Tower Failures and How to Prevent Them

Having a tower fail is one of the worst things that can happen to a broadcaster. Tower failures put people at risk, can be enormously expensive and take a broadcaster's life blood, the radio signal, off air. A session which is part of the Engineering Program at this week's NAB Radio ShowTM (Philadelphia, Pa., September 23-25, 2009, www.nabradioshow.com) will cover the major causes of tower failures and offer advice on how you can work to prevent a catastrophic situation. This session will be held on Wednesday, September 23, 2009 from 9-10 a.m. in room 201B of the Pennsylvania Convention Center. The NAB Radio Show Engineering Program is sponsored by Stainless, LLC.

Hosting this session will be David Davies, Director of Structural Products and Services, Electronics Research, Inc. (ERI, Chandler, Ind., www.eriinc.com). David has a 27-year history in the tower industry including 19 years as an engineer with ERI. He is named in several patents including the LAMBDA antenna mounting system and the ULTRA guy anchor design. He has participated in projects through out the U.S. and foreign countries, and is a member of the TIA/EIA committee responsible for the composition of the design standards governing antenna and antenna tower design and fabrication.

The first part of David's presentation will focus on the five most common causes behind tower failures, which are anchor failure (#5), aircraft collision (#4), special wind conditions (#3), ice and wind over ice (#2), and problems with construction (#1). This ranking is a result of an ERI study conducted in 2009 which investigated over 70 tower failures since 1960, and interestingly this ERI ranking is very similar to a ranking from a study conducted by tower manufacturer Stainless in 2006. An example of each failure mode, taken from David's presentation follows. An interesting list of additional failures is available on the Internet at: http://en.wikipedia.org/wiki/List_of_catastrophic_collapses_of_radio_masts_and_towers.

Anchor failure - picture at right shows what's left of the 528-foot tower of WMGX (93.1) and WYNZ (100.9) in Portland, Maine, which came crashing down on December 11, 2003. David indicates in his presentation that the tower wasn't all that old - WMGX had built in 1986 (17 years) - but it suffered from corrosion in the guy wire anchor. The tower plunged in the opposite direction (from where the guy wire anchor was located), crushing a couple of cars and coming within feet of hitting the studio and some warehouses.

Aircraft collision - the CBC Tower, near Shawinigan, Quebec, Canada was a 1,217-foot high guyed tower used for FM radio and TV transmissions. On April 21, 2001, a Cessna 150 single-engine plane piloted by Gilbert Paquette flew into the tower while flying in heavy fog. Rather than plummeting to the ground, the plane became firmly wedged into the side of the tower (see arrow in photo at left), and a subsequent analysis determined that as a result of this impact, the tower had been knocked several feet off-center. Apparently a number of options were considered and ultimately it was decided to bring the structure down in a controlled demolition. A video of the demolition is available for viewing on You Tube at: http://www.youtube.com/watch?v=udenD7RXGg0. This is believed to be the tallest structure ever demolished with explosives. A detailed account of the implosion is given on the "Implosion World" Web site at www.implosionworld.com/cbc1.htm.

Special wind conditions - on the night of August 23, 2000, a thunderstorm with winds in excess of 70 miles per hour went through the town of Mexico, Mo,, taking down the 408-foot tower of KXEO which was also home to the microwave system that feeds the nearby 1,203-foot KWWR tower (see photo at left). The power lines feeding the nearby studio were knocked down, as well. As can be seen from the photo at left, the tower just barely hit the northeast corner of the studio building. According to reports from the scene, there was some damage to cars in the parking lot from breaking guy wires, but no one was injured.

Ice and wind over ice - as reported in the Waterloo Cedar Falls Courier, on February 24, 2007, the tower of FM station KHKE, just south of Waterloo, Iowa, was felled by the combination of a 1-inch thick coating of ice and 30- to 40-mph winds. The upper half of the 420-foot tower came crashing down when the top two guy wires snapped (shown in photo at right).

Problems with construction - this is the most common reason that towers fail, and according to David's research is responsible for 30% of the tower failures studied by ERI in 2009. In March of 2008, a tower under construction in La Mirada, Ca. collapsed (see photo at left), injuring a construction worker. While the final height of this tower was to be 684 feet, it's height at the time of the collapse was approximately 250 feet. David believes that although, for example, "ice" or "storm" may be the reported "cause of failure" in many tower collapses, it is likely poor design and/or installation, tower overloading and lack of maintenance that are contributing factors.

David explains that hidden causes of failure, such as galvanic corrosion often go undetected and over time will weaken and eventually destroy a tower structure. The latter part of his presentation will focus on important detection methods that he feels are both highly accurate and cost effective for preventing many tower failures.

2010 NAB Show Call for Speakers
Call for Technical Papers – NAB Broadcast Engineering Conference

The 2010 NAB Show will host the 64th Broadcast Engineering Conference. This world-class conference addresses the most recent developments in broadcast technology and focuses on the opportunities and challenges that face broadcast engineering professionals. Each year hundreds of broadcast professionals from around the world attend the conference. They include practicing broadcast engineers and technicians, engineering consultants, contract engineers, broadcast equipment manufacturers, distributors, R&D engineers plus anyone specifically interested in the latest broadcast technologies.

Do you have something to share?
If you feel qualified to speak at the NAB Broadcast Engineering Conference, we invite you to submit a technical paper proposal.
Not all acceptable submissions can be included in the conference, due to the large number of submissions that are received and the limited number of available time slots.

The deadline for submitting your proposal is October 23, 2009. If you have any questions, contact John Marino, VP Science and Technology at (202)429-5346.

PLAN TO ATTEND!
The IEEE Broadcast Technology Society
59th ANNUAL BROADCAST SYMPOSIUM
14 -16 October 2009
The Westin Alexandria
Alexandria, VA, USA
www.ieee.org/bts/symposium

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