Nondestructive bending tests on Douglas-fir utility poles as a potential tool for pole sorting and for prediction of their behavior in service

Abstract

Abstract Wood poles are a critical part of the electrical transmission system in North America. Wood poles are normally selected on the basis of visual features such as knots, slope of grain or other defects, but there is currently no simple, nondestructive bending (NDB), pre-flexural testing for sorting poles prior to use. In the present paper, the potential for NDB based on bending below the proportional limit was examined to calculate modulus of elasticity (MOE) and thereby predict actual modulus of rupture as determined by destructive bending (MORDB). The investigation was performed on 92 full length 13.3-m long Douglas-fir pole sections. Pre-flexural testing was reasonably correlated with MOEDB, but less well correlated with MORDB. The testing also revealed that visual selection of the best face of a pole, which is used to select a pole oriented to line direction (the “best face”), was poorly correlated with pre-flexing. Increasing the number of NDB tests did not noticeably improve the prediction. The results suggest that pre-flexing might be useful for identifying poles’ performance in service, if more data are available.