Concrete footing size on a cylindrical silo
Concrete footing size on a cylindrical silo
(OP)
I have a 30ft x 6'-5dia Silo that weighs 10,000lbs empty (dead load) and 16,500lbs (live Load) when in use. The wind speed in the area is 120 mph. I need to get a rough estimate the concrete slab size for bidding purposes only.
I looked through different engineering handbooks and on this site, but I cant find a good formula to use for this.
i used this formula for wind force but i'm not sure what to do with it.
Force = A × P × Cd
A = projected area of the item (cylinder = 2Πrl)
P = wind pressure (lb/ft2) = .00256 x V^2 (V= wind speed in mi/hr)
Cd = Drag coefficient = 2.0 for flat plates. For a long cylinder (like most antenna tubes), Cd = 1.2. Note the relationship between them is 1.2/2 = 0.6, not quite 2/3
F= (2Π x30'x3.25')ft^2 x (.00256x120^2 mph)lb/ft^2 x (1.2) = 27,099.9 lbs
I looked through different engineering handbooks and on this site, but I cant find a good formula to use for this.
i used this formula for wind force but i'm not sure what to do with it.
Force = A × P × Cd
A = projected area of the item (cylinder = 2Πrl)
P = wind pressure (lb/ft2) = .00256 x V^2 (V= wind speed in mi/hr)
Cd = Drag coefficient = 2.0 for flat plates. For a long cylinder (like most antenna tubes), Cd = 1.2. Note the relationship between them is 1.2/2 = 0.6, not quite 2/3
F= (2Π x30'x3.25')ft^2 x (.00256x120^2 mph)lb/ft^2 x (1.2) = 27,099.9 lbs






RE: Concrete footing size on a cylindrical silo
RE: Concrete footing size on a cylindrical silo
RE: Concrete footing size on a cylindrical silo
RE: Concrete footing size on a cylindrical silo
Also, are you in a seismic region?
I suggest you talk to a local structural engineer to get a preliminary design based on local conditions.
RE: Concrete footing size on a cylindrical silo
RE: Concrete footing size on a cylindrical silo
BA
RE: Concrete footing size on a cylindrical silo
RE: Concrete footing size on a cylindrical silo
BA
RE: Concrete footing size on a cylindrical silo
RE: Concrete footing size on a cylindrical silo
RE: Concrete footing size on a cylindrical silo
In wind terms, the projected area is just the width x height. What you used is the surface area all around the cylinder.
You should not be using this site for preparing bids based on guesswork. That may get you into lots of trouble.
RE: Concrete footing size on a cylindrical silo
So A = 6.5 * 30 = 195 SF
p = 0.00256 * 120^2 = 36.9 psf
F = 195 * 36.9 * 1.2 = 8630# acting 15' above the base.
M = 8630 * 15 = 130,000'#
BA
RE: Concrete footing size on a cylindrical silo
As csd72 pointed out that if one has questionable soil requiring piles then the cost could be much much higher than the following
normal setup.
Assune soil capacity to be 2000psf.
Size the slab to resist the overturning moment with a safety factor of 1.5....this gives a min. value.
Then check soil pressure at toe, if it is less than 2000psf then you are ok with min. size.
If it is greater then the soil allowable, then increase size of slab untill you get below the allowable soil press.
It all hinges on the assumption of the allowable soil press.
Perhaps you can include with your bid a statement to that effect, absence any soil info.
RE: Concrete footing size on a cylindrical silo
http://websoilsurvey.nrcs.usda.gov/app/