DCPCUP-2016-02355 - Laserfiche WebLink

Home Browse Search

SádtrjEs- Towers and Poles July 28, 2015 Mr. Yuri Dobrowolsky Director of Construction Central States Tower 323 South Hale Street, Suite 100 Wheaton, IL 60187 RE: Proposed 160 ft Sabre Monopole for CTY B Spring,WI Dear Mr. Dobrowlosky, Upon receipt of order, we propose to design and supply the above referenced Sabre monopole for a Basic Wind Speed of 90 mph with no ice and 40 mph with 3/4" ice, Structure Class II, Exposure Category C, and Topographic Category 1, in accordance with the Telecommunications Industry Association Standard ANSI/TIA-222-G, "Structural Standard for Antenna Supporting Structures and Antennas". When designed according to this standard, the wind pressures and steel strength capacities include several safety factors, resulting in an overall minimum safety factor of 25%. Therefore, it is highly unlikely that the monopole will fail structurally in a wind event where the design wind speed is exceeded within the range of the built-in safety factors. Should the wind speed increase beyond the capacity of the built-in safety factors, to the point of failure of one or more structural elements, the most likely location of the failure would be within one of the monopole shaft sections. This would result in a buckling failure mode,where the steel shaft would bend beyond its elastic limit (beyond the point where the shaft would return to its original shape upon removal of the wind load). Therefore, the overall effect of an extreme wind event would be localized buckling of the monopole shaft. Assuming that the wind pressure profile is similar to that used to design the monopole, the shaft will buckle at the location of the highest combined stress ratio in the upper portion of the monopole. This would result in the portion of the monopole above"folding over"onto the portion below, essentially collapsing upon itself. Please note that this letter only applies to a monopole designed and manufactured by Sabre Towers& Poles. In the unlikely event of total separation,this would result in collapse • the section above,within a radius equal to 50%of the monopole height. 0 0 • * ••i••, . • Sincerely, �� 'co , : �•At67►# r Robert E. Beacom, P.E. 11143W-�1Z't ! N Design Engineer II +,� IA. ,•••-KY `\'�, r••• ,t, Knit+►uot, Sabre Towers and Poles • _ '1 VI ,L1 5 e • -0 : c 55 • Siut.' ',_ ;. ., :I I( ' n6:3 P .- _ -, E_ i' F: ii, 2. ,) U::_1 W ...,,_L,a:, e (,„,1,-1 ll ole �.