<p>This study investigates the enhancement of defective cantilevered reinforced concrete beams (RCBs) with insufficient negative moment steel overlap through the application of a strain-hardening cementitious composite (SHCC) layer. The research focuses on the casting method of the SHCC layer (cast-in-situ or precast) and the use of anchorage systems (U-shaped stirrups or anchor bolts) to optimize the interaction between the SHCC layer and the RCB. Eight RCBs, categorized into three distinct groups, were tested to assess their flexural behavior. The proposed strengthening technique effectively mitigated the deterioration caused by inadequate reinforcement overlap, as evidenced by the test results. Beams strengthened with precast SHCC layers exhibited fewer, more distributed cracks in the negative moment zone compared to those with cast-in-place SHCC layers. Debonding was observed in beams with U-shaped stirrups, whereas those with anchor bolts primarily experienced flexural failure. Specimens with cast-in-place SHCC showed a slight increase in stiffness with a nearly unchanged yielding load but achieved a higher failure load than those with precast SHCC. Notably, anchor bolts proved more effective than U-shaped stirrups in enhancing both failure load and failure mode. The experimental results demonstrated that strengthening defective beams using an externally bonded SHCC layer significantly improved their load capacity. When the SHCC layer was cast directly onto the beam surface, the load capacity increased by 73%, compared to a 65% increase with a precast layer. Adding U-shaped stirrups as shear connectors for the cast-in-place SHCC layer further enhanced the load capacity to 93%, while using steel bolts as shear connectors resulted in a 104% increase. A numerical study conducted using Abaqus confirmed a strong correlation between the proposed numerical model and the experimental findings. </p>