All Sciences Proceedings http://as-proceeding.com/ 5 th International Conference on Applied Engineering and Natural Sciences July 10-12, 2023 : Konya, Turkey https://www.icaens.com/ © 2023 Published by All Sciences Proceedings 374 Stiffened Hollow Structural Section Joints in Fire Emre ÖZYURT * 1 Civil Engineering Department, Gümüşhane University, Türkiye * (emre.ozyurt@gumushane.edu.tr) Abstract – This research examines the ability of stiffened Hollow Structural joints to withstand elevated temperatures when subjected to axial compressive loads on the brace. Extensive numerical simulations were conducted to assess the impact of geometrical factors in the main members and reinforcing plate on the fire resistance of SHS T-joints. The accuracy of the numerical models was verified by comparing them to existing test results. The findings demonstrate that the use of stiffener significantly enhances the ability of SHS T-joints to withstand elevated temperatures. The fire resistance of the reinforced joints primarily relied on the brace-to-chord width ratio and the reinforcing plate thickness to chord wall thickness ratio. However, increasing the reinforcing plate thickness beyond 1.5 times the chord wall thickness did not yield any beneficial effects on fire resistance. Additionally, factors such as half-width to thickness ratio of the chord, reinforcing length, and reinforcing type had negligible effects as long as they adhered to the required limit values based on Eurocode 3 EN 1993-1-8. Keywords – Stiffened Hollow, Joints, Wall Thickness I. INTRODUCTION Tubular structures are widely employed in both onshore and offshore applications due to their notable benefits from both structural and architectural perspectives. Square Hollow Section (SHS) is among the commonly used section types in these structures. Joints play a critical role in tubular structures, and typically, failure occurs in the chord member. This is attributed to the smaller transverse stiffness of the chord member compared to the axial stiffness of the brace members. Moreover, the mechanical properties of steel undergo significant degradation at high temperatures, necessitating the consideration of reinforced joint behavior in fire conditions. There have been a couple of studies on the behaviour of the stiffened SHS T-joints at ambient temperature until now. Feng et al. [1] and Ozyurt and Das [2] experimentally and numerically examined the joint resistance of collar and doubler plate reinforced SHS T-joints with compressive load in the brace member. They noted that using either a collar plate or doubler plate considerably increased the joint capacity. Ozyurt and Das [2] noted that the current method in the Eurocode 3 EN 1993-1-8 [3] may not be safe for all configuration of reinforced SHS T-joints and introduced a simple design method to predict their capacity, considering geometrical parameters of the main members and reinforcement plates. Extensive research studies have examined the joint resistance of Circular Hollow Section (CHS) T-joints reinforced at ambient temperatures. Choo et al. [4] and van der Vegte et al. [5] conducted experimental and numerical investigations on both unreinforced and reinforced CHS T-joints. They observed a significant increase in joint capacity when an appropriately sized reinforcing plate was used. Shao et al. [6] focused on the effect of local reinforcement in the chord member on the capacity of CHS T-joints under axial compression in the brace member. Their numerical study revealed that increasing the chord thickness at the intersection beyond its original thickness altered the joint's failure mode. Nassiraei et al. [7-10] conducted parametric studies on collar plate and doubler plate