Innovative use of steel plates to strengthen flange openings in reinforced concrete T-beams

This study suggests using steel plates to strengthen large and small circular, rectangular and square reinforced concrete (RC) T-beam flange openings. Steel plates have been used to compensate for the flange concrete that is removed due to the construction of the openings. The used steel plates were mainly under compressive stresses; therefore, their buckling controlled their strength. Thirteen full-scale T-beams divided into five groups were constructed and tested under two concentrated loads until failure. Three groups dealt with single large openings and two groups dealt with four small openings. All beams had the same reinforcement amount and dimensions of 2500 mm in length, an overall depth of 300 mm, an effective flange width of 390 mm and a 130 mm web width. The results showed that, the presence of unstrengthened single large circular, rectangular and square openings in the flange reduced the T-beam capacity by about 42%, 40% and 34% and increased the midspan deflection by about 25%, 13% and 8%, respectively, when compared with the reference solid beam. After strengthening these large openings using 6 mm steel plates, the ultimate capacity increased by about 34%, 24% and 44%, while the midspan deflection increased by about 24%, 18% and 19% for circular, rectangular and square openings, respectively. On the other hand, the presence of four unstrengthened small circular and rectangular flange openings led to a reduction in the T-beam strength capacity by about 15% and 21%, in addition to increasing the midspan deflection by about 7% and 34%, respectively, when compared with the reference solid beam. Strengthening those small openings using 2 mm steel plates increased the ultimate capacity by about 12% and 16%, as well as increasing the deflection by about 36% and 22% for circular and rectangular openings, respectively.