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RE: Seismic Design of Nitrogen Storage Tank[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>
- Subject: RE: Seismic Design of Nitrogen Storage Tank
- From: Harold Sprague <spraguehope(--nospam--at)hotmail.com>
- Date: Wed, 5 Nov 2008 14:56:21 +0000
You are correct that Bob Wozniak one of the original developers of the seismic impulsive and convective fluid forces. He was with Chicago Bridge and Iron (now CBI since they are no longer in Chicago, don't do bridges and don't fabricate iron). Among his group at CBI were Greg Soules (still with CBI in Texas) and Steve Meier (currently a VP with Tank Industry Consultants).
The work of Wozniak was predicated on the work of Dr. George Housner's in the 1960's from the nuclear power industry. Another major contributor to the world of fluid response in earthquakes was Nick Legatos (retired from Preload Tank). Nick was the primary developer of ACI 350.3 Seismic Design of Liquid-Containing Concrete Structures. The ACI 350.3 is a particularly valuable document for the study of seismic impulsive and convective fluid responses because of the work Nick put into the commentary. After all, fluid response is fluid response. Just because it is in a concrete document does not change that.
There is also a lot of good commentary contained in the NEHRP Provisions and Commentary available for free at the BSSC web site. Contributors to the NEHRP were Greg Soules, Steve Meier, and Nick Legatos.
Regards, Harold Sprague
Subject: Re: Seismic Design of Nitrogen Storage Tank
Date: Tue, 4 Nov 2008 15:15:03 -0800
Look in the ASCE Guidelines for Seismic Evaluation and Design of Petrochemical Facilities, page 4.A-4: T=7.78/10^6*(H/D)^2*(12*W*D/T)^(1/2). For your tank, safely assume 1/2" shell thickness.
This formula is recommended for tanks on legs, but actually is for a cylindrical column. I discovered that legs significantly affect the tank rigidity, and may require special consideration during the T analysis.
Yours appears to be a 6000-gallon LIN tank of some earlier construction. Calculated more or less accurately, the period of such tank is about 0.16 sec.
It should be noted that after all research I've done, the formulas of ASCE7 13-15 appear to adequately reflect the force - consistently with AWWA D100 and the above ASCE book. At the end of the day, it all comes down to a good old 0.3*W (ASD, CA away from faults), so it may not be worth your time to go really deep into that.
Regarding sloshing - back in 2001, I had a long talk on the subject with Bob Wozniak who apparently is one of (if not the) main structural gurus behind the AWWA D-100. He informed me that for smaller D/H, sloshing becomes a force-reducing factor and can be safely ignored (as is routinely done). This can be also derived from the AWWA formulas.
V. Steve Gordin, SE
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