Abstract
Ultra-high performance fiber-reinforced concrete (UHPFRC) offers exceptional compressive strength, tensile ductility, and durability, making it an ideal material for modern bridge engineering and structural rehabilitation. In this study, the flexural behavior of UHPFRC girders strengthened with externally bonded carbon fiber reinforced polymer (CFRP) sheets was experimentally investigated. Five large-scale UHPFRC girders with a clear span of 3000 mm were cast and tested to failure under four-point monotonic loading. The primary experimental variables included the number of CFRP sheet layers (one, two, and three layers) and the configuration of end-anchorage U-wraps. The experimental results demonstrated that externally bonded CFRP sheets substantially enhanced the flexural capacity of UHPFRC girders by 18.5% to 42.1% compared to the unstrengthened reference girder. Owing to the high tensile strain-hardening and micro-cracking mitigation of the UHPFRC matrix, premature concrete cover separation—a common failure mode in conventional reinforced concrete—was effectively eliminated. Instead, the failure transitioned from intermediate crack debonding to tensile rupture of the CFRP laminates when mechanical U-wrap anchors were utilized. Although the ductility decreased slightly with increased CFRP plies, the girders exhibited considerable energy dissipation capacity. The findings confirm that the synergistic interaction between the steel fibers in UHPFRC and the externally bonded CFRP laminates enables superior composite action and structural resilience.
