How to stop more towers from collapsing

Drawings of tower buckling at Mountain Lake PBS

Loaded with 200 tons of ice from an April storm, Mountain Lake PBS’s tower buckled at its weakest point. The top of the tower took the remainder down, a forensic engineer said. (Graphics from animation by Mountain Lake PBS.)

At Mountain Lake Public Broadcasting in upstate New York, Alice Recore put $1.2 million into reinforcing and preparing WCFE’s 30-year-old tower for the DTV age.

Across the continent at KSPS in Spokane, Wash., Bob Wyatt assiduously maintained and upgraded the station’s 40-year-old tower.

But that wasn’t enough in either case. Both towers suffered catastrophic collapses within the past year, at costs that are still mounting.

Theoretically, towers don’t have to fail. “If a tower is properly maintained, correctly loaded and meets today’s engineering standards, its life cycle should be unlimited,” says Jean-Alain Lecordier, P.E., co-founder of Tower Consultants Inc. (TCI).

But those are big “ifs.” In the real world, many stations have loaded additional antennas on towers that were erected decades ago, when builders had fewer standards to follow for climate, anchoring and other crucial design aspects.

As towers age, they can suddenly show the effects of design flaws, manufacturing mistakes, maintenance shortcomings and other human errors, which are hidden until metal fatigue sets in or a particularly brutal storm rolls by.

In other words, evidence suggests that the WCFE and KSPS disasters are akin to canaries that succumb in a coal mine.

An icy lesson

To prepare for DTV conversion, Mountain Lake in Plattsburgh, N.Y., hired a tower firm in 2004 to assess its vintage 1974 mountain top tower. Federal DTV transition aid from CPB covered the upgrades recommended by the tower firm to “meet current standards” and to add a digital antenna. Work was completed in 2005.

Then, in mid-April of this year, a late winter storm covered the Northeast with a thick coat of ice. When the skies cleared on the morning of April 18, the station’s 400-foot tower lay twisted on the ground.

Recore, president of Mountain Lake, huddled with her top managers to develop a plan. One had recently read about the Spokane tower failure in Current. Recore phoned Wyatt, director of engineering at KSPS, who gave advice and referred her to a tower firm qualified in forensic engineering.

Neighboring stations alerted the public to Mountain Lake’s dilemma and one — CBS affiliate WCAX in South Burlington, Vt. — carried Mountain Lake’s signal on a digital subchannel, putting it within reach of the satellite TV operators and local cable systems.

Consultations with PBS, the FCC and communications attorneys suggested that the CBS-facilitated digital signal was well within the law. But would cable and satellite TV operators accept the signal?

Within 10 days, all but EchoStar’s Dish Network were carrying the signal. Mountain Lake was back for an estimated 50 to 60 percent of its 600,000-household audience across northeastern New York and southern Quebec.

But the EchoStar’s refusal meant another 60,000 households lost WCFE. EchoStar refused to comment on what precipitated its refusal, raising concerns that it will reject future calls for assistance in other regions.

To establish its own link to cable and satellite TV operators, Mountain Lake eventually set up a low-power temporary digital transmitter, which EchoStar and others accepted. As a result, Mountain Lake is reaching 60 to 70 percent of households as its August pledge drive approaches. To date, costs not covered by insurance total about $300,000.

Forensic engineers investigating the collapse meanwhile estimated that the tower had collected about 200 tons of ice, according to Ernie Jones, P.E., of Electronics Research Inc. (ERI). “The tower failed near the third guy level, at its weakest point,” Jones explains. “Above that point, the tower’s superstructure was hollow steel tubes. Below that point, the tower was composed of solid steel rods.”

Broken rods anchoring the tower’s guy wires at KSPS were made of an alloy long known to break in the cold, a materials scientist discovered after the top of the tower fell. (Photo: GT Engineering.)

Overloaded with ice, the hollow-tube segment of the tower broke away and plummeted to earth, ripping out guy wires that braced the lower segment. It was small consolation that the tower fell away from the transmitter building, damaging only one of its walls instead of smashing it.

Although wind and ice imbalance may also have been present, it was a moot point Jones says. Bottom line: There was too much ice for the weakest area, which had not been reinforced.

When the tower was retrofitted two years ago, the Television Industry Association (TIA) design standard then in effect, TIA-222-F, didn’t contain precise specifications for heavy icing. But the TIA’s standards committee had been working on a significantly revised version since 1997, says ERI’s Jones, whose company was not involved in Mountain Lake’s 2005 retrofit. Mountain Lake was unaware of the new standard, which addresses heavy icing. It was publicly released Aug. 2, 2005, and took effect Jan. 1, 2006, more than a year before the Plattsburgh tower fell.

Timberrrr!!!

The tower failure in Spokane involved neither wind nor ice. Instead, aging brought to light an unknown metallurgical defect in the 1967 structure. During an unseasonable cold snap, the upper third of the 600-foot KSPS structure tore off.

Early estimates indicate costs will exceed $1.3 million.

In the tower’s original construction, each of its guy wires was connected to its underground anchor by a group of old-style lollipop-shaped takeup rods. When the guy wires contracted on the chilly Thanksgiving weekend, two takeup rods on a single guy wire failed, destabilizing the tower. Tension from the two other guy wires ripped off the tower’s upper segment.

Miraculously, the top fell without damaging the lower segment, permitting a backup antenna to be mounted atop the remaining 400 feet. The transmission outage affected only over-the-air viewers and was remedied within seven days.

The months-long metallurgical analysis of the broken parts is nearing conclusion, but findings already point to two types of deficiencies. First, the takeup rods were defectively manufactured, according to materials scientist Robert A. Clark, Ph.D., of GT Engineering in Redmond, Wash. Nondestructive analysis of the remaining 34 intact rods indicated a similar defect.

Secondly, the alloy used in the takeup rods is questionable at best, Clark says. “Similar metallurgy was proven insufficient in cold temperatures when it was used for shipbuilding in World War II,” explains Clark, who is analyzing the metal used in Spokane. “As a result, Liberty ships broke in half and sank in the North Sea.”

Therefore, the effects of low temperatures were well known when the KSPS structure was designed and erected, Clark says. However, he’s still investigating whether tower standards back then addressed the problem.

Because the KSPS investigation is ongoing, Clark and Wyatt declined to name the tower company. However, they did say the takeup rods came from a parts supplier and were not fabricated by the tower manufacturer.

Clark suggests that other stations check whether defective tower components could put them off the air. “In other words,” he says as a forewarning, “I can’t believe only 36 of these rods were ever made.”

Given what consultants have already discovered, Wyatt commissioned a complete structural analysis of the KSPS tower. “It included every bent cross piece and every nut that’s not tightened down enough,” he says. When the report comes in, Wyatt intends to deal with any concerns that it raises.

“For instance, it only cost $5,000 to replace all 36 outdated takeup rods,” Wyatt says. “If someone would have told us a better technology was available so cost-effectively, we’d certainly have considered upgrading before the collapse.”

What’s more, says ERI’s Jones, “Towers can now be designed to withstand the inadvertent loss of any one guy wire. Retrofitting an old tower may or may not be cost-effective.”

Accidents waiting to happen

For other broadcasters, the risks worth mitigating go beyond those that downed the Plattsburgh and Spokane structures. According to tower engineers, potential problems commonly include mishandling of tower maintenance, inadequate tower anchoring systems and improper tower loading.

Regarding tower anchors, a staggering number are inadequate. “As many as 50 percent of all towers in the U.S. have substandard anchoring,” estimates TCI’s Lecordier, who has been in the industry for nearly 30 years. Possible remedies depend on the soil at a tower’s site and the anchors’ condition.

Many station execs rely on substandard anchors because of their misconceptions about galvanized metal. “Galvanizing doesn’t have infinite life—it gets used up like paint on your house,” explains GT Engineering’s Clark. “It’s a function of surrounding conditions and could take 5 years or 50. Just because metal was galvanized is insufficient insurance.”

Under-sized anchors have been blamed for the collapse of a new DTV tower still under construction for commercial station WSKY in northeastern North Carolina, according to news reports. The incomplete tower, already at 760 feet, toppled in early March after a 40-mph wind gust, crushing the new transmitter building. No ice was present.

Serious problems also can arise when inadequate structural analysis leads to improper tower loading. “In many cases, tower owners allow renters to place antennas and cabling without completing a structural analysis,” says Lecordier. “Also, tower owners often fail to require documentation for what’s actually added. As a result, different equipment ends up on the tower, and in different places, than the owner agreed upon.”

When it comes to maintenance, pubcasters may actually be somewhat ahead of the pack. “Public broadcasting towers are among the best maintained in the system,” says Troy Kyman, founder and president of the tower construction, maintenance and repair contractor Precision Communications Inc. (PCI) of Grove, Okla.

“Unfortunately,” Kyman adds, “several towers have already fallen as a result of tower maintenance persons taking shortcuts. Generally, shortcuts occur when people are not qualified for the type of tower they’re working on. For example, an eighth-of-an-inch pit on a gusset plate is insignificant on a communications tower at your studio, but is a serious problem for a tall broadcasting tower.”

Most tragically, improper practices can have fatal results. On July 10 the cable-riding system used by two tower workers failed as they installed a cellular antenna on the tower of Kansas City’s NBC affiliate. Both men died in the fall.

And the collapse of a tower can become a long-term setback for a station. Once a tower is down, it may be impossible to replace if development occurs around the site. “If your tower falls, you could discover that zoning laws prevent rebuilding,” says Kyman. At a minimum, the red tape can raise rebuilding costs.

Tougher, safer standards

Considering the array of dangers, how did they fly under pubcasters’ radar? Several factors appear to be at work.

First, the tower-building profession, compared with the builders of bridges and skyscrapers, is a relative infant. “Physics and engineering are catching up with each other in relation to towers,” says PCI’s Kyman. “And, the engineering has come a long way since I started in the business 25 years ago.”

The second factor is how standards evolve. Not surprisingly, TIA standards are based on data and standards generated by other organizations such as the American Society of Civil Engineers (ASCE).

“For example, prior to 1998 there wasn’t any ASCE ice map for guidance on the type and thickness of ice to expect,” ERI’s Jones says. Factors such as the location, type and thickness of icing, or the force and direction of wind, can have vastly different effects on a tower.

A contributing factor is that there’s no independent body regulating the tower industry.

One consequence is that the industry’s latest standard isn’t always integrated into local building codes. In fact, the most recent version of the TIA standard has been effective for a year and a half but isn’t yet part of the International Building Code (IBC) that underlies local codes. Also, the standard permits various exemptions for existing towers that make them more vulnerable.

The standards also contain caveat emptor clauses that could be called loopholes. In other words, “meeting the standard” requires only that tower firms conform to certain minimum criteria. The burden is on tower owners to be aware of this nuance and to insist that their tower be designed to withstand site-specific climate conditions.

Regardless, enforcement is in the hands of local building inspectors and insurance carriers, neither of which is catastrophically harmed if a pubcaster’s tower fails. And the TIA, which is a vendor consortium, not a broadcasting organization, is careful to call their standards “voluntary.”

But pointing fingers solely at the tower industry and its standards would be myopic. A starring role belongs to America’s ubiquitous the low-bid culture. For instance, tower standards began incorporating guidance for ice and wind loading as early as 1986, says Jones, but the extra cost of resilient design often placed engineers at odds with budget-minded decision-makers.

Put another way, the designers of enduring structures such as the Brooklyn Bridge (completed in 1883) and the Golden Gate Bridge (1937) weren’t asking the question, “What’s the minimum required for the bid?”

All other factors aside, the universal underestimation of Mother Nature has resulted in relatively poor contingency planning, as demonstrated by Hurricane Katrina.

Seismic shift

According to tower experts there is good news. Notably, you can save your structure by heeding the science behind the latest tower standard, ANSI/TIA-222-G.

“Due to advances in the body of knowledge, the G standard is much more sophisticated” than the previous one, says Murty Madugula, Ph.D., P.Eng., a civil and environmental engineering professor emeritus at the University of Windsor in Ontario.

“Previously, the entire standard was only several pages,” continues Madugula, a former ASCE member who spent 38 years performing research for standards development. “By contrast, the G standard is several hundred pages.” And that standard continues evolving. Its first addendum, G-1, is now being completed.

Most importantly, Madugula recommends that pubcasters go with the full standard, eschewing exemptions, exceptions and allowed minimums. “It may not be legally required,” he says, “but it is good design practice.”

If there’s a moral to this story, it’s that a perfect storm of conditions are converging to put all older pubcasting towers at risk. Just as stressing the human body causes systems to fail with time, so too will accumulations of human errors catch up with broadcasting structures. Further, disasters like Mountain Lake and Spokane can be cost-effectively prevented, if pubcasters are aware that the burden is on them to ensure their tower goes beyond simply “meeting the standard.”

What pubcasters can do collectively

Based on their tower experiences, KSPS’s Bob Wyatt and Mountain Lake’s Alice Recore say it’s time for pubcasters to take a new approach. And they’re stepping up to the plate.

“There are too many nuances and loopholes for public broadcasters to cost-effectively navigate the tower quagmire as individual organizations,” says Wyatt. “I’m calling on others, from both TV and radio to assist me with forming a group to identify areas that need attention and begin taking action, now. I’ll spearhead the initiative, but I need others to join me to make it work.” Wyatt’s e-mail address is [email protected]

For her part, Recore has been saving information on every step of Mountain Lake’s recovery effort so she can give it to other pubcasters. “We want the lessons we’ve learned to benefit others,” she says.

To get a handle on tower risks, Wyatt says, pubcasters can collaborate on such things as a database on the particulars of towers, guidelines for assembling effective RFPs, a set of best practices for various phases of a structure’s life cycle, and recommendations for disaster recovery. “In other words, we need specific tools and not just a study that sits on a shelf,” says Wyatt.

“When an encoder breaks, you can replace it reasonably quickly and inexpensively,” he says. “But a tower isn’t a commodity product that’s easy to replace. And unlike any individual piece of broadcast equipment, our towers are our livelihood.”

EARLIER STORIES

A blizzard in Iowa and a tornado in Georgia put towers out of service in winter 2007.

Precautions to prevent tower accidents and other serious setbacks were on the agenda for a joint meeting of pubTV and pubradio engineers in April 2007.

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