I am designing a Vessel having seismic factor of 2.4g for horizontal. My vessel is in in low internal pressure but too large. I am working on an excel spreadsheet for saddles. I am confused about whether I should calculate Circumferential Compressive forces at the bottom of the saddles or not if I am using stiffening rings on saddles. which as per PVElite is =
(Q*( K.9/( TEM9*( B+1.56 * Sqrt( R * TEM9 ))))

In PV Elite if I use rings these are calculated but as per PD5500, G3.3.2.5.1.2 (Shell Stiffened by rings),it has not been mentioned to be calculated but as per G.3.3.2.5.1 (Shell not stiffened by rings), where it says that without rings compression at the lowest point of cross-section to be calculated.

For me its very critical because if I consider this compression with rings around the saddles I might have to go for local thicker plate of the shell.

Thanks