07-13-2005 Council Agenda - Laserfiche WebLink

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Communications Corporation Tm Guyed end Self - Supporting Towers Monopoles HF Antenna Systems and Turnkey Installations July 6, 2005 Mr. Jason Hall Dear Mr. Hall, I am writing this letter in reference to your request for Sabre Communications Corporation TM to determine the mode of collapse for monopoles used as communication structures. The 150' Sabre Communications monopole you inquired about is for Little Canada, MN in Ramsey County. Monopoles are designed in accordance with the Electronics Industry Association Standard EIA/TIA- 222-F 1996, which is a nationally approved A.N.S.I. Standard for communication structure design. Although it is extremely rare for a monopole to collapse (we have never heard of any) most failures would occur in a catastrophic wind such as a tornado or a hurricane. Mike Coghlan The most important phenomenon, which would prevent the monopole from a free fall type failure, is the nature of the force being applied. We would expect this force to be produced by the wind. A wind that would cause overstressing of the monopole would be greater than the basic wind speed, the gust factor and the factor of safety combined. A gust would soon dissipate and after this peak wind is gone, the stress in the monopole would be reduced. Monopoles are flexible, forgiving structures, which are not generally susceptible to damage by impact loads such as a wind gust It takes some time for the entire structure to "see" the impact loading. Even if the pole were to experience some localized distortion, it would still have a significant capacity. It is this capacity along with the transitory nature of the loading that prevents a pole from "falling over'. In the very unlikely event of a monopole failure, the top portion of the monopole would collapse first. This falling portion would be "hinged" to the top portion of the remaining structure, Consequently, the probable fall zone for the collapse of the referenced monopole due to natural causes is a circular area having a radius equal to 50 feet.. We trust that this information is helpful in explaining that the monopoles are designed to survive rather than collapse. Please let us know if you have any questions or require additional information.. Sincerely, SABRE COMMUNICATIONS CORPORATION TM Mike oghlan West Region Sales Manager 2101 Murray Street • P O. Box 658 Sioux City, IA 51102 -0658 712 258 6690 Fax 712.258 8250