New tower standards coming: are you ready?
Did you know existing standards for broadcast and communications towers are currently in the midst of the biggest revision, some say, since their inception in 1949? The structural engineers in our field are very aware of this, but many Chief Engineers are not. The new standards have been in the works for six years. The standards committee, made up of members from TIA and EIA, is labeled "TR-14.7." The number of the standard is 222 and we're on revision F right now - - our existing standard. The last major revision was revision D in the late 80s. The next revision of the ANSI/TIA/EIA standard "Structural Standards for Steel Antenna Towers and Antenna Supporting Structures" will change the loads and design criteria for communication towers including broadcast structures. It will also have an impact on the load carrying capacity of existing structures.
The committee's leading industry engineers, consultants, designers, and manufacturers collectively bring an unmatched breadth of knowledge and experience to the process. The final version has was approved 10/20/04 at a meeting held in Denver and went back though for public response/comments 12/16/04. Once comments/balloting is complete, the committee will resolve any negative comments. If negative comments are persuasive, and changes will affect technical data, the standard will need to be re-balloted. The committee hopes to have the standard published in Q3 '05.
For sheer volume of information, the 222-G standard will outstrip its predecessors by three or four times, including more than 150 pages devoted solely to state-by-state map graphics illustrating wind, ice, frost and seismic factors. The large amount of material contained in this version will require electronic versions to also be made available (we get into specifics later). All new tower construction and major renovations of existing structures must conform to 222-G after its adoption. Existing towers will not be affected unless physical alterations are made or antenna loading exceeds the original, approved design.
"The committee's intent is to create an internationally recognized and acceptable standard that can be implemented beyond the North American market. The committee believes the standard will eclipse the state of the art in any other standard in the world. The standard is incorporated by reference in the International Building Code, which means that by default it becomes the most widely recognized tower standard of most countries, states and municipalities for their building codes, although there is often a lag of two to three years for the local level to catch up," comments Craig Snyder, President/Sioux Falls Tower, Chairman of the TIA/EIA TR14.7 (Standard 222-F) Committee and Chairman of Board/National Association of Tower Erectors.
"The purpose of the new revision is to reflect that structural analysis is done a bit differently today than it used to be-there are some new methods out that have recently been included in all the building codes. The structural standards for towers is out of sync with those codes. So it has to be brought in compliance with the building codes because sometimes when you apply for a permit they want to see the calculations. If it's the wrong method, they'll throw you out," warns Sterling Smith, Director of Business Development, OTL (tower lighting). "Because of this, there could be slight variations in the results of your structural analysis of your tower. Some towers will come off a little better off, with a little more 'fat,' if you will, in them. And some will come out a little skinnier. This has a small effect on the loading you can put on your tower. In rare circumstances, it will have a major effect."
Tomorrow we get into specifics
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