The failure risk of defected reinforced concrete (RC) beams is considered a potential threat. This risk is experimentally identified, numerically analyzed, and thoroughly diminished to enhance structural safety and sustainability to mitigate the potential for structural collapse during construction. This research investigates the efficacy of an external post-tensioning mechanism in enhancing the behavior of defected RC beams lacking shear reinforcement, employing both experimental and numerical approaches. Fourteen RC beams were tested to evaluate the impact of posttensioning force levels and the inclination angle of post-tensioning bars. The study found that regardless of force magnitude or angle, post-tensioning improved the failure characteristics of the non-stirrup beam. The failure mode transitioned from brittle to ductile, resulting in a more advantageous distribution of cracks. Reinforced beams exhibited increased cracking and ultimate loads, with the enhancement more pronounced at higher post-tensioning force levels. Inclined post-tensioning at angles of 75°, 60°, and 45° demonstrated substantial enhancement in cracking and ultimate loads, as well as elastic stiffness. The findings highlighted the superiority of inclined post-tensioning configurations, especially at 60°, for reinforced beams. Moreover, the study revealed a significant increase in absorbed energy with the proposed strengthening system. Additionally, finite element modelling (FEM) was used to replicate the tested beams. FEM accurately predicted the crack development, ultimate capacity, and deformation, aligning well with experimental observations.