May 1, 2011 1:00 AM, By Jeremy Ruck, PE
As engineering budgets get stretched thinner and thinner, there seems to be a tendency to concentrate efforts at the studio at the expense of the transmitter facility. Neglecting the transmitter site, and tower in general can have catastrophic effects. Many large market stations are privileged to have multiple sites, but in the small- to medium-sized markets, the failure of vertical real estate results in not only a large reconstruction budget, but also the potential long term hemorrhaging of money.
Photo by Frederick Noronha. Used under a Creative Commons license.
First and foremost in any tower maintenance program is to build a solid relationship with a tower crew; and you get what you pay for. The crew that performs the work for bargain basement prices may tend to have greater personnel turnover, and lower experience and quality levels. This tends to limit continuity between visits, and reduces the opportunity for your crew to observe trends in a particular structure over time. If unsure about the skill or reputation of a crew, seek out your colleagues in the market or region.
Set a plan
Once your crew is lined up, it is a very good idea to meet with the supervisor and discuss your maintenance program. Meeting face-to-face enhances the comfort zone and puts all parties on the same page. Face-to-face communications also sometimes jog memories too, so an opportunity to share historical information about a site is gained. The passing of this knowledge may wind up being crucial down the road to preventing a failure.
In general, consultation with a structural engineer is probably unnecessary for routine tower maintenance. Obviously if items outside of the design criteria are to be added to the structure, a review by an engineer is necessary. Similarly, if a routine inspection uncovers out of the ordinary items such as broken bolts, foundation failure, etc., a reputable structural engineer should be called in as soon as possible to review the findings and recommend a necessary course of action.
Two other persons should form your tower maintenance team: The first is a competent antenna engineer. This person does not necessarily need to be in close proximity to you, but he or she should be readily available for consultation and fieldwork if necessary. The final member of the team is of course the station engineer, who has the most frequent and regular contact with the structure. The engineer should be making cursory examinations, but these are never a substitute for a full-blown inspection.
The frequency of a more in-depth inspection can vary depending on the nature of the site. A naked tower that is a member of an AM directional array in the middle of a cornfield may not need to be fully inspected as often as an older, fully loaded tower in a densely populated area. Regardless of what schedule you utilize to maintain and inspect the tower, it is usually a good practice to have the tower climbed at least once per year. However, exposure to earthquakes and severe storms, etc., might affect the integrity of the structure and will necessitate a greater climbing frequency.
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May 1, 2011 1:00 AM, By Jeremy Ruck, PE
Most tower companies follow a checklist when performing inspections. At a minimum your report should include details about the physical condition of the tower, including mounting hardware, connections, foundations and guy anchors if applicable. Also included in the physical condition should be comments on the paint or galvanizing as applicable, the tension and condition of guy wires, and alignment, that is plumb, of the tower. On the electrical side, issues with grounding, conduits and lighting should be investigated. For the RF portion, visible physical damage and anomalies to antennas, transmission lines, waveguides, insulators and skirts should be noted. In all cases, your crew should be ready and willing to provide adequate documentation including a robust quantity of photographs, which will ultimately protect both parties involved.
Inspection items uncovered during a climb may or may not be rectifiable during the current visit by the crew because of materials and/or personnel. Such items should, however, not be relegated to the back burner. Make necessary corrections at the earliest possible opportunity, which will probably reduce future catastrophes.
Not just a slap of paint
Perhaps one of the planned activities for tower maintenance that tends to be delayed or neglected is that of painting. A reasonable frequency of painting is probably every five to seven years. In certain environments, especially those that are corrosive due to ambient salinity from oceans or industrial pollution, this interval may need to be shortened considerably. Painting serves not only the obvious end of increasing structure visibility, but also provides a protective coating to the tower material. Failing to adequately maintain the paint on the tower increases the likelihood of aeronautical accidents or failure of the structure from corrosion.
Also often neglected is the removal of obsolete items from the structure. Sometimes these items belong to the station, but more often than not, they were installed by another tenant. Vertical real estate tenants sometimes have insufficient respect for the tower owners, and may consider your tower their own personal landfill. This situation can typically be avoided through appropriate language in the lease or licensing agreement they sign for use of the tower, but despite your best actions as a structure owners, some still slip through the cracks and the onus of removal falls to you.
Portions of the structure that lurk below ground can also sink the ship that is your station. Due to the significant increases in technology, equipment at the transmitter site can be just as susceptible to lightning as that at the studio. The necessity of installing and maintaining proper grounding cannot be understated.
Appearances can also be deceiving with guy anchors. This topic has gained a lot of attention in recent years due to spectacular failures, or the identification of impending failures. Although the anchor may look just fine above ground level, the portion below ground, or in concrete, may be a failure waiting to happen. All sites are at risk of galvanic corrosion of the guy anchors; however, those in proximity to pipelines face a much greater risk. Pipelines tend to charge their systems so that everything is deposited on pipeline as opposed to the reverse where the pipeline is deposited on the guy anchors. This means that guy anchors, and even ground systems, wind up migrating to the pipeline. This situation can be rectified through various schemes that employ a sacrificial anode. These systems, however, require maintenance, but are much cheaper to replace than towers.
With some forethought and prior planning, you can significantly reduce the potential of that dreaded phone call. While proper tower maintenance will not prevent all failures, it will certainly go a long way towards reducing their potential of occurrence.
Ruck is a senior engineer with D.L. Markley and Associates, Peoria, IL.