Structural performance of RC beams incorporating post-installed shear reinforcements with damages under water conditions

Post-installed shear reinforcements (PHSRs) are widely used to strengthen underground reinforced concrete (RC) members where single-sided access limits conventional retrofit. While prior studies have examined PHSRs retrofitted onto already-damaged members, the behavior of sound members retrofitted with PHSRs that subsequently experience damage and water exposure has not been systematically investigated. This study experimentally examines the reversed cyclic response of four RC beams, three retrofitted with PHSRs and one with plain round bars to investigate the role of mechanical anchorage. The beams were subjected to controlled static pre-damage at pre-peak or peak levels, followed by reversed cyclic loading at successive amplitudes from ±1 mm to ±6 mm under partial water submersion. Residual load-carrying capacity, secant stiffness degradation, residual displacement, strain evolution, cumulative energy absorption, and the evolution of arch and beam action contributions were examined. Peak-damaged beam tested in water showed consistently lower residual capacity and cumulative energy absorption than the air-tested beam, with accelerated transition from arch-dominated to beam-dominated shear behavior. At 2 and 3 mm, the pre-peak damaged beam retained residual loads at or slightly exceeding the static pre-peak capacity ( η P = 1.004 and 1.04, respectively). Water exposure altered the shear-transfer response in beam with peak damage, with V arch / V beam reaching 0.67 compared with 0.80 in air at 6 mm, while the beam with plain round bars exhibited a substantially lower ratio of 0.10 in water. The outcomes highlight the critical effect of pre-damage severity, water exposure, and the condition of mechanical anchorage on cyclic shear performance of PHSR-retrofitted RC members.