Experimental evaluation of the effect of openings on the structural performance of diagonally reinforced coupling beams.

In some cases, it is necessary to create openings in coupling beams to accommodate utility pipes and ducts. The presence of these openings can alter the behavior of coupling beams, making their performance differ from that of solid coupling beams (without openings). However, research on the structural performance of coupling beams with openings is limited. To address this gap, three diagonally-reinforced half-scale specimens were investigated in this study, two with openings near the span end of coupling beams and one without (solid) which served as the reference. For one sample, the use of additional diagonal bars at opening corners together with short stirrups above and below the openings were investigated as an attempt to mitigate the effect of opening. The results should help design engineers to understand the behavior of coupling beams containing openings and give solution to mitigates the negative effect of openings when necessary. Based on the conducted experiments, it is shown that the presence of openings has a pronounced effect on the overall behavior of coupling beams. Adding an opening with relative dimensions of (lo/l = 0.14 and ho/t = 0.24) near the end span of the beam increased the number and width of cracks, and reduced both the beam strength and ductility by 16.25% and 20.30%, respectively, compared to the corresponding solid coupling beam. Nevertheless, reinforcing the opening with diagonal bars as well as using short stirrups in beam parts above and below the opening mitigated the negative effects of the opening presence. Specifically, this added reinforcement controlled cracking, and increased beam strength and ductility by 10.46% and 23.60%, respectively. This brought the beam behavior closer to that of a solid one (without openings). It is also found that the ACI-318's shear capacity equation for diagonally reinforced coupling beams is conservative and needs to be modified. The later findings agree with a number of previous studies.