Vertical & Horizontal Reinforcing for Ground Storage Tank (GST) Foundation

oengineer,

I would say your ring r/f (steel on the side of the ringwall) is horizontal. But I would also wager that that the amount of steel required by the design of the ring will likely be much larger than .0020/.0025 of the area.

Please note that is a "v" (as in Violin) not a "y".

WinelandV said:

oengineer,

I would say your ring r/f (steel on the side of the ringwall) is horizontal.

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Do you possibly have any technical document that explicitly states this? Or where it is mentioned in ACI?

Chapter 14, in the older formatted ACI 318 is for walls, not grade beams, so this section wouldn't apply to your ring beam.

However, the ring beam would be, in my view, considered as a foundation, or possibly just a beam. In that case, minimum values of reinforcing would be handled per those applicable sections.

As WinelandV states, your ring beam longitudinal (horizontal) reinforcement needed for the tension force will be more than any minimum value.

I opened up API650, went to appendix B.4.2.3:

API 650 B.4.2.3 said:

a) ringwall shall be reinforced to resist direct hoop tension...

b) ringwall shall be reinforced to resist the bending moment resulting from the uniform moment load (eccentricity of the shell and pressure loads relative to the centroid of soil pressure)

c) ringwall shall be reinforced to resist the bending and torsion moments resulting from lateral loads

d) total hoop steel area required to resist the loads noted above shall not be less than the area required from temp changes and shrinkage. Hoop steel area req'd for temp changes and shrinkage is 0.0025 times the vertical X-sectional area of the ringwall or the minimum r/f for walls called from in ACI 318, Chapter 14.

e) For ringwalls, vertical steel area req'd for temp changes and shrinkage is 0.0015 times the horizontal x-sectional area of the ringwall or minimum r/f for walls called for in ACI 318, chapter 14...

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There is no other reference to "horizontal steel" outside of the hoop steel in API 650 Appendix B.

Please note that is a "v" (as in Violin) not a "y".

FYI, "ACI 318, Chapter 14" in the 318-11 and earlier (-08, -05, etc.) is the chapter on walls. Even though my copy of the API 650 is from 2020, no one there apparently bothered to update the ACI code references.

Please note that is a "v" (as in Violin) not a "y".

API 650 B.4.2.3 said:

e) For ringwalls, vertical steel area req'd for temp changes and shrinkage is 0.0015 times the horizontal x-sectional area of the ringwall or minimum r/f for walls called for in ACI 318, chapter 14...

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Even the way it is mentioned in API can be confusing....it says vertical reinforcement but tells you to use the "horizontal x-sectional area of the ringwall" .

The hoop steel (shown as dots in the section) is the horizontal steel. Including steel on each side and additional bars at top and bottom.
The enclosed stirrups are the vertical steel. In some cases, those may be shown as vertical bars on each face rather than enclosed stirrups.
ACI 318 is for buildings, and it is not obvious how some provisions would apply to a ringwall, and that's one reason some of these minimums were incorporated into API-650.
For small tanks, minimum hoop steel requirements will control.
For large tanks, steel required due to hoop force will govern.
Due to increased loading on the inside part of the ringwall, you can also generate a net moment in the ringwall section, and that may be why they put additional bars at top and bottom rather than putting them all on the sides.
The center of the ringwall can be offset from the nominal shell radius if desired.
Depending on the fabricator, the nominal diameter may be inside of the plates, outside of the plates, or centerline of the plates.

The picture attached does not give a lot of info regarding the tank size , diameter, ..and design loads

The anchors and T & B reinf ( 20*30M) .implies the tank is subject to uplift .

I would understand ;

- The vertical reinf. M15X300 (E.F.) As v= 2*177*1000/300=1180 mm2/m ratio=1180/(600*1000)=0.002

- The horizontal reinf . 22*30M+ 20*30M( T&B) Ash= 42*707=29690 mm2 ratio =29690/(600*2200)=0.022

I will suggest you ;

- If you write ( Best Practice , Storage Tank Ringwall Foundation Design ) and search the web, one of the outcomes attached below..

- Consider to provide more info . to get better responds..







I cannot give you the formula for success, but I can give you the formula for failure..It is: Try to please everybody.

oengineer (Structural) said:

Even the way it is mentioned in API can be confusing....it says vertical reinforcement but tells you to use the "horizontal x-sectional area of the ringwall" .

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I don't think it's that confusing. If you were designing a concrete column, the cross section you'd use to check for minimum steel (1% in the ACI code) would be a "horizontal cross section".

Please note that is a "v" (as in Violin) not a "y".

To recap, based on what has been mentioned in this thread, the horizontal reinforcement is for the side walls of the ringwall concrete foundation. The vertical reinforcement is for the top & bottom of the ringwall concrete foundation.

This seems to be inline with the gross area that the PIP example uses for calculating the reinforcement: