pca circular concrete tank compression ring

huangyhg

pca circular concrete tank compression ring
when going through pca's "circular concrete tanks without prestressing", there does not seem to be any accounting for loads on the outside of the wall.  i've heard references to compression ring action which makes sense but could someone tell me where i could find some documentation on this.  i'm also concerned that for larger diameter tanks, the compression ring would tend to start acting one way instead...could someone please give me some direction here...thanks in advance
the pca manual provides for loads on one side of the wall only, neglecting the oposite side. loading condition 2 indicates an empty tank with all loads imposed by the backfill on the outside of the tank. the design example gives a pretty good description of the philosophy and procedures involved.
since the ringwall is usually slightly above grade there would be no major difference in soil heights on either side of the ringwall.  there is little chance for the exterior soil to become passive since this would require the ringwall to move outward.  any loading on the ringwall from an exterior source would probably be transitory, truck traffic etc.  this would place a surcharge loading on a portion of the ringwall.  this action would be similar to a  ring with an external compressive force.  
see formulas for stress and strain by roark or theory of elastic stability by timoshenko & gere.  there is little problem with this external loading.
best, tincan