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Research Papers

Similitude Laws and Small-Scale Model Experiments Characterizing Dynamic Failures of Flawed Utility Poles

[+] Author and Article Information
James F. Wilson

Professor Emeritus
ASME Life Fellow
Department of Civil and
Environmental Engineering,
Duke University,
6319 Mimosa Drive,
Chapel Hill, NC 27514
e-mail: jwilson@duke.edu

Contributed by the Design Automation Committee of ASME for publication in the JOURNAL OF MECHANICAL DESIGN. Manuscript received August 14, 2013; final manuscript received June 12, 2014; published online July 3, 2014. Assoc. Editor: Shinji Nishiwaki.

J. Mech. Des 136(9), 091401 (Jul 03, 2014) (7 pages) Paper No: MD-13-1351; doi: 10.1115/1.4027886 History: Received August 14, 2013; Revised June 12, 2014

The principles of similitude were employed to scale the equations of motion of wood utility poles to small, practical laboratory size. The derived dimensionless system parameters were used to design experiments in which model pole bending moments at failure were measured in response to simulated steady and gusting wind loads. Measured were the effects of artificial flaws on a pole's integrity under these loads, with flaws represented as radial holes. Modeled in static and dynamic tests to failure were shallow pole holes at the base designed to deliver termite and rot control chemicals in a prototype; shallow holes to simulate loose knots and through holes needed for utility hardware attachments. The groundline moment data for both static and dynamic tests showed either shear or tensile failure. An application illustrates the use of small-scale model data to explain the wind-induced base failure of a generic prototype utility pole.

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References

Figures

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Fig. 1

A typical longitudinal shear failure. Photograph by Houser and Dennis [4].

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Fig. 2

A transverse groundline tensile rupture. Photograph by Wilson.

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Fig. 3

(a) A generic prototype utility pole showing key points of wind loading. The cross section shows the wood grain orientation of the prototype and model. (b) The companion prototype pole with the same base reaction moment MR as the generic prototype.

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Fig. 4

Photograph of the pole model's static test apparatus

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Fig. 5

Key components for the pole model's static test apparatus

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Fig. 6

Photograph of the pole model's dynamic test apparatus

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Fig. 7

Key stages for the pole model's dynamic test apparatus. (a) Stationary system prior to dropping mass M. (b) Mass M and chain at the instant of pole engagement. (c) Typical dynamic displacement of M and the model pole.

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Fig. 8

(a) A typical time history of Q measured for a model pole which resisted fracture in a low impact dynamic test (small h); (b) a typical time of Q measured for a model pole undergoing base tensile rupture during a high impact dynamic test (larger h)

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Fig. 9

(a) A typical model failure in longitudinal shear; (b) a typical model failure in transverse base tension

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