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<br />MN BLDG CODES & STDS Fax:651-297-1973 <br /> <br />'- <br /> <br />st'A1& t)F""II~;rr.:r.SOT.a.. <br />Department of <br />.dministration <br /> <br /> <br />4D8 !'-Ictrn SqllOU'l!! BuildinB <br />Scverllh:and Roblin: Sl"'~l <br />Sai.ru: Pa\ll. ~IlMC$Db S,sllll <br />PhDRr:: 611 296-14J9 <br />FAX; 612::97~19'j13 <br />61:2 J,97.51S3 <br />(TDD.Minncsot.a Jlt'by Service) <br />&00 6.S1.3$:!9 <br />(Cillll:L&4r Minnl!!&Ot:L TDD- <br />M,innoot:l. Rd,ll,Y Scrv~l <br /> <br />. <br /> <br />. <br /> <br />Sep 13 '99 <br /> <br />8:29 <br /> <br />P.05/06 <br /> <br />}If <br /> <br />Ut:ILDl~C CODES" ;;T.~SD~ l~~ <br /> <br />December 8, 1993 <br /> <br />Mr. Roger Barton, P.E. <br />Andrew Corporation <br />2701 Mayhill Road <br />Denton, TX 76208 <br /> <br />Dear Mr. Barton: <br /> <br />Subject: <br /> <br />Our response to your request of November 24, 1993 regarding <br />the design of tower stnlctures for wind and ice. <br /> <br />Rule part 1305.4800 of the Minnesota State Building Code amends Uniform <br />Building Code Section 2311, Wind Design. This amendment requires that <br />one-half inch of radial ice be included in the design of open frame towers. As <br />no reference is made either in this rule or in UBC 2303(f) to a load <br />combination reduction of ice and wind, it is assumed that both the ice and <br />wind be considered to act simultaneously at their design load conditions. <br /> <br />The second paragraph of 1305.4800 states that certain structures, such as the <br />communication towers you reference, be designed in accordance with approved <br />national standards. Ai'lSI Standard EIA/TIA 222-E will be referenced in <br />section 2303(b) of the 1994 UEC as a recognized guideline standard. <br /> <br />Section 2.3.16 of 222-E permits a design based on dead load plus 75% of the <br />wind load plus the ice load. However, the footnote states that when the basic <br />wind speed is specified as occurring simultaneously with an ice locui by the <br />purchaser or locai IZUthority, no reduction factor shall be applied to the wind load.. <br />From our conversations with two local engineers experienced in tower <br />construction, it appears that Minnesota's climatic conditions generally would <br />not produce maximum simultaneous design wind and ice loadings. However, <br />as stated in appendix. H of 222-E, simultaneous application of maximum wind <br />and ice loadings may be required if in some geographical areas, seasonal high <br />winds and icing could OCCUI simultaneously. This implies that for each specific <br />installation, the design engineer is responsible to detennine if the maximum <br />simultaneous loads of wind and ice could occur in that geographic location. <br />