Laboratory Validation and Initial Field Evaluation of a Vibration-Based Technique for Condition Assessment of Timber Utility Poles

1 online resource (209 pages) : PDF

2018

University of North Carolina at Charlotte

Timber is the most common material used for the utility poles that support the transmission and distribution lines of the electrical grid in the United States. Timber is well-suited for use in utility poles but is subject to decay from fungi and other organisms, particularly in the area directly beneath the ground line where the high moisture and oxygen levels provide an environment suitable for the growth of these organisms. Utilities develop pole inspection and maintenance programs in order to extend the lifespan of decayed but serviceable poles through the addition of reinforcement and remedial treatment as well as identify poles that are unfit for service and present a danger of immediate collapse, resulting in interruptions in service and costly emergency repairs. Severely decayed poles also create an occupational hazard for the utility workers who climb the poles to perform maintenance on the electrical and telecommunications infrastructure supported above. Conventional inspection methods used by maintenance workers to identify decay in poles rely on a combination of visual inspection and crude nondestructive evaluation that is limited in identifying decay below ground. Recently, a nondestructive test method that utilizes natural frequency measurements of a utility pole along with parameter identification of a physics-based Rayleigh-Ritz model and through a genetic algorithm and local gradient optimization. In this thesis, the method is validated on a second set of laboratory poles, and an initial assessment of the method in field conditions is performed on a set of five poles. Additionally, the performance of the method is evaluated in the laboratory on poles encased in asphalt. Refinements to the method are explored, including a weighted objective function recommended to reduce error caused by the uncertainty associated with the estimation of higher frequencies in the measured bandwidth. Additionally, independent vibration measurements from two orthogonal axes are used instead of an average response in order to evaluate the ability of the method to locate asymmetric patterns of decay. Decay in the poles is characterized through destructive testing in order to evaluate the performance of the method in these laboratory and field scenarios. A first-generation prototype utilizing a MEMS accelerometer interfaced with a single-board computer is developed to record vibration measurements, and the performance of the prototype is evaluated. Recommendations for future iterations of the device and strategies for field implementation and refinement of the condition assessment algorithm are presented.

masters theses

Engineering
Civil engineering

M.S.

Decay in Timber
Parameter Identification
Timber Utility Poles
Vibration

Civil Engineering

Whelan, Matthew

Young, David
Braxtan, Nicole

Thesis (M.S.)--University of North Carolina at Charlotte, 2018.

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Dulin_uncc_0694N_11734

http://hdl.handle.net/20.500.13093/etd:119