Modeling and Characterization of Hollow and Concrete-Filled FRP Piles

Traditional piling systems for marine applications have been constructed of steel, timber, and reinforced concrete. These systems have well-known, predictable material properties. The major shortfall of the traditional materials in this application is their susceptibility to corrosion and environmental degradation. The use of composite materials to construct the piles is an option that can extend the service life of marine piling structures. Several companies in the U.S. have recognized the benefits of composites in this application and are producing fiber reinforced polymer (FRP), cylindrical, tubular piles that can be installed as hollow members, or can be filled with concrete to improve the structural properties. One major hurdle for widespread acceptance of FRP piles is the lack of established and accepted design methodology. Contractors and engineers are uncomfortable designing structural systems with these piles because of the new, and relatively unfamiliar, procedures used to characterize the piles. A structural design methodology describing the appropriate analytical procedures to design piles is needed to encourage growth in this new industry. Review of literature on the subject has revealed several models that have been developed to predict pile behavior, including numerical models for bending and compression of FRP tubes filled with concrete. These analytical methods include both simplified analysis methods, and a nonlinear moment-curvature model. In this project, the numerical methods developed by past research are combined to analyze hollow and concrete-filled FRP piles in four-point bending. These model results are compared to full-scale flexural test results of piles fabricated at Harbor Technologies in Maine. The test matrix included four-point bending tests on 24 hollow piles and 16 concrete-filled piles. The objective of the testing program is to verify the validity of the proposed numerical models for predicting the flexural strength and stiffness of hollow and concrete-filled FRP piles, and to propose a workable design methodology for both hollow and concrete-filled FRP piles