode,critical point,deformation and displacement of T-shaped tubular joints strengthened with three internal rings under different initial defects are studied.(4)The finite element program is used to establish the Y-shaped joints with two or three rings,and the damage variable is introduced,the effects of different damage grades and different angles between main pipe and branch pipe on the temperature displacement curve,critical point,damage evolution and stress distribution before fire and after earthquake were studied.In summary,through the analysis and research on the fire resistance performance of reinforced Tubular T/Y-joints under post-earthquake fire,it is found that the damage variable has a significant effect on the fire resistance performance of reinforced tubular joints,the research results are of great theoretical and practical significance in clarifying the failure mechanism of reinforced T/-Y joints under the post-earthquake Secondary Fire and revealing the whole process of the reinforced T/Y-joints under the post-earthquake fire,it also has the potential extensive application prospect.