This study investigates the structural performance of reinforced concrete beams strengthened in flexure and shear using high-performance fiber-reinforced cementitious composite (HPFRCC) sheets. In flexural strengthening, HPFRCC sheets were applied in the tensile zone of the beam in combination with polymer (GFRP) rebars, while in shear strengthening, the same sheets were installed independently along the beam web without polymer reinforcement. To evaluate the mechanical properties of the composite system, direct tensile, compressive strength, and three-point bending tests were conducted on HPFRCC specimens. Additionally, two reinforced concrete beams were subjected to four-point bending tests under uniform loading, and numerical modeling was performed using Abaqus to validate the experimental results. Subsequently, 45 beam models were analyzed numerically, examining variables such as shear strengthening type, flexural reinforcement configuration, and steel rebar diameter ranging from 8 to 16 mm. For beams with 8 mm steel rebars, the load-carrying capacity increased from 15.83 to 156.52 kN and energy absorption from 364.34 to 5249.33 kN·mm, corresponding to improvements of 889% and 1341%, respectively, compared to the control specimen. For 12 mm rebars, the load capacity reached 182.59 kN and energy absorption rose to 6534.50 kN·mm, representing increases of 466% and 607%. These findings demonstrate that targeted use of HPFRCC sheets in both flexural and shear strengthening, combined with optimized reinforcement design, significantly enhances the load-bearing capacity and energy absorption of reinforced concrete beams.