Finite element modeling of insulated FRP-strengthened RC beams exposed to fire

The fire performance of reinforced concrete (RC) members strengthened with externally bonded fiber-reinforced polymer (FRP) laminates has been an issue of significant concern, particularly for building applications. To achieve structural fire-resistance ratings as specified in building design codes, an insulation layer often needs to be provided. This paper presents the first three-dimensional finite element (FE) approach for the fire performance simulation of insulated FRP-strengthened RC beams. The proposed approach gives careful considerations to the constitutive modeling of concrete, steel, and FRP, as well as the bond-slip behavior of FRP-to-concrete and steel-to-concrete interfaces. Comparisons between FE predictions and existing test data are presented to demonstrate the accuracy of the proposed FE approach. Numerical results obtained with the present FE approach show that the assumption of perfect bonding between FRP and concrete as adopted in previous numerical approaches leads to underestimations of deflections and thus unsafe predictions of fire resistance. The FE approach presented in the paper can be directly applied in performance-based fire safety design, or in parametric studies aimed at developing simplified design rules.