Effects of Structural Size on Postearthquake Fire Resistance of HSS-CHS-SHS T-Joints under Nonuniform Elevated Temperatures

Limited research has been conducted on the fire resistance of high-strength steel (HSS) T-joints after an earthquake. The aim of this study is to assess postearthquake fire resistance and determine the optimal design dimensions of HSS-circular hollow sections-square hollow sections (CHS-SHS) T-joints considering the nonuniform temperature field effect through parameter analysis. The computational models of HSS T-joints developed in this study were validated against existing test results. Twenty four computational models related to HSS-CHS-SHS T-joints were established using the finite element software ANSYS; further, a sequential temperature-displacement analysis method was used to perform a parameter study. Subsequently, parameter analysis was conducted on HSS-CHS-SHS T-joints by varying parameters such as chord-width-to-thickness ratio ($\gamma$), brace-to-chord-thickness radio ($\tau$), brace-to-chord-width ratio ($\alpha$), chord-length-to-height ratio ($\beta$), and damage variable ($\tilde{D}$). The results indicate that the failure of HSS-CHS-SHS T-joints is attributed to plasticization of the chord surface, and that parameters $\alpha$ and $\tilde{D}$ have a significant influence on the postearthquake failure mechanism and catastrophic process. Moreover, an empirical theoretical model for determining the bearing capacity of HSS-CHS-SHS T-joints after exposure to fire is proposed and validated.

The HSS-CHS-SHS T-joint is widely used in offshore platforms, building frames, transmission towers, etc. Secondary fires occur frequently after an earthquake, which typically cause huge casualties and economic losses. Since earthquakes may produce residual stress and deformation in HSS-CHS-SHS T-joints, the failure mechanism of HSS-CHS-SHS T-joints under fire cannot be used to accurately evaluate their reliability and safety under a postearthquake fire. Thereby, the investigation of this study can provide valuable reference for design, repair, and reinforcement of HSS-CHS-SHS T-joints.