light pole bases
Iam looking to find out if there is a formula for sizing the concrete base for light poles. I am installing 20 foot aluminum poles with two heads each. Thanks in advance
Rules of thumb.... three times the bolt pattern diameter for concrete diameter. A 20' pole often has an 8" bolt pattern, so you'd use a 24" round sono-tube. For depth, I use 1' below ground for every 5' above ground. For a 20' pole, I do 4' below grade. I also try to undercut the hole at the bottom so that it's a bit wider down there.
People do smaller diameter tubes and shallower holes, but I find my rules of thumb to work well. Cars bump into these things, and snow gets plowed up against them. Smaller concrete bases can permit the pole to be out of plumb over time.
I'm curious, does the design usually specify that the bottom of the base is below the frost line? It would seem that if it weren't there would be a chance that the poles could heave during the winter.
I just thought I should add that your wind zone and particular local soil geology will effect your pole base detail. You might be better served by getting more local information.
Perhaps, but even the most conservative pole base details will always have the base sufficiently deep to always be below the frost line no matter where you live. It's not like someone's gonna try 2' of concrete below grade for a 20' pole. You could probably push that over by hand.
Originally Posted by infinity
Consequently, if you don't own a bucket truck with a jib or a boom truck, there's a pretty cool tool out for one-man parking lot light pole setting.
There's tons of ways to set the poles, but that tool seems neat. I've managed to scuff up a pole or 10 in the past by lashing them to the backhoe bucket.
One more question , Do the bases have to come out of the ground or is this just good practice? My lights are in a parking lot but they are actully in a grass area past the pavement
Have to? Not sure... I've never seen any manufacturer information that says they must. Getting down on my knees to work in the handhole isn't real appealing to me. Getting the poles beat up by mowers and string trimmers doesn't seem like a good idea either. If you don't like the typical 30-36" base height, I'd struggle to have some concrete height there to protect the pole from groundskeepers. It will keep the connections in the handhole out of the snow, also.
Originally Posted by 101010
EDIT... most of your parking lot pole manufacturers will give you a paper with drawings of a typical pole base detail if you ask for it. I did work in one jurisdiction that wanted this detail engineered. If your soil is odd or you're in a high wind coastal area, perhaps spending the couple sheckels to an engineer to seal a pole base detail would be a good idea.
Last edited by mdshunk; 10-28-06 at 12:51 PM.
The UBC has (or at least had ~10 yrs. ago) a great section on calculating light pole foundations. It took into account soil types, luminaire/pole effective projected area (EPA), local wind gust (geography based), exposure conditions at the very least. I loved it. I had a spreadsheet and just pluged and chugged. I have since moved to NY and am under an IBC based code. I struggled to find something similar with no luck, asked a civil engineer for guidence and was thrown multiple buzz words like scooping factor, shearing of the in-situ soil, etc. I wish I still had my UBC Codebook and spreadsheet!
Sorry I'm no help.