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Tank design

Tank design

Tank design


I am new to this forum, so I am not sure how things work over here.

I have been working on a foundation for a tank ( 22' tall with a 12' diameter) but I am all stuck wiht the convective and impulsive components for the forces seismic design.

I am using the AWWA D100 standarts and also ASCE. ASCE doesn't have a lot equations to calculate all the varibles I need. AWWA has all the equations but its design method is complete different. Which standard should I use. Does anyone has a design guide that I can use?

I canvassed the internet but have not been very lucky with it.


Milene La Torre

RE: Tank design

I believe ASCE 7 sloshing requirements act as amendments to other codes like AWWA, API, ACI, etc. In other words, follow AWWA but substitute certain values as per ASCE 7. The tank chapter is kind of a mess and I've always struggled to sort it all out.

RE: Tank design

We usually request the calcs from the tank vendor, verify that their seismic design values are accurate, and use the reaction forces listed in their calcs.

At our firm, we always specify that the tank vendor shall provide calcs for approval prior to fabrication. In my experience, the vendors are in the best position to run the numbers because they have all the design criteria at their fingertips. Not to mention, software packages for designing tanks will automate the calcs and should provide more consitent results (in theory).

RE: Tank design

Follow primarily AWWA D100-11 (or API-650 as applicable).
Ss, S1, TL from the maps in ASCE 7, AWWA D100, or from ATC website.
Site Class from the soils report or assume Site Class D if not available.
Fa, Fv from tables in ASCE 7 or AWWA.
SMS, SM1 from Eq. 13-5 and 13-6 in AWWA (same as ASCE 7)
SDS, SD1 from Eq. 13-7 and 13-8 in AWWA (same as ASCE 7)
Ie, Ri, Rc from Table 24 and Table 28 in AWWA.
Tc from Eq. 13-22 in AWWA.
Take Sai as SDS per paragraph
Ai and Ac from Eq. 13-17 and 13-18. In Eq. 13-18, that should be Rc, not Ri.
Wi and Wc from Eq. 13-24 through 13-27 in AWWA.
Xi and Xc from Eq. 13-28 though 13-30 in AWWA.
Ws, Xs, Wr, Ht from physical dimensions and weights of the tank.
Ms from Eq. 13-23.
wL from Eq. 13-37. The 1.28HDG will control for small tanks like yours.
Av from paragraph
J from Eq. 13-36.
And that tells you if the tank is anchored or not. Unless subject to uncommonly high wind or seismic, a 22'x12' tank won't need anchor bolts.
And unless seismic loads are very high, seismic hoop stresses won't govern on a small tank and unless borderline on the J criteria, shell compression won't govern.
Check seismic freeboard required. For a slab-supported tank, there's an additional moment on tank bottom, calculated by using different values fro Xi and Xc.

Agreed with the poster above on ASCE 7 being a mess in the tank/vessel area, and that's been true through multiple revisions. Note that AWWA is service-level, not strength-level, so if you calculate moment per ASCE 7-10 or later, you also multiply by a 0.7 factor to compare to the AWWA values.

RE: Tank design

For a tank this small in diameter, impulsive forces predominate. I would not worry too much about the convective component.

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