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Tower Maintenance: the Best Investment You Can Make
"Do we really need this?" That's the question generated every year when we submit operational budgets in regard to one line item: tower maintenance.
Let's face it, most non-technical types see towers every day -- some have been there for 50 years or more -- so why are we spending all this money? Don't they just stay up there? As engineers, we read about tower failures and many of have experienced it, either your own or perhaps another station in the market.
The fact is that tower failures really don't happen that often. Electronics Research gave a presentation a few years ago where it went back to 1960 and determined that all the reported tower failures fell into one of five categories:
A link to the report can be found at sbe.org/sections/documents/TOWERFAILURES.pdf. Take note that most of the failures of existing structures (taking construction out), particularly those caused by ice or wind were triggered by some external event, but perhaps the underlying cause of some of those might be attributable to poor maintenance or overload. In the case of aircraft strikes, they didn't find a clear correlation to tower marking and strikes, however a structure that is not properly marked according to FAA circular AC-70/7460-1K is inviting a fine, or worse, risking a collision with an aircraft.
Perhaps the most overlooked parts of a guyed tower are the anchor points. Even in a correctly installed anchor system, the components are subject to some form of deterioration primarily due to galvanic or electrolytic corrosion, which is a result of current flow in the subsurface portions of the anchor system.
Recommendations for maintenance intervals for guyed and self-supporting structures are addressed in TIA/EIA 222-G. This recommends that maintenance and condition assessments are performed at a minimum of every three years for guyed and every five years for self-supporting structures. Further, it recommends that inspections be performed for all structures after a severe wind or ice event. It also recommends these intervals be shortened for structures in coastal areas or for all Class 3 structures. Class 3 towers are used primarily for essential communications such as: civil or national defense; emergency, rescue or disaster operations; military and navigation facilities.
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