Three-dimensional finite element modelling of the fire behaviour of insulated RC beams strengthened with EBR and NSM CFRP strips

This paper presents numerical simulations of the fire behaviour of reinforced concrete (RC) beams flexurally strengthened with carbon fibre reinforced polymer (CFRP) strips installed according to the externally bonded reinforcement (EBR) and near surface mounted (NSM) techniques. Three dimensional (3D) finite element (FE) models of the beams were developed, in which the temperature-dependent thermophysical and mechanical properties of the constituent materials was considered. The CFRP-concrete interaction was modelled by means of bi-linear bond-slip laws previously calibrated by the authors for different temperatures. Comparisons between numerical and previous experimental results confirmed the accuracy of the models in predicting the thermo-mechanical response of insulated CFRP-strengthened RC beams exposed to fire. The results obtained highlight the possibility of exploring the CFRP mechanical contribution in fire through a “cable” behaviour by applying a thicker insulation in the CFRP anchorage zones. Moreover, the numerical results confirmed the better fire performance of the NSM strengthening technique when compared to EBR: with the latter technique CFRP debonding occurred after considerably shorter periods of fire exposure and for much lower average temperatures in the adhesive in the anchorage zones, from 1.2 × Tg to 1.4 × Tg, with such range being 2.4 × Tg to 4.2 × Tg for the NSM system.