On the extension of a plastic-damage model to high temperature and fire

Concrete modelling at high temperature is not an easy task due to its highly nonlinear behaviour. When simple members are at issue, numerical modelling can take advantage of uniaxial constitutive laws. On the contrary, when walls and tunnel linings have to be studied, finite elements must be used, thus requiring the multiaxial constitutive behaviour to be properly defined. The aim of this paper is to show the calibration of the main parameters of a plastic-damage model via inverse analysis, on the basis of experimental data available in the literature, regarding tests under multiaxial state of stress in both hot and residual conditions. The results indicate that there is a strong dependence on temperature of the ratio between biaxial and uniaxial compressive strength in hot conditions, while it is definitely less evident in residual conditions. As regards the variation of the shape of the failure surface with temperature, it appears to be of secondary importance.