This paper presents a detailed investigation into the failure analysis of heavy duty semi-autogenous grinding mill. The influence of the presence of ribs at the trunnion-end plate junction on the redistribution of stress levels, the effect of centrifugal forces, support conditions and thickness of the major parts of the mill are studied. The analysis is based on finite element method and full advantage of the rotational periodicity is taken by which it is possible to study the entire structure by analyzing only one repeatable sector (sub-structure) in the circumferential direction.