New alternative techniques for strengthening deep beams with circular and rectangular openings

Numerous deep beam design models have been proposed; however, even the most recent design manuals provide limited guidance for deep beam design, especially when the beams have complicated features such as web openings. The openings cause a geometric discontinuity, which makes the distribution of nonlinear stress along the depth of the beam more complicated. In this paper, the structural behavior of the deep beams with openings was investigated experimentally via a total of twenty concrete beam specimens and analytically in four themes. In the first theme, eleven concrete beam specimens with circular and rectangular openings, including the reference solid specimen, were tested to examine how the shape, size, and position of the openings affected the structural behavior of the deep beams. According to earlier studies, the crack patterns and modes of failure for the specimens were discussed in the first theme, and various techniques for strengthening the openings, whether circular or rectangular, were suggested in the second theme. Six concrete beam specimens with rectangular openings were strengthened; three of them were internally strengthened using various thickness plates around the openings, and the other three were strengthened using external fasteners subjected to torque moments. As for the concrete beam specimens with circular openings, these openings were strengthened with three different reinforcement techniques in the three tested beams. The load capacity, deflection, and crack patterns for the strengthened and unstrengthened specimens were recorded and discussed. The experimental results indicated that the load capacity and stiffness of the tested beams were significantly reduced by the presence of openings. Additionally, there was a distinct variety in how the size, position, and shape of the openings affected the beams performance. The results also demonstrated that concrete beam specimens with rectangular openings that were strengthened externally by the fasteners were the best, whereas the efficiency of the remaining strengthening was lower than expected. In the third theme, a numerical study using the nonlinear finite element model (NLFE), the program ANSYS V-19.2, 2018 was conducted on some of the tested strengthened and unstrengthened specimens. The analytical study's findings demonstrated the effectiveness of the NLFE model by comparing with load carrying capacity and load-deflection curve of the tested specimens. In the fourth theme, based on Bi-directional Evolutionary Structural Optimization (BESO), an algorithm developed in MATLAB and integrated with the FEA solver SAP software was used to build the optimal strut and tie model (OSTM) for two concrete beam specimens with rectangular and circular openings. This was undertaken with the objective of seeking and finding a strengthening technique that is more effective and is dependent on a clear methodology, not on trial and expectation. In agreement with the final obtained OSTM, new alternative strengthening techniques were proposed and evaluated using NLFE. In comparison to the other techniques that were described in this research, the proposed strengthening techniques based on BESO was the best and most effective, they increased the ultimate load in some cases by 72.7 %. BESO can be used efficiency for strengthening the deep beams with openings.