[TowerTalk] de-rating tower wind loading limits

[Bruce Horn]

Hi,

As a data point regarding de-rating crank-up towers as a function of wind
speed and mast height, here's the results of the calculations I did on my
U.S. Tower HDX-589 based on the professional engineer's furnished
calculations. In other words, I used his calculations and varied the wind
speed and mast height for the tower fully extended (89 feet).

For a two-inch diameter mast with the antenna mounted 1 foot above the tower:
Maximum allowable antenna area at 60 mph is 79% of that at 50 mph
Maximum allowable antenna area at 70 mph is 47.5% of that at 50 mph
Tower is unable to support itself (no antenna) above 82 mph

For a two-inch diameter mast:
Maximum allowable antenna area at 11 feet above the tower (100 feet) is 75%
of that at 1 foot above the tower (90 feet).

Hope this helps give a feeling of the degree of de-rating.

73 de Bruce, WA7BNM   (bhorn@hornucopia.com)



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