To obtain the complete solutions describing the balance of cast iron beam, it is necessary to introduce a behavioural law characterizing the physical properties of material. The goal of this work is to study the response of cast iron beam by taking into account the variation of the shear retention parameter (aggregate interlock) and the mesh density. The cast iron as a brittle material was assumed as elastic-plastic material and follow concrete model failure criterion with associated flow rule. The element includes a smeared crack approach for handling cracking in tension zones and a plasticity algorithm to account for the possibility of crushing in compression zones. The amount of shear transfer across a crack can be varied between full shear transfer and no shear transfer at a cracked section. This option is controlled by a coefficients called shear retention factor and range between 0 (no aggregate interlock) to 1 (full aggregate interlock). It is also noted that the best choice of a shear retention factor play a significant role in the total response of the structure. The numerical results obtained are compared with other results obtained in the literature.