Shear behavior of pre-damaged RC members with post installed headed shear reinforcements under dynamic loading: Novel experimental insights in air and submerged conditions

Post-construction shear strengthening offers a practical solution in enhancing the load carrying capacity of RC structures subjected to seismic motion, particularly underground facilities in nuclear and thermal power plants where conventional retrofitting techniques due to site constraints are limited. For this reason, this study experimentally investigated the shear performance of pre-damaged RC beams strengthened with post installed headed shear reinforcements (PHSRs) in air and water submerged environments subjected to dynamic loading conditions. Four RC beams were pre-loaded monotonically until peak and pre-peak load damage occurred then retrofitted with PHSRs and subjected to dynamic reverse cyclic loading to evaluate the impact of damage severity, effect of water, and absence of PHSRs under severe environmental exposures. The strengthening efficiency was evaluated with respect to load-displacement responses, PHSRs and concrete strain behavior with displacement, variation in sustained load under different dynamic loading amplitudes, shear resistance mechanisms, cumulative energy absorptions and crack patterns. The results revealed that RC beams retrofitted with PHSRs achieved higher load-bearing capacities, energy absorptions and improved crack distributions than the un-strengthened beam, regardless of damage severity and environmental condition in this specific scenario. Beam strengthened at pre-peak damage stage exhibited slightly superior load capacities and concrete dominated shear resistance mechanisms for longer displacements than those with peak damages in air environment. However, beam in submerged conditions experienced slight reduction in PHSRs effectiveness at higher displacement amplitudes, it still exceeded the pre-retrofit static load capacity. These findings underscore the effectiveness of PHSRs in improving the load carrying capacity of RC beams. • PHSRs improved shear capacity in RC beams, regardless of the varying levels of pre-existing damage. • Dynamic reverse cyclic tests conducted in both air and submerged water environment. • Early-stage retrofitting (pre-peak damage level) improved load capacity and crack control. • Water exposure reduced load carrying capacity, but PHSRs effectively enhanced load bearing beyond pre-retrofit peak load.