50 feet cantilever pole footing design

[denguy]

Hello,

I'm hoping for some inputs to see (or guide me) if I'm going in the right direction.

I have a 50' cantilever pole with a base diameter of 30" and tapers up to 15" at the top and is located in a zone with 100 mph wind speed.

I'm using AASHTO Structural supports for HW Signs Luminaires and Traffic Signals:

Kz = 1.09
Kd = 0.95
G = 1.14
C_d = 1.0

P_z = 0.00256(Kz)(Kd)(G)(V^2)(Cd)= 30.22 psf (Eq. 3.8.1-1)

After inputting my shear and moment values based on the above wind pressure in Enercalc. I got a footing size of 48" dia. x 9 ft. deep.

For soil properties, I inputted:

Allowable lateral passive pressure: 150.0 psf/ft
Max. lateral pressure limit: 1,500 psf.

Do these values seem reasonable? Please let me know if I'm missing something.

Thank you!

 

[MIStructE_IRE]

How do you dig a 4ft x 9ft dp hole?

 

[Agent666]

Sounds like a pile to me not a footing. Maybe check using something like broms if you aren't too worried about deflections (since its a strength method only).

 

[EdStainless]

I would be real curious about the defection of the pole at that loading.
I have designed poles, but not the footing.
Most of ours were smaller, 40' tall and <10" at the base, steel (actually stainless).
Using a 4'dia x 8' deep footing for ours was not uncommon.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[BridgeSmith]

Depending on what the moment on the pole is, that could be reasonable, far too small, or way too large. Our high-mast light towers have a similar base diameter and the same drilled shaft diameter, but are typically 16' to 22' deep. They're also 120' tall. Our 50' luminaire poles are typically much smaller diameter, have much smaller drilled shaft foundations, and go about the same depth as you have, but they have very little mass and projected area at the top. I must assume if you need a 30" pole base, there's something fairly big at the top of it, but without the design moment and shear at the pole base, we can't even hazard a guess on whether that foundation is adequate.

 

[SlideRuleEra]

Utility poles are embedded to a depth = 10% of length + 2 feet. Seven feet deep for a 50 ft. pole. Diameter of 4 ft. diameter is about right for a 30 in. diameter pole.

Can't speak about the input values, but output, 48" dia. x 9 ft. deep, seems reasonable.

http://www.SlideRuleEra.net