high mast lighting pole -wind load 1

[dgkhan]

I have 100 feet high and may be 29" dia at lower end.Tapers at top, do not know to what dia.
Which formula of ASCE -7- 2005 I should use.
(Fig 6-21 on page 74 ?)

 

[miecz]

I would design this according to AASHTO's "Standard Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals."

 

[dgkhan]

Can I get a copy from somewhere. My company will not buy just for one pole

 

[miecz]

Sorry, I don't know of any discount publications. To address your original question, 6.5.15 limits you to 6-21, 6-22, and 6-23. A light pole doesn't fit any of the three figures, but it seems closest to Fig. 6-21.

 

[JStephen]

I would be concerned about vibration on something like that, and would look for something more specifically geared towards that type of structure. I would assume the people that normally build these also can do designs on them as well.

 

[JedClampett]

Take a look at:

http://www.dot.state.fl.us/structures/proglib.htm

There is a program there that designs high mast light poles per 2001 AASHTO Requirements. You'll need MathCad.

 

[miecz]

Following up on JStephen's comment, try to get a hold of NCHRP Report 469 "Fatigue-Resistant Design fo Cantilevered Signal, Sign, and Light Supports." I believe it's available cheap from the National Cooperative Highway Research Program, as I have a copy, and I don't remember spending alot on it.

 

[kilroy73]

There's .pdf files of NCHRP 469, probably can be found at trb.org There's two files - one is examples. (I think it's free - at least it used to be)

I think most manufacturers have design tables, including foundation forces; I can remember only having to design foundations and letting contractor pick from an approved list of manufacturers.

Some manufacturers are Summit, Valmont, Holophane, Millerbernd, possibly Union Metals and Ameron. (Some of this info is 15 years old)

Fatigue is definitely a big issue; I am aware of several HML that failed well before they should have - weld quality is a big issue.

I guess none of that answers your question, though. Drag coefficient will be dependent on what shape the manufacturer uses for the pole - I think dodecagonal is typical. The aforementioned AASHTO guide covers this shape; it doesn't look like ASCE does. I'd push to get a copy of AASHTO Sign, Signal and Luminaire specs as it'll cover all your questions - it's only a couple hundred bucks and should pay for itself quickly, even if you don't use it much.

 

[JStephen]

Actually, I wasn't thinking of fatigue so much, but rather that if the pole can vibrate in the wind, maximum wind loads may be much higher.

On the cantilevered signal light poles, they have a horizontal flat plate out near the end that serves no obvious purpose. I inquired one time with a manufacturer and found that it was a spoiler to prevent or lessen vibration in the wind (vertical movement, I thnk). You wouldn't ever come up with that design from a static analysis per AISC 7. Similarly, tall stacks can oscillate crosswise in the wind, which is not accounted for in the normal building codes. I assume flag poles have similar issues.

 

[kilroy73]

JStephen - what you describe is what AASHTO considers fatigue, so we are talking about the same thing. There's four types of fatigue to design for: galloping (what you described), natural wind gusts, truck gusts and vortex shedding. For high mast lighting only vortex shedding and natural wind gusts are applicable.