Reinforcement Design of Concrete Ringwall Foundation

Can you provide a reference that says it is not acceptable?

Klitor said:

Can you provide a reference that says it is not acceptable?

Click to expand...

Could you please elaborate? Are you asking me to provide info saying it is not acceptable to just apply the reinforcement to each face of the Concrete Ringwall?

My goal is to determine if it is recognized as acceptable industry practice (i.e. from either ACI, PIP, or API) to apply the reinforcement to each face.

The images that I provided in my original post show different ways of reinforcement distribution in the cross section of ringwall foundations.

If the width to diameter ratio is small, thin walled cylinder stress distribution says the tension stress in the ring will be almost the same at the inside wall as the outside wall. Otherwise use a thick walled ring formula.

The second and third pictures are copy and paste from PIP STE03020 . My opinions and suggestions based on past design experience are;

- there is no specific requirements of ACI for this specific case , however, the minimum Temperature and Shrinkage Steel requirements should be adopted as suggested in PIP STE03020..

- The ring reinf. could be evenly distributed to each face of the Concrete Ringwall. However,it is reasonable if the exterior face reinf . is greater than interior face as far as min. reinf. and spacing requirements are met..

- The third picture, width of ring wall 18 in, and inside edge distance L = 8 in.. I always preferred ( L ≥ W/2 ) to minimize the twisting moment and for more uniform soil stress under the ring wall..

I have not seen a ring with such an apparent large eccentricity of the shell bearing on the wall. Is it as great as it appears?

This being more typical placement to my experience.

HTURKAK said:

The second and third pictures are copy and paste from PIP STE03020. My opinions and suggestions based on past design experience are;

- there is no specific requirements of ACI for this specific case , however, the minimum Temperature and Shrinkage Steel requirements should be adopted as suggested in PIP STE03020..

- The ring reinf. could be evenly distributed to each face of the Concrete Ringwall. However,it is reasonable if the exterior face reinf . is greater than interior face as far as min. reinf. and spacing requirements are met..

Click to expand...

The 2nd & 3rd images are from PIP STE03020.

Is their any technical info (i.e. ACI, PIP, or API) that talks about evenly distributing the reinforcing to each face of the Concrete Ringwall?

I was informed that Twist steel is placed in the bottom of the beam for self-anchored tanks and in the top of the beam for mechanically anchored tanks.

When using the STAAD Foundation Advanced, I was also informed that the program (when it comes to hoop tension steel) first tries to distribute the bars evenly between the top and bottom faces. Based on the examples from PIP, it seems odd to me for their to only ever consider rebar steel for just the top & bottom face of the Concrete Ringwall.

I'd put them on the outside face as much as possible (maybe 2/3, 1/3), but it likely doens't matter. Are your bursting forces so great that you need that much reinforcing?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

dik said:

Are your bursting forces so great that you need that much reinforcing?

Click to expand...

Could you please elaborate on this statement?

I do not know any specific requirements of ACI, API, PIP... for the distribution of hoop + twisting reinf. In past, i preferred evenly distributed hoop + twisting reinf and follow the minimum spacing rules. I have never designed ring found having large eccentricity.( e.g. for figure A1, DE 1, i would prefer L=20 in. rather than 8 in. for W=30 in footing..)



Refer to Figure 5. ( Calculation of Twist Moment) . The best place for the steel to resist twist moment are the corners of the section (bottom corners..).IMO, it is more reasonable to minimize the twist moment.





I do not know the algorithm of STAAD .. The hoop reinf. should be distributed on outer and inner face .. You may prefer to model the ring beam with shell elements..
If seismic loading governs,

- for self anchored tanks , some portion of the tank may experience uplift and axial compression will develop at the opposite side ..in this case, if the ring beam modelled as beam on elastic foundation, you may need bottom reinf.

- for mechanically anchored tanks, the assumption is, the seismic moment would be resisted by anchors ( not by some portion liquid content ) and the moment will be triangular distributed to the anchors. This concept could be reasonable for the mat foundations or ring foun. supported on piles.. However, i DO NOT see the logic for a shallow ring found that ,would not experience uplift while 100 times heavier tank can uplift..

My suggestion would be,

- If your zone is API zone, follow the rules of API 650 etc and STE03020.
- Pls look NZSEE: Seismic Design of Storage Tanks: 2009 to understand the behavior and the concept ..
- The following doc. gives valuable info for the seismic behavior of tanks and anchors..


P.S. Regarding the first picture ( typical ring beam foun.) 10D25 T& B rebars provided and there are anchors with unknown diameter and no's..The ring foundation ( having dims 600 X2200) has unit wt 33 kN /m probably cannot resist to the uplift force transfered with anchors ...

The reinforcing appears to be fairly high and can resist a significant tensile force (bursting). The large amount of reinforcing may be to limit strains?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik