Guidance for Treatment of High-Temperature Creep in Fire Resistance Analysis of Concrete Structures

Concrete structures develop high levels of transient creep strain when exposed to fire, especially when temperatures in a member exceed 500°C. This high-temperature creep strain can dominate the deformation response under severe fire scenarios and needs to be properly accounted for in the fire resistance analysis. Most of the current approaches for fire resistance calculations, including advanced analysis methods, do not consider the transient creep strain to the full extent. This paper presents design recommendations for the treatment of creep in the fire resistance analysis of concrete structures. Three design alternatives are proposed for incorporating creep in fire resistance analysis depending on the conditions encountered during fire exposure. The first solution is ‘creep-not critical’ scenario where the temperature-induced creep strain can be neglected in a structural member subjected to low stress level and experiencing low sectional temperatures. In the second scenario (‘creep-implicit’), where temperature-induced creep strain is moderate, creep can be incorporated implicitly in the analysis. Finally, in situations where creep is significant (as in the case of high stress level and sectional temperatures), it needs to be incorporated explicitly in the fire resistance analysis (‘creep-explicit’ scenario). The practicality of the proposed solution in accounting for creep in the fire resistance analysis of concrete members at different levels is demonstrated using three case studies.