Deflection-time Behavior and Fire Resistance of GFRP-steel Reinforced Concrete Beams Exposed to Different Fire Conditions

This paper explores the effects of fire conditions and reinforcement configurations on the deflection-time behavior and fire resistance of hybrid glass fiber-reinforced polymer (GFRP)-steel-reinforced concrete (RC) beams. The reinforcement configurations of these hybrid beams are characterized by ρ_f/fs, which is the ratio of GFRP area to the total area of both GFRP and steel. The considered values of ρ_f/fs were 0 (steel RC beams), 0.2, 0.4, 0.6, 0.8, and 1.0 (GFRP RC beams).

SAFIR finite element models were developed, verified, and used for analyses. The fire resistance and deflection-time behavior of hybrid beams were determined.

When ρ_f/fs increased from 0 to 1, the fire resistance of hybrid beams was shifted from the state governed by the deflection limit to the state governed by the deflection rate limit. Increasing the number of fire-exposed surfaces from 1 to 4 detrimentally affected the deflection-time behavior of the beams. Compared with exposure to the bottom surface, exposure to 2, 3, and 4 surfaces significantly decreased the fire resistance by up to 74.2%. The increases in ρ_f/fs and the number of fire-exposed surfaces detrimentally affected the deflection-time behavior and fire resistance of hybrid beams.

This phenomenon is attributed to the faster reduction in the mechanical properties of GFRP compared with those of steel. In addition, the cross-sectional temperatures were significantly affected by the number of fire-exposed surfaces.

Both ρ_f/fs and the number of fire-exposed surfaces should be considered in the assessment of hybrid GFRP-steel RC beams exposed to fire.