United States Department of Transportation
i
Rehabilitation of Deteriorated Timber Piles using Fiber Reinforced Polymer (FRP) Composites
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2022-03-01
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[PDF-8.37 MB]
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Edition:November 2015-April 2021
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Abstract:Fiber reinforced polymer (FRP) composite wraps have been used for timber pile repair. However, design guidelines including strengthening equations are lacking for FRP-wrapped timber piles. This study evaluated the bond, bending, shear, and compressive strengths of five FRP-wrapped timber pile systems. Five glass FRP-wrap systems were evaluated: three with different epoxy formulations and one each with polyurethane and phenolic resins. FRP wraps over timber piles with 12-in. bond lengths provided a higher capacity than the ones with 6-in. bond lengths. However, bond strength per inch of bond length is reduced suggesting a non-linear relationship. Epoxy based systems that utilized slow cure and low-viscosity resins developed high bond strengths due to their better penetration into timber substrate. Samples subjected to wet/dry conditions exhibited higher bond strengths due to post curing of the epoxy systems. The pull-off tests resulted in values similar to the bond tests, proving it a useful field evaluation technique. The epoxy and phenolic systems failed under compression with matrix failure (delamination) between layers resulting in highly localized buckling of the fibers. — ii — Failure of the simulated rehabilitation samples with full-cross sectional cuts of timber piles was similar to the test results under pull-off, bond, bending, shear, and axial compression. The evaluation of the crack fillers showed a number of readily available materials exist to repair section loss in a timber pile. The results were applied to design and load rating equations that were developed as a part of this program. These equations account for both the bond and axial strengths based on the test data. In-situ repair guidelines were developed based on the experience in manufacturing the samples for this work and on previous experience. Inspection guidelines were prepared to permit the inspection of FRP-wrapped piles both visual and with advanced nondestructive evaluation techniques. This study also evaluated shear, flexure, and axial compression strengths for the traditional repair methods of timber piles and for the method of FRP-wrap splicing. The two are compared in strength as well as cost of repair. The FRP-wrap method proved to be a superior alternative to traditional methods of repair.
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