Assessment of the bearing capacity reduction of FRC elements subjected to fire

The use of Fibre Reinforced Concrete (FRC) in structural applications with higher responsibility (e.g., TBM-bored tunnels; bridges; offices and residential structural elements) is increasing. In this regard, the residual structural response during and after a fire event is an issue of paramount importance which should be researched so that practitioners can provide safe and reliable designs. For this purpose, a FE thermal and structural model has been developed to predict the behaviour of FRC cross-sections exposed to fire. The model is capable to provide for any fire curve (at any exposure time): (1) the magnitudes of the thermal-dependant parameters of the concrete; (2) the temperature and stress-strain distributions along the cross-section and (3) the M-N envelopes for the ULS design. The constitutive equation of the FRC for steel fibres to simulate the full-tensile stress-strain (crack width) relationship has been derived considering the results of an experimental program carried out at the Universidade de Sao Paulo (Brazil) within the framework of an extensive research project devoted to characterizing the mechanical behaviour of FRC subjected to fire. This constitutive equation allows considering the progressive degradation of the FRC post-cracking response for different temperature levels. The model together this constitutive equation has been used to perform a parametric study oriented to precast FRC segmental linings considering different FRC classes, fire curves and thicknesses of the segments. The residual bending moment capacity, stress-strain distributions and other relevant results are presented and analysed aiming at understanding the cross-sectional effects of this accidental load on FRC elements.