Electro/Telecom Industry Trends
Nov 2005
TIA-222-G: An Insider’s Perspective
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Craig Snyder is chair of TR-14.7, the Telecommunications Industry Association (TIA) committee that managed the development of TIA-222-G, Structural Standard for Antenna Supporting Structures and Antennas.
Q: Who uses this standard?
The users include tower designers, structural engineers, manufacturers, consultants, and owners. And while a lot of government entities have their own standards, they might use TIA-222 as a reference.
Q: Do the local government bodies that approve the erection of towers in their jurisdictions use TIA-222?
Yes. But because it’s a voluntary standard, there is no mandating body that requires use of TIA-222 other than when it’s codified by the state or local government. They can either adopt it by writing it into their ordinances, ensuring that all towers built in their jurisdiction are designed and constructed based on the TIA-222 specifications, or they can adopt it through the International Building Code, which references it. Right now, the IBC is coming out with its 2005 revision; unfortunately, due to bad timing, we were unable to get the latest version in it. Our hope is that by next year, when the IBC is revised, it will include revision G.
Q: TIA-222-G is markedly different from the previous version, revision F. Why is this?
One of the reasons is that there is a lot of new data that became available in the last five years that wasn’t available before. For example, there is a lot more comprehensive information available on wind and ice loading around the country. Better tests have been conducted in the states and counties, so there is a whole new wind and ice section. In the previous standard, we were also pretty generic about factors such as ice, which was considered to always be a half-inch thick. We knew all along but just didn’t have the data to prove it that ice accumulations are heavier in certain spots and not as heavy in other spots. So now, you can go to an ice map and the county listings and what you see about wind speed and ice accumulation will be different from the previous standard.
Q Is the county appendix new to this standard?
We had a county appendix in the previous document, but it’s completely different now. You can still look up your tower by county, but it’s completely new data compared to the previous standard.
Q: What about the ice maps?
The county list takes care of everything. The ice maps have less detail, so when you want information on your county, you can go to the county listing table and find the ice and wind values. But if you live in the northern half of a big county and the contour on the ice map goes right through it east to west, the table is going to default to the higher of the two ice thicknesses. The map will help you determine if you can use the lesser ice value.
Q: What’s the relationship between TIA-222-G and the American Society of Civil Engineer’s document Minimum Design Loads for Building and Other Structures, also known as ASCE 7?
We referenced ASCE 7 throughout the standard. Much of the engineering data used in TIA-222 is taken from ASCE and obviously the most recent published version, ASCE 7-02, offers the best data out there. This is one of the major reasons why standards like TIA-222 get updated every five years or so—because of new and updated data provided by other engineering bodies like ASCE.
Q: How does the updated standard affect existing structures?
TIA has always had a principle that when a new standard comes out, the old standard becomes obsolete. So as of January 1, 2006, revision F will be obsolete. All new towers and any towers that require upgrades or reanalysis will be need to be analyzed under revision G. But there is a provision in TIA-222-G that says that only towers with added loads or other similar changes will have to be reanalyzed under revision G. So unless you add antennas, transmission lines, or make some other change to the structure, you don’t need to analyze it under revision G. Of course, maintenance of the structure doesn’t initiate a reanalysis. So if you’re replacing a faulty antenna with the same model, that’s considered maintenance, and therefore doesn’t require reanalysis, but if you replace an antenna with a different model, this can constitute a change and therefore will require reanalysis.
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