Abstract
The strength of reinforced concrete members can be enhanced by using the externally bonded reinforcement (EBR) and near-surface mounted (NSM) methods. However, very few studies have adopted the NSM method for torsional strengthening. Although previous studies have reported the efficacy of using epoxy-resin-bonded NSM steel bars in increasing the flexural and shear strength of RC beams, no study has examined the use of steel bars and epoxy adhesives for torsional strengthening. Therefore, this study investigates the behaviour of RC beams subjected to the combined actions of torsion and bending moment when they are strengthened with NSM steel bars (Ø10 mm) in different configurations. The practical part of this investigation consisted of seven cast and tested beams of 150 × 250 × 2000 mm dimensions. One beam was reference, which is not strengthened; meanwhile, all the other beams were strengthened with two U-shape-welded NSM steel bars. During the testing process, the twist angle at the torque intervals, first cracking torque, ultimate torque, and ultimate twist angle of the conventional beam were compared with those of the strengthened beams. The torsional performance of the RC beams was significantly improved by using NSM steel bars, whereas in various NSM configurations, the 90° NSM beams outperformed the 45° NSM beams.
Highlights
Strengthening materials can be applied to RC elements in two techniques, namely, (1) the externally bonded reinforcement (EBR) method, where the strengthening materials are externally applied to the concrete surface, and (2) the near-surface mounted (NSM) method, where the strengthening materials are inserted within grooves that are precut into the concrete cover [1]
Considered as a proper alternative to the EBR method, the NSM strengthening technique comprises cutting grooves in the concrete cover of a specimen and inserting rods into the grooves by using an adhesive. e NSM method presents numerous advantages over the EBR method, including its higher bonding productivity and better protection. e NSM method can address the limitation of the EBR method in its maximum strain, which is lower than the ultimate strain due to premature debonding. e greater confinement granted by the adhesive and the surrounding concrete is considered the best advantage provided by the NSM method [2]. is strengthening technique has already been proven to be effective for the shear strengthening [3,4,5,6] and flexural strengthening of RC beams [7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22]
Al-Bayati et al [30] tested 10 beam specimens, with two beams serving as controls and the other eight beams strengthened by applying CFRP laminates to their four sides. ese beams were inserted into grooves by using the NSM method
Summary
A considerable amount of torque can accumulate in many concrete members, including curved bridge elements, spandrel beams, horizontally curved members, and eccentrically loaded beams. e torsional capacity of these members needs to be maximised due to several factors, including structural damage, deterioration, eccentricity in loading, skewness, curved box girders, and increased loading. In [31], Al-Bayati et al applied the same torsion strengthening technique, but instead of applying CFRP laminates to the four sides of the beam, they tied a CFRP rope around the cross section of beams with an equivalent carbon fibre percentage. In their experiment, they used a cement-based adhesive and tested four beams: two matching control beams and two supplemental beams, where torsion has been strengthened by using a CFRP rope and epoxy. To fill this research gap, this study examines the characteristics of RC beams subjected to the combined actions of torsion and bending moment when they are strengthened by NSM steel bars in different configurations
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