Semester

Spring

Date of Graduation

2017

Document Type

Problem/Project Report

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Civil and Environmental Engineering

Committee Chair

Hota GangaRoa

Committee Co-Chair

Udaya Halabe

Committee Member

Mark Skidmore

Abstract

Fiber reinforced polymer (FRP) composite wraps have been used for timber pile repair, but there is a lack of empirical data for the development of design guidelines and strengthening equations. To address this need, this study evaluated both the bond and compressive strength of four FRP wrap systems on whole timber piles. Wrap systems evaluated used glass fabric with epoxy, polyurethane, and phenol formaldehyde resins. Bond strengths were evaluated through push-out and pull-off bond testing data on new (unused) treated timber. The push-out test evaluated the bond strength of the wraps on timber by applying axial loads on wrapped (6" and 12" bond lengths) timber samples until bond slippage occurred. Modified pull-off tests ASTM D7522, (FRP wraps on concrete substrates), were conducted to establish pull-off bond strengths. Axial compression tests were performed on hand layup shells with varying numbers of wrap until failure. To evaluate bond strength and compressive capacity simultaneously, simulations of timber pile rehabilitation were performed also. For the simulations, two portions of timber separated by a gap (to simulate decayed timber with near zero strength) were wrapped and tested in axial compression until failure. Results revealed that while 12" bond lengths provided a higher capacity than 6" bond lengths, their bond strengths (P/A) were reduced suggesting a non-linear relationship between bond strength and bond length. Epoxy and phenol formaldehyde resin systems predominately displayed timber failure whereas the polyurethane system failed in bond. Systems that utilized slow cure, low-viscosity resins developed high bond strengths, suggesting good timber penetration. Compression evaluations showed additional wrap layers increased the compression capacity of the shells. Some shells developed bending moments from unintended eccentric loading which reduced compressive capacity. Epoxy and phenol formaldehyde systems failed in the fibers while the polyurethane system failed due to delamination. Systems with high fiber volume fractions in the axial direction displayed the highest axial capacity. Compressive strength results corresponded well with values predicted by mechanics based FRP design equations. Since no current models for FRP bond strengths on timber are available, these results will greatly aid in their development.

Embargo Reason

Patent Pending

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