Thermal Degradation of Mechanical Properties in Super Ductile Reinforcing Steel Bars: A Comparative Study with Conventional Bars

This study investigates the behavior of super ductile (SD) reinforcing steel bars after exposure to elevated temperatures, highlighting their distinctions and superior performance compared to conventional steel types such as cold-worked, hot-rolled, and thermo-mechanically treated (TMT) bars. The research examines the changes in mechanical properties, including yield strength, ultimate strength, modulus of elasticity, and ductility, through detailed stress–strain analysis and mechanical property evaluation across varying temperature ranges. The findings demonstrate that SD bars exhibit enhanced mechanical properties under high-temperature conditions, retaining higher yield and ultimate strengths, and maintaining a more pronounced strain hardening region compared to other steel types. Specifically, SD bars preserve higher residual strength after exposure to 800°C, significantly outperforming cold-worked and hot-rolled bars. The modulus of elasticity of SD bars shows better stability at moderate temperatures and a less pronounced decrease at higher temperatures, reflecting their superior ability to absorb energy before failure. Parabolic regression models were developed to predict the degradation in yield and ultimate strengths, while polynomial curve fitting methods were used to establish stress–strain models for post-heating scenarios. This research fills a critical gap in the current understanding and provides robust degradation models that are essential for the design and safety assessment of reinforced concrete structures using SD550 steel under thermal stress conditions.