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ik PiROD me -• - <br />r; <br />November 29, 1989 <br />1200 N. OAK RD. <br />P.O. BOX 128 <br />PLYMOUTH, INDIANA 46563-0128 <br />(219) 936-4221 <br />FAX (219) 936-6796 <br />Mr. Tim Malloy <br />D.S.U. Inc. <br />300 First Ave. North <br />Suite 210 <br />Minneapolis, MN. 55401 <br />Dear Mr. Malloy: <br />Thank you for your inquiry regarding self-supporting cower design <br />ractices and predicted failures. <br />While failure is extremely rare in any king of cower, it <br />especially so for self-supporting towers. In fact, only i: <br />tower were subjected to a direct hit from a tornado or <br />severest of hurricanes would failure be predicated. <br />is <br />a <br />the <br />We are aware of only a verv few documented instances of self- <br />supporting cower failure. In each o: these Instances. the <br />failure was in the upper middle region of the cower, with the <br />upper portion of the tower remaining connected and ’’bowing over <br />against the base of the tower. The fact that the wind is <br />normally greater on the upper portion of the structure <br />contributes to the likelihood of this type of failure. In <br />addition, the factors of safety in the tower in the upper miadle <br />region are kept somewhat below Che factors of safety in cne rest <br />of the tower. Thus, if a failure condition is reached, it ^-Iv-uld <br />be reached in the upper middle region of the cower first. <br />Needless to say, the engineering codes which govern cower designs <br />are extremely conservative. Towers are designed for extreme wind <br />conditions, and even under these extreme conditions, .scrirc.Mit <br />factors of safety are required. <br />Should you have any questions, on the roregoing, pleai^e do rot <br />hesitate to contact us. <br />Sincerely, <br />Myron C. Noble P.E. <br />President <br />MCN/lsc <br />I Hereby eeriiiy tbei <br />r '.>• <br />wf^-^^^^Rlstered No.^nii 0 .EXHIBIT I <br />T- ir Tr^tw. ,■ -