Temperature-Dependent Stress–Strain Response of SD 550 Reinforcing Steel Bars

Abstract

This study examines the behavior of superductile 550 (SD 550) reinforcing steel bars after exposure to elevated temperatures followed by cooling to ambient conditions. The research provides comprehensive mechanical property data, including yield strength, ultimate strength, modulus of elasticity, ductility, strain hardening, and elongation. The findings reveal that SD 550 steel experiences significant degradation in strength when exposed to temperatures exceeding 500°C, with residual strength stabilizing at approximately 60%–70% of its original values upon cooling. 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. The study also compares the results with existing literature on conventional steel types, such as hot-rolled and TMT bars, highlighting the unique performance characteristics of SD 550 steel. The comprehensive data provided offers valuable insights into the stochastic nature of SD 550 steel’s mechanical properties at ambient temperatures and post-thermal exposure. 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 SD 550 steel under thermal stress conditions.