An incremental analytical method capable of tracing the response of beams to shear is proposed. The model is based on the truss mechanism. The compatibility of strains and the equilibrium of stresses of cracked and shear reinforcement are applied to the shear model using constitutive laws of materials taking into account the effect of aggregate interlocking. This model is capable of predicting not only the shear strength but also the shear failure modes by adopting an incremental analytical method. Calculated shear strength and failure modes from the analysis are compared with experimental results and are shown to be in good agreement.