I have 5'x10' sign to put on top of a 20' pole. Could somebody help me with the required pole size for this sign. What additional information is needed?
Posted by jimmy chatham (Member # 525) on :
8" round or 6" square 1/4" thick walls
Posted by Jerry Mathel (Member # 526) on :
Casey, for your own liability and peace of mind, you should probably have an engineer design your sign structure, but here is a "hip pocket" formula for you:
Total sq. ft. of sign, times the required windload, (Usually 30 psf. but check with your building department) times the heigth measured at the middle of the sign, times .42 (engineering factor for steel pipe), gives you the required section modulus of the support column.
In your case: 50 sq. ft. x 30 psf. x 22.5 heigth, = 33.75k bending moment at the base of the pole, x .42 factor for steel = 14.175 sq. in. required section modulus. An 8" schedule 40 steel pipe has a section modulus of 16.81 sq. in. A 6" pipe would fall short of the required support.
Data was taken from "Sign Structures & Foundations" by Peter B. Horsley which is available from "Signs of the Times". Good reference book to have in your library if you do much of this kind of work.
Posted by Dave Sherby (Member # 698) on :
Yep, that's the way I do it too. That book is the cheapest insurance I've ever bought.
Don't forget to calculate the required cubic feet of concrete. Got to have ballast.
Another tip. Whenever I put up 2 poles for a between pole mount, I usually go up some more in steel and concrete. Many times the customer will want to add a sign or banner. If you're at the limit, another sign gets added, wind blows it over, you'll get the blame even when it isn't your fault.
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