Light Pole Foundation

[blackpotter]

My boss at a electrical consulting firm asked me to learn how to design the foundation for a light pole. Through my research I have heard the use of Brom's method and others. If anyone could give me a point in the right direction, I would greatly appreciate it. The poles I will be working with are approx. 40ft tall with a 9in base diameter. I need to know what type of foundation is usually used (cylindrical, or square) and what calculations need to be made to design the foundation. If Brom's method is a good method to use, I also need to know where I can go to learn how to use it and how it was derived.

Thank you for your help.

 

[Focht3]

Wow. As Yogi Berra once quipped, "It's deja vu all over again." I've seen this a lot over the years...

Mind you, I don't blame you for your boss' directions. But turning over one of the most critical parts of the design - the foundation - to a staff engineer with no geotechnical engineering training at all is extremely foolish. Your boss needs to have his posterior kicked. Hard.

Okay, enough ranting. Where is the project site? Is a civil engineering firm involved with the project? Has someone drilled soil borings already? What is the local practice for this type of structure?

You need to hire a geotechnical engineer to help you with this problem. Honest. When your boss squawks about the cost, ask him if the firm's professional liability insurance is paid up - and if the insurer will cancel the policy if one (or more) of the light poles fail and they find out he is practicing way outside his area of expertise...

Put it another way: what would your boss think about civil engineers doing electrical engineering work? I'll bet he'd think they were idiots...



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[blackpotter]

I'm not sure I was clear in my original question. My boss is not saying that he wants me to design the footing for the light pole and then send the design out the door. He wants to know how it is designed so that we can both learn how to do it. He has the design done by another firm who does structural design. He wants me to learn how they do it and I'm sure he realizes that there is a lot to consider when doing foundation design.

 

[Focht3]

Okay - that's different. But not much. I think it's a very bad idea to begin with - think of it as going to a proctologist for lasik surgery. Lasik surgery that he does very infrequently. It's likely to give you a 'certain' outlook on life...


What you and your boss clearly don't understand is that there are an awful lot of factors that go into foundation design. It's a lot more than reading Bengt Broms' two 1964 (hint...) papers (piles in sand, piles in clay), plugging in loads, and getting an answer. You will need soil borings, lab tests - and someone to interpret that information. Brom's work assumes that you have done all of the requisite investigative work - it is not a replacement for a proper investigation.

Frankly, you would be better off having a geotechnical engineering firm do the actual design, and then your firm can complete the drawings. It sounds like a direct embed approach is best - fewer details and simpler construction. The geotech firm can use the results of their geotechnical study for the calculations. But you shouldn't undertake this unless you plan to take some classes at the local university - with a geotechnical engineering program. Bengt's papers are good - but I know that he would tell you that they are no substitute for a qualified geotechnical engineer -



Please see FAQ731-376 by [blue]VPL[/blue] for tips on how to make the best use of Eng-Tips Fora.

 

[BigH]

Blackpotter: I agree with John on this. This has been a topic covered in at least 4 threads since I joined this forum. A geotechnical engineer or a structural engineer with geotechnical experience is needed. I note that you are mechanical engineer (perhaps similar to your boss) - and I will assume you are a PE. One of the caveats of being a PE is to undertake only that work for which you are qualified - and seeing a design by others for a one time only does not qualify you in my view. I think this is critically important to understand. I am a geotechnical engineer and have brought in, on numerous occasions, other geotechnical engineers whose experience was considerably greater than mine on specific aspects of our profession - and rightly so, in my view. For instance I used a rock specialist to provide comments on rock excavation for a deep excavation - why? - because he was certainly better able to handle the details than I felt I could - especially when big bucks (baht, pounds - or whatever other currency you prefer) are at stake. I certainly would not design mechanical systems (except, perhaps, for my own design of a weight trainin bench with pulleys, etc.) - but then I lift a lot.

 

[DRC1]

If you are interested in pursuing this on an informational level - I agree with Focht3 and BigH about the actual design, Light pole foundations are usually drilled in concrete piers. Typical deatils for your area should be available as standard drawings from your DOT. A guide to get started is AASHTO Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals, 4th Edition. 2001. (

http://www.aashto.org)

Also J. Bowels Foundation Analysis and Design McGraw-Hill gives a pretty good overview of foundation design