Abstract This study experimentally and numerically investigated the shear behavior of UHPFRC deep beams with internal-opening reinforcement, focusing on how internal-opening reinforcement detailing can mitigate opening-induced shear capacity loss. The test program included eight simply supported UHPFRC deep beams tested under four-point loading and arranged into two groups with different geometries. Group I comprised five beams with an a/d ratio of 0.61, including one solid reference beam and four beams with a square opening within the shear span, and intersected the load path. Group II comprised three beams with an a/d ratio of 0.79 and different opening sizes. Three internal opening reinforcement techniques with different ratios were examined: (1) additional vertical and horizontal bars around the opening ( µ av = µ ah = 2.7% or 2.4%), (2) additional stirrups ( ρ va = 4.2% or 5.6%) with vertical and horizontal bars around the opening ( µ av = µ ah = 2.7% or 2.4%), and (3) diagonal cross-bars around the opening ( µ ax = 1.8%). The results showed that the unreinforced opening reduced the cracking load by 41.4% and the ultimate load by 40.4%, compared with the solid beam. Techniques (1), (2), and (3) increased ultimate shear capacity by 16.5%, 69.2%, and 25.3%, respectively, versus the unreinforced opening beam, achieving approximately 54.6%, 79.4%, and 58.8% recovery of the solid-beam capacity. A 3D numerical model using concrete damage plasticity reproduced damage and load–deflection responses, with mean experimental-to-numerical ratios of 1.08 for ultimate shear load and 1.30 for midspan deflection, supporting the model’s predictive reliability for deep beams with internal opening reinforcement.
Yousef et al. (Sun,) studied this question.