Fourth International Conference on FRP Composites in Civil Engineering (CICE2008) 22-24July 2008, Zurich, Switzerland - 1 - 1 INTRODUCTION The durability and the actual life expectancy of concrete slabs reinforced with steel bars, above all if exposed to severe environmental conditions, represent nowadays key problems. An interesting application, which has already been used in some countries in the bridge slab field, is represented by the use of FRP bars or grids instead of the traditional steel reinforce- ments. There are several advantages of the technological solution based on FRP bars or grids embedded in concrete, replacing steel bars: the excellent resistance to corrosion as well as to environmental agents, like chemical attacks and freeze-thaw cycles, the standardization and the simplicity of the building process, the facility of moving within the yard and the low transporta- tion costs due to material lightness, the low times of placing. Nevertheless, an important aspect of the concrete slabs reinforced with FRP behaviour is given by the effects of the exposure to fire at slab’s top and bottom, possible both for bridge decks outside and for residential or industrial building decks. In those cases, the mechanical properties’ deterioration of the fiber-reinforced composite materials and of the bond at high temperatures determines a reduction of the resistance and stiffness of the elements working in flexure. Obviously, the high temperature effects result critical for RC elements strengthened with externally bonded FRP reinforcements (Nigro et Al. 2006), but they results significant also for concrete elements reinforced with internal FRP bars (Bisby, Green & Kodur, 2005). The aim of this paper is to examine the fire resistance of unprotected concrete slabs rein- forced with FRP bars or grids, to individuate the main parameters that characterize the behav- iour and to suggest simplified design/check methods. 2 THERMO-MECHANICAL CHARACTERIZATION OF THE MATERIALS Studying the behaviour at the elevated temperatures of the structural members reinforced with FRP bars or grids it is necessary, for each material that composes the member, to define the thermal and mechanical properties in function of the temperature. A brief synthesis of the FRP reinforced concrete elements behaviour background is contained in a recent paper of Bisby, Green & Kodur (2005). Several research activities are reported in the literature studying the high-temperature mechanical properties of FRP materials and the behav- High-temperature behaviour of concrete slabs reinforced with FRP bars Emidio Nigro , Gaetano Manfredi , Edoardo Cosenza & Giuseppe Cefarelli Department of Structural Engineering, University of Naples “Federico II”, Naples, Italy ABSTRACT: The paper deals with the structural behaviour of concrete slabs reinforced with FRP bars or grids in the case of high temperature. The experimental data available in the litera- ture about the behaviour of fiber-reinforced composite materials as well as of concrete slabs re- inforced with FRP bars or grids at high temperature have been carefully examined, determining deterioration curves of bars mechanical properties as a function of the temperature. An accurate calculation procedure has been implemented and validated in order to assess the deterioration curves of the FRP reinforced concrete slabs bearing capacity depending on the main geometrical and mechanical parameters. Some simplified design methods have been also suggested.