Torsional strengthening of reinforced concrete beams using near-surface mounted steel bars: Performance evaluation and practical engineering application

This study investigates the torsional behavior of reinforced concrete beams strengthened using the near-surface mounted technique with steel bars. Eight full-scale reinforced concrete beams were tested under pure torsional loading to evaluate the effectiveness of this strengthening method. Two beams served as reference specimens, while the remaining six beams were reinforced using different configurations of steel bars embedded within the concrete cover. The key parameters investigated included the influence of variations in bar spacing and diameter and the effectiveness of different configurations of U-shaped stirrups which are used for strengthening. The experimental results demonstrated that beams strengthened with nearsurface mounted steel bars exhibited significantly enhanced torsional resistance compared to the reference beams. Beams reinforced with four faces of double U-shaped stirrups increased their ultimate torsional capacity by up to 58 percent, while those with three faces of U-shaped stirrups exhibited enhancements ranging from 6 to 41 percent. Reducing the spacing between the steel stirrups resulted in improved load-carrying capacity, and increasing the diameter of the embedded steel bars also contributed to higher torsional strength. However, the addition of longitudinal near-surface mounted steel bars had minimal impact on ultimate torsional resistance. The study concludes that the near-surface mounted strengthening technique using steel bars is an effective and economically viable method for enhancing the torsional performance of reinforced concrete beams, particularly when applied with optimal spacing and configuration of U-shaped stirrups.