Residual structural performance of fire-exposed concrete slabs reinforced with hybrid GFRP-steel bars: Experimental and numerical studies

The use of glass fiber–reinforced polymer (GFRP) bars in concrete structures, such as bridge decks, has increased significantly due to their superior corrosion resistance in severe environments. To enhance ductility, hybrid steel-GFRP reinforcement solutions have been proposed for GFRP-reinforced concrete structures. This study presents the experimental results of twelve full-scale one-way reinforced concrete slabs, including both control and fire-exposed specimens. The slabs were reinforced with GFRP bars, steel bars, or hybrid reinforcement, with test variables including bar arrangement, mechanical reinforcing ratio, and the ratio of steel bar area to GFRP bar area. Six specimens were subjected to a reduced-scale standard fire with a maximum temperature of 650°C testing in a tunnel-type gas furnace, cooled to ambient temperature, and then tested under four-point loading until failure. Furthermore, a finite element model was developed, validated, and used to conduct a parametric study examining the impact of key reinforcement parameters on the structural behavior of fire-exposed slabs. Results indicate that fire exposure reduces the ultimate load-bearing capacity of all specimens. However, the reduction in GFRP-reinforced specimens is comparable to that of steel-reinforced specimens. Additionally, hybrid reinforcement with a higher steel-to-GFRP area ratio improves the residual performance of fire-exposed specimens. Notably, the ductility of hybrid-reinforced specimens remains largely unaffected by fire exposure.