Re: Fundamental period of tanks

The majority of our business involves rectangular and circular concrete tanks, so we use the provision of ACI 350.3. Chapter 9 describes the dynamic model. Since most of the walls or our tanks are of uniform thickness, we use the approximation for the wall stiffness given in the commentary of section 9.2.4 (rectangular tanks). It does require a bit of calculation to come up with the impulsive period (T-sub-i), but we have developed several spreadsheets that greatly speed up the work. Circular tanks are similar, but the formulas for stiffness are directly in the code, not the commentary.

--Kipp Martin
Carollo Engineers
Portland, OR

>>> "Dave Adams" <davea@laneengineers.com> 12/27/2007 12:04 PM >>>
Hello everyone,

Those of you who deal with non-building structures: How are you
spending your time determining the fundamental period of flat-bottom
tanks (T-sub-i in ASCE 7-05, Section 15.7)? Are you actually modeling
and calculating the value or using simplified equations from material
standards (i.e. AWWA or API)? ASCE 7 appears to really discourage the
use of simplified equations.

Thanks,
Dave K. Adams, P.E., S.E.
LANE ENGINEERS, INC.
Tulare, CA 93274

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