A MULTIAXIAL CONSTITUTIVE MODEL FOR CONCRETE IN THE FIRE SITUATION

摘要

Performance-based design in fire engineering leads to increasing demand for advancedrntemperature-dependent material models for the load bearing materials used in building structures.rnThese models must be valid in natural fire situations including cooling down phase and must bernsufficiently robust for complex numerical calculations such as, for example, the analysis of tensilernmembrane action in composite slabs. Although structural concrete is widely used in civil engineering,rnproper modelling of its thermo-mechanical behaviour remains a challenging issue for engineersrnmainly because of the complexity of the phenomena that result from the microcracking process in thisrnmaterial and because of the necessity to ensure the numerical robustness of the models.rnThis paper presents a new multiaxial concrete model based on a plastic-damage formulation andrndeveloped to meet the specific requirements of structural fire engineers and researchers. The model,rnwhich incorporates an explicit term for transient creep strain and encompasses a limited number ofrnmaterial parameters, has been implemented in a finite element software dedicated to the nonlinearrnanalysis of structures in fire. The paper presents a series of numerical simulations conducted tornhighlight the model ability to capture the main phenomena that develop in concrete under firern(permanent strains, degradation of the elastic properties, unilateral effect) as well as its ability to bernused for the fire analysis of large-scale structural elements. As an example, the new concrete model isrnused in the numerical analysis of a full scale fire test on a composite steel-concrete slab and it isrnshown that the computed and measured results agree.