Building Codes and RS222-G
EIA/TIA 222-F was adopted in 1996, expanding to include the effects of ice loading. Basically, it provided two methods for analysis of ice. Both assume an accumulation of ice based on that specified by the engineer; however, the wind load applied to the tower could be analyzed at full-speed or at about 75 percent of the full assumed speed.
The current version ANSI/EIA/TIA-222G took effect Jan. 1, 2006, and was essentially a top-to-bottom rewrite. It is also the most comprehensive standard to date and takes into account certain classifications of a structure based on its location and anticipated wind, ice and seismic factors. It considers topography that may affect a structure's exposure to wind, i.e. behind a mountain, atop a hill, etc. In previous standards the design of a structure was based on "allowable stress" 222G bases designs on "Limit State Loading." In this case Limit State Loading is based on two conditions: Strength Limits, which essentially define the maximum loading a structure can tolerate and still be safe for the subject location and classification; and the "Serviceability Limits State" describes how the tower will perform under more normal conditions. There are now requirements for towers located in seismically active zones.
222G also expands on the safety requirements that were addressed in the previous version. It categorizes the experience of individuals that might climb a structure and specifies specific safety items to be included with the design of a tower, i.e. safety cables, ladders, rest platforms, etc.
222G vs. ASCE 7 vs. IBC
New tower construction became more prevalent over the last 10 years largely due to the widespread deployment of wireless mobile telephone networks. The majority of municipalities were not prepared for the volume of applications to construct new towers. In many cases, weak (or no) zoning ordinances were on the books, leading to confusion and several heated zoning meetings. More recently most of these same municipalities have become much more sophisticated in terms of balancing the needs of the tower owner with those of the public. While the zoning piece of the deployment process is well defined, there has been confusion with the permitting and subsequent inspection of an approved structure.
Early building codes did not address the unique nature of tower construction. Once a permit is issued, how (and on what) does the municipality perform a proper building code inspection? The general answer is that an inspector will only sign off on the foundation(s) and assume the structure passes if the design/construction is based on drawings stamped/sealed from a professional engineer licensed in that state. In the earlier revisions of the 222G standard (E and below) there was no correlation between the standard and any building code.
- continued on page 3
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