Quenched reinforcement exposed to fire

摘要

Idealised data are derived for the tensile strength of quenched and tempered prestressing steel and of quenched and self-tempered reinforcing bars for fire safety design. 0.2% stresses are derived as a function of the maximum temperature and, in addition, 2.0% stresses are provided. A strain of 2.0% is seldom found in 'slack' (not prestressed) reinforcement, but 2.0% stresses might be relevant for reinforcement in T-shaped cross sections and for prestressed structures, where large strains can be applied. All data are provided in a 'HOT' condition during a fire and in a 'COLD' condition after a fire. The COLD condition is relevant for analyses of residual load-bearing capacity of a structure after a fire exposure. It is also relevant for analyses of concrete structures exposed to fully developed fire courses. The reason is that compression zones of concrete are always the weakest in the cooling phase after a fire, and therefore data for the reinforcement are needed in this phase as well as in a HOT condition in order to assess the minimum of the load-bearing capacity of a structure. Quenched and self-tempered steel is widely used, but its properties at fire exposure are rarely investigated. Therefore, two test series have been made, which are presented in the present paper. In one test series, transient properties are found in a HOT condition during a fire and in the other, residual properties are found in a COLD condition after a fully developed fire course.