Reinforcement methods of an reinforced concrete beam with the circular opening in the plastic hinge region under cyclic loading

Transverse opening in the plastic hinge region of reinforced concrete (RC) beam is generally not recommended due to increased risk of shear failure rather than flexure or flexure-shear failure. However, in recent years, the actual pipeline configuration requirements have posed challenges in arranging such opening in the plastic hinge region of an RC beam member. To address this issue and propose design guidelines, this work examines the mechanical behavior of nine specimens subjected to cyclic loading. The test results are compared with the design methods suggested in other guidelines and research. Additionally, a set of design guidelines and novel reinforcement methods, utilizing Double-square hoop and U-shaped stirrups, are proposed and compared with traditional reinforcement methods for RC beams with circular openings. Three distinct regions for reinforcing beams with transverse circular openings are proposed based on their distance from the column support. In the first region, extending from three times the opening diameter to one beam depth (1H), the opening is reinforced with two inclined U-shaped stirrups on each side and double-square hoops on both faces. The second region (1H to 2H) utilizes one inclined U-shaped stirrup on each side, along with double-square hoops on both faces. Beyond twice the beam depth (2H) in the third region, the opening is reinforced solely with double-square hoops on both faces. The sets of design methods provide valuable insights for future design considerations.