A Numerical Investigation into the Effectiveness of Composite Jacket Strengthening (CJS) on Fire-Damaged Concrete Beams

Abstract

After a fire exposure, reinforced concrete (RC) structures typically retain their integrity, yet they incur significant damage due to material degradation and thermal expansion. The restoration of fire-damaged RC structures is a complex structural engineering challenge. This study presents a numerical investigation on the post-fire behavior of RC beams, subjected to parametric fire for different durations (15, 30, 60, and 90 minutes) and their retrofit method. Initially, the impact of high-temperature conditions on the residual load-bearing capacity is assessed, with a focus on beam length and support conditions as key geometric variables. Repair methods aimed at improving the post-fire performance of damaged beams are then evaluated. These methods include the use of additional reinforcement and the implementation of steel jacketing, complemented by concrete of varying compressive strengths (25, 30, 35, and 40 MPa). Eurocode models for both concrete and steel materials are used in the simulations using SAFIR software. Results indicate a decrease in load-carrying capacity with prolonged fire exposure, with capacity reductions reaching 85% for beams subjected to 90-minute fire scenarios. Application of steel jacketing markedly enhances both bending and shear resistance of the compromised beams, with the ability to restore the load-bearing capacity of one-hour fire-exposed beams by up to 112%. The correlation between repair effectiveness and the inherent resistance of the RC beams is also elucidated. Furthermore, an analytical expression is proposed for estimating the post-fire load-bearing capacity of reinforced beams, offering a practical and accurate tool for engineering assessments.