Storage Tanks - Ringwall Foundation Design with Footings

[Trin.Eng.]

The API 650 states in Appendix B that "when the ringwall width exceeds 460 mm (18 in), using a footing beneath the wall should be considered".
What is the technical basis for this recommendation?

 

[EireChch]

I dont know if there is a technical basis for it. If your 460mm wide ringwall has enough structural capacity to support the tank and the underlying soil is stiff/strong enough to limit settlement/bearing capacity failure then I dont see why you would need a footing.

Maybe if it needs to be wider to prevent bearing capacity failure you could consider adding a footing to spread the load, the entire wall wouldnt need to be widened.

 

[HTURKAK]

Appendix B is informative .. So, the info. provided is advisory rather than mandatory requirement.

In order to satisfy bearing capacity requirement, the designer may choose the use of footing under the ring wall with keeping the ring wall thk. the same ( literally inverted tee ) rather than increasing the width of ring wall..

 

[fel3]

A couple other things to consider:
[ul]
[li]If space is limited, using an inverted tee design can help a little.[/li]
[li]Is the savings in concrete worth the somewhat more complicated construction?[/li]
[/ul]

For an example of the first point, let's say you want to erect two large tanks and provide 15' clear between ringwalls for vehicle access (I've used this dimension for water storage tank designs). If tank loads and soil properties require 30" wide ringwalls, you can save 12" between the tanks by using 18" wide ringwall stems and 30" wide ringwall "flanges" underground. I have never dealt with this scenario in my own designs, but I have performed the QA/QC reviews on two project where inverted tee ringwalls were used to save both space and concrete.

For an example of the second point, the first tank I ever designed (early 1980s) required a 30" wide ringwall. My boss told me about inverted tee designs but he didn't think the savings in concrete justified the more complicated construction. However, given the current price of concrete he might have a different opinion today. I haven't had to think about this question recently, so I haven't dug into it enough to compare the two using current costs.


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[1503-44]

20m H x 100m D

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