What is the efficient foundation system for elevated tanks? 4

[IJR]

Pals


This one always makes me uncomfortable and I can use your experience.

Elevated tanks supported on 4 steel braced legs, will usually have 3units of compression on 1 pair of legs and 1 unit of tension on the other pair when wind or quake works on it.

Say +75ton on each of the compressed pair and -25ton on each of the other


spaced say 25ft apart, and taking any two legs at a time:
with medium level bearing capacity, say sandy clay

1) combined footing wont usually work

2)my favorite 2 footings with a strap beam wont usually work



and I am usually left to join all 4 legs with a mat(Piles are expensive in remote areas where these structures are built)

and if it turns out that one leg can not join the mat, for some space-based reason, I get a funny mat with 3 legs on it.


Isnt there a better simpler and more efficient system?


Lets discuss

Thanks. IJR

 

[KAM_imported]

If tension loading is the problem, couldn't you use individual footings with helical anchors (CHANCE or Atlas piers) to provide the uplift resistance?

 

[IJR]

Thanks KAM

Your single footing suggestion is most welcome.

Do you want to give me more info on helical anchors. Never heard of them before


Once more thanks

IJR

 

[KAM_imported]

For more info on helical anchors, go to

http://www.atlassys.com,

or to

http://www.hubbell.com/abchance

 

[Riz]

IJR,
Why not a circular strip footing. I found it to be very economical for a masonry water tank (60m3). U will also realise its strapping advantage.
What do u propose against overturning when tank is empty?
Riz

 

[IJR]

Riz,

Nice to have you back. My problem is NOT about TANK ON GRADE. It is about ELEVATED TANK supported on 4-steel legs, braced between one another.

Thanks for commenting on ring foundations, which I usually use for tanks on grade. You mentioned strapping there which I never thought about. Thanks for that.

Regards,

IJR

 

[Ron]

Agree with KAM. We have had to retrofit towers for additional loading and the anchors worked well. Combinations of footing and anchors can reduce the footing mass for overturning moment.

 

[IJR]

Thanks Ron, I am now after helicals. Guess what, we face this problem all the time, and I usually end up relying on soil mass. There was a day I had this dream: a chunk of soil mass melting like ice-cream and a bunch of columns flying like a stick.

Thanks once more and again

IJR

 

[Riz]

IJR,
The circular strip footing was for an elevated tank. U can elect to taper the ends for economising concrete.
Riz

 

[IJR]

Riz, I havent yet understood you. If you dont mind come back and lets get you more clearly.

I have a feeling you probably have a point, insisting on circular strip footing.

I have four steel columns to carry the tank 8m (24ft above), sort of a braced frame.

Right now I cant figure out how to run a circular strip footing to contain the column locations.

Please let me see your point closely.

Respects,
IJR