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.
We continue from yesterday:
How are broadcasters most likely to be affected?
"Most are concerned that the standard will increase the cost of new structures or render existing structures obsolete due to the high cost of modifications to bring them up to the level of the new standard," says 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. "It is difficult to say how each structure will react when analyzed under the new standard. Our preliminary trial runs show some getting heavier and some actually getting lighter. What the committee has tried to do is bring the latest engineering information and data to the table and apply it to the way towers are designed and engineered today. Driving up cost was certainly a major consideration in our work, but not the only consideration. It's a delicate balance we try to reach between maintaining a reasonable cost tower while at the same time using the best science available."
Why is the new standard so much more restrictive than the previous few?
"While it is true that this version standard defines a lot more than earlier versions, its offsetting benefit is users of the standard-owners, engineers and purchasers-now can find all the information required in one source, ensuring that acceptable minimum requirements for a tower design are well defined," explains John Wahba, SVP/Engineering Radian Communication Services, who has been actively involved in the development of this standard since 1998. "In other words, it helps leveling the playing field which, in the end, provides the customer with the confidence that their tower-new or modified-meets all the applicable requirements without supplier interpretation."
Revision G has a section dedicated to the analysis of existing structures which defines two types of analysis: a preliminary review and a detailed (rigorous) analysis. Says Wahba: "Broadcasters are to make sure that a rigorous analysis is performed prior to adding or removing antennas and lines on a tower because in some cases, this loading adjustment may overstress the tower in other areas."
"In my opinion, the most significant change is the classification of a rigorous analysis," says Sterling Smith, Director of Business Development, OTL (tower lighting). "This allows an engineer to perform an assessment so that an owner can determine if it is feasible to add additional loading without the full cost of a detailed rigorous analysis. However, the new standard makes it clear that a full rigorous analysis is required prior to actual placement of additional loading. No more shortcuts, which in the long run is to the benefit of the owner. Broadcasters need to insure that they are employing a well-recognized engineer that will adhere to the ethical practices of their profession. Remember that broadcast towers can cost millions with the cost of lost revenue due to a tower failure far exceeding the cost of the tower. A lot of engineering can be performed for $5,000. Don't skimp on structural engineering!"
Are you reading this from a forwarded email?
