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'FILE No. 375 09/13 '96 08:12 ID:SPRINfsPECTRUilMPLS 6126862700 PAGE 3 SEP.~2.1996 4:44PM COMM -rWR 402 359 5856 NO. 655 P.3/4 Valmonl Indu;trllli, Inc. . Wast HIghway 21'5 · P.O. BOl( 358 . Voli~, Nebraska 00064-0358 U,aA, · (~36e-2201 installation. There is a 1.69 gust response factor imposed in order to account for sudden changes in wind apeed, a h.,jght coef&ient to ecoount for increasing wind speed with height, and an exposure coefficient to ac<:ount (to SOnul degree) the terrain effects. Sprint Speetrum ba. requeated lI;bat thell' POlel be dealgn.ed for a HfiUtest mile" wind speed of 95 mph, wblch will me IU1 that ti1~ pole wlll a.c:-colQmodate gustt of oyer US mph. The loads genmated by thIlI wind and the weight oftbe members (along w3th any ice considered) are then used 10 size members oftlw pole. There is ~t least a 25% factor of safety te4uired under these. conditio os. This assumes that the wind bloWing from the worst possible direction. ~;01M directions are worse than othets, depending on the -equipment attached to the ..pole, the arrangemeut, and the orfo.ntatlon. 'I'he wind must exceed all our eatimfttea fht~, duration, be at the worst orleotatlon and ov&coma the motor of sa.fi3ty. Let us ftSSLU11e that It pole becomes overloaded. TIw typlcal consequence ofthls overloading is "local buckllng" where a relatlvely smallportlan of tho shaft distorts and ~Jdnks" the steeL This doe,s not cause a free falling pole. After ilia buckle, the cross JeCtlon of1he po~ is capaltle of carrying the entire vertical (wef8ht) load and e. substantial portion of the load that ca:llSed the buokllng. The pole is likely, however) to be out of plumb. This may be somewhat dramatlc and the buokled section should be replaced. There are 3 met'MniRJIlB wblch prevent the pole from a free fall typa fiillura. First, as the pole disto%Ul this distortloJl. may relieve the load from tho pole ehher by orlentina the po~ more favorably in the wind or, if buckling has occurred, by reducing the moment ann of the wind force. The second ~nl1nl..m Involves a redlitributioD of the stress in. the pole o:fter b11~ldln8 toward the Iermrlnn,g portion or the craBS section that has UIJ11Sed oapacity. The third phenomenon anti IDOl'C important, is the nature of the force being IIpp1ied. We expect the wind to prod~J this for~. A wind that would cause a buckle would be larger than the basIc wind speed, the gust factor, and the factor of safety c:oInblned. A gust would soon dissipate and, aftertbIs peak wind IsBone~ the stress in the pole would be reduced. Poles are f1exIlm!, furgiving structures whloh are not sMllflllly Buscept:iblc to . damage by impact loads su.ch as Ii wind gust or earthquake shocks. It takes some tim8 for the entire fit:ructure to "see" the impact loadlng. Even after Ii local buckle) tM pole has sJgnftltl8t1t capacity. It is this capacity along with the transitory nature of the loading that prevents a pole from "falling over"'.