Code interpretaion differences

[Polecat]

Re: Telecommunications Standard TIA 222-G
I'm having a disagreement with another engineer about the interpretation of this standard's definition of shielding (Section 2.6.9.4 of TIA 222-G, and Figure 2-11).

His contention is that coax cables strapped to a smooth round pole structure would be classified as completely shielded when the wind direction is coming from the opposite side of the pole, and that the cables would be treated a cluster mount (Fig 2-12) with the wind direction 90 degrees to that.

My argument is that a smooth round pole acts as an airfoil under high wind and that the cables would produce a considerable drag regardless of their placement on the pole or the wind direction. However, I can't seem to find any published justification for this view other than the reference in ASCE 7-02 under "Other Stuctures", Fig 6-19 which defines force coefficients of different shapes and h/D ratios. This section shows an increased drag coefficient depending on the roughness of the pole's surface varying as a function of the protruding elements (i.e., the coax cable) and the pole's diameter at a given level.

Can anyone provide me with another reference that might support this claim, or am I simply looking at this application too conservatively? Does the TIA standard really mean to define a cable strapped to a pole as completely shielded from the wind in one direction?

Any enlightenment on this would be appreciated.

http://www.spiraleng.com

 

[paddingtongreen]

I don't know the standard, but a circular shape is not an airfoil in a high wind velocity. A partial vacuum forms on the leeward side adding to the pressure on the windward side, your cable simply fills in part of the vacuum, it may even, in real life, reduce the total wind by tending to make it a real airfoil.

The wind only pulls back on the far side when the conditions for Laminar Flow exist.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[JoshPlumSE]

Polecat -

I think this issue is partially addressed in the TIA G standard, though I am hardly an expert.

Table 2-7 (which lists the Cf Force Coefficients for Pole structures) talks about Sub-critical, Transitional and Supercritical flow. There are adjustments to the Cf calculation based on having "linear appurtenances attached on the outside of the pole shaft".

I tend to think that means that the appurtenances would still be completely shielded, but that the pole force has been increased to account for the air flow changes caused by those lines.

Josh