An appropriate fire safety measure provision is important for structural member design. The focus on computer model fire resistance evaluation has increased with performance-based codes' recent introduction. Concrete and reinforcing (prestressing) steel high-temperature properties are one of the key components of reinforced concrete (RC) member resistance evaluation. High-temperature constitutive relationship information, even to date, is limited. The authors illustrate concrete high-temperature property variations and present a high-temperature concrete constitutive relationship comparative study. Review and comparison of available constitutive relationships for American and European concrete and steel standards and published experimental results are presented. Case studies illustrate different fire resistance predictions that result from high-temperature material property variations. For performance-based RC member design, recommendations for suitable constitutive relationship adoption are drawn.