Single Head, 30' Road Poles Cracking At Weld

[dwinkels]

Has anyone experienced a similar issue:

Single head, 30' road/lot poles are experiencing unusual fatigue and cracking above the weld, where the base connects to the pole. Two of these poles have completely failed and have fallen over (see attached picture). Approximately nineteen more have been identified with significant cracking above the weld (see attached picture) - these poles were taken down for safety concerns. There are 106 poles total. The poles are on site at a Federal Penitentary located at a remote site in the Central Valley of California. This area is not typically described or known as a high-wind area. AASHTO and ASCE wind maps place this region in the lowest zone on their wind chart. The pole in question is a Cooper, 5" x 30' square, straight, steel pole with an 11" diameter base plate. The wall thickness is .120". It has one 400W Metal Halide Fixture affixed to it. According to White Papers published by Cooper, the damage is attributed to pole vibration - more specifically a phenomena identifed as Vortex Shedding (Second Mode Vibration). This is caused by winds, but is not necessarily attributed to high winds or gusts. On the day these two poles fell, the gusts did not exceed 50 mph, which is well within the allowable range of winds that this pole is designed to handle. This situation has occured at other locations, and for some reason, it is only the combination of the 5" x 30' square, straight, steel pole with a single head affixed to it that experiences the pole fatique. Similar pole/ fixture configurations that are taller and similar poles of the same height and design but with two or three heads seem to not be affected. Unfortunatley, Cooper excludes this from their warranty. Why they would allow this combination to be sold is uncertain to me and is a topic for a different forum. My question to readers that can identify with this problem is how did you ultimately resolve this? To what level did Cooper get involved. What pole did you replace with? Did you replace similar poles that showed no signs of cracking? How did you handle the warranty with the owner, general contractor, distributor and manufacturer? Is there anything I seem to be overlooking or not considering?

 

[texie]

You might take a look at this EC&M article: http://ecmweb.com/lighting/stadium-light-pole-failures-20100201/index.html

 

[steve66]

You can get vibration dampers as an option on some 30' poles. THat is supposed to help with the harmonic vibration problem.

I've also heard this doesn't occur with the tapered poles, for some reason - probably due to less weight at the top of the pole.

 

[weressl]

Has anyone experienced a similar issue:

Single head, 30' road/lot poles are experiencing unusual fatigue and cracking above the weld, where the base connects to the pole. Two of these poles have completely failed and have fallen over (see attached picture). Approximately nineteen more have been identified with significant cracking above the weld (see attached picture) - these poles were taken down for safety concerns. There are 106 poles total. The poles are on site at a Federal Penitentary located at a remote site in the Central Valley of California. This area is not typically described or known as a high-wind area. AASHTO and ASCE wind maps place this region in the lowest zone on their wind chart. The pole in question is a Cooper, 5" x 30' square, straight, steel pole with an 11" diameter base plate. The wall thickness is .120". It has one 400W Metal Halide Fixture affixed to it. According to White Papers published by Cooper, the damage is attributed to pole vibration - more specifically a phenomena identifed as Vortex Shedding (Second Mode Vibration). This is caused by winds, but is not necessarily attributed to high winds or gusts. On the day these two poles fell, the gusts did not exceed 50 mph, which is well within the allowable range of winds that this pole is designed to handle. This situation has occured at other locations, and for some reason, it is only the combination of the 5" x 30' square, straight, steel pole with a single head affixed to it that experiences the pole fatique. Similar pole/ fixture configurations that are taller and similar poles of the same height and design but with two or three heads seem to not be affected. Unfortunatley, Cooper excludes this from their warranty. Why they would allow this combination to be sold is uncertain to me and is a topic for a different forum. My question to readers that can identify with this problem is how did you ultimately resolve this? To what level did Cooper get involved. What pole did you replace with? Did you replace similar poles that showed no signs of cracking? How did you handle the warranty with the owner, general contractor, distributor and manufacturer? Is there anything I seem to be overlooking or not considering?
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Sounds like a resonant frequency problem. Finite element analysis based on wind tunnel simulation measurements could result in the full understanding of the problem, but it would be considered an overkill for such commodity item and would add a cost for the item that would make the price noncompetitive. The vibration dampener sounds like a good idea, but one would need to have SOME data to size it.

 

[hurk27]

Back about 15 years or so ago we had a couple Cooper poles fail the same way, the weld at the base of the pole failed and it fell in about 30 MPH winds but they were supposed to be 100 MPH rated poles, because we had to warranty them we replaced all 10 with a similar pole from RUUD lighting, the way the bases are welded on the RUUDs made us a believer and we never had another pole fall.

http://www.ruudlightingdirect.com/poles-tenons/premium-straight-square-steel-poles/ps4s30htbz.html

Click on the enlarge photos of the base, the triangles you see on the side, are part of the base plate that is stamped out of it, as one piece giving a much larger area to weld to the pole.

 

[weressl]

Back about 15 years or so ago we had a couple Cooper poles fail the same way, the weld at the base of the pole failed and it fell in about 30 MPH winds but they were supposed to be 100 MPH rated poles, because we had to warranty them we replaced all 10 with a similar pole from RUUD lighting, the way the bases are welded on the RUUDs made us a believer and we never had another pole fall.

http://www.ruudlightingdirect.com/poles-tenons/premium-straight-square-steel-poles/ps4s30htbz.html

Click on the enlarge photos of the base, the triangles you see on the side, are part of the base plate that is stamped out of it, as one piece giving a much larger area to weld to the pole.

Indeed and it also gives a much thicker corrosion allowance.

One thing was not clear from the OP pictures and comments if investigating the failure closer does the freshly broken area was a large proportion of the total welded length or small and there were evidence of previous long term gradual failure. The former would indicate sudden failure, eg. inherent design weakness, the other would tend to make one think of corrosion and recurring mechanical stress playing together over time.