Research On Fire-resistance Behavior Of Welded Tubular T-joints And T-joints Reinforced With Collar Plate

Welded steel tubular structures are widely used all over the world. Tubular joints,served as the key components of tubular steel structures, are considerably important insteel structural design. The welded tubular joint is one of the most commonly used jointtypes due to no stiffening accessories, rapid erection and low steel consumption. Steelmaterial is of good ductility and reliability, but its fire resistance is poor. Yield strengthand the elastic modulus decrease as temperature increases. Fire is a very importantsecurity problem for welded steel tubular structures. However research on fire resistancebehavior of welded tubular joints remains limited. Consequently, in the dissertation, thefire resistance behavior of tubular T-joints is experimentally and numerically analyzed.The main research contents are as follows:Firstly，two (2) tubular T-joint specimens were tested to failure with constant braceaxial load under ISO834heating process. One of the tested specimens is reinforced withcollar plate and the other without any reinforcement. Both of the tested specimens haveidentical geometrical and material properties. The temperature response, deformationcharacteristics, failure mode and chord ends strain behavior of the two (2) tubular T-jointspecimens are investigated. A comparison of the fire resistance behavior between thetubular T-joint reinforced with collar plate and the specimen without any reinforcementwas conducted. Then the finite element (FE) package ABAQUS with sequentiallycoupled thermal stress analysis is adopted to simulate the joint specimens. The FE and theexperimental results are shown in good agreement after the verification of thetemperature-time curves, temperature-fire endurance time curves and failure modes. Inother words, the FE models are reliable and accurate enough to conduct the parametricstudy.A comprehensive parametric study of tubular T-joints is carried out with the verifiedFE method. It includes geometric parameters (D、α、β, τ, γ), thermal parameters (h, ε) and loading rate n, as well as their effect on critical temperature and fire endurance time.Based on the above study, the relationships between each parameter and criticaltemperature and fire endurance time are obtained. Datafit is used to conductmulti-variable regression analysis to derive parametric equations of the criticaltemperature and fire endurance time under axial loading. The reliability of the two (2)parametric equations is assessed according to the acceptance criteria of Fatigue GuidanceReview Panel.Finally, the same method is used to conduct the parametric study of tubular T-jointsreinforced with collar plate. It includes five geometric parameters (β, τ, γ, τc, ξ) andloading rate n, as well as their effect on critical temperature and fire endurance time. Thefire resistance of tubular T-joints reinforced with collar plates is compared with that oftubular T-joints without any reinforcement.