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PAUL J. FORD AND COMPANY <br /> S T R U CTURAL E NGINEERS <br /> 250 East ercad Street • Suite 500 • Colurnb�;s.Ohio 43215 • <br /> July 16, 1998 > <br /> u.S. West Wireless L.L.C. 22199 <br /> 426 North Fairview Ave. Room 101 SEP <br /> St. Paul, MN 55104 <br /> • e <br /> ATTN. r. Dale T M <br /> RE: Existing 700 ft. guyed tower <br /> Located in Arden Hills, Minnesota <br /> (PJF No. T98-028) <br /> Dear Mr. Thorne, <br /> We have completed our structural analysis of the existing 700 ft. guyed tower located in Arden Hills, <br /> Minnesota. As you kna.w,the tower is a Unarco-Rohn model #80 originally constructed in 1981.The <br /> tower was originally designed for a constant wind pressure of 65 psf in accordance with the old EIA <br /> RS-222-C standard. Ice accumulation was NOT considered in the original tower design. <br /> The purpose of our analysis was to determine if the existing structure could meet the requirements of <br /> the Minnesota State Building Code while supporting the revised antenna and coax loading as shown <br /> on page one of the enclosed sketches. The Minnesota State Building Code is modeled a-ter the <br /> Uniform Building Code.(UIBC 1994) and now requires that ice accumulation be considered. The <br /> Minnesota State Building Code does not list design wind loads for structures over 400 ft tall and <br /> recognizes the Electronics IndustryAssociation standard ANSVEIA-222-E as an acceptable national • <br /> design standard. <br /> Our analysis .vas performed in accordance with the recommendations of the At\SVEIA-222-E standard. <br /> The Minnesota State Building Code requires a minimum design wind velocity of 80 mph and also <br /> requires that all structures in the state be designed for IV of radial ice.The EIA standard allows the <br /> basic design wind velocity to be decreased to 69 mph when radial ice accumulation is considered. The <br /> existing tower has the capacity to safely withstand only 79 mph winds when supporting the antenna listed <br /> on pago 1 of the enclosed sketches.; You wiIf note that the existing tower very nearly meet today's code <br /> requirements when ice is not considered. <br /> When % inch radial.iee.accumulation is considered."tower has the capacity to safely withstand only <br /> 25 mph winds.In 680 ft out of the 700 ft of.tower,the tower legs are ove.rst.essed to some extent. This is <br /> due to the.(ad that tv,he tower has a very severely shape in the lnd.`NiOst of the guy cables and all <br /> of the existing foundations are overstressed when ice accumulation is considered. We also analyzed the <br /> towerwith larger guy cables at some elevations in an attempt to control the deflected shape(a straight- <br /> line deflection reduces tower shaft stresses)of the tower shaft. This helped considerably but a large , <br /> portion of the tower(560 lineal ft) was still severely overstressed. We do not feel that it is feasible to <br /> reinforce this tower to meet the ice loading requirements of the Minnesota State Building Code. <br /> COLUMBUS, OHIO • ATLANTA, GEORGIA • ORLANDO, FLORIDA <br /> 614•:21.6679 404-266-2407 407-498-9039 <br /> FAX 614.221.2340 FAX 404469.4608 FAX 407-697-3662 , <br /> • WWW.pifweb.com • <br />