What is the greatest height that a tower can be designed and constructed?

Discussion in 'Design, Development and Standards Discussions' started by Wireless Estimator, Nov 9, 2008.

  1. Wireless Estimator

    Wireless Estimator Administrator Staff Member

    The country?s and world?s tallest tower is located in Blanchard, North Dakota where KTHI-TV?s guyed tower easily pierces the clouds at 2,063?. Theoretically, how tall of a self supporting (three-leg laced) or guyed tower could be designed and constructed? How would you design for unknown high altitude wind speed events? Is there a height limitation to Revision G?s 3-second gust wind speeds?
  2. Simon Weisman

    Simon Weisman Industry Observer

    With respect to how high: Theoretically, if you use a 50 KSI steel and build a mountain, so that stability and superimposed loads are not at issue, with the notional safety factor from TIA 222 G, you should be able to go to about 14,000 ft., about half as high as a commercial airliner typically flies.

    If you build a latticed tower and the self weight can be half of the total load in the legs, then you should be able to go up to about 7,000 ft. If the self weight must be no more than 25% of the total load, then the limit is about 3,500 ft., etc. Every load you add, reduces the maximum height that you can go.

    With respect to wind: In fact, high altitude winds tend to be more predictable than the low altitude winds, because their source is better known and there is less interference with the earth's surface at high altitudes. TIA 222 G sets the maximum wind speed at 900 ft. to be about 41 % higher than that at 33 ft., At 1400 ft. it is 48% higher, at 3500 ft. 64% higher, and at 7,000 ft 76% higher than at 33 ft. elevation. So, you can see that the increase above 900 ft. tapers off quite a bit.

    As you can see from the above, there is no height limit to the application of the TIA 222 G 3-sec gust wind speeds.

    You should keep in mind that the near surface wind speeds are derived from measurements taken at 33 ft. elevation, but the wind speed adjustments with height are based on the computed reduction of the high altitude wind speeds as they are expected to be slowed down by friction with the earth's surface.

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