full text is available online.
|Author:||Antonis Petrou Michael|
|Title:||Repair of Wood Piles with Fiber Reinforced Composites|
|Committee Chair:||Roberto Lopez-Anido, Assistant Professor of Civil Engineering|
|Committee Members:||Thomas C. Sandford, Associate Professor of Civil Engineering; Barry Goodell, Professor of Wood Science and Technology|
|Date of Defense:||2002|
Piles made of treated wood have been traditionally used for the construction of piers and other waterfront structures. The main concern related to wood piles is deterioration due to marine borers, which limits the lifespan and requires frequent repair and replacement. Furthermore, since the use of preservative treatments for wood piles has been reduced due to environmental concerns, there is a current need for efficient methods for wood pile protection. Marine borer activity in Maine coastal waters was assessed through a survey directed to harbor masters correlated with historic data. In order to illustrate the type and extent of wood pile deterioration, two case studies in Maine harbors are presented. A special prefabricated Fiber Reinforced Polymer (FRP) composite shield or jacket was developed to repair wood piles in the field. FRP composite shells or sleeves are bonded with an underwater curing adhesive to form a shield. The main concern for durability of the adhesive bond is the resistance to freeze-thaw cycles. To assess adhesive bond durability, single lap shear tests were performed after exposure to freeze-thaw cycles. Two types of load-transfer mechanisms between the wood pile and the FRP composite shield were developed and tested: (1) cement-based structural grout; and (2) steel shear connectors with an expanding polyurethane chemical grout. Push-out tests by compression loading were performed to characterize the interfaces and discriminate the effect of the design parameters. The outcome of the push-out tests was the evaluation of the shear force-slip non-linear response and the progressive failure mechanism. The structural response of full-size pre-damaged wood piles repaired with the FRP composite shield system was characterized. A three-point bending test procedure was used to simulate the response of a pile subjected to lateral loads. The loaddeformation response, deflected shape profile, relative longitudinal displacements (slip), strain distribution, ultimate bending moment capacity and mode of failure were evaluated. Wood piles were pre-damaged by reducing approximately 60% of the crosssection over a portion of the pile. It was found that a pre-damaged wood pile repaired using the FRP composite shield with cement-based grout exceeded the bending capacity of a reference wood pile. The repair system using the FRP composite shield with steel shear connectors and polyurethane grout did not fully restore the bending capacity of a reference wood pile; however it can be used for marine borer protection when wood damage is not critical. A beam structural model to predict stiffness and strength properties of wood piles restored with FRP composite shells was developed. The model accounts for different pile dimensional properties and various amounts of pre-damage. The structural model was successfully correlated with experimental data from three-point bending tests of wood piles.
Michael, Antonis Petrou, University of Maine, CEE2002-006