For pressure vessel I normally use numerical method to calculate the base shear and overturning moment at base. Recently my client come back with their seismic calculation using Autopipe which differ a lot with my result - the base shear are the same but the overturning moment are much smaller than numerical calculation. From the report I can see that my client treat the vessel (with skirt support) as a vertical pipe with the base anchored. After running the model they get the force & moment for the anchor point, and treat it as the base shear force and overturning moment. In numerical method the overturning moment is roughly base shear force x 2/3 vessel height. My question is, can the reaction force be treated as the total overturning moment of vessel and use as the basis for support design?
Thank you.