Compressive stress-strain relationship for stressed concrete at high temperatures

It is well documented that the load during heating process has significant impacts on mechanical properties of concrete at high temperatures. However, this important effect is not adequately covered in the existing constitutive models. This paper presents an experimental study on the uniaxial compressive stress-strain relationship of concrete specimens stressed with different load levels (0%–70%) at high temperatures (400 °C–900 °C) to simulate the real situation of mechanically loaded concrete structures subjected to fire attack. It was found that the compressive strength and the elastic modulus increase with the load level, especially at temperatures ranging from 460 °C to 580 °C. On the contrary, the peak strain decreases with the applied stress level, and the decreasing rate is significantly increased above 680 °C, which could be attributed to the compact of thermal cracks and development of transient thermal creep. Based on the experimental analysis, an advanced constitutive model for stressed concrete at high temperatures is proposed. The main novelty and contribution of this study is the quantification of the effect of the applied stress during heating process on the uniaxial compressive stress-strain relationship of concrete at high temperatures.