Agenda - Planning Commission - 03/06/2000

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'98 01: I~M · Valmont Industries, [ne. · Wa~t Highway 275, P.O. Box 858. Valley, Nebraska 68064-0358 U.8,A. - (4~) 359-2201 US West Wireless, LLC 426 North Fairview Avenue. Suite 101 St. Paul, MN 55104 Attention: Mr. Ad~am 5chottroff E-bject: Failure Medes for Poles a~d a Description of the Design Criteria US West Wireless Site: SCL005 Valmont Order No, 17453-98 August Dear Mr. Schottroff: I have b~n ~.ked :to write to you abouI the mode of~ for ~le ~o s~S used to appon ~eIess p~ ~.n~s ~ ~meng ~ ~e some ~o~fion m ~low you to judge how mmo~ ~ ch~ces off~ o~g would be. I think it wo~d be approp~ate ~ ~ off by a b~ef d~or~fion of~e d~i~ c~'~t ~ ~ic~y ~ed. The poles Valmont supplies are designed in aceordane~ with E.I.AIrz.A. 221l Revision F entitled "Structural Standards for Steel Antenna Towers and Antenna Supporting Structures." Tiffs is .an approved A2q.8I. standard that ~ dealt with the design of lattice type structures for a number of years. Rev/sion E is the fn'st version that goes into extensive detail about the design of pole type structures. The provisions of the standard have, as their foundation, provisions of other mlfionally known specifications and standards that have a long history of reliability. This history should be of interest to you considering the hundreds of thousands (if not millions) of sites throughout the United States which have structures designed with concepts spelled out in publications like "The Design of Ste~l Transmission Pole Stmaures' (published by A.S.C.E.), and "Standard Specifications for Structural Supports for Highway Signs, Luminaries and Traffic Signals" (published by A.A.S.I-LT,O.). Many of the concepts used to design poles in these two publiea.tions are inclucled in the EIAJT. I.A. 221l Revision F Standard. The EZAYT. I.A. 7-22 Revision F requirements dietat~ a basic design wind speed. The wind speed'.n be used depends ontM Ioeation of the site within the state. Vahnont'/policy is to use the wi~d loading in E.I.AdT.IA. 222 as a mkLknum loading. Statistically, the wind speed li~ted in E.I.,kYTI.A. 222 has been determined to be that w~d which has.an average reoccurrence of 50 years. This wind is also a "faStest mile" wind which means that it is the average velocity of a mile wind passing a point. For example, a 70 mph average fastest mile wind would take 51 seconds to pass a point. This stan~ "fastest mite" wind is customized with fa~-tors that apply to the particular installation. There is a 1.69 gust response factor imposed to account for sudden