Experimental investigation on the post-fire mechanical properties of YSt-355FR (0.1 % Mo) low-alloyed fire-resistant steel

Abstract

Fire-resistant steel (YSt-355FR (0.1 % Mo)) has become the most utilized structural steel due to its superior performance at elevated temperatures compared to traditional structural steel at both the material and structural levels. However, its performance after exposure to fire remains questionable. This study investigates the post-fire performance of cold-formed fire-resistant steel at the material level. A total of 132 steel coupons and 84 Charpy test specimens were exposed to temperatures ranging from 100°C to 1000°C. These temperature-exposed steel coupons were subjected to four different cooling conditions: furnace cooling (FC), air cooling (AC), water-jet cooling (WJC), and water cooling (WC). Tensile tests were performed on the cooled steel coupons to obtain post-fire stress-strain curves, from which the residual mechanical properties were determined. Charpy impact tests were also conducted on the cooled steel specimens to obtain impact energies and identify the fracture patterns. Key observations regarding the post-fire behavior of fire-resistant steel in terms of strength, deformability, stiffness, and toughness parameters were made. Both the exposure temperature and the cooling condition significantly influence the post-fire performance of fire-resistant steel. Fire-resistant steel demonstrates superior post-fire behavior compared to traditional structural steel. Constitutive equations were proposed to predict the mechanical properties of fire-resistant steel under various post-fire conditions, and a sound reliability analysis was performed to examine the reliability of the predicted design parameters compared to the test results. The findings presented in this paper are significant as no prior investigation has assessed the post-fire performance of fire-resistant steel; thus, they may encourage the steel construction industry to prefer fire-resistant steel over traditional structural steels and promote the reuse of temperature-exposed fire-resistant steel for sustainable construction.