Modeling of the interface shear transfer (aggregate interlock) and dowel action mechanisms as means of transferring shear stresses along preformed cracks is of great importance in determining the stiffness characteristics of reinforced concrete. An expression of an “effective” tangent shear modulus of precracked reinforced concrete panels subjected to combined in-plane shear and biaxial tension is presented based on equilibrium, compatibility, and constitutive relationships for the average stresses and strains in the concrete and steel. The proposed engineering model for shear transfer is compared with experimental results of concrete panels orthogonally reinforced with #6 bars.