RESULTS OF LABORATORY TESTING AND FIELD EVALUATIONS SHOW THAT TROPICAL HARDWOODS offer an environmentally safe and robust alternative to preservative-treated woods for poles and crossarms in electric distribution and transmission overhead systems. The findings from these studies show that tropical hardwoods offer superior mechanical strength and durability, as well as high resistance to deterioration by belowground moisture and aboveground insects without the need for preservative treatment.

The availability of tropical hardwood products, with performance now documented through standardized testing, offers electric utilities a novel option for new and replacement pole installations. Moreover, these tropical hardwoods are grown in sustainably managed forests in the Amazon. Utilities using these products demonstrate their commitment to environmental stewardship within their service territories as well as help to preserve sensitive rainforest habitat.

MANAGING WOOD POLES

Preservative-treated wood poles and wood crossarms are the primary support structures for most North American electric distribution overhead systems. There are approximately 130 million wood poles installed in the United States. Between 1% and 4% of these poles are replaced every year. Preservative-treated wood presents challenges associated with the leaching of preservatives from in-service poles and the disposal of poles at the end of their service life.

Some North American utilities are taking the initiative to explore and implement alternatives to treated wood products. Alternative approaches include not treating some woods, such as western red cedar poles and yellow cedar crossarms, or using butt encapsulation to minimize leaching. Concrete, steel and fiberglass poles are examples of other alternatives to treated wood poles but are used to a much lesser extent.

OBJECTIVE INFORMATION

To provide the utility industry with objective information on pole alternatives, the Electric Power Research Institute (EPRI), Rogers International Consulting, and Washington State University's Wood Material & Engineering Laboratories tested several all-natural tropical hardwood species for application as poles and crossarms. Before these tropical hardwood poles and crossarms could be introduced to the electric utility industry, they underwent rigorous testing according to criteria established by the American National Standard Institute's (ANSI's) O5 Foreign Wood Species requirements.

Table 1. Tropical hardwood species for pole applications.

Common Name	Botanical Name
Acariquara	Minquartia Guianensis
Abiurana Ferro	Chrysophyllum Prieuri
Mata Mata' Preto	Eschweilera Truncata

Table 2. Tropical hardwood species for crossarm applications.

Common Name	Botanical Name
Cupiuba	Goupia glabra Aubl.
Piquia	Caryocar villosum (Aubl.)
Tauari Vermelho	Cariniana Rubra
Guajara	Pouteria Oppositifolia
Timborana	Pseudopiptadenia spp.

TROPICAL HARDWOOD SPECIES

Eight tropical hardwood species were evaluated. Five were evaluated for their suitability for crossarms and the other three for their suitability as poles. Tables 1 and 2 list these species by their common and botanical names.

These tropical hardwoods have excellent environmental credentials. They are grown in sustainably managed forests in the Amazon region and are certified by the Forest Stewardship Council with that organization's chain of custody standard, as well as the Brazilian government's Environmental and Renewable Natural Resources Department, IBAMA. Each pole and crossarm will carry the Forest Stewardship Council stamp, which is also referred to as the “Green Seal.”

NATURAL DURABILITY

The natural durability of tropical hardwoods is well known in the Amazon region and has been demonstrated in actual field use for more than 80 years. The poles have known lives in excess of 40 years in the Amazon soil, with tens of thousands of tropical hardwood poles in use today by the electric utilities of the Amazon. The Central Eletrica do Amazonas (CEAM) uses the poles throughout its service territory outside the city of Manaus, the capital of the Amazon. As an example, on the highway linking Manaus to the city of Itacoatiara, approximately 260 km (162 miles), tropical hardwood poles are used almost exclusively, with some concrete poles intermingled along the way. More than 2000 tropical hardwood poles are installed along this highway, many with field lives in excess of 40 years. The same is true for the electric utility Central Eletrica do Para' (CEPA), which also uses tropical hardwoods throughout its service territory.

Table 3. Adjusted fiber strength values for flexural crossarm testing.

Species	Bending Axis	MOR (psi)	Adjustment Factor	Adjusted MOR (psi)
Piquia	Major	10,100	0.979	9888
Tauari Vermelho	Major	8584	0.975	8369
Timborana	Major	10,780	0.973	10,490
Cupiuba	Major	10,290	0.976	10,040
Guajara	Major	11,050	0.992	10,960
Piquia	Minor	9802	0.977	9577
Tauari	Minor	9230	0.98	9045
Timborana	Minor	11,490	0.977	11,230
Cupiuba	Minor	10,320	0.977	10,080
Guajara	Minor	11,090	0.993	11,010

Tropical hardwoods also make exceptional natural wood pilings. More than 24,000 tropical hardwood pilings have been in service since 1997-1998 in the Baltic Sea off the coast of Germany. The area is known for its marine borer Toredo Navalis, which has had devastating effects on other treated wood species. However, the tropical hardwoods have proved impervious to this wood-boring worm.

Three significant stake tests have been performed in the Amazon involving the tropical hardwood species being evaluated for poles and crossarms. Two tests were performed at the University of São Pãulo for 8 and 10 years, respectively. The third test, performed at IBAMA's forest products laboratory, has been ongoing since 1984.

Table 4. Average results for full-scale flexural pole testing.

Species	Maximum Applied Load (lb)	Equivalent Tip Load (lb)	MORGL (psi)	MORGL Standard Deviation (psi)	MORGL COV (%)
Abiurana Iron	68,970	9030	15,730	2810	17.8
Acariquara	23,060	3110	7730	1870	24.2
Mata Mata'	48,930	6620	12,680	3030	23.9

Table 5. Average results for small, clear specimen testing.

Species	MOR (psi)	MOE (psi)	Flexural Moisture Content (%)	Maximum Compression Stress (psi)	Compression Moisture Content (%)
Abiurana Iron	21,800	3,330,000	26.1	10,900	15.9
Acariquara	19,500	2,370,000	27.9	8800	18.1
Mata Mata'	17,400	2,600,000	32.5	7400	20.1

In these tests, researchers monitor the condition of numerous wood stakes set into the soil to determine the effect of moisture, fungus and insects on the wood samples over time.

The Amazon's environmental conditions are notoriously harsh on wood. High rainfall results in high soil moisture, while high humidity promotes fungus encroachment, which in turn invites wood-attacking insects. Any wood that stands up to these conditions is, by definition, durable. The wood species selected for poles and crossarms showed zero-mass loss degradation in the Amazon graveyard test sites.

EXTREMELY LOW MOISTURE ABSORPTION

Moisture absorption is perhaps the key determinant of the longevity of wood poles. Preservative treatments are applied primarily to prevent moisture from entering the wood and initiating decay processes. The tropical hardwood species exhibit extremely low moisture absorption. In fact, none of the tropical hardwood species will accept preservation treatment, even under vacuum.

Consulting engineering and testing firm Professional Service Industries in Oakbrook Terrace, Illinois, U.S., performed a simple test in its Seattle laboratory that demonstrated the moisture-absorption resistance of tropical hardwoods. Investigators oven dried samples of the wood species Abiurana Iron, took mass measurements of the wood samples and then submerged them in water for 96 hours. The maximum water retention of the wood samples was measured at 17.2% (by weight) from the water-submerging experiment, which is very low compared to the Southern Yellow Pine's or Douglas fir's maximum water-retention levels, which at a minimum reach 40% (by weight). This simple experiment has demonstrated that moisture absorption is extremely low, and explains why the tropical hardwood species have such exceptional natural durability in ground contact. These tropical hardwoods absorb little moisture due to oil and resin content. When the wood is cut, oils and resins naturally seal the cut, so little or no moisture encroaches and no exudates ooze out to the surface of the poles; instead it is retained in the wood fibers of the tropical hardwoods.

FULL-SCALE TESTING

Researchers at Washington State University's Wood Material & Engineering Laboratories facilities in Pullman, Washington, U.S., tested five tropical hardwood species for their suitability for crossarms, and three species for their suitability as poles. Researchers tested 30 poles and 60 crossarms of each species. The tests conducted provide a basis for comparing the tropical hardwoods to Douglas fir and Southern Yellow Pine, which are traditionally used for poles and crossarms in North America.

The full-scale testing for poles was performed per ANSI O5.1, Annex D, Foreign Wood Species Test requirements. Testing for the crossarms followed the ANSI O5.3 standard.

FIBER STRENGTH OF CROSSARMS

The tests showed that all five tropical hardwood species on average are 29% superior in strength to the Douglas fir and Southern Yellow Pine crossarms.

Applied load and centerline displacement data were recorded throughout each crossarm flexure test. These data were used to calculate the Modulus of Rupture (MOR) for each specimen. MOR values were calculated using equations provided in ANSI 05.3 - 2002 Annex B and ASTM D 198 Appendix X2, respectively. Table 3 provides average results and adjusted MOR (statistical significance) for each of the five species. For comparison purposes, the MOR for Douglas fir and Southern Yellow Pine is 7800 psi.

FIBER STRENGTH OF POLES

As with the tropical hardwood crossarms, the tropical hardwood poles showed considerably greater strength than the treated Douglas fir and Southern Yellow Pine poles. Investigators recorded applied load and ground line displacement data throughout each pole flexure test. These data were used to calculate modulus of rupture at ground line (MORGL) values for each specimen. MORGL values were calculated using equations provided in ASTM D 1036 - 99, Section 23.2. For comparison purposes, the MOR for Douglas fir and Southern Yellow Pine is 8000 psi. Table 4 shows the average test results.

In addition to the full-length pole testing, 10 small clear specimens were tested for static-bending strength and compression strength parallel to grain, according to ASTM D 143 - 94, Standard Test Methods for Small, Clear Specimens of Timber, Sections 8 and 9, respectively. Table 5 presents the test results. Note the very high MOR values for each species.

COMPARING TEST RESULTS WITH DOUGLAS FIR AND SOUTHERN YELLOW PINE

The graph above compares the ultimate horizontal force for the tropical hardwood poles to those required for the treated Douglas fir and Southern Yellow Pine poles. We are using a Class 2 Douglas fir/Southern Yellow Pine (DF/SYP) pole (black line). Extending a vertical line (blue line) to intercept the green line for the Mata Mata Black pole and the yellow line for the Abiurana Iron pole, and then tracing the interceptions horizontally until they touch the black line for the DF/SYP pole, we can verify the class equivalency for the Mata Mata Black to be H2, and H4 for the Abiurana Iron pole. The class equivalency for the Acariquara pole is the same as the DF/SYP.

The superior mechanical strength and class equivalency shown in this example provides the groundwork for consolidating the existing multiple pole classes into one standard pole class. In turn, this consolidation will help reduce the storage and inventory-carrying cost for the poles, just two of the many cost benefits.

RECOMMENDED BEST PRACTICES

Regarding recommended best practices for working with the tropical hardwood poles in the field, contact Rogers International (www.rogersinternational.com). The work practices are very much the same as those currently employed by utility field crews. Minor changes address the drill speeds, staple and lag bolts lengths, and hammering lag screws in the pole.

SUPERIOR MECHANICAL STRENGTH

As electric utilities strive to manage wood pole inventories in a cost-effective manner, tropical hardwoods represent a viable, environmentally friendly alternative to preservative-treated wood for distribution poles and crossarms.

Lab testing has demonstrated the superior mechanical strength of these wood products. Field experience with installed poles shows these woods to be highly durable and resistant to moisture, even in harsh conditions. Evaluations by U.S. utilities demonstrate that tropical hardwood poles can be climbed and worked by field personnel with no changes in work practices or tools and equipment.

Finally, these tropical hardwoods come from sustainably managed forests and are certified to assure they have met the strict environmental requirements imposed by the Forest Stewardship Council. Utilities can use these poles and crossarms with the knowledge that they are satisfying their customers' desire for environmentally safe infrastructure, as well as promoting sustainable growing practices in ecologically sensitive rain forest habitat.

ACKNOWLEDGEMENTS

EPRI would like to recognize and acknowledge the following utilities for their participation and guidance in this project as pioneers to further the research into tropical woods for use as utility wood poles and crossarms: Consolidated Edison Company of New York, Public Service Electric and Gas, Northeast Utilities, Lincoln Electric System, Texas Utilities, Kansas City Power & Light and CenterPoint Energy.

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J.R. Gonzalez is a technical advisor with Rogers International Consulting LLC. A registered professional engineer in the states of Washington and Oregon, Gonzalez has an MBA degree and 26 years of experience working in the United States, Canada, Europe and Latin America, 16 years of which was in the electric utility industry at Puget Sound Power & Light Co., and eight years in the wireless telecommunications industry at Bechtel Enterprises & General Dynamics Wireless Services. Currently, Gonzalez is a program manager with the Safety and Reliability Section of the Oregon Public Utility Commission. josergonzalez2@comcast.net

Ashok Sundaram is a project manager in the Power Delivery and Markets Division at the Electric Power Research Institute in Palo Alto, California, U.S. He joined EPRI in April 1993 and has been responsible for managing projects related to power electronics and distribution systems. Sundaram received a BSEE degree from the University of Madras, India, in 1978, and an MSEE degree from Southern Illinois University in 1984. He has also completed the course requirements for his Ph.D. in electrical engineering. His areas of specialization are power system analysis, electrical machines, control systems, power electronics and power quality. He is a member of the IEEE and has been an invited speaker, lecturer, and session chairman at many power-quality-related conferences and seminars, and has published several articles and papers in this field. asundara@epri.com

UTILITY FIELD OBSERVATIONS

Several U.S. utilities have evaluated the tropical hardwood poles discussed in this article at their training centers to assess their workability in the field. Consolidated Edison Company of New York is one such company that evaluated the tropical hardwood poles at its Learning Center. This is how they stacked up against Con Edison's existing poles:

• Climbing: Easier/better to climb than existing poles.

• Drilling: Using the hydraulic hand drill, it was easier to go through than the existing poles.

• Cutting: No problem; the same for existing poles.

• Nailing/stapling: 2.5-inch nails and staples are difficult to hammer in without bending. There were no problems with shorter nails and staples, or with longer nails and staples with predrilling.

• Driving lag screws: Driving with drill no problems; however, hammering the lag screw was very difficult.

Luis Ortega, senior engineer, distribution engineering with Con Edison, made the following statement about the tropical hardwood poles after the evaluation was complete: “Although logistics issues have to be formalized and addressed, we believe that tropical wood utility poles can play a very important role to enhance our environmental excellence while assuring reliable service and maintaining system integrity. These poles have inherent fungi and insect-resistant properties, so chemical-preservative treatment is not required.”

Kansas City Power & Light (KCP&L) also evaluated the tropical hardwood poles. KCP&L installed five tropical hardwood poles in its distribution-training center for evaluation. Instructors and apprentice lineman made the following assessments:

• The tropical poles are more difficult to gaff than the penta-treated Southern Yellow Pine poles.

• The tropical poles are easier to climb than the CCA-treated poles.

• Drilling presented no problem as long as drill speeds were reduced.

• Staples and nails set well, although length might have to be evaluated.

• Lag screws twisted in well, although hammering in to start was next to impossible.

KCP&L has ordered additional 45-ft (14-m) and 65-ft (20-m) poles to build a test section of line and place it in actual service for evaluation.

Paul Beaulieu, senior engineer, transmission and substations with KCP&L, said, “We are enthusiastic about participating in the evaluation. We continually look for initiatives to protect the environment and the use of natural wood pole products without chemical preservatives is intriguing.”

Wade Malcolm, vice president, power delivery and markets at EPRI, summed up, “The tropical hardwood project has demonstrated there is a viable environmentally sound wood option for treated poles and crossarms for the electric utility industry. EPRI is proud of sponsoring this project with participation from seven U.S. electric utilities. The tropical hardwood poles and crossarms mark a new era for the wood structure needs of our industry.”