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Self-Anchored vs. Mechanically-Anchored Storage Tanks

03/23/2009 7:05 AM

Could anybody explain me in simple words on differentiation between self-anchored and mechanically anchored storage tanks?

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#1

Re: Difference between self anchored and mechanical anchored storage tanks

03/23/2009 9:28 AM

Mechanically-anchored tanks are held down with mechanical fasteners.

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#2
In reply to #1

Re: Difference between self anchored and mechanical anchored storage tanks

03/23/2009 10:00 AM

So what holds a self anchored unit down?

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Guru
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#3
In reply to #2

Re: Difference between self anchored and mechanical anchored storage tanks

03/23/2009 10:26 AM

Gravity. Either that or the Earth sucks.

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#4
In reply to #3

Re: Difference between self anchored and mechanical anchored storage tanks

03/23/2009 4:03 PM

GA!

(in locations and cases where the wind and/or seismic effects do not warrant anchor bolts, then yes - the tank just sits there)

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#6
In reply to #4

Re: Difference between self anchored and mechanical anchored storage tanks

03/23/2009 11:49 PM

Does you all mean that the self anchored storage tanks are not fastened by anchor bolts? Then what will happen during seismic loads & wind loads?

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#7
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Re: Difference between self anchored and mechanical anchored storage tanks

03/24/2009 1:42 AM

That is correct - a self anchored storage tank has NO anchor bolts; nothing happens to it during seismic/winds loads because it has been determined that the overturning moments do not exceed the dead load resisting moment of the empty tank (the wind/seismic loads are low due to location and tank size/parameters).

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#8
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Re: Difference between self anchored and mechanical anchored storage tanks

03/24/2009 1:48 AM

But I am refering to API 650 11th Edition. Appendix E.6.2 and these explanation is not inline with the code. Would you please refer and clarify the same again.

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#9
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Re: Difference between self anchored and mechanical anchored storage tanks

03/24/2009 2:08 AM

E.6.2.1

Resistance to the design overturning (ringwall) moment at the base of the shell may be provided by:

  • The weight of the tank shell, weight of roof reaction on shell Wrs, and by the weight of a portion of the tank contents adjacent to the shell for unanchored tanks.
  • Mechanical anchorage devices.

------------------------------------

E.6.2.1.1

"..........................................."

The tank is self-anchored providing the following conditions are met:

  1. The resisting force is adequate for tank stability (i.e., the anchorage ratio, J≤1.54).
  2. The maximum width of annulus for determining the resisting force is 3.5% of the tank diameter.
  3. The shell compression satisfies E.6.2.2.
  4. The required annulus plate thickness does not exceed the thickness of the bottom shell course.
  5. Piping flexibility requirements are satisfied.

-----------------------------

E.6.2.1.2 Mechanically Anchored

The tank configuration is such that the self-anchored requirements can not be met, the tank must be anchored with devices such as anchor bolts or straps.................

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#10
In reply to #8

Re: Difference between self anchored and mechanical anchored storage tanks

03/24/2009 2:21 AM

I hopefully didn't confuse you regarding my comments on the empty tank earlier - I was lazy and looking at an old edition (10th Addendum 2):

-----------------------

3.11.2 For an unanchored tank, the overturning moment
from wind pressure shall not exceed two-thirds of the deadload

resisting moment, excluding any tank contents, and shall be calculated as follows:

---------------------------

But have since smartened up and I am currently looking at the 11th - 2007 edition (2008 Addenda) seeing as how you are a "serious" questioner and actually have the code in front of you.

The design overturning moments have changed (much like everything else in this VERY DYNAMIC code).

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Guru
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#11
In reply to #6

Re: Difference between self anchored and mechanical anchored storage tanks

03/24/2009 4:20 AM

And flooding? They become boats instead (been there, done it, etc.).

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#5
In reply to #3

Re: Difference between self anchored and mechanical anchored storage tanks

03/23/2009 10:18 PM

You just "Earthed" him right in with that first answer, didn't you!

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Guru
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#12
In reply to #5

Re: Difference between self anchored and mechanical anchored storage tanks

03/24/2009 4:21 AM
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