Quantitative evaluation of the effect of opening shape, size, and location on the shear strength of reinforced concrete beams with varying shear spans

• Opening location primarily determines shear capacity in stirrup-less beams. • Large openings placed near supports reduce shear strength by up to 80%. • Square openings cause greater capacity loss than circular shapes. • Post-cracking energy absorption drops by over 80% for large openings. • A unified geometry-based model predicts shear capacity reduction. This study quantifies the influence of web‑opening shape, size, and location, as well as the shear span, on the shear capacity of reinforced concrete (RC) beams without transverse reinforcement. A nonlinear finite‑element (FE) model was validated against published experimental results and used to conduct a systematic parametric investigation of simply supported beams containing circular and square openings with opening‑to‑depth ratios (dₒ/H = 0.2, 0.4, and 0.6). Openings were placed at multiple normalized locations (x/a) along the shear span for (a/d) = 2.7, 5.5, and 8.2. The FE model reproduced the experimental peak loads and corresponding deflection within ±2% (one deflection outlier: +11%). Results indicate that opening effects are strongly coupled with size and location. At a/d=2.7, openings with dₒ/H=0.4 placed at critical locations reduced peak load by 36% (circular) and 41% (square), whereas openings with dₒ/H=0.6 reduced peak load by 70% and 80%, respectively. Small openings (dₒ/H = 0.2) resulted in a negligible reduction. Most cases showed that the maximum shear capacity losses were close to the supports and decreased toward the loading point. An empirical geometry-based solution is proposed to estimate the reduction in shear capacity and provide quantitative limits for the placement of support openings.