Foundation Design For Silos 1

[alumpkin]

Gentlemen,

Can anyone please advise concerning the design of ring foundations for silos using piles? Looking for reference material and examples. Thanks.

 

[LGARG]

hi alumpkin
well i´ve designed two or three silos some time ago. i used the ACI code and a book of juan Ravennet that is in spanish. its quite simple but you have to take into account that depending on the height to width ratio(>2.5) the stresses in the walls or the base are different and you have overpressure effects when the material is taken from the silo.

i could help you if you want. just let me know



LG

 

[alumpkin]

Thanks for your rsponse LG. My structure is a manufacturing tower but very similar to a silo in the proposed construction. It will be slip-formed up to its' full height of 265 ft. The footprint is a 50 foot diameter concrete stack.

I want to put the tower on a ring foundation supported by caissons. I anticipate the ring to be 7 ft wide by 3'-6" deep on 4 ft diameter caissons spaced at 7'-0" c/c.

I need help in checking the design of the ring.

Thanks.

 

[SlideRuleEra]

alumpkin - For a structure that tall, compared to it's diameter, overturning under wind or seismic loading could be the governing case. If so, you may have to consider a relatively wide and thick mat foundation.

A mat needs to be wide to allow sufficient lever arm for the outer caissons to resist uplift forces.

A mat needs to be thick to minimize deflection under dead and live loading so that caissons at the perimeter of the mat are loaded essentially equally as those directly under the silo.

http://www.SlideRuleEra.net

 

[csd72]

To get the wind/seismic component of the pile axial loads, you could use a formula we use for pole anchor bolts in a circular pattern.

F(pile) = 4M/ND

Where: M = overturning moment
N = number of piles (at least 12 or the formula is not accurate)
D = diameter of circle through the centerline of the piles.

 

[LGARG]

alumpkin, so you dont have to calculate the walls of the silo? is a`premaufactured silo and you only have to design the foundation? is this alright?. I think that overturning could be critical when the silo is empty, and seismic when the silo is totally filled. Also i think that a mat foundation will have more probalilities of differential settlements than a ring with piles.In my opinion the influence of the loaded silo supported by a mat will be important until a depth equals to two times the silo´s diameter, so your soil must be very good and non compresible to avoid important settlements. There are good examples of silos foundation design in the Ravennet book.
( As always,I apologize for my english)

LG

 

[LGARG]

Alumpkin i´ve checked the Bowless Foundation Analysis and Design book and in chapter 9 you will find an example of a ring foundation for a circular water tank as a beam on elastic foundation.

LG

 

[alumpkin]

LGARG,

No silo/tower wall designs are required. They will be reinforced concrete by the tower contractor.

I do have Bowles' textbook but you cannot utilize Chapter 9 very well unless you have his ring foundation program.

If anyone has this old fortran program please advise.

Thanks.