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A Study on Fire Behavior of Reinforced Concrete Elements―Modelling of Mechanical Properties of Concrete at Elevated Temperature―

by Takeshi Morita

The estimation of structural fire behavior for the structural fire safety design of buildings is usually done by applying methods such as the Finite Element Method. The accuracy of the numerical analysis of structural fire behavior is strongly dominated by material models for high temperatures. Concrete models for numerical analysis, and fire tests on centrally loaded columns are discussed in this paper.

A concrete model for high temperatures, which can take into account stress history, was modified in order to take into account more rationally the transient creep strain and modulus of elasticity as functions of stress and temperature. Fire tests on centrally loaded columns were carried out in order to investigate load bearing capacity during heating and after cooling down. Furthermore, fire test results were numerically simulated by applying the modified concrete model, the original concrete model and the EUROCODE 4 model.

As a result of the fire tests, it can be said that the collapse time of columns depends on the load level and not on the restraint of thermal elongation, and that the load level is not an overriding factor for the magnitude of the maximum restraint load of thermal elongation. Though more comparisons with fire tests may be necessary in order to validate and confirm the modified concrete model, the results of the numerical simulations applying the modified concrete model show good agreement with the test results.