Canada Research Chairs CONCRETE-FILLED FRP TUBES FOR PILE APPLICATIONS: AN OVERVIEW Amir Fam, P.Eng. Associate Professor and Canada Research Chair in Innovative and Retrofitted Structures Queen s s University
Description of CFFT Fiber Composite tube Conventional concrete pile Concrete core To replace f x, E x f y, E y Layers of fibers oriented at various directions Strength & stiffness in axial & hoop directions
Why FRP Tube? Permanent / structural Form-work Multi - directional non-corrosive reinforcement More efficient concrete confinement & protection Ribbed outer surface to improve skin friction or uplift resistance Ice smooth Rough
APPLICATIONS
Most Common Applications High M, Low N High N, Low M I I I I I Marine Piles Bridge Piers
Bridges: Route 40 Bridge, Virginia 14 13 mm diameter strands #5 gage wire spiral ties 3 in. 508 mm 508 mm 1 in. pitch 3 in. pitch 6 in. pitch 13.1 m 5 turns 16 turns 16 turns 5 turns 3 in. pitch 1 in. pitch 5.4 mm GFRP tube (E-glass / polyester composite) [ ± 34 / 85 / ± 34 ] Concrete f u = 221 MPa (axial), 353 MPa (hoop) E = 15.2 GPa (axial), 17.7 GPa (hoop) +34 +85 +34-34 Layer 3 Layer 2-34 Layer 1 625 mm 13.1 m 0.213 in.
Marine Piles (Total ~ 3000-6000 piles in US) Washington Texas
EXPERIMENTAL BACKGROUND UNREINFORCED CFFTs
Bending Tests (M) 450 400 Compression 350 zone 300 Prestressed pile (Analytical) 6 in. 250 Moment (kip.ft) 200 150 Tension (cracked) 100 zone 50 0 Test 1 Test 2 Analytical Composite pile 0 200 400 600 800 1000 6 Curvature x 10 (1/in.)
Axial Load Tests (N) 2.5 Axial Compression Tests Confined Normalized strength stress / f c 2 1.5 1 0.5 0 8.7 ksi 3.7 ksi 0 1 2 3 4 5 6 Normalized strain
Combined Bending & Axial Load Tests (M & N) 8000 Load 7000 Axial Load (kn) 6000 5000 4000 3000 2000 Theoretical Experimental 1000 Tension failure Compression failure 0 0 50 100 150 200 250 300 Moment (kn.m)
Spun-Cast CFFTs.. Lighter for large diameter t = c Sealed Form
EXPERIMENTAL BACKGROUND REINFORCED & PRESTRESSED CFFTs
Why? Relatively Low Flexural Stiffness GFRP GFRP E = 40 GPa E <<< 40 GPa Objective & Methodology: 1. Use Prestressing or internal reinforcement 2. Tube still contributes longitudinally, but largely for confinement
Prestressed CFFTs.. Parameters Degree of prestressing D = 325 mm x y Jacking stress 80%, 40 % f pu Prestress. reinf. ratio: 4, 8 strands Pre-tensioned vs. unbonded post-ten. t = 4.5 mm Laminate structure of tube (Axial / hoop) (y : x) = (1:2), (2:1) (2:1) tube 8 φ 13 steel (2:1) tube 8 φ 13 steel (1:2) tube 4 φ 13 steel (1:2) tube 4 φ 13 steel Spiral 8 φ 13 steel f jack = 0.8 f pu f ce = 10.73 MPa f jack = 0.4 f pu f ce = 5.36 MPa f jack = 0.8 f pu fce = 5.36 MPa f jack = 0.8 f pu fce = 5.36 MPa Post-tensioned f jack = 0.8 f pu f ce = 10.73 MPa
Fabrication.. Pre-Tensioned Wooden bulkhead Steel abutment GFRP tubes Concrete pump Steel strands Hosepipe
Fabrication.Post.Post-Tensioned Inserting strand through ducts Inserting anchorages Hydraulic jack
Results 0.2 GFRP tube vs. steel spiral 8 φ 13 steel strands f jack = 0.8 f pu f ce = 10.7 MPa Normalized Moment 0.1 M D o f c M = 3 Normalized Moment 0.15 Steel 0.125 spiral 0.1 GFRP tube 0.075 0 40 80 120 Deflection (mm) 0.05 0.025 Yielding of bottom strands Rupture of tube in tension PCFFT- 4 CFFT ( Literature) 0 0 5 10 15 20 25 30 35 40 Normalized Curvature [ψ.d o ] ( x10-3 )
Failure Modes Crushing after yielding of tension strands (No tube) Failure of tube in comp. side after yielding of strands Hydraulic jack Tension failure of tube after yielding of strands
GFRP Tube GFRP Tube Spiral Spiral None None 10M 10M steel steel 1.6% 1.6% 15M 15M steel steel 3.2% 3.2% 5/8 5/8 GFRP GFRP 3.2% 3.2% 3/8 3/8 GFRP GFRP 1.1% 1.1% 15M 15M steel steel 3.2% 3.2% 15M 15M steel steel 3.2% 3.2% 3/8 3/8 CFRP CFRP 1.1% 1.1% Cardboard tube Cardboard tube GFRP tube GFRP tube GFRP GFRP Bars Bars Steel Steel Spiral Spiral Reinforced Reinforced CFFTs CFFTs
Flexure Effect of Tube 140 120 100 Tension Compression Steel 3.2% Load (kn) 80 60 With Tube: 40 1) Progressive Warning Signs of Failure 20 0 Steel 3.2% 2) Higher Strength 50 100 150 200 250 Deflection (mm) Confinement Steel 3.2% 3) 0Still Confining After Axial Tension and Compression Failures
Flexure.. Effect of Rebar Type 140 Steel rebar 3.2% 120 100 Load (kn) 80 60 GFRP rebar 3.2% 40 GFRP Rebar vs. Steel Rebar: 20 1) Comparable Moment Capacity (GFRP 5% Higher) 2) No Ductility 0 Compared to Steel 0 50 100 150 200 250 FRP rebar not justified in this case.also no corrosion risk! Deflection (mm)
Shear Steel Spiral FRP Tube 16 14 Shear Stress (MPa) 12 10 8 6 4 2 0 0 2 4 6 8 10 12 14 16 18 Deflection (mm)
EXPERIMENTAL BACKGROUND PILE DRIVING, JOINTS & SPLICES
Joint to RC Beam.Route 40 bridge, VA 39.4 in. 30 in. 18 in. 33.4 in. 6 in. 6 No.7 No.4@ 6 in. 2 No.4 2 No.4 2 No.4 2 No.8 4 No.8 17.6 in. 24.6 in.
Splicing a Long Pile Steel plate I-shape key 8 No. 20, 2.7 m T- groove Threaded end steel rebar screwed into plate
Pile Driving Driving 1 st segment Splicing 2 nd segment Firm silty clay soil Conventional pile driving hammer (rated energy = 3665 kg.m) 50 mm thick wooden cushion Piles were driven to refusal @ depth = 14.3 m
Pile Extraction 600 mm diameter holes drilled around pile
Effect of Driving on Flexure, Spliced Pile 275 load (kn) 250 225 200 175 150 125 100 Reduction > 4 % Control undriven Control undriven 75 50 Driven 25 0 0 20 40 60 80 100 120 Deflection (mm)
Splice Effectiveness - Failure Mode M r = 200 kn.m (unspliced) crushing M r = 215 kn.m Fracture of bars slip
EXPERIMENTAL BACKGROUND DURABILITY
Experimental Program Hydraulic ram Load cell CFFT specimens Steel plates Threaded rods 50% Sustained load + 300 Freeze-thaw cycles Temp. ( C). 15 10 5 0-5 -10-15 -20-25 -30-35 Concrete core Air 0 1 2 3 4 5 6 Time (hrs)
Results Confined strength (MPa) 80 70 60 50 40 30 20 10 Normal weight ( = 22 MPa) FS-nw F-nw f ' c RS-nw R-nw Light weight ( = 41 MPa) FS-lw F-lw ' f c RS-lw R-lw 0 Freeze-Thaw + Sustained load Control Freeze-Thaw + Sustained load Control
ANALYSIS & DESIGN
Classical Lamination Theory - ULF FRP / constitutive relationships x y 1 Classical lamination theory Progressive & ULF approach θ 1 Predicted θ 2 Input: 0 [ E 12 G θ ] E1 2 Output: [ E E,...] x Stress (MPa) y 350 300 250 200 150 100 50 2 1 2 Experimental Failure of [-88] 5 layers n υ 0 5 10 15 20 25 30 12 K=1 C Strain ( x 10-3 ) Failure of [+8] 4 layers +8 o 40% E y T 60% -88 o T E x
Flexural Analysis - Equilibrium - Strain compatibility Layer - by - layer / cracked section analysis For ε = M & ψ =?? M =? c ε = ψ C f shell concrete C c T T c f M = ψ = strain d 2 y ψ = y = d x 2 Moment - area method stresses ψ dx dx = y ψ 1
Axial Load Analysis & Confinement ε cc Use radial displacement compatibility to estimate the confining pressure: σ R Radial σ R =? u R u R u R = u R ( ) tube ( ) core ε cc u R σ R u R Only the core is loaded: σ R R = R E t Core and tube are loaded: σ = s s υc ε 1 υc + E ( υc υ s ) ε R 1 υc + E t E c c cc cc
Failure Criteria σ x (tension) σ y (Comp.) σ x (tension) at failure σ x = ( σ x ) u at failure σ x < ( σ x ) u axial compressive strength ( σ ) y u σ y stress path σ x bi-axial stress failure envelope (Tsai-Wu) ( σ x ) u hoop tensile strength
Beam Column Analysis 300 mm Axial Load (kn) 4500 4000 3500 3000 2500 2000 1500 Small e Fibre Ratio (Axial : Hoop) 1:9 1:1 9:1 t = 2 mm D/t = 152 1000 Large e 500 0 0 20 40 60 80 100 120 140 160 Bending Moment (kn.m)
Sample Design Charts Unreinforced CFFT Moment-curvature design charts of the composite piles in bending Moment (kn.m) 300 250 200 150 100 50 0 Axial load (kn) 8000 7000 8000 FOS = 1.5 6000 7000 FOS = 2 5000 FOS = 3 4000 3000 Axial load - strain design charts of the composite piles Axial load (kn) 6000 5000 4000 Axial load moment interaction charts for composite piles 16.5 in. 16.5 in. 14.4 in. 12.7 14.4 in. in. 12.7 in. 10.7 in. 16.5 in. 10.7 in. 14.4 in. 12.7 in. 2000 3000 FOS = 1.5 10.7 in. 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 1000 2000 FOS = 2 FOS = 3 Curvature (1/m) 0 1000 Balanced condition 0 0.002 0.004 0.006 0.008 0.01 0.012 0 Axial strain (mm/mm) 0 50 100 150 200 250 300 350 400 450 Bending moment (kn.m)
Sample Design Charts Reinforced CFFT Rebar Reinf.. Ratio - Varied from 0 to 4.8% Moment (kn m) 80 70 60 50 40 30 20 10 0 Varied from 3 Hoop:1 Axial 4.8% to 1 Hoop:3 Axial 90 80 1H:3A 3.2% 70 1H:1A 1.6% 60 70 0% 3H:1A 50 0.3% 60 40 50 0 0.5 30 1 1.5 2 2.5 20 Curvature (m 40-1 ) 10 30 Moment (kn m) Tube Laminate Structure Varied from 3 Hoop:1 Axial to 1 Hoop:3 Axial 0 Moment (kn m) Concrete Strength - Varied from 25 to 75 MPa 20 75 MPa 25 MPa 0 0.5 10 1 1.5 2 0 Curvature (m -1 ) 0 0.5 1 1.5 2 2.5 Curvature (m -1 )
Closing Remarks. Fundamental research on CFFTs is well established.. Mechanics & behavior are now very well understood For some products design charts readily available.. No single simple equation like conventional RC (at least not yet). What is needed is more field applications.engineering community needs awareness, encouragement & realization of system & advantages
Acknowledgements All my Graduate Students ISIS Canada Lancaster Composite VDOT Queen s s University Virginia Tech
Thank You, fam@civil.queensu.ca (613) 533-6352 Check out ACI Committee 440... ask for J