Rehabilitation of wooden utility poles with sprayed-GFRP composites

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Chen, Shukai
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Wooden utility poles have been used for over a century due to their sustainability, accessibility, excellent nonconducting properties, and construction flexibility. However, the main problem is the loss of load-carrying capacity, which is caused by decay. Rehabilitation techniques were investigated to extend the service life of wooden poles including steel trusses and wrapping with externally bonded (EB) fibre-reinforced polymer (FRP) laminates. Although the performance of the EB-FRP was reported to be prominent, the installation procedures are complicated, and it has associated debonding issues. To overcome these issues while maintaining the benefits of the FRP material, the sprayed-FRP composites technique is introduced in this study. This research aims at evaluating the performance of sprayed glass FRP (GFRP) composites and near-surface mounted (NSM) GFRP bars in rehabilitation of wooden utility poles. The mechanical properties, bond performance, and confinement effects of the sprayed-GFRP composites were determined. Then an analytical procedure was developed to predict the load carrying capacity of wooden poles retrofitted with sprayed-GFRP. To verify the predicted capacities, twelve 6.7 m-long (22 ft) wood poles were rehabilitated with sprayed-GFRP composites and/or NSM-GFRP bars (No. 10) and tested under monotonic horizontal loading up to failure. The test parameters include the sprayed-GFRP coating thickness (4, 6, and 8 mm), the sprayed-GFRP coating length (1.0 and 2.0 m), and the rehabilitation technique (sprayed-GFRP composites and NSM-GFRP bars). The results showed that using the sprayed-GFRP layer to restore the load-carry capacity of the old and damaged poles is a feasible rehabilitation method that can strengthen the old poles to reach even a higher load-carry capacity than their original one, given that the length of the sprayed layer is sufficient. In addition, the load-carrying capacity of the retrofitted poles was not affected by the increase of the sprayed-GFRP thickness beyond 6 mm. Therefore, it was deemed that using 6-mm thick sprayed-GFRP composites to rehabilitate wooden utility poles is a cost-effective rehabilitation option. Moreover, the results also showed that using NSM-GFRP bars solely to rehabilitate damaged poles is not cost-effective or structurally efficient compared to the sprayed-GFRP composites.
Sprayed-GFRP composites, Rehabilitation, Wood poles, NSM-GFRP bars, Lateral load