I would appreciate hearing from anyone that has had experience in storage tank settlements, both uniformly & differentially.API 650 doesn't address this very much that I can find other than:Par. 18.104.22.168 d. "The columns shall be effectively....in the event of vertical movement of the columns relative to tank bottom of up to 3 in.".Par. 22.214.171.124 (hydro test)"...differential settlement greater than 1/2" per 32 ft. of circumference or uniform settlement of 2 in."......Neither of these paragraphs address differential settlement across the tank bottom. Other paragraphs refer to "excessive" settlement without defining what is meant by "excessive".Case in point - I am designing a tank that is 100' Dia. x 64' Shell Height, 1% bottom crown up from center to outer shell. Single center column-supported roof with rafters.Geotech report says I can expect settlement of 8.4" at edge and 15" at center of tank which equates to differential settlement of 6.6" Question: do I take the 3" vertical movement of "up to 3" mentioned in Par. 126.96.36.199 d, as the max. differential allowable or am I missing something here?Any thoughts, suggestions, past experience, etc. would be really appreciated.I realize that API 653 has some guidelines but this is a new tank and thus API 653 does not apply. Any other industry standards that would apply?
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