A Levels-of-Approximation Unified Mechanical Model for the Shear Strength of Slender and Short Reinforced and Prestressed Concrete Beams with Steel, FRP, or Fiber Reinforced Concrete

This paper presents a Levels-of-Approximation (LoA) unified mechanical model for the shear strength of slender and non-slender reinforced and prestressed concrete beams, with rectangular, T- or I-shaped sections. It applies to members reinforced with steel or fiber-reinforced polymer (FRP) bars, or fiber-reinforced concrete (FRC). Derived from the Multi-Action Shear Model (MASM), the model integrates the key shear transfer actions, including shear carried by the compression chord, residual tensile stresses across the critical crack, dowel action of longitudinal reinforcement and contributions from stirrups, if present. Structured within the LoA framework, the model offers increasing complexity and accuracy for various structural design and assessment scenarios, from preliminary design (LoA 0) to detailed assessment (LoA III). Its adaptability is demonstrated through different extensions, including fatigue for RC beams without stirrups. The model is validated using 2,714 test results from 14 experimental databases, showing consistent predictions with reduced scatter, especially at higher LoAs. This unified mechanical model provides a robust tool for both the design and assessment of structural concrete elements, offering a systematic approach to integrate advanced mechanical understanding with practical engineering needs.