Review of in-service assessment of timber poles

Timber utility poles form an essential component of lifelines in all communities. In Australia, it is estimated that there are more than 5 million timber utility power poles in service with more than 75,000 new poles are installed per annum. For lifelines, including electricity distribution systems, to continue functioning after an earthquake event, they must have sufficient inherent capacity to withstand the imposed actions. While timber poles may have high initial strength, they often experience deterioration and decay over their design life due to fungus or termite attacks. In most cases the damage is not visible and often below ground. Thus, electricity distribution companies conduct specific routine inspections on their poles, typically every 5 years, to assess their structural integrity. This paper provides a brief review of the common types of pole degradation and presents relevant deterioration models which predict loss of section over the design life. The paper also reviews common and new in-service assessment methods including drilling, sounding, modal testing and stress wave propagation technique which is emerging to be very effective in detecting damage above and below ground.