Degradation of flexural performance of ultra-high-performance fiber-reinforced concrete (UHPFRC) beams reinforced with hybrid CFRP and steel bars exposed to elevated temperature

초록

"The combination of hybrid reinforcement using CFRP and steel bars in ultra-high-performance fiber-reinforced concrete (UHPFRC) offers potential advantages; however, performance evaluation after thermal exposure remains limited. This study investigates the flexural behavior of UHPFRC beams reinforced with hybrid bars following exposure to elevated temperatures. The test parameters included heating temperatures (20, 400, and 600 °C) and reinforcement arrangements (single-layer and double-layer). The results for cracking behavior, load–slip response, load–deflection behavior, and ductility index were compared with those of specimens reinforced solely with CFRP bars. After exposure to 400 °C, all specimens exhibited approximately 4–11 % higher values compared to unheated beams, with the most significant improvements observed in the hybrid-reinforced specimens. The single-layer configuration demonstrated about 5 % greater capacity than the double-layer configuration, despite a lower reinforcement ratio. After exposure to 600 °C, the post-peak load exhibited a gradual decline after reaching the ultimate strength, which is attributed to the presence of inner-layer steel bars. Sectional analyses showed good agreement with the experimental data, with errors generally within 12 %. The ratio of the predicted value to the experimental result obtained from sectional analysis was 1.06, and the coefficient of variation (COV) remained within 5 %. Based on the 500 °C isothermal method, a discrepancy of approximately 22 % after exposure to 600 °C was observed between the predicted results under three-sided and four-sided heating conditions. © 2025 Elsevier Ltd

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