03-24-1999 Council Agenda - Laserfiche WebLink

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UG.25.1998- 2:26PM COMM TWR 402 359 5856 VALMONT MICROFLECT COMM TWR Valmont Industries, Inc. • West Highway 275 • P.O. Sox 358 Valley. Nebraska 68064 -0358 U.S.A. • (402) 3592201 August 25, 1998 US West Wireless, 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 Site: SCL005 Valmont Order No. 17453-98 NO.760 p.1/3 RUG 25 '98 01 :16PM Dear Mr. Schottroff: I have been asked to write to you about the mode of failure for pole type structures used to you to support wireless phone antennas and equipment, and give some information to allow appropriate to it judge how remote the chances of failure occurring would be. ed. start off by a brief description of the design criteria that is typically The poi s Valmont supplies are designed in accordance with E.I.A./T.I.A. 222 Revision i Fes :' entitled "Structural Standards for Steel Antenna Towers and Antenna Supporting This is an approved A.N.S.I. standard that has dealt with the design of lattice type structures for a number of years. Revision E is the first version that goes into extensive detail about the design of of pole type structures. The provisions of the standard have, as their foundation, , provisions iiio. This other nationally !mown specifications and standards that have a long history 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 Steel Transmission Pole Structures" (published by A.S.C.E.), and "Standard Specifications for Structural Supports for Highway Signs, Luminaries and Traffic Signals" (published by AA.S.H.T.O.). Many of the concepts used to design poles in these two publications are included in the E.LAJT.I.A. 222 Revision F Standard. The E.I.A./T.IA. 222 Revision F requirements dictate a basic design wind speed. The wind speed to be used depends on the location of the site within the Sstate. the Valmont's poll spes t listed the wind loading in E.LAJT.IA. 222 as a minimum loading. in E I.AJT.I.A. 222 has been determined to be that wind 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 apply seconds to pass a point. This standard "fastest mile" wind is customized need with of c ors tha sudden to the particular installation. There is a 1.69 gust response factor imp Page 41