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. Valmont Industries0 Ino, · WeSt Highway 27S, P.O. 8ox ;358.. VaJley, Nebraska 68084-0358 U.SoA. · (4432) 359-2201 · . August 25, 1998 US West W/mless, LLC 426 North Fairview Avenue Suite 101 St. Paul, MN' 55104 Attention: Mr. Adrian Schottroff Subject: Failure Modes for Poles and a Description of the Design Criteria US West Wireless Sit~: SCLO05 Valmont OrderNo, 17453-98 Dear Mr. Sohottroff: I have been asked to write to you about the mode of failure for pole type structures used to support wireless phone antennas and equipment, and give some information to allow you to judge how remote the chances of fal/uro occurring would be. I think it would be appropriate tn start off by a brief description of the dczign criteria, that is typically used, The pol.'.s Valmont supplies are designed in a~cor; anco with EJ.AdT.I.A. 222 R~vision F entitled "Stnmtural Standards for Steel Antenna Towers and Antenna Supporting Structures." Tlds is '.an approved A2q. S.I, standard that trna dealt with the design of lattice typo structures for a number of years. R~vision E is the first version tha~ goes into extensive detail about the d~sign of pole type structures. The provisions of the standard have, as their foun~tion, provisions of other nationally known spc~ificatious and standards that have a long history ofmt~ability. 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 conc0pts spelled out in publications h'ke "The Design of Steel Transmission Pole Structures" (published by A.S.C.E.), and "Standard Specifications for Structural Suppom for H/ghway Signs, Luminaries and Tra~c Signals" (published by A.A.S.I-LT.O,). Many of the concepts used to design poles in these two publico.dons are included in the E-rAdT,I~ 222 Revision F Standard. The E~I.A./T.I.4. 222 R~vision F requirements clictat~ a basic design wind spc~d. The wind speed so bo used depends on the location of the sit~ within the state. Valmont'a policy is to use the w/.ud loading in EJ.AJTJ~,, 222 as a minimum loading. Statistically, the wind speed listed in E,I.AfLI.~, 222 ha~ been dotermined to be that wind which has an average reoccurrence of 50 years. This wind ii 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 $I seconds to pass a point This standard 'Tastest mile" wind is customized with £a~tors that apply to tho particular installation. There is a 1,69 gust response factor imposed to account for sudden I i I i I I I 1