Volume 27, Issue 3 (May 1999)
Evaluation of Wood Poles Using a Free Vibration Technique
The current method of sorting wood poles is restricted to a visual inspection approach. It has long been recognized that a mechanical sorting approach will be more efficient in properly utilizing the wood pole resources because mechanical methods are generally more capable of segregating wood products into different strength categories. This paper presents a vibrationbased method for evaluating mechanical properties of wood poles. The evaluation parameter is modulus of elasticity. A theory is presented that relates the first natural frequency to the modulus of elasticity of a tapered beam. The method is based on the measurement of the first natural frequency of a wood pole under free vibration. From the first natural frequency the modulus of elasticity is calculated. Comparison of moduli of elasticity of ten wood poles from static bending and the proposed vibration methods reveals a generally strong correlation between the moduli measured by both methods. However, an outlier was noted that, upon examination of the failure mode, suggested that there was prior damage in the pole. This result indicates that the proposed method is not reliable in detecting any poles that have been weakened by internal defects.