A Brief History
Composite, fiber-reinforced polymer (FRP), or "fiberglass" utility poles were first installed in Hawaii in the early 1960s. After almost 50 years of service, these poles were removed from service and replaced not for structural reasons but because of fiber blooming concerns from ultraviolet (UV) light exposure. It should be noted that these early poles did not contain the modern UV inhibitors or surfacing veils that provide protection for composite poles today, which allow an average life span of 80 years or more.
Since these first composite poles were installed, significant advancements have been made in composite pole and polymer technology, resulting in lighter, stronger, safer, more durable and longer-lasting utility pole products and accessories. Duratel, based in Chicago, entered the market five years ago and has become one of the leading manufacturers of composites. Their products have been successfully implemented for distribution and transmission utility applications, street lighting projects and wireless telecommunications.
While composite technology is not new, advances made in specialized resins, material formulations, catalysts and fillers have created broader acceptance of composite poles by utilities. Utilities are especially interested in scenarios where traditional pole materials-such as wood, steel or concrete-are difficult to use or are prohibitive from a cost, technical or environmental standpoint.
Composite Pole Technology
In general, composite products represent a wide variety of manufacturing processes that utilize similar glass reinforcements in combination with thermo-set resin systems. These systems also incorporate other ingredients such as fillers, catalyst, UV inhibitors and pigments. All the various processes focus on one common goal: to produce non-conductive products that offer many advantages over wood, concrete and steel.
Material inputs and processes for composite poles and accessories are environmentally sustainable, and life cycle studies have shown the manufacturing process represents a lower carbon footprint when compared to wood utility poles. With composite products there is no need for maintenance and no requirement for application of potentially toxic preservatives, which, for other pole materials, has raised concerns with leaching into surrounding soil and groundwater.
The two most common processes for manufacturing composite poles are pultrusion and filament winding. In the pultrusion process utilized by Duratel, material is physically pulled through a heated die. The glass reinforcement of continuous strand mats, unidirectional roving, surfacing veils, resins and internal chemicals are laid out and then incorporated into the orientation of glass placement within the desired pultrusion profile. This process produces non-tapered, uniform shape and diameter profiles. Filament winding produces tapered tubular poles by pulling fibers through a resin system and then winding this mixture around a mandrel.
Significant structural testing has been performed on composite poles and crossarms. The standard test scheme is the static cantilever bending test per American Society for Testing and Materials (ASTM) D1036. Results from multiple manufacturers have shown that composite poles produce a near linear load vs. deflection curve with consistently low coefficient of variation among tested samples. Failure is usually because of local stress on the compression side and is commonly associated with local buckling. Even at these levels, composite poles are engineered to have an extremely high strength-to-weight ratio, and, as such, lighter poles can typically carry a higher load than comparable materials.
Applications for Composite Poles
Composite poles have been well received in the utility market. The composite poles are now available in lengths up to and exceeding 95 feet and strengths well into the high H classes. Engineers are writing specifications for these poles and recognizing their distinct advantages over wood, steel or concrete distribution and transmission products. As this occurs, utilities are finding applications for composite poles beyond simple replacement of existing poles and structures.
Woodpecker and Pest Damage Replacement
Utility and telecommunication companies spend millions of dollars each year replacing wood poles that are damaged and destroyed by woodpeckers, ants and termites. Many utilities and regulators are realizing it is not economically feasible to replace damaged wood poles with more wood poles every few years, and that there is a cost-effective solution with the use of composite poles.
Duratel's composite distribution and transmission poles and structures are virtually impervious to damage caused by birds and insects and are being used extensively in the Midwest. The lightweight composites also require less manpower and equipment to transport and install in the many remote areas prone to damage from pests and birds. Utilities must currently resort to patching existing poles or wrap special material around the wood poles to prevent birds from nesting. Composites are strong enough to effectively shoulder the required loads without reengineering a solution and durable enough to withstand attacks from troublesome termites, ants and birds.
Rocky Ridges and Difficult Access Locations
One of the biggest advantages of composite poles is their high strength-to-weight ratio. Utilities are finding it more convenient and cost-effective to transport and install composites in many locations including backyards, restricted access areas and remote or difficult terrain sites.
Duratel's composite poles have been installed on rocky ridges using prefabricated, reinforced core baseplates where blasting for traditional poles was prohibited. The maintenance-free nature of composite poles and ease of access with minimal equipment have encouraged utilities to choose composites for many ridge and rocky terrain installations.
Coastal Environments and Corrosion
Many coastal utilities, including Caribbean and island power producers, have started using composite solutions for areas where both salt and high humidity are constant problems for wood, steel and concrete materials. Longer life spans and virtually no maintenance make composite poles an attractive option for utilities faced with frequent repair or replacement of poles due to rot and corrosion from exposure to harsh environmental conditions. In addition, the ability of manufactured composite poles to deflect in a controlled and predictable manner under greater stress and wind conditions, rather than shear or break, allow utilities to install them in areas regularly exposed to extreme winds caused by hurricanes or tropical storms. In the event of downed lines or damaged poles, lightweight, easily deployed composites can greatly expedite recovery efforts.
Unguyed Angle and Deadend Structures
Advancements in composite pole design, resulting in increased strength, have allowed for installation of unguyed, i.e., self-supporting, angle and deadend structures. The ability to offer unguyed monopoles to handle significant turn angles assists utilities in avoiding problems with easements, rights-of-way and inconvenient guy wires. Duratel poles offer a smaller footprint than wood, steel and concrete poles, allowing installation closer to roads or highways and in restricted areas without sacrificing strength or quality.