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|Title:||Structural Performance of Wood Plastic Composite Sheet Piling|
|Committee Members:||Habib J. Dagher, Professor of Civil Engineering ; Roberto A. Lopez-Anido, Associate Professor in Civil Engineering ; William G. Davids, Associate Professor of Civil Engineering ; Douglas J. Gardner, Professor of Wood Science & Technology|
|Subjects:||Composite materials -- Testing; Fibrous composites -- Testing; Plastic-impregnated wood -- Testing; Polymeric composites -- Testing; Structural engineering|
|Date of Defense:||2009|
This document describes the structural performance of an innovative wood plastic composite (WPC) sheet piling. A strain rate analysis was done, test methods were developed, full-scale bending tests were conducted, and installation methods were studied to characterize the performance of the pilings as part of a larger effort to develop a structural design methodology. In this study, WPC sheet piling specimens were produced at the AEWC Advanced Structures & Composites Center at the University of Maine. Tensile coupon tests were performed to identify loading rate and material properties. Full scale four-point bending tests were conducted up to failure on 20 sets of joined pairs of Z-piles of four different span lengths for WPC and commercially available vinyl sheet pilings. Following the quasi-static tests, cyclic loading with amplitude equal to 40% the mean ultimate strength was performed to assess residual deformation under repeated loading. Creep rupture testing was developed and conducted for one set of joined pair of Z-piles in a four-point bending set-up. Freeze-thaw behavior was monitored for full size sections. Sheet pilings installation methods were selected and tested by driving the sheets into the ground. Data analysis includes moment capacity, modulus of rupture, apparent modulus of elasticity, failure modes, freeze-thaw behavior, creep performance, and structural comparison between WPC and vinyl sheet pilings. Four-point bending test results indicate that the test configuration used in this study gives repeatable results and reasonable failure modes. WPC short spans failed predominantly in shear while longer spans failed in tension, and the ultimate strength coincides with failure. Vinyl specimens failed by flange compression buckling. Compression failures or buckling of the compression flanges were not present in the WPC tests, demonstrating the stability of the voided Z-section used in this study. In order to connect the pilings to one another, the sheets had a C-T edge configuration which did not restrict the rotation of adjacent piles with respect to one another for both materials. Cyclic flexural tests conducted in the linear load-deflection range indicate that small permanent deformations do accumulate, although there is no apparent stiffness degradation for both materials. Creep behavior was predicted using the Findley's power law and there was a good agreement between the experimental data and the calculated values. The test set-up developed is adequate to assess creep rupture of WPC sheet pilings. For cold climate construction, water should be prevented from entering the sheet piling voids. In consequence, filling the voids with an impermeable material or using solid WPC sheet piling is recommended to prevent the entrance of water and ice formation. The most promising methods for installing WPC sheet piling were determined to be the vibratory hammer and the pneumatic impact hammer. While the vibratory hammer driving tests were not ultimately successful, this method should not be discarded for driving WPC sheet pilings. Driving into different soil conditions found in typical composite light duty sheet piling applications should be attempted. The pneumatic hammer is a feasible method of installation for composite piling in loose sands. However, the pneumatic hammer driving tests were not successful in stiff clay. The findings show significant promise for WPC light duty sheet piling retaining wall structures.
Alvarez-Valencia, Daniel, University of Maine, CIE2009-001