Agenda - Planning Commission - 01/04/2000

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- Valmont Industries, Irm, · West Highway 275 * P.O. Box 3,~R. Valley. Nebraska 68064-0358 U.$.A.· (402) 359-2201 US W~st Wireless, LLC 4:26 North Fairview Avenue Suite 101 St. Paul, MN 55104 Attention: Mr. Adrian $chottroff Subject: Failure Modes for Poles and a Description of the Design Criteria US West Wireless Sit~: $CL005 .. Valmont Order No. !7453-9g August 25, 1998 Dear Mr. Schottroff: I have been asked to write to you about the mode of failure for pole type structures used to support wireless phone ant~nns~ and equipment, and give some infonnafion to allow you to judge how remote the chances of failure occurring would be. ! think it would be appropriate to start off by a brief description of the d~ign criteria, that is typically use& The pobs Valmont suppFms are desired in gcordance with E3~dT.Ia~. 222 Ravlsion F entitled "Stnmtural Standards for Steel Antenna Towers and Antenna 8upport/ng Structures." Tl~s is .an approved A2q.$.I. standard tlnt has dealt with the design o£1attico typo sU'uctures for a number of years. Revision E is the first version that goes into extensive detail about the design of pole type structures. The provisions of the standard have, as their foun~fion, provisions of other m~fionally known specifications and ~andards that have a long history of reliability. This history should be of interest to you ccmsidering the hundreds of thousands (if not millions) of sites throughout the United States which have slruetures designed with concepts spelled out in publications like "The Design of Steel Transmission Pole Structures" (published by A.S.C.E.), and "Standard Specifications for Slnaemral Suppom for Highway Signs, Luminaries and Traffic Signals" (published by Aak. S.I-LT.O.). Many o£tbe ooneepts used to design poles in these two publications are included in the EX.AdT. I.A. 222 Revision P Standard. The E.I.A./T.I.A. 222 R~vision F requirements diota~ a basic design wind speed. Tho wind speed ~ be used depends on the location of the sit~ wiflfiu thc state. Valmont's policy/~, to usc the wind loading in E.LA./T.I.~ 222 as a minimum loading. Statistically, the wind speed listed in E.I.,kdT.I.A. 222 has been determined to be that wind which tins. 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 standard "fa~test mile" wind is eustomLzed with factors that apply to the particular installation. There is a 1.69 gu~ response factor imposed to account for sudden