FRP Composite Piles Applications & Durability Considerations by Miguel A. Pando, Felipe J. Acosta, P.E. UPRM mpando@uprm.edu, facosta@uprm.edu Jack Lesko Virginia Tech Virginia Fiber-Reinforced Composites Showcase Bristol, VA, September 20-21, 2006
Outline Case Histories involving use of FRP piles: Route 40 bridge Route 351 bridge Cost comparison Durability Studies Work at Virginia Tech and with NCSU (w/ Amir Fam) Joint work Virginia Tech and UPRM Recommendations for future work Acknowledgments
Background Recent work at Virginia Tech (Pando, Lesko, Filz - FHWA project) Investigate the feasibility of using composite piles for load bearing applications such as in bridge substructures. Assessment of driveability, axial capacity, lateral capacity, and long-term durability of composite piles Route 40 project This presentation Route 351 project This presentation Evaluate their long-term durability This presentation
Case Histories: - Rte. 40 Bridge - Rte. 351 Bridge
Route 40 Bridge N I-64 I-66 Stony Creek 657 Nottoway river I-81 I-77 I-85 Virginia I-95 I-95 40
Location of FRP Piles Concrete slab 85.34 m RC cap beam Battered piles Elevation 11.25 m 18.52 m 18.52 m 18.52 m 18.55 m Test pile area 1 2 3 4 Plan view : Prestressed pile : Composite pile
Route 40 Bridge
a) Photograph of composite piles installed at Pier No. 2 of the Route 40 Bridge Longitudinal direction θ = +35 o (1.13 mm) θ = -35 o (1.13 mm) θ = +85 o (1.13 mm) θ = +35 o (1.13 mm) θ = -35 o (1.13 mm) Inner liner (1.68 mm) Five FRP layers constitute the structural wall thickness of the FRP tube b) FRP tube laminate structure of composite pile
0 2 Blows per 0.25 m 0 10 20 30 40 50 60 COMPOSITE PILE (0.62m) PCP PILE (0.51 m) 3000 kips F a) Composite Pile: EA/c = 180.7 kips-s/ft F V 16.6 ft/s V 4 Sand 6.2 ms 51.2 6 b) Prestressed Concrete Pile: 8 10 Clay 3000 kips F EA/c = 168.2 kips-s/ft F V 17.8 ft/s V 12 Pile Tip @ -10.25 m 6.0 ms 51.2 PILE DRIVING RECORDS END-OF-DRIVING PDA
PILE HEAD AXIAL DISPLACEMENT (mm) 0-2 -4-6 -8-10 -12-14 -16-18 -20 AXIAL STATNAMIC RESULTS Davisson Failure Criteria COMPOSITE PILE PRESTRESSED PILE 0 500 1000 1500 2000 2500 3000 3500 4000 4500 EQUIVALENT STATIC AXIAL LOAD (kn)
LATERAL STATNAMIC RESULTS EQUIVALENT STATIC LATERAL LOAD (kn) 200 180 160 140 120 100 80 60 40 20 0 COMPOSITE PILE PRESTRESSED PILE 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 PILE HEAD LATERAL DISPLACEMENT (m)
The new Route 40 Bridge over the Nottoway river in Virginia Composite Piles
Lessons from Route 40 Driveability: No major differences in driving behavior (FRP piles can be installed) Axial Capacity: Both piles performed similarly Composite pile: P ult = 4360 kn ( y =18 mm) PCP pile: P ult = 4190 kn ( y = 13 mm) Lateral Capacity: Both piles appeared to have similar ultimate lateral load capacity Composite pile had lower flexural stiffness after initial concrete cracking which appeared to occur at 50 kn Composite piles were designed as specified for axial load only Use of concrete-filled FRP composite piles for bridge foundations feasible & practical based on this project.
Case Histories (continued): - Rte. 40 Bridge - Rte. 351 Bridge
Rte. 351 Bridge in Hampton, VA I-64 Existing Rte. 351 bridge
Prestressed Pile Composite Pile Recycled Plastic Pile
Subsurface conditions 0 Description CPT q c (MPa) of material 0 2 4 6 8 10 12 Fill (SM ) Sand (SM) SPT N field 0 5 10 15 20 25 30 5 10 15 Clay (CL) Sand (SM) 20
Pile driving records Depth below ground surface (m) 0 5 10 15 20 Plastic pile FRP pile Prestressed pile 0 10 20 30 40 50 60 Pile blows per 0.25 m
Static Axial Load Tests
Static Axial Load Test Results Pile head displacement (mm) 0 20 40 60 80 100 A pplied axial load (kn) 0 500 1000 1500 2000 2500 3000 3500 Prestressed pile FRP pile Plastic pile
Load Transfer during Static Load Tests 0 Load (kn) 0 500 1000 1500 2000 2500 3000 3500 Depth (m) 5 10 15 Plastic pile FRP pile Prestressed pile 20
Comparison of Axial Load Test Results with LCPC Method 4000 3500 Q ult (kn) 3000 2500 LCPC (Concrete) Load Test 2000 1500 0 Prestressed concrete pile FRP pile LCPC (Steel) Plastic pile
Static Lateral Load Test Results 350 Lateral load (kn) 300 250 200 150 100 FRP pile Prestressed pile Plastic pile 50 0 0 20 40 60 80 100 120 Lateral deflection at ground surface (mm)
Lessons Route 351 Penetration resistance during driving increases in order: plastic pile, FRP pile, prestressed concrete pile Pile capacities (Davisson) increase in the same order: Plastic pile, Q ult = 2130 kn (239 tons) FRP pile, Q ult = 2260 kn (254 tons) Prestressed concrete pile, Q ult = 3095 kn (348 tons) Traditional methods FRP pile and prestressed concrete pile exhibit similar stiffnesses in axial loading, plastic pile is not as stiff FRP pile and prestressed concrete pile exhibit similar stiffnesses in lateral loading, plastic pile is not as stiff
Cost information at two case studies Initial costs of composite piles were higher than those for prestressed concrete piles 77 % higher at Route 40 bridge project 289% and 337% higher for plastic and FRP piles, respectively, at Route 351 bridge Cost effectiveness of composite piles is expected to improve as production volume increases, and by considering life-cycle costs of low-maintenance composite piles
Durability Studies
Experimental durability study Assumptions: Moisture is the dominant damage mechanism Homogenized FRP Residual strength is only moisture dependent Moisture diffusion is not stress dependent No chemical processes Creep rupture behavior is not considered FRP-concrete friction is not affected Track FRP moisture content Track FRP residual stiffness/strength FRP Pile strength (Fam & Rizkalla, 2001) Prediction of Residual Pile Life
Material characterization Lancaster 12- and 24-inch: Filament wound E-glass fiber 12-inch = epoxy, [-88/+8/-88/+8/-88/+8/-88/+8/-88], t = 6 mm 24-inch = polyester, [+35/-35/+85/+35/-35], t = 7.3 mm Hardcore 12- and 24-inch: VARTM E-glass fiber (multi-axis fabric Quad Q-9100) Vinyl ester 12-inch = 3 plies [0/+45/-45/90], t = 5.7 mm 24-inch = 4 plies [0/+45/-45/90], t = 8.9 mm
Evaluation of FRP Shell Properties Axial Hoop Split Disk
Testing As received properties Tensile stress (MPa) Axial 600 500 H-12 400 H-24 300 200 L-12 100 L-24 0 0.0 0.5 1.0 1.5 2.0 Strain (%) Tensile stress (MPa) Hoop 250 200 L-12 150 L-24 100 50 H-12 0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 Strain (%)
Moisture absorption Lancaster 24-inch Hardcore 24-inch Moisture content, m (%) 0.6 0.5 0.4 0.3 0.2 0.1 0.0 22 o C Langmiuirian Fickian 0 20 40 60 80 100 120 140 160 Square root of time (hours1/2) Moisture content, m (%) 0.25 0.20 819 days 681 days 0.15 0.10 0.05 0.00 22 o C Langmiuirian Fickian 0 20 40 60 80 100 120 140 160 Square root of time (hours1/2)
Property degradation Normalized strength X T /X o 1.2 1.0 0.8 0.6 20% loss 0.4 0.2 0.0 0.0 0.2 0.4 0.6 0.8 Moisture content (%) Normalized hoop modulus E T /E o 1.4 1.2 1.0 0.8 0.6 17 % loss 0.4 0.2 0.0 0.0 0.2 0.4 0.6 0.8 Moisture content (%) (Data for Hoop tests on Lancaster 12-inch)
SEM Images As received & Aged As-received Aged
Hardcore Lancaster
Normalized Axial Strength vs. Time 1.00 Normalized Axial Strength 0.95 0.90 0.85 Experimental Data 0.80 0.75 0 50 100 150 200 250 Submergence Time (Days)
Axial testing of concrete-filled FRP stubs 1,200,000 1,000,000 50% stiffness loss in secondary region 800,000 Load (Lbs) 600,000 400,000 200,000 Concrete-filled tube (Fresh) Concrete-filled tube (Aged 2 months) Concrete-filled tube (Aged 7 months) Plain concrete core Slight increase in ε f 0 0 1000 2000 3000 4000 5000 6000 microstrain (Axial)
Estimated long-term axial capacity Axial Load (kn) 5000 4500 4000 3500 3000 2500 2000 1500 1000 500 Predictions using Fam and Rizkalla 2002 Assumed % reductions: - 25% hoop stiffness - 40% hoop strength As-received 5 % decrease at 0.014 strain Initial properties: Concrete f' c = 20 MPa E co = 22.4 GPa 12-inch Lancaster FRP shell OD = 324 mm t = 6.1 mm E hoop-frp = 13 GPa σ hoop-frp = 195 MPa Aged 0 0 2 4 6 8 10 12 14 16 Axial strain (ms)
Estimated long-term flexural capacity 250 Moment (kn-m) 200 150 100 50 0 As-received Assumed % reductions: - 25% axial stiffness - 40% axial strength 0 20 40 60 80 100 120 140 Curvature (1/m) x (10-3 ) 199 kn-m 24% decrease 147 kn-m Aged
Joint Work VT and UPRM Objectives To evaluate the material hygrothermal degradation of CFFRP tubes Constituents level (FRP and concrete) Structural level (CFFRP) Include larger number of replicas using smaller size specimens
Experimental Program Aged FRP at three different water temperatures (30 C, 40 C, and 50 C) Axial and hoop direction (Special fixture was designed for hoop tests) Aged CFFRP at 30 C Periodical tests over the course of 2,000 day long study (Near 300 days completion) Work distribution CFFRP tubes and concrete (UPRM) FRP tubes (VT) Concrete subjected to triaxial loads (UPRM)
Conclusions Durability study Significant strength and stiffness degradation due to moisture absorption Little degradation effect of exposure to freeze-thaw cycles on longitudinal tensile properties of saturated FRP tubes Small impact of FRP degradation on long term axial capacity Significant impact of FRP degradation on flexural capacity
Future work Durability studies Durability studies involving small diameter concretefilled FRP piles to study the durability of axial and flexural structural capacity A durability study that includes exposure to salt water and other aqueous solutions representing other groundwater conditions Other recommended studies degradation due to UV and exposure to high temperatures resistance to fire corrosion of steel cage in PPI piles
Future work Structural tests Determine the influence of temperature on structural behavior, and effects of differences in coefficients of thermal expansion of the different pile constituents on pile performance Expand testing under combined axial load and bending to establish the full interaction diagrams of composite piles Behavior under cyclic loading Creep under axial compression Establish design guidelines for design of composite piles (FAM s work is helping with this)
Acknowledgments Carl Ealy (FHWA) Mike Hall (VDOT) Dr. Ed Hoppe (VTRC) Drs. George Filz and Jack Lesko (VT) Dr. Amir Fam (Queen s University)