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05/01/2002
The Tower Industry Cleans Off Its Specs
The Tower Industry Cleans Off Its Specs originally appeared in the Fall/Winter 2001 issue of Site Management & Technology and is republished here with permission of PRIMEDIA Business Magazines & Media Inc. Copyright 2001, PRIMEDIA Business Magazines & Media Inc. All Rights Reserved.
“G” usually suggests “gravity” to technical types, but the letter will come to represent a force of a different nature to the tower industry over the next five years.
The TR-14.7 Committee, which sets antenna structure standards used by the American National Standards Institute, the Telecommunications Industry Association and the Electronics Industry Association, is completing editorial revisions of the updated bible for the tower industry: ANSI/TIA/EIA-222, “Structural Standards for Steel Antenna Towers and Antenna Support Structures.” The standard, which is reviewed every five years, is currently in its sixth incarnation, 1996's version “F,” which was reaffirmed in 2001 to preserve the cycle and to allow some extra time for the completion of its successor. The new standard, version “G,” should be ready to submit to the TIA general membership for balloting and comment this spring. Final adoption is forecast for late in the third quarter of 2002.
For sheer volume of information, the 222-G standard will outstrip its predecessors by three or four times, including more than 150 pages devoted to state-by-state map graphics illustrating wind, ice, frost and seismic factors. The depth of the material will require electronically published versions to be made available. 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. Which standard applies is usually a decision of the engineer of record.
Revision “G” will contain new material and expanded content, and it will, “really represent a new idea of what the state of the art is,” said John Erichsen, P.E., vice president of engineering for Plymouth, Indiana-based tower manufacturer PiRod. Erichsen is a member of the TR-14.7 executive and editorial subcommittees for the standard. The new standard, comprising 16 chapters, has been prepared by eight subcommittees, covering technical issues such as wind and ice loading, seismic loading, design stresses, safety and climbing, and geotechnical requirements. Presentations and panel discussions to acquaint the tower industry with the revisions will be given at the spring 2002 meetings of the National Association of Tower Erectors and the National Association of Broadcasters.
Addressing any additional comments from the general TIA engineering community during the April/May ballot shouldn't pose too much of a challenge, Erichsen said.
“We've been doing subcommittee affirmations of the content to-date, so the controversy should be laid down early enough that once [the revisions] get out in the marketplace, there should be fairly little,” he said. The only fly in the ointment might be new ideas from anyone “who hasn't participated in the last four years and then steps in at the 11th hour.”
As an example of changes in the new standard, Erichsen cited revisions in geotechnical definitions, such as “normal soil,” for determining lateral load capacities, bearing load capacities and resistance to pull-out.
“‘Normal soil,’ right now, is a set of parameters that was always intended for bidding purposes,” Erichsen said. “Over the years, it became practice, and in some instances they actually installed foundations for that. So we've eliminated the term ‘normal soil,’ and we're going to give them, in the appendix and the annex, values that are representative of a soil type, similar to what the building codes do.”
“We'll have a value that's representative of sand, a value that's representative of clay, etc. It will be up to the customer to tell us which one is representative. If they don't, there's a default value that all bids are supposed to be completed against,” Erichsen said.
The committee's aim was to determine real-world, conservative values, he added. “The intent is to drive them toward a geotech report because that's the best way to solve all of the initial installation problems and economics.”
Safety and climbing issues
Other issues, like safety and climbing requirements, have been thornier for the subcommittees to finalize, but the ultimate standard will probably include increased requirements for signage and uniformity in climbing. Gin poles used in tower erection, for example, will be a separate standard from 222-G. The challenge in preparing a standard like 222-G is limiting it to structural criteria and engineering standards, without attempting to impose subjective best practices, Erichsen said.
“What we have to be careful about is not creating a standard that reads like a specification, that's based on preferences,” Erichsen said. “We're trying to create a minimum. Now, that becomes real dicey when you get into safety issues,” he said. “When we've looked at the safety issue, our mantra has been, ‘We have to create a minimum standard for safety, but we can't create the ideal standard for safety because that's not the standard's intent.’ We have to be careful of the economic impact to make sure that we're not creating a situation that is onerous for the general public and the users unless there's a justifiable safety reason involved.”
Erichsen characterized Revision G as the most sweeping change in the 222 standard since Revision D was implemented 20 years ago. “The intent is to create an internationally recognized and acceptable standard that we can push beyond the North American market,” he said. “We actually think this will eclipse the state of the art in any other standard in the world.”
The significance of the revision extends beyond the tower and rooftop support industry itself. The standard, already used by ANSI, TIA and EIA, is also incorporated by reference in the International Building Code. This means that by default it becomes the standard of most nations, 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.
“The great benefit of ‘G,’ beyond all the other technical issues, is that it's going to allow the user to tune the situation to site-specific issues and to take some of the things that cause these towers to be overbuilt off of the table,” Erichsen said.
D. A. Keckler is technical editor. A PiRod pamphlet discussing this new tower industry standard, “Revision G: How It's Going to Impact Your Job,” can be obtained for free at www.pirod.com or by calling 877-467-4763.
D.A. Keckler
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