Mechanical properties of undamaged and damaged steel rebars at elevated temperatures

Evaluation of mechanical properties of undamaged and damaged steel rebars at elevated temperature finds its applications in development of steel material models likely to be used in designing reinforced concrete structural members subjected to earthquake triggered fire. In the present experimental investigation, 84 rebar specimens (cylindrical) of length 700 mm and diameters 8 mm, 10 mm, 16 mm and 20 mm were tested. Test specimens were prepared from the materials used in construction of full-scale reinforced concrete frame subjected to earthquake and fire. The specimens were initially stressed to a certain known limit (0.58 times yield stress fy) to simulate damage caused by an earthquake. After inducing the damage, they were exposed to a desired temperature level (20 °C, 250 °C, 500 °C and 750 °C) in a circular furnace arrangement coupled with a 400 kN universal testing machine. The temperature was sustained inside the furnace for about 30 minutes to ensure a steady state heat transfer inside the specimen. The bars were then tested under uniaxial tensile loading conditions to failure. The elongation was recorded by using two LVDTs fixed between gauge lengths of 265 mm at the mid-height. Results obtained in the tests were utilized to carry out multiple linear regression analysis and propose constitutive models for damaged steel rebars and various relationships: Tensile Strength, Peak-Strain, Elongation and Elastic Modulus vs. Temperature, Stress vs. Strain at elevated temperatures.