Post-Drilling Structural Damage Assessment in Existing Reinforced Concrete Beams: Experiment and Simulation

Drilling openings in the web of reinforced concrete (RC) beams to accommodate pipe installations effectively increases the clear height of buildings, facilitates construction, and is economical and practical. This technique has been widely adopted in the renovation of existing RC structures. In this study, the flexural and shear behaviors of eight full-scale RC beams were tested to investigate the influence of circular openings on their load-bearing performance. These openings were introduced after the specimens had been formed, thereby simulating real-world conditions. The failure modes, flexural and shear capacities, moment/shear-deflection relationships, as well as the strains in concrete and reinforcement of the RC beams were analyzed by taking into account various factors. These factors include the depths of the top chords, the statuses of stirrups, and the distances between opening centers and supports. The results indicated that the impact of the opening on flexural capacity was relatively weak, while its influence on failure mode was pronounced. The RC beam with a 100-mm top chord exhibited quasi-brittle bending failure behavior. Furthermore, the presence of an opening within the shear span significantly reduced the shear capacity of the RC beam. Additionally, numerical simulations were conducted to investigate the mechanical properties of the RC beams further by varying the top chord depth and shear span ratio. The simulation results revealed that ductile failure occurred in beams with a minimum top chord depth of 130 mm within the pure bending span, while the most critical opening location was identified at the center of the shear span. Finally, a refined equation of high precision was proposed to predict the shear capacity of RC beams with circular openings. These findings are valuable for evaluating the flexural and shear capacities of RC beams that incorporate such openings.