Within the framework of study of concrete structures subjected to fire, .a theoretical and experimental work was conducted. The aim of this study was to investigate and to model the damage mechanisms of concrete after their exposure to high temperatures. The multiphase Digital Concrete Model as well as the damage model, MOD EV, which were both implemented on the finite elem~rit software package, SYMPHONIE, were used simµltaneously to assess the thermal damage of the concrete. In order to validate the thermal damage model, an experimental investigation was performed. The mechanical characteristics of 5 cementitious materials, which included cement paste, mortar, ordinary concrete and 2 HSC concretes, were measured with 3-point bending tests immediately succeeding heati11g/cooling cycles of 393, 523 and 6n K The experimental tests on the 3 different materials were then compared to the numerical simulations and are presented for temperatures up to 673 K Several applications were investigated after the validation of the models, one of which was the fire resistance of concretes when simultaneously· subjected to both compressive and high temperature loads.