Tower Maintenance: the Best Investment You Can Make

February 7, 2014


"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:

pie chart

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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While a qualified professional should perform maintenance, you can learn a lot about the condition of your tower by simple visual inspection (which is recommended to be performed every year for guyed and every three years for self-supporting structures). In my opinion you should perform a visual assessment every time you visit the site, especially in remotes areas that might be subject to attracting the attention of fun-loving locals.

tower site

Eric Eaglstun/flickr.com


 

I make it a habit to look at the tower from a short distance to see if everything looks in alignment. Of course the eye won't catch small variations, but once I noticed some sections of the tower looked a little crooked, which turned out to be a guy anchor that apparently was hit by a vehicle. I also recently had an experience with a guyed tower at a not-so-remote location, that happened to be owned by a city, stood next to its E911 call center and was used as a primary microwave link to its other radio sites. Someone unscrewed the turnbuckle on one side and released a level of guy wires. Fortunately it was noticed and addressed before the tower collapsed. You should also take note of the condition of the paint and/or the operation of the lighting system.

Check every visit

When I arrive at a site I usually check to see if the fence has been breached. It is very common to see openings in the fence, which usually means there is going to be -- at the very least -- some copper, transmission lines or AC compressor missing; but, it's also not unusual to find the doors open. While this isn't directly addressed in maintenance requirements, a broken ground ring will create problems (and potential safety issues) and should be repaired ASAP. You can also easily check the anchors and foundations for unusual cracking, connections to the guy wires, and rust or corrosion.

For a self-supporting tower, items that seem to get overlooked are the bolts that connect the foundation to the tower legs. These are typically bolted above and below the plate, to allow for some minor adjustments to level the tower base. Normally once the tower is built, they pack the lower bolts with concrete (between the base plate and foundation) to protect them from moisture or water pooling. I have seen many self-supporting towers with these exposed and rusting.

None of this should take the place of a proper full inspection of the tower, which includes:
■ Climbing the structure and noting (and hopefully correcting) loose bolts, documenting bent members, rust, improperly attached line and antennas, electrical connections to tower lighting, missing grounds, improperly functioning safety items or anything else unusual. They should take lots of pictures to document the problems that should be included with a comprehensive report.
■ They should use a transit to determine the vertical alignment of the tower shaft and guy wires
■ The tension of the guy wires should be measured and corrected if needed, every three years.
■ The lighting system and tower paint should be inspected annually per FAA Circular AC-70/7460-1K.
■ The integrity of a ground system should be inspected and conductivity tests performed annually. You can learn a lot about the performance and deterioration of a ground system by noting the measurements each year. Try to perform them around the same time of year. A poorly functioning ground system can cause deterioration of metals through possible galvanic or electrolytic corrosion.

A properly maintained tower can stand for more than 50 years -- that's the best return on investment you can have.


 

McNamara is president of Applied Wireless, Cape Coral, FL.


 


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