Stability of Tapered Wood Utility Poles under Extreme Loading

During a storm, a tree fell across a highway, downing utility lines on both sides of the road. County employees responded to clear the roadway encumbrance. A steel messenger wire that was pinned beneath the fallen tree, but still connected to its wood poles, was dragged along the ground as the fallen tree was towed from the roadway. At some point, the force exerted by the messenger wire on one of the poles to which it was attached caused the pole (which was otherwise undamaged) to fail and injure a utility worker as it fell. This paper explores the stability of the tapered wood utility pole subject to the changing forces imparted on it as the messenger wire was dragged. Catenary forces from utility lines in spans adjacent to the pinned messenger wire, as well as the effect of those forces on the failed wood utility pole, are also discussed herein. Additionally, modelling complications are addressed, such as determining the varying moment of inertia associated with the tapered pole's cross-section, and addressing the iterative nature of determining the P-Delta force on the wood pole associated with the changing position of the pinned messenger wire.

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