Flexural behavior of RC beams with multiple parallelogram openings

Abstract

On account of the detrimental effects of the post-drilling holes in hardened RC beams, designing the beams with transverse openings before construction is becoming more popular in the last decades. The contribution of the transverse openings to the overall economy and efficiency of construction by reducing the unusable dead space in the floor height is a rather significant motivation behind the vast number of studies on this topic. In search for the opening geometries and reinforcement schemes with the least negative effects on the beam behavior, the present study focused on the parallelogram (diamond) opening geometry, which is thought to facilitate the transmission of diagonal compression forces in the beam web thanks to the inclination of the posts. Within this scope, a total of 12 beams, including two reference beams without openings, were tested under four-point bending. Circular, square and parallelogram (45°−60°−75°) opening geometries were adopted and the test results were evaluated based on the opening geometry and the longitudinal reinforcement ratio. In order to avoid various shear failure modes of beams with openings, different special reinforcement schemes were employed around the web openings. Two different longitudinal reinforcement ratios were used to understand if pure flexural failure can be reached in RC beams with openings without being affected by different shear failure modes (beam- and frame-type diagonal tension and diagonal compression). The inclination angle of the posts between the openings in parallelogram opening geometry was found to be the most crucial parameter in the final beam failure and beam ductility. The use of diagonal cables surrounding the openings and connecting the posts and chords was established to be obligatory in square and parallelogram opening geometries to reach a ductile beam behavior without being affected by Vierendeel panel action and different shear failure modes.