Electro/Telecom Industry Trends
Nov 2005
TIA Releases Dramatically Different Tower Standard
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The latest version of the Telecommunication Industry Association’s (TIA’s) Structural Standard for Antenna Supporting Structures and Antennas represents the most sweeping changes made to the standard in nearly 20 years. More than twice as long as its predecessor, TIA-222-G is comprised of 15 chapters and 14 annexes that provide users with the minimum criteria for specifying and designing steel antenna towers and antenna-supporting structures. It covers technical issues such as wind, ice, and seismic loading; design stresses; safety and climbing; and geotechnical requirements. The document also provides guidelines for antennas, mounts, and lines.
Revision G offers important new content in a number of areas, including data associated with wind and ice loads, both of which have a significant impact on the design of a tower. Much of this new information reflects changes in how these factors are measured, says Craig Snyder, chair of TR-14.7, the TIA committee responsible for the development of the new standard. “For example, the way we look at wind is different now. We used to look at it as the fastest mile per hour, and now it’s averaged as a three-second gust.”
Besides providing detailed maps that illustrate ice and wind conditions throughout the United States, TIA-222-G also includes an annex that delivers this information in the form of a county list that provides the minimum and maximum wind and ice load values for every county in the United States and its territories. In addition, the electronic version of the standard provides the county list as a Microsoft Excel spreadsheet, allowing users to easily import county-specific data into the programs they are using to design their towers without having to manually reenter the information.
TIA-222-G also includes newly available seismic load data. While briefly mentioned in revision F, earthquake sustainability has become increasingly important in TIA-222-G. Yet it still will continue to play a smaller role in tower design compared to other load factors. “Seismic loads rarely govern over wind and ice,” says Snyder. “Because of their relatively low mass, most towers are resilient to seismic and lateral loads. What they can’t take is sustained pressures, such as wind or wind on top of ice.”
Another significant change made to the standard is the elimination of the normal soil designation used in revision F. Developed as a set of parameters intended only for bidding purposes, the normal soil definition gradually became used as part of design and engineering processes. TIA-222-G has replaced normal soil with a new presumptive soils annex, which provides values for soil types similar to those used in building codes, such as sand and clay. According to TIA, the goal of the presumptive soils annex is to provide real-world, conservative values for soil and to encourage designers and owners to invest in geotechnical reports to solve potential installation problems.
Even though it was released in July, TIA-222-G will not go into effect until January 1, 2006. “The committee felt it was important that the public and the users of the standard had some time to adjust to such a major revision over the last version,” Snyder says.
To purchase a copy of the standard, visit Store.IHS.com
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