Pole crossarm design

[Kom3]

Hi, I am trying to figure out how pole crossarms work. Please see the attached images. The way I see it, if there is an imbalanced longitudinal(horizontal) load due to one wire failing on one side, the crossarm would twist about the pole's vertical since there is only one pin connecting the crossarm to the pole. Thus, there is no moment capacity in the connection. Am I missing something? Is the crossarm intended to twist and not resists forces? I believe these are standard details for crossarms on utility poles.

Thanks.

 

[RPMG]

The crossarm would appear to be moment connected and cantilevered or braced by a kicker.

Twisting about the vertical axis would be torsion on the pole, and resisted by the foundation.

 

[BridgeSmith]

The bracing bar under the crossarm is pinned to the pole and connected to the crossarm also, isn't it? If so, then the crossarm is attached to the pole at 2 points and held perpendicular to the pole, is it not?

Rod Smith, P.E., The artist formerly known as HotRod10

 

[Kom3]

Hi Bridge, sorry for the confusion but see the attached image for clarification. I am not concerned about the vertical load but the horizontal load.

Thanks.

 

[SlideRuleEra]

...if there is an imbalanced longitudinal(horizontal) load due to one wire failing on one side, the crossarm would twist...

The detail you have posted appears to be for a 3-phase distribution line, probably about 7200 volts. These poles typical don't have a foundation; they are direct buried. So, you are right... but:

The wires (actually the electricity they conduct) is what is important. If "one wire fails" electric service (for a lot of customers) goes out... soon to be restored (including repairs to pole/crossarm if needed), except in widespread disasters.

There are millions of poles/crossarms in service, therefore cost per pole/crossarm is critical and if a few "fail" after one wire is lost... so be it. Overall reliability of electric service is pretty high... not much of a "problem". Low cost is more important, in this case.

http://www.SlideRuleEra.net