Flexural Strengthening of Reinforced Concrete Beams with Substandard Tension Lap Splices Using a Novel Pre-stressing Technique

Abstract Sudden failure of reinforced concrete (RC) beams with substandard tension lap splices due to low resistance to flexure is a critical issue that needs to be addressed. Accordingly, a novel pre-stressing technique is presented in this paper, which offers a promising solution for strengthening RC beams with substandard tension lap splices. The technique involves the use of external steel bolts, load-transferring brackets, and bearing plates. Eleven test specimens sized 100 × 200 × 1500 mm 3 were utilized in a series of experimental investigations to assess the effectiveness of the suggested approach. These specimens consisted of one specimen without a tension lap splice, one with a sufficient tension lap splice equal to 60 d b , and nine beams with insufficient tension lap splices equal to 25 d b . The investigation considered three main variables for eight strengthened specimens: the length of the strengthening plate ( L s = 60 d b , 80 d b , and 100 d b ), the number of bolts ( N b = 2, 3, and 4 pairs), and the pre-stress level in the bolts (PL = 0.1 f y , 0.2 f y , and 0.3 f y ). The effects of the proposed strengthening technique on ultimate load ( P ult ), first cracking load (Pc), deformation behavior, failure pattern, cracks distribution, deflection ductility, flexure toughness, and elastic stiffness were investigated. The findings demonstrated that the pre-stress approach considerably enhanced the ultimate load (61.52–218.65%) and first crack load (80.15–106.40%) of the strengthened specimens compared with the control specimen. In addition, there was a notable improvement in flexural toughness and elastic stiffness, with an average value of 205.5% and 101.35% for all strengthened specimens, respectively. Also, strengthened RC beams showed considerable improvements in ductility, with an average increase in peak ( μ p ) and ultimate deflection ( μ uf ) indices of 120.16% and 94%, respectively. In general, the novel pre-stressing technique enhances the structural performance of the beams by increasing their load-carrying capacity, improving ductility, and enhancing crack resistance.