7.1 Shear Failure of RC Beams without Shear Reinforcement 7.1.1 Shear in homogeneous beams In mechanics of materials,the shear stress of homogeneous各向同性，elastic and uncracked beams can be calculated by S T二 Ib where -shear force S-first moment of area (S=4.7.1 Shear Failure of RC Beams without Shear Reinforcement 7.1.1 Shear in homogeneous beams • In mechanics of materials, the shear stress of homogeneous各向同性, elastic and uncracked beams can be calculated by VS I b τ where V - shear force S – first moment of area ( S  A y )