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RE: pole structure connections

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Hello Paul,

 

I realize this is a late response, but hopefully still better than never.

 

You are right to be concerned about fatigue, especially if your design is similar to standard details used for highway signs and luminaires.  Because of recent fatigue failures, the industry (pole manufacturers, AASHTO, NCHRP) had recently been researching and improving fatigue resistance of the base details.  As I recall, that research demonstrated that the standard detail, based on testing, should be considered in a “bad” fatigue stress category – say E or F.  I think the principal culprit for light poles is cross-wind vibration from vortex shedding along the cylindrical pole, which may not be as important for a canopy structure, where buffeting may give you the dominant combination of stress and cycles.

 

As Harold stated, the failures are sometimes related to the anchor rods, but I have also seen failures of the pole-to-base-plate welds. I am not current with what the latest recommendations are, but I can point you towards NCHRP Report 469 at http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_469-a.pdf and AASHTO has a standard specification for supports of light standards and luminaires (probably not available on line, unless you count book stores).  I’m sure Google can provide more technical references, hopefully more up to date than these.  (IIRC, research was done at a university in Iowa.)  I think that specifying a tough weld electrode is a good idea, but may not get you all the way there.

 

Happy 4th & 5th,

Brian McDonald

 

 

From: Harold Sprague [mailto:spraguehope(--nospam--at)hotmail.com]
Sent: Sunday, July 04, 2010 5:35 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: pole structure connections

 

Paul,
I have diagnosed many problems like this.  The usual cause is the stretch of the anchor rods.  Tensioning the anchor rods will likely correct the problem.  If they are 36 ksi material, just put a cheater on a spud wrench and stretch them out.  You can calculate the stretch you need for about 50% of the tensile strength without fear of breaking the anchor rod.  High strength anchor rods are tensioned to 70% of the tensile strength.  If you want more precission, you can use a hydraulic tensioner. 

Regards, Harold Sprague


 


From: PFFEI(--nospam--at)aol.com
Date: Mon, 28 Jun 2010 16:06:53 -0400
Subject: pole structure connections
To: seaint(--nospam--at)seaint.org


I am working on  a project that includes a canopy shade structure supported by a single pole.  The pole is welded to a base plate that is anchored to a concrete footing.  (not possible to embed pole in concrete).  The pole has architectural limits on size, but at that dimension, I have double capacity when subjected to a 1g lateral load and am also within code displacement limits (0.02)h (sx). 

 

However, the pole oscillates when pushed on.  Do I need to be concerned with fatigue at the joint of the pole to the plate?  Should I spec a special electrode for that joint?  The model is similar to the pole structures that support light in parking lots or street intersections - is anything special done in those instances for welding and material space?

 

Thank you,

 

Paul Franceschi, S.E.

 


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