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<br />, <br /> <br />, <br /> <br />e <br /> <br />e <br /> <br />e <br /> <br />,- <br /> <br /> <br />PAUL J. FORD AND COMPANY <br />STRUCTURAL ENGINEERS <br />~so [Ht SrCid Slru! " ~uiu 300 " Colu:mb\i~, Ohio 43215 <br /> <br />. <br /> <br />~EO <br />SEf' 2'2. i998 <br />O'i {)l; ~\~",US <br /> <br />July 1 &, 1998 <br /> <br />U.S. West Wireless L.L:C. <br />42& North F~irview Ave. Room 101 <br />SI. p~ul, MN 55104 <br /> <br />AnN: Mr. OaleT~ 1-17.q8 <br /> <br />RE: Existing 700 II. guyed lower <br />Located in Arden Hills, Minnesota <br />IPJF No. T96"()26) <br /> <br />Dear Mr. Thorne, <br /> <br />We ha,'e completed ou'r slruC1ural analysis of the exining 700 It, guyed tower located in Arden Hills, <br />Minnesota. As YOU know, the tower is a Unarcc-Rohn model ~80 origin~lIy conmu,cted In 198\. The <br />lower was originally designed lor a constant wind pressure 0165 psI in accordance with the old EIA <br />RS-222"( standard. Ice accumulalion was ~ considered in the original tower design. , <br /> <br />The purpose 01 our ana.lysis was 10 determine if the existing structure could meet the requirements of <br />the Minnesota Stale Building Code while supporting the revised antenna and coax loading as shown <br />on page one of the enclosed sketches. The Minnesola Slate Building Code is modeled after the <br />Uniiorm Building Code.(UBC , 994) and now requires that ice accumulation be considered. lhe <br />Minnesota Slate Building Code does nOllist design wind loads for Slrvclures over 400 It tall and <br />recognizes the Electronics Industry Associalie.n standard ANSllEIA.222-E as an acceptable national <br />design standard. ' <br /> <br />Our analysis was performed in accordance with Ihe recommendations of the Ar-:SllEl....222.E standard. <br />The Minroesota Stale Building Code requires a minimum design wind velocity of 60 mph and also <br />requires Inat all structures in the state be designed lor y,' of radial ice. The EIA standard allow, the <br />ba,ic design ,.i~d velocity to be decreased to 69 mph when radial ice accumubtion is considered. The <br />exi'lin~}c,:e' .has the capacity to ,alely withstand only 79 mph winds when supporting the amennalisted <br />on page ,io(~l-I.e"enclosed sketches. You will nole thallhe exisling tower very nearly meel> today', code <br />requirementsWnen ice is not considered. <br /> <br />When}j inchradialice.accumulation is considered,the IOW2r ha, lhe capaci'ty 10 safely withstand only <br />25 mph winds:ln680 It out of lhe 700 It of lower, the tower legs are o"!-!l,rstr!"ssedtosome extent. Tijis is <br />due 10.lne (;i~ that the lower has a "ery severely bent shape in the windf' M<>>lo( the guy cobles and all <br />olthli ejdstirigloundations are overstressed when ice accumulation is considered. We also analyzed the <br />tower with larger guy cables al some elevations in an atiempllO control the deflecled shape (a stralght- <br />line defleclion reduces tower shaft Slresses) of !he lower shaft. This helped considerablybul a large <br />portion of the tower (560 lineal 1;) was still severely overstre5Sed. We do not feel that it is feasible 10 <br />reinforce this tower 10 meet lhe ice loading requirement; of the Minnesota Slate Bdlding Code. <br /> <br />. <br /> <br />COLUMBUS, OHIO <br />&1"111~679 <br />'J>:1. &H.]21.2140 <br /> <br />. ATLANTA, GEORGIA . <br />404-266-l4<l7 <br />F..AX .04-IL'~60! <br />. www.p/fweb.com · <br /> <br />ORLANDO, FlOII.10^ <br />'07~9H019 <br />FAX 4<l7..97.1l>&2 <br /> <br />t <br /> <br />'ll...u...."....l..~.._,oI_.........""''1'''^'........ <br />