Post-Fire Exposure on the Residual Mechanical and Structural Behavior of Hot-Rolled YST-240 Steel Tubes

Determining the feasibility of reusing fire-exposed hollow steel sections poses challenges for designers and structural engineers due to a lack of reliable data, as existing guidelines focus on the behavior of steel tubes at elevated temperatures during a fire but lack sufficient research on their post-fire mechanical properties. The paper details an investigation of the post-fire mechanical behavior of YST-240 (mild steel) Square Hollow Steel Tubes (HST), a material widely used in construction. A systematic experimental program was conducted in this regard on the HST stub column and tensile coupon (extracted from HST stub columns) specimens having a thickness of 3 mm. All the HST stub column and tensile coupon specimens were exposed to a range of temperatures (ambient to 1000 °C) with exposure conditions ranging from mild, moderate, and severe (i.e., 30 min, 60 min, and 90 min, respectively). The research introduces novel temperature-dependent equations to quantify the percentage degradation in both material strength and the load-bearing capacity of HST stub columns following fire exposure. Further, predictive equations are proposed for evaluating the residual mechanical properties of YST-240 steel at various temperatures and compared with the existing equations given in IS 800:2007 and AISC360-16. The findings provide critical insights into the fire-induced deterioration of structural steel, offering enhanced predictive capabilities for post-fire structural assessments and design modifications.