Concrete Ring Beam Foundation for Storage Tank 4

[oengineer]

I am working on the design of a Concrete Ring Beam Foundation for a Storage Tank and I am trying to ensure that the space within the ringwall is suitable to provide support for the tank dead load and the product surcharge load.

In the PIP Guidelines for Tank Foundation Designs, the design examples (Appendix A - Ringwall Foundation Design Examples) show the design of the actual Concrete Ring Beam Foundations but do not show how to verify the capacity of the soil in the space within the ringwall.

I would think that the Concrete Ring Beam is supporting all of the loads from the Tank, but it appears based on PIP that may not be the complete case.

My soil report states the following regarding the site preparation (see information in the link):

https://files.engineering.com/getfi...d68-4d9c-b603-9e18e38e6b06&file=soil_info.pdf

Is there an example calculation on how to verify the load capacity of the space within the ringwall?

Comments/suggestions are appreciated.

 

[oldestguy]

Looks like a good report recommendation. The only thing missing from what you provide is test boring information. However if there was a problem in deeper soil, it would have mentioned it and the treatment needed. It would be expected that, since nothing is mentioned about the deeper soil and possible treatment, an acceptable amount if settlement would occur. Normally reports like this do the settlement estimating and do not expect the user to do any comps on settlement.

 

[HTURKAK]

The allowable soil-bearing pressure is site specific information and should normally be provided by the geotechnical engineer acc. to the bor-log data and lab tests.


The ring foundation primarily to support the shell and confine the soil in the space within the ringwall. The ringwall is provided with hoop reinforcement to resist the active thrust from confined soil. The tank essentially supported by ground.


The attached document provides general recommendations and does not provide site specific info.

If you want to receive more valuable responds, provide more info .(i.e. tank dimensions, content, roof type, soil data.. )

 

[r13]

The first you need to know the type of tank bottom - self support, or sub-framing (see sketches below). Then furnish this information and the maximum content weight to your geotechnical consultant to obtain recommendation on soil bearing and potential settlement, which will increase the stress on tank steel, and affect the ring wall foundation.

 

[SlideRuleEra]

...do not show how to verify the capacity of the soil in the space within the ringwall.
Is there an example calculation on how to verify the load capacity of the space within the ringwall?

Load capacity of the existing soil within the ringwall is not needed. Per the PIP document (page 12 of 81), that soil is removed and replaced:

Replacement material is specified in your soil report:

Here is the link to the specification for TxDOT Standard Specifications Item 247, Type A or D, Grade 1-2.

http://www.SlideRuleEra.net

 

[JStephen]

Generally, the load capacity inside the ringwall is just taken as allowable bearing as specified in the soils report.
The net bearing will include any fill above grade and the tank bottom plate as well.
The extent of fill under the bottom should be confirmed with the geotechnical engineer, and will not necessarily involved new fill all the way to the bottom of the ringwall.
It is not uncommon to see soil reports that will specify allowable bearing for the ringwall that is lower than the product pressure inside the ringwall (IE, 3,000 psf allowable for the ringwall, but the product depth gives 4,000 psf inside the ringwall.) In that case, contact the geotechnical engineer and confirm that is the intended recommendation and not just an oversight. In a lot of cases, that allowable bearing will control the depth of the tank.
For petroleum tanks, the long-term static loading may be somewhat less than the hydrotest load due to differences in product density. There again, contact the geotech to see how that should be handled if the load bearing is marginal for the application. Review any hydrotest recommendations (depth of filling and rate of fill, available water flow rates) to see how prolonged that hydrotest will be.
Generally, it is assumed that when you have a uniform load over a large area, that the column base plate loads can still exceed that load by a reasonable amount.

 

[oengineer]

Load capacity of the existing soil within the ringwall is not needed. Per the PIP document (page 12 of 81), that soil is removed and replaced:

Replacement material is specified in your soil report:

Here is the link to the specification for TxDOT Standard Specifications Item 247, Type A or D, Grade 1-2.

The TXDOT Type A material says "Type A: Crushed stone produced and graded from oversize quarried aggregate that originates from a single,naturally occurring source. Do not use gravel or multiple sources."

But from PIP, it appears that the Crushed Stone Ringwall is a different type of foundation than the Concrete Ringwall Beam. So, would crushed stone still be applicable for a Concrete Ringwall Beam fill for the space within the ringwall?

Generally, the load capacity inside the ringwall is just taken as allowable bearing as specified in the soils report.
The net bearing will include any fill above grade and the tank bottom plate as well.
The extent of fill under the bottom should be confirmed with the geotechnical engineer, and will not necessarily involved new fill all the way to the bottom of the ringwall.
It is not uncommon to see soil reports that will specify allowable bearing for the ringwall that is lower than the product pressure inside the ringwall (IE, 3,000 psf allowable for the ringwall, but the product depth gives 4,000 psf inside the ringwall.) In that case, contact the geotechnical engineer and confirm that is the intended recommendation and not just an oversight. In a lot of cases, that allowable bearing will control the depth of the tank.
For petroleum tanks, the long-term static loading may be somewhat less than the hydrotest load due to differences in product density. There again, contact the geotech to see how that should be handled if the load bearing is marginal for the application. Review any hydrotest recommendations (depth of filling and rate of fill, available water flow rates) to see how prolonged that hydrotest will be.
Generally, it is assumed that when you have a uniform load over a large area, that the column base plate loads can still exceed that load by a reasonable amount.

I may need to do the portion of the quote in BOLD.

 

[SlideRuleEra]

But from PIP, it appears that the Crushed Stone Ringwall is a different type of foundation than the Concrete Ringwall Beam. So, would crushed stone still be applicable for a Concrete Ringwall Beam fill for the space within the ringwall?

A Crushed Stone Ringwall is different than a Concrete Ringwall... but that is like comparing apples and oranges.

You have told us your design is for Concrete Ringwall.

If you are going to use the PIP guidelines, follow the Concrete Ringwall section (Paragraph 5.1 and sub paragraphs - pages 11 & 12).
Note that the section I quoted above is Paragraph 5.1.11, which applies to Concrete Ringwalls.

The requirements for Crushed Stone Ringwalls (Paragaph 5.2 and sub paragraphs - page 12) have nothing to do with a Concrete Ringwall.

http://www.SlideRuleEra.net

 

[r13]

I think your geotechnical engineer owes you the allowable bearing strength of the specified backfill material following compaction. Also, you shall ask whether the ring wall shall be founded on the same material, source of the crashed stone that corresponding to the report, method of the compaction adjacent to the wall, and finally, any concerns on ground water beneath the backfill.