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sabre Industries - <br />Towers and Poles " <br />May 11, 2017 <br />Mr. Yuri Dobrowolsky <br />Central States Tower <br />323 South Hale Street, Suite 100 <br />Wheaton, IL 60187 <br />RE: Proposed 255' Self -Supporting Tower for Trader Lake, WI <br />Dear Mr. Dobrowolsky, <br />Upon receipt of order, we propose to design and supply the above referenced tower for a Basic Wind Speed of <br />90 mph with no ice and 50 mph with 1/2" radial ice, Structure Class 11, Exposure Category C, and Topographic <br />Category 1, in accordance with the Telecommunications Industry Association Standard ANSI/TIA-222-G, <br />"Structural Standard for Antenna Supporting Structures and Antennas". <br />When designed according to this standard, the wind pressures and steel strength capacities include several <br />safety factors, resulting in an overall minimum safety factor of 25%. Therefore, it is highly unlikely that the <br />tower will fail structurally in a wind event where the design wind speed is exceeded within the range of the <br />built-in safety factors. <br />Should the wind speed increase beyond the capacity of the built-in safety factors, to the point of failure of one <br />or more structural elements, the most likely location of the failure would be within one or more of the tower <br />members in the upper portion. This would result in a buckling failure mode, where the loaded member would <br />bend beyond its elastic limit (beyond the point where the member would return to its original shape upon <br />removal of the wind load). <br />Therefore, it is likely that the overall effect of such an extreme wind event would be localized buckling of a <br />tower section. Assuming that the wind pressure profile is similar to that used to design the tower, the tower is <br />most likely to buckle at the location of the highest combined stress ratio in the upper portion of the tower. This <br />would result in the portion of the tower above the failure location "folding over" onto the portion of the tower <br />below the failure location. Please note that this letter only applies to the above referenced tower <br />designed and manufactured by Sabre Towers & Poles. In the unlikely event of total separation, this, in <br />turn, would result in collapse within a radius equal to 25% of the tower height. <br />Sincerely, <br />Josh Gosiak, P.E. <br />Design Engineer I <br />�'N"� gC ... N <br />ti. 1.,,.. / ., <br />JOSHUA L. <br />GOSIAK <br />E-45437-6 <br />SIOUX CITY <br />Sabre Towers and Poles • 7101 Southbridge Drive • P.O. Box 658 • Sioux City, IA 51102-0658 <br />P: 712-258-6690 F: 712-279-0814 W: www.SabreTowersandPoles.com <br />