Strengthening of Reinforced Concrete Beams ‌‌Having Circular Openings Using Near Surface Mounting Steel Bars

ABSTRACT

                    Reinforced concrete (RC) beams characterized by circular openings present inherent structural challenges, resulting in a compromise of their load-bearing capacity and overall structural integrity. This thesis endeavors to confront and resolve this issue through the implementation of an innovative approach involving Near Surface Mounting (NSM) steel bars. Circular openings, integral to architectural designs, frequently engender a diminution in the strength of beams. This study investigated the effectiveness of utilizing near-surface mounted (NSM) steel bars to restore the shear strength of deep beams and the presence of openings in slender beams. The experimental work involved testing fourteen simply supported reinforced concrete beams. These beams were divided into two groups, each consisting of beams with different shear span-to-depth ratios (a/h = 1.5 and 3.65). Two specimens served as control samples, while the remaining beams had openings located at various positions. The openings were categorized as large or small, with opening height ratios (h_o/h) of 0.4 and 0.2, respectively. In the second group, six specimens were strengthened using near-surface mounted (NSM) steel bars arranged in three different stirrup configurations: (square, diamond, and parallelogram). All the beams had a cross-section of 100 mm × 200 mm and a total length of 2000 mm. The variables examined in the tests included the sizes and locations of the openings, the diameter of the bars, and the arrangement of the strengthening bars around the openings. The test results revealed that the presence of openings in the beams led to a reduction in the ultimate load. For specimens with large circular openings in the deep beam's shear zone, large circular openings in the slender beam subjected to shear, large circular openings subjected to shear and flexural loads, and small openings in the slender beam subjected to shear and flexural loads, the ultimate load decreased by approximately 45%, 18.7%, 14.6%, and 19.5%, respectively. Additionally, the test results showed that specimens strengthened with diamond stirrup bars exhibited an improvement in the ultimate load of up to 33.1%. Meanwhile, specimens strengthened with square and parallelogram stirrup bars demonstrated improvements of up to 21.5% and 26.5%, respectively. Changing the bar diameter had a slight effect on increasing the ultimate load, specifically for the parallelogram and square schemes, resulting in an increase of approximately 10% and 7%, respectively.