Stress-Strain Relationships for Concrete at Elevated Temperatures

This paper is on the compressive stress-strain behavior of unreinforced concrete under elevated temperatures from fire. Relationships are developed for the temperature-dependent compressive strength, elastic modulus, strain at peak stress, and ultimate strain of concrete by conducting a comprehensive multiple least squares regression analysis on the existing experimental data, including the effects of aggregate type, test type, and compressive strength at room temperature. These relationships are then used to produce predictive compressive stress-strain models for concrete under fire. High-strength and normal-strength concrete with normal-weight as well as light-weight North American aggregates are considered in the study. Unlike previous models, creep deformations are not included in the proposed models, resulting in baseline relationships to which time-dependent creep strains can be explicitly added in the future. It is shown that the relationships developed provide a good statistical fit to the available experimental data.