Shear strength reduction due to introduced opening in loaded RC beams

The reduction of shear strength due to the introduction of an opening is an ongoing problem for reinforced concrete (RC) beams. Fifteen rectangular section (150 mm × 300 mm × 1650 mm) specimens were tested and divided into six groups under three considerations: 1) opening dimensions and shape, 2) time needed to create an opening for a new or an existing building; 3) external and internal strength of the opening in RC beams. The results demonstrate that a reduction in stiffness occurs due to the presence of an opening. The stiffness reduces further when the opening is placed under loading because of the reduction in the effective moment of inertia due to formation cracks around the opening as a result of the opening process. The stirrups besides the opening resisted shear force with ratios between 35% and 65% from the yield strength of steel bars and must be considered for shear resistance. Finally, the initial proposal equation that calculates the resistance shear force taken by the vertical stirrups around the opening can serve as a guideline for the introduction of an opening in RC beams.