Less than a decade ago, FRP composite utility pole manufacturers were going to utility companies to make the value case for installing their more expensive, yet significantly lighter weight products in difficult-to-access areas. Then came Hurricane Sandy in 2012, followed by Irma, Maria and Michael among other massive hurricanes and two years of record-setting wildfires in California. Suddenly there’s been an explosion in discussions about – and funding for – hardening the nation’s electric grid.
Today, the case has been made and utilities are turning to composite pole and crossarm manufacturers for solutions. “In the last two years, it’s like someone threw a switch. All of a sudden we can’t make enough of these poles,” says Galen Fecht, director of technical service and international sales for composite utility pole manufacturer RS Technologies Inc.
Withstanding Fire Tests
Perhaps nowhere has this trend been more dramatic than in response to the wildfires tearing through California. 2018 became the worst year on record for wildfires in the state, but a state climate change assessment predicts that by the end of this century the average burned area in California will increase by 77%. Wooden poles contribute to the problem when they snap under strong winds and live wires fall onto dry grass, providing sparks that ignite some of the most destructive fires. As utility companies face public scrutiny – and in some cases lawsuits – they are no longer standing idly by.
A couple years ago, California utilities began reaching out to FRP pole manufacturers in search of a solution that could better withstand wildfires. “Most composite poles and crossarms are inherently self-extinguishing, so they perform well in fires,” Fecht says.
There are other factors that set composite materials apart from traditional wood materials, too. “Fiberglass crossarms are stronger and more consistent than wood crossarms, resulting in less crossarm breakages and reduced likelihood of energized conductors dropping and starting fires in the first place,” says Michael Schoenoff, vice president of engineering for FRP crossarm manufacturer Geotek. “Additionally, the smooth surface of a fiberglass crossarm is less likely to build up with contaminants and is therefore less likely to lead to arc tracking.” Schoenoff notes that several utilities have reported a significant reduction in pole-top fires after switching to composite crossarms.
Eric Haddad, composite unit general manager for Valmont Industries, shares that PG&E, with support from San Diego Gas & Electric, sponsored a series of tests of FRP distribution poles in September 2019. Independent labs Southwest Research Institute and EDM organized a fire test, followed by a bend and break test to validate the structural integrity of the poles after fire.
The goal of these tests, says Dustin Troutman, director of market and product development for Creative Pultrusions Inc., has been to prove the survivability of FRP materials compared to traditional materials and construction, in terms of crown fires and brush fires. “Crown fires are when the fire travels across the top of the trees and then the brush fires are when it’s on the bottom,” he says.
Fecht elaborates that utility poles only have to withstand about two minutes of exposure to intense heat to pass this test. A brush fire, he adds, typically resides at a single location for about 30 seconds and for a crown fire in a heavily coniferous forest only 90 seconds.
In 2011, RS Technologies began to undertake its own series of utility pole fire tests under the direction of a fire expert from the University of Alberta, so Fecht was familiar with the process. The initial full-scale test was designed to match the total heat flux (the amount of energy exposure) and flame conditions present in a two-minute fire, which is representative of a severe forest fire. “In following studies conducted with input and participation from California utilities, the testing time was increased to three minutes to represent an extreme fire event,” Fecht says.
Others have made formula adjustments to meet this growing demand. “We went through a lot of different iterations to finally get to the solution that we tested,” Haddad says. Without getting into proprietary detail, he explains that Valmont has added an intumescent material into its pole. “When the intumescent gets hit with the temperature of a fire, it will expand and protect the structural glass,” Haddad says.
The test results were a win for FRP overall. But composites manufacturers already knew their products would prove up to the test, and several are launching new facilities to support the explosion in demand for composite utilities products. For example, over the past five years, Geotek has made significant investments in its capacity and buildings, nearly doubling its manufacturing footprint to keep up with the demand.
Additionally, Valmont is opening its new crossarm and pole manufacturing facility in the second quarter of 2020. The plant will switch from fabricating its fire distribution poles with a centrifugal cast process to a filament wound process because the latter allows for increased throughput.
Understanding Deflection Limits
Haddad says this apples-to-apples style fire testing was eye-opening for utilities and pole fabricators alike. “We learned in this test that the requirements from the utility customers around deflection are actually more important than strength,” he says. “What they’re finding in wildfire areas is the fire either is accelerated because of the wind or it spreads a lot faster because of the high wind. They don’t want the pole really moving at those higher wind speeds.”
Traditionally, poles are specified on a required strength basis, and pole deflection has not necessarily been a focus of the initial structural analysis. Understanding the important role that deflection plays in utility structure performance, FRP pole manufacturers target certain deflection limits as their goal and inherently exceed the required strength requirements expected.
“A lot of people are under the misunderstanding that composite poles deflect more than wood poles,” Fecht adds. “Although composite materials can have a lower stiffness ratio on a strength equivalent basis, composite manufacturers understand that their products must have comparable deflection performance under load when being installed alongside traditional wood poles, and they design accordingly to achieve this. This is why deflection, and not strength, is typically the governing design characteristic for utilities seeking wood pole equivalency.” And that’s one reason fabricators are encouraging shifts in how utility structures are specified.
As Fecht explains, utility customers typically look for engineered poles to provide “wood pole equivalent” performance. If a utility typically uses an ANSI-designated 50-foot Class 1 wood utility pole, that’s what they would request from a composite pole manufacturer. But Fecht’s response is that what the utility is requesting is a solution as strong as a 50-foot Class 1 wood pole that also deflects in the same range as that specific length and class wood pole. As a result, the term ‘serviceability equivalency’ has emerged to capture both the initial strength requirement and the required deflection performance and is the recommended design approach to use when designing comparable/compatible FRP poles, says Fecht.
“Where it gets interesting is a lot of people don’t understand deflection even on wood poles,” Fecht says. The flex in a wood pole will vary depending on its length and class and also the specific species of wood utilized. Southern yellow pine, western red cedar and Douglas fir, for example, each have a different modulus of elasticity, resulting in different deflection performance. However, reported deflection values for wood poles represent a mean value rather than an absolute, and some in the industry have used these mean wood pole values as absolute value for composite pole deflection. This practice inadvertently results in a stiffer than required, unnecessarily more expensive composite pole to be specified when serviceability equivalency was the initial goal.
The recently released second edition of the American Society of Civil Engineers’ Manual of Practice (MOP) 104, Recommended Practice for Fiber-Reinforced Polymer Products for Overhead Utility Line Structures, addresses this. “The section on deflection, Section 3.10.8 Deflection Serviceability Equivalency, where the term serviceability equivalency has been established in the utility lexicon, has been introduced to more clearly address this specific design approach,” Fecht says.
An added benefit of using FRP over wood is that the composite pole will achieve the specific deflection requirement more consistently than wood. As Amol Vaidya, senior global innovation leader with Owens Corning, explains, “We are able to tailor the performance of those products to meet customer needs.”
Vaidya offers an example: “If the customer is looking for higher shear performance, that is typically driven by what we put on the glass in terms of chemistry [glass sizing]. This size drives the compatibility with the resin and can be customized.”