Limited research exists on reinforced concrete (RC) beams incorporating polyvinyl-alcohol (PVA) fibers. This study addresses that gap through analytical investigation combined with numerical validation and parametric analysis. The results demonstrate that the shear behavior of PVA-reinforced RC beams can be reliably predicted without further experimental testing. PVA fibers enhance the mechanical performance of concrete by improving bond strength, crack control, post-cracking response, and overall shear resistance. Using the nonlinear finite-element method (NLFEM), 14 normal-strength slender beams and three ultra-high-performance deep beams made of PVA fiber-reinforced concrete (PVAFRC) were analyzed. The key parameters studied were concrete strength, fiber volume fraction, longitudinal reinforcement ratio, vertical stirrup ratio, and shear-span-to-depth ratio. The numerical results covered the evolution of shear capacity, load-deflection behavior, and crack pattern. A modified Strut-and-Tie Model (STM) was proposed to improve shear prediction. The model features a tapered diagonal strut, a prismatic top strut, and a composite tie system integrating steel bars, stirrups, and PVA fibers. Regression analysis established efficiency factors and compressive-strength relationships for fibrous concrete, accounting for fiber volume and aspect ratio. Validation against 49 experimental beams showed a strong correlation, with an average experimental-to-predicted shear ratio of 1.045 and a standard deviation of 0.168.