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RE: Fundamental period of tanks

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Tom is on target as usual. 
It was never the intent to discourage the use of the formulas in API or AWWA.  The intent of the NERHP and the ASCE 7 was to foster updating to the more current ground motions and to present equations on how to employ the new ground motions.  As the API and AWWA have developed, the NEHRP and ASCE have referenced those documents. 
In the future, the NEHRP will represent more of the cutting edge of code development using the ASCE 7 as the base.  You will also find the NFPA 59A currently provides some information regarding vertical seismic ground motions not present in the current codes, but can drive the design of liquid containing structures especially in areas of close proximity to thrust or subduction faults. 

Harold Sprague

To: seaint(--nospam--at)
Subject: Re: Fundamental period of tanks
From: Tom.Hunt(--nospam--at)
Date: Thu, 27 Dec 2007 12:43:59 -0800


From API 650, the first mode sloshing wave period (Tc), in seconds, is taken from the below formula:

Tc = Ks x square root of D

Ks = 0.578 / square root of tanh(3.68H/D)

Thomas Hunt, S.E.

"Dave Adams" <davea(--nospam--at)>
12/27/2007 12:04 PM
Please respond to seaint
Fundamental period of tanks

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.
Dave K. Adams, P.E., S.E.

Tulare, CA  93274

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