RC Deep Beams with Vertical Openings: Behavior and Proposed Mitigation Techniques

Vertical openings in beams and girders are sometimes used to facilitate the passage of essential services such as HVAC, electricity, and sewage. There is a lack of research on the effects of vertical openings on deep reinforced concrete beams. In this work, 11 RC deep beams were tested to failure, examining key parameters, namely, location of opening, opening shape, and strengthening technique around the opening. The beam ultimate load ($P_u$) and to a lesser extent stiffness were found to be affected by the presence of openings, wherein those located in the shear span reduced $P_u$ by 12%–19% and those in the constant-moment region contributed to a respective decrease of 8%–13%. The reduction in $P_u$ is also related to the opening shape with rectangular and circular shapes, resulting in the largest and smallest decrease, respectively, and square being in the middle. Two techniques were proposed to mitigate the openings effects, namely, using ultrahigh-performance concrete (UHPC) in the vicinity of the opening, and reinforcing the surrounding opening area with horizontal and vertical steel bars. Both were found effective, with the former resulting in 14% and 10% increase in $P_u$ relative to beams with openings located in the shear and moment regions, respectively, and no strengthening. Additionally, $P_u$ from tests were compared with those calculated using the strut-and-tie model (STM) and an empirical formula from current US standards. Modifications to the STM model, which resulted in better predictions than the expression from current standards, but still needed improvement, were presented, and resulted in an analytical-to-experimental $P_u$ ratio of 0.99 to 1.05.