|dc.description.abstract||Typically, foundation piles are made of materials such as steel, concrete, and timber.
Problems associated with use of these traditional pile materials in harsh marine
environments include steel corrosion, concrete deterioration, and marine borer attack on
timber piles. It has been estimated that the U.S. spends over $1 billion annually in repair
and replacement of waterfront piling systems. Such high repair and replacement costs
have led several North American highway agencies and researchers to investigate the
feasibility of using composite piles for load bearing applications, such as bridge
substructures. As used here, the term â composite pilesâ refers to alternative pile types
composed of fiber reinforced polymers (FRPs), recycled plastics, or hybrid materials.
Composite piles may exhibit longer service lives and improved durability in harsh marine
environments, thereby presenting the potential for substantially reduced total costs.
Composite piles have been available in the North American market since the late 1980â s,
but have not yet gained wide acceptance in civil engineering practice. Potential
disadvantages of composite piles are high initial cost and questions about engineering
performance. At present, the initial cost of composite piles is generally greater than the
initial cost of traditional piles. Performance questions relate to driving efficiency, axial
stiffness, bending stiffness, durability, and surface friction. These questions exist
because there is not a long-term track record of composite pile use and there is a scarcity
of well-documented field tests on composite piles.
This research project was undertaken to investigate the engineering performance of
composite piles as load-bearing foundation elements, specifically in bridge support
applications. The objectives of this research are to: (1) evaluate the soil-pile interface
behavior of five composite piles and two conventional piles, (2) evaluate the long-term
durability of concrete-filled FRP composite piles, (3) evaluate the driveability and the
axial and lateral load behavior of concrete-filled FRP composite piles, steel-reinforced
recycled plastic composite piles, and prestressed concrete piles through field tests and
analyses, and (4) design and implement a long-term monitoring program for composite
and conventional prestressed concrete piles supporting a bridge at the Route 351 crossing
of the Hampton River in Virginia. A summary of the main findings corresponding to
each of these objectives is provided below.
A laboratory program of interface testing was performed using two types of sands and
seven pile surfaces (five composite piles and two conventional piles). The interface
behavior of the different pile surfaces was studied within a geotribology framework that
investigated the influence of surface topography, interface hardness, and particle size and
shape. In general, the interface friction angles, both peak and residual, were found to
increase with increasing relative asperity height and decreasing relative asperity spacing.
The interface shear tests for the three pile types tested at the Route 351 bridge showed
that, for medium dense, subrounded to rounded sand, with a mean particle size of 0.5
mm, the residual interface friction angles are 27.3, 24.9, and 27.7 degrees for the FRP
composite pile, the recycled plastic pile, and the prestressed concrete pile, respectively.
Interface shear tests on these same piles using a medium dense, subangular to angular
sand, with a mean particle size of 0.18 mm, resulted in residual interface friction angles
of 29.3, 28.8, and 28.0 degrees for the FRP composite pile, the recycled plastic pile, and
the prestressed concrete pile, respectively.
A laboratory durability study was completed for the FRP shells of concrete-filled FRP
composite piles. Moisture absorption at room temperature caused strength and stiffness
degradations of up to 25% in the FRP tubes. Exposure to freeze-thaw cycles was found
to have little effect on the longitudinal tensile properties of saturated FRP tubes.
Analyses were performed to investigate the impact of degradation of the FRP mechanical
properties on the long-term structural capacity of concrete-filled FRP composite piles in
compression and bending. The impact was found to be small for the axial pile capacity
due to the fact that the majority of the capacity contribution is from the concrete infill.
The impact of FRP degradation was found to be more significant for the flexural capacity
because the FRP shell provides most of the capacity contribution on the tension side of
Full-scale field performance data was obtained for two composite pile types (concretefilled
FRP composite piling and steel-reinforced recycled plastic piling), as well as for
conventional prestressed concrete piles, by means of load test programs performed at two
bridge construction sites: the Route 351 bridge and the Route 40 bridge crossing the
Nottoway River in Virginia. The field testing at the two bridges showed no major
differences in driving behavior between the composite piles and conventional prestressed
concrete piles. Pile axial capacities of the composite piles tested at the Route 351 bridge
were between 70 to 75% of the axial capacity of the prestressed concrete test pile. The
FRP and prestressed concrete piles exhibited similar axial and lateral stiffness, while the
steel-reinforced plastic pile was not as stiff. Conventional geotechnical analysis
procedures were used to predict axial pile capacity, axial load-settlement behavior, and
lateral load behavior of the piles tested at the Route 351 bridge. The conventional
analysis procedures were found to provide reasonable predictions for the composite piles,
or at least to levels of accuracy similar to analyses for the prestressed concrete pile.
However, additional case histories are recommended to corroborate and extend this
conclusion to other composite pile types and to different soil conditions.
A long-term monitoring program for composite and conventional prestressed concrete
piles supporting the Route 351 bridge was designed and implemented. The bridge is still
under construction at the time of this report, therefore no conclusions have been drawn
regarding the long-term performance of concrete-filled FRP composite piles. The longterm
monitoring will be done by the Virginia Department of Transportation.
In addition to the above findings, initial cost data for the composite piles and prestressed
concrete piles used in this research were compiled. This data may be useful to assess the
economic competitiveness of composite piles. The initial unit cost of the installed
composite piles at the Route 40 bridge were about 77 % higher than the initial unit cost
for the prestressed concrete piles. The initial unit costs for the composite piles installed
at the Route 351 bridge were higher than the initial unit cost of the prestressed concrete
piles by about 289% and 337% for the plastic and FRP piles, respectively. The cost
effectiveness of composite piles is expected to improve with economies of scale as
production volumes increase, and by considering the life-cycle costs of low-maintenance
|dc.rights||I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee.
I hereby grant to Virginia Tech or its agents the non-exclusive
license to archive and make accessible, under the conditions specified below,
my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report.||en_US