Effects of Cold Temperature and Strain Rate on the Stress-Strain Behavior of ASTM A706 Grade 420(60) Steel Reinforcement

This paper discusses the results of an experimental study conducted on ASTM Grade 420(60) mild steel reinforcement at varying temperatures and strain rates to aid in the design of structures that experience seasonal freezing. The test data for this study were collected by performing monotonic testing of standard reinforcement samples at 20°C (68°F), 5°C (41°F), $-1°\mathrm{C}$ (30.2°F), $-20°\mathrm{C}$ ($-4°\mathrm{F}$), and $-40°\mathrm{C}$ ($-40°\mathrm{F}$) in an environmental chamber that maintained the desired temperature throughout testing. In addition, the response of samples subjected to different strain rates were examined at $-1°\mathrm{C}$ (30.2°F) and $-20°\mathrm{C}$ ($-4°\mathrm{F}$). The effect of cold temperature and/or strain rate on the following key parameters, used to define the stress-strain behavior of the reinforcing steel, was examined: yield strength, elastic modulus, onset of strain hardening, ultimate tensile strength, and ultimate tensile strain. The study revealed that the yield and ultimate tensile strengths increase moderately as the temperature decreases and the strain rate increases. The strength increases associated with low temperature occurred even before reaching 0°C (32°F), confirming that the change in behavior of reinforcing steel is gradual. The elastic modulus and ultimate strain, however, were largely unaffected by both cold temperature and strain rate.