Probabilistic characterization of ultrasonic wave propagation in wood poles

Abstract

Wood poles are widely used in North America to support power electric transmission and distribution lines. Wood poles are continuously exposed to wide ranging temperature and moisture conditions, making them vulnerable to internal decay and rotting. The resulting loss of strength makes the poles vulnerable to failure under adverse weather conditions, such as wind and snow storms. These failures can result in forced outages and customer disruptions with significant economic losses. Ultrasonic testing is a non-destructive method that has been used for detection of internal deterioration of in-service wood poles, which is based on the comparison of the measured wave velocity with a reference wave velocity associated with sound wood. The current ultrasonic methods assume that the reference wave velocity for a given wood species is constant in a pole cross section. This approach is simplistic because wood is an orthotropic material with highly variable material properties. This paper presents a method for probabilistic characterization of ultrasonic wave propagation in wood poles considering wood as an orthotropic material. A better understanding and characterization of ultrasonic wave propagation in a pole cross section will contribute to improve the condition assessment of in-service wood poles based on ultrasonic tests. As an example, P-wave velocity, surface waves, frequency response function, and magnitude spectrum area are used to characterize the propagation of ultrasonic waves at a cross section of a Douglas-fir pole of 25 cm diameter.