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Research Papers

Failure of Flawed Utility Poles in Wind Gusts

[+] Author and Article Information
James F. Wilson

Department of Civil and Environmental Engineering, Duke University, 6319 Mimosa Drive, Chapel Hill, NC 27514jwilson@duke.edu

J. Mech. Des 132(11), 111006 (Nov 12, 2010) (7 pages) doi:10.1115/1.4002763 History: Received December 31, 2009; Revised July 30, 2010; Published November 12, 2010; Online November 12, 2010

The purpose of this study is to account for failures of wood utility poles in wind storms based on dynamic analysis and pole imperfections. The utility pole supporting multiple overhead transmission lines is modeled as a uniform Bernoulli–Euler cantilevered beam fixed at the base and subjected to three types of suddenly applied transverse loads that simulate a wind gust: a uniform pole pressure, a point load at the tip accounting for line and transformer drag, and another point load near midlength, accounting for drag on lines strung from that location. The dynamic pole moments are based on normal mode calculations rather than static calculations with a dynamic impact factor, and the critical flexural stresses include stress concentrations arising from pole imperfections such as holes, knots, and surface gouges. A case study illustrates the results for one of about 400 failed wood poles downed in a single New Jersey storm in 2003 with 107 km/h (67 m/h) wind gusts. Here, the critical pole stress based on the dynamic model and a hole imperfection exceeded the proportional limit stress of the wood. The predicted dynamic stresses are higher than those based on the National Electrical Safety Code.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Utility poles with a wind gust perpendicular to the overhead lines

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Figure 2

(a) Planar model of the failed utility pole 60103 and (b) step approximations to the pole wind gust loads

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Figure 3

Stress concentration factor at a through-hole in a local section of an isotropic circular cylinder. Applied to a utility pole, the bending moment M is caused by the wind gust, which is perpendicular to the pole in the left insert (data adapted from Pilkey and Pilkey (7)).

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Figure 4

Stress concentration at the corner A of a shallow notch or gouge in local section of an isotropic circular cylinder. Applied to a utility pole, the bending moment M is caused by the wind gust, which is perpendicular to the pole in the left view (data adapted from Pilkey and Pilkey (7)).

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Figure 5

(a) In the foreground is a section cut from the ruptured pole 60103. (b) The ruptured pole section shows longitudinal shear failure.

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