CONCRETE-FILLED FRP TUBES
FOR PILE APPLICATIONS:
… AN OVERVIEW …
Canada ResearchCanada ResearchChairsChairs
CONCRETE-FILLED FRP TUBES
FOR PILE APPLICATIONS:
… AN OVERVIEW …
Amir Fam, Amir Fam, P.EngP.Eng..Associate Professor and
Canada Research Chair in Innovative and Retrofitted Structures
QueenQueen’’s Universitys University
Description of CFFTDescription of CFFTFiber Composite tube
Concrete core
Layers of fibers oriented at various directions
fx , Ex
fy , Ey
Strength & stiffness in axial & hoop directions
Conventional concrete pile
To replace
Multi - directional non-corrosive reinforcementPermanent / structural Form-work
Why FRP Tube ?Why FRP Tube ?
Ribbed outer surface to improve skin friction or uplift resistance
Rough
Ice
smooth
More efficient concrete confinement & protection
APPLICATIONSAPPLICATIONS
Most Common Applications Most Common Applications
I I I I I
High M, Low N High N, Low M
Marine Piles Bridge Piers
Bridges: Route 40 Bridge, VirginiaBridges: Route 40 Bridge, Virginia
508 mm
508 mm
14 – 13 mm diameter strands
1 in. pitch
3 in. pitch
6 in. pitch
3 in. pitch
1 in. pitch
5 turns 16 turns 16 turns 5 turns
#5 gage wire spiral ties
3 in.
13.1 m
+34
-34
+85+34
-34Layer 1Layer 2Layer 3
625 mm0.213 in.
13.1 m
(E-glass / polyester composite) [ ± 34 / 85 / ± 34 ]
Concrete
5.4 mm GFRP tube
fu = 221 MPa (axial), 353 MPa (hoop)E = 15.2 GPa (axial), 17.7 GPa (hoop)
Marine Piles Marine Piles (Total ~ 3000(Total ~ 3000--6000 piles in US)6000 piles in US)
TexasTexas
WashingtonWashington
EXPERIMENTAL BACKGROUNDEXPERIMENTAL BACKGROUND
UNREINFORCED UNREINFORCED CFFTsCFFTs
Bending Tests (M)Bending Tests (M)
6 in.
Compression zone
Tension (cracked)zone
6 in.
Compression zone
Tension (cracked)zone
0
50
100
150
200
250
300
350
400
450
0 200 400 600 800 1000
Test 1 Test 2
Analytical Composite pile
Prestressed pile(Analytical)
Curvature x 10 (1/in.)6
Mom
ent (
kip.
ft)
0
50
100
150
200
250
300
350
400
450
0 200 400 600 800 1000
Test 1 Test 2
Analytical Composite pile
Prestressed pile(Analytical)
Curvature x 10 (1/in.)6Curvature x 10 (1/in.)6
Mom
ent (
kip.
ft)
Axial Load Tests (N)Axial Load Tests (N)Axial Compression
Tests
0
0.5
1
1.5
2
2.5
0 1 2 3 4 5 6
Normalized strain
Nor
mal
ized
stre
ssC
onfin
ed s
treng
th /
Con
fined
stre
ngth
/ ff cc’’ 3.7 3.7 ksiksi
8.7 8.7 ksiksi
Combined Bending & Axial Load Tests (M & N)Combined Bending & Axial Load Tests (M & N)
Compression failureTension failure
0
1000
2000
3000
4000
5000
6000
7000
8000
0 50 100 150 200 250 300
Moment (kN.m)
Axi
al L
oad
(kN
)
Theoretical
Experimental
Load
0
1000
2000
3000
4000
5000
6000
7000
8000
0 50 100 150 200 250 300
Moment (kN.m)
Axi
al L
oad
(kN
)
Theoretical
Experimental
LoadLoad
SpunSpun--Cast Cast CFFTsCFFTs …….. Lighter for large diameter.. Lighter for large diameterSealed FormSealed FormSealed FormSealed Form
t = ct = c
EXPERIMENTAL BACKGROUNDEXPERIMENTAL BACKGROUND
REINFORCED & REINFORCED & PRESTRESSED PRESTRESSED CFFTsCFFTs
Relatively Low Flexural StiffnessRelatively Low Flexural Stiffness
Why ?Why ?
GFRP
E = 40 GPa
GFRP
E <<< 40 GPa
Objective & Methodology:1. Use PrestressingPrestressing or internal reinforcementinternal reinforcement
2. TubeTube still contributes longitudinallycontributes longitudinally, but largely for confinementconfinement
PrestressedPrestressed CFFTsCFFTs ……. Parameters. ParametersDegree of prestressing
Jacking stress 80% , 40 % fpu
x
yD = 325
mm
t = 4.5 mm
Prestress. reinf. ratio: 4 , 8 strands
Pre-tensioned vs. unbonded post-ten.
Laminate structure of tube (Axial / hoop)(y : x) = (1:2), (2:1)
(2:1) tube8 φ 13 steelfjack = 0.8 fpu
fce = 10.73 MPa
(2:1) tube 8 φ 13 steelfjack = 0.4 fpu
fce = 5.36 MPa
(1:2) tube4 φ 13 steelfjack = 0.8 fpu
fce = 5.36 MPa
Spiral8 φ 13 steelfjack = 0.8 fpu
fce = 10.73 MPa
(1:2) tube4 φ 13 steelfjack = 0.8 fpu
fce = 5.36 MPaPost-tensioned
Fabrication Fabrication ……. Pre. Pre--Tensioned Tensioned
Steel strands
GFRP tubes
Steel abutment
Wooden bulkhead
Concrete pump
Hosepipe
FabricationFabrication…….Post.Post--Tensioned Tensioned
Inserting strand through ducts
Inserting anchorages
Hydraulic jack
ResultsResults
0 40 80 120
0.1
GFRP tube vs. steel spiral8 φ 13 steel strands
fjack = 0.8 fpu
fce = 10.7 MPa
Steel spiral
GFRP tube
0 40 80 1200 40 80 120
0.1
GFRP tube vs. steel spiral8 φ 13 steel strandsGFRP tube vs. steel spiral8 φ 13 steel strands
fjack = 0.8 fpu
fce = 10.7 MPa
Steel spiral
GFRP tube
0 40 80 120
0.2
Deflection (mm)
Nor
mal
ized
Mom
ent
Normalized Curvature [ψ.Do] ( x10-3)
Nor
mal
ized
Mom
ent
0 5 10 15 20 25 30 35 40
0.15
0.125
0.1
0.075
0.05
0.025
0
Yielding of bottom strands
Rupture of tube in tensionco fD
MM ′= 3
CFFT( Literature)
PCFFT- 4
Failure ModesFailure 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 TubeGFRP Tube
SpiralSpiral
NoneNone
10M10Msteelsteel1.6%1.6%
15M15Msteelsteel3.2%3.2%
5/85/8””GFRPGFRP3.2%3.2%
3/83/8””GFRPGFRP1.1%1.1%
15M15Msteelsteel3.2%3.2%
15M15Msteelsteel3.2%3.2%
3/83/8””CFRPCFRP1.1%1.1%
Cardboard tubeCardboard tube
GFRP tubeGFRP tube
GFRP GFRP BarsBars
Steel Steel SpiralSpiral
Reinforced Reinforced CFFTsCFFTs
Deflection (mm)
Load
(kN
)
50 100 150 200 2500
100
80
60
40
20
0
120
140
Steel 3.2%
Steel 3.2%
Steel 3.2%
With Tube:
1) Progressive Warning Signs of Failure
2) Higher Strength
3) Still Confining After Axial Tension and Compression Failures
TensionCompression
Confinement
FlexureFlexure…… Effect of TubeEffect of Tube
Deflection (mm)50 100 150 200 2500
Load
(kN
)
100
80
60
40
20
0
120
140 Steel rebar 3.2%
GFRP rebar 3.2%
GFRP Rebar vs. Steel Rebar:
1) Comparable Moment Capacity (GFRP 5% Higher)
2) No Ductility Compared to SteelFRP rebar not justified in this case….Also no corrosion risk !
FlexureFlexure……. Effect of Rebar Type. Effect of Rebar Type
ShearShear
FRP TubeSteel Spiral
0 2 4 6 8 10 12 14 16 180
2
4
6
8
10
12
14
16
Deflection (mm)
Shea
r Str
ess
(MPa
)
0 2 4 6 8 10 12 14 16 180
2
4
6
8
10
12
14
16
Deflection (mm)
Shea
r Str
ess
(MPa
)
0 2 4 6 8 10 12 14 16 180
2
4
6
8
10
12
14
16
Deflection (mm)
Shea
r Str
ess
(MPa
)
0 2 4 6 8 10 12 14 16 180
2
4
6
8
10
12
14
16
Deflection (mm)
Shea
r Str
ess
(MPa
)
EXPERIMENTAL BACKGROUNDEXPERIMENTAL BACKGROUND
PILE DRIVING,PILE DRIVING,JOINTS JOINTS
& SPLICES& SPLICES
Joint to RC BeamJoint to RC Beam…….Route 40 bridge, VA.Route 40 bridge, VA30
in.
18 in
.
24.6 in.17.6 in.
6 No.7
2 No.4
2 No.42 No.4
2 No.84 No.8
33.4
in.
6 in
.
39.4 in.
No.4@ 6 in.
Splicing a Long Pile Splicing a Long Pile
8 No. 20, 2.7 m
Steel plate I-shape key
T- groove
Threaded end steel rebar screwed into plate
Pile DrivingPile Driving
Splicing 2nd segment
Piles were driven to refusal @ depth = 14.3 m
Firm silty clay soil
Driving 1st
segment
Conventional pile driving hammer (rated energy = 3665 kg.m)
50 mm thick wooden cushion
Pile Extraction Pile Extraction
600 mm diameter holes drilled around pile
Effect of Driving on Flexure, Spliced Pile Effect of Driving on Flexure, Spliced Pile
0
25
50
75
100
125
150
175
200
225
250
275
0 20 40 60 80 100 120
Deflection (mm)
load
(kN
)
Controlundriven
Controlundriven
Driven
Reduction > 4 %
Splice Effectiveness Splice Effectiveness -- Failure ModeFailure Mode
MMrr = 200 = 200 kN.mkN.m ((unsplicedunspliced))
slip
Fracture of bars
crushing
MMrr = 215 = 215 kN.mkN.m
EXPERIMENTAL BACKGROUNDEXPERIMENTAL BACKGROUND
DURABILITYDURABILITY
Experimental ProgramExperimental Program
-35-30-25-20-15-10-505
1015
0 1 2 3 4 5 6Time (hrs)
Tem
p. (˚
C)
.Concrete core
Air
-35-30-25-20-15-10-505
1015
0 1 2 3 4 5 6Time (hrs)
Tem
p. (˚
C)
.Concrete core
Air
Hydraulic ram
Load cell CFFT specimens
Threaded rods
Steel plates
Hydraulic ram
Load cell CFFT specimens
Threaded rods
Steel plates50% Sustained load
+300 Freeze-thaw cycles
ResultsResults
0
10
20
30
40
50
60
70
80
FS-n
w
F-nw
RS-
nw
R-n
w
FS-lw
F-lw
RS-
lw
R-lw
Normal weight ( = 22 MPa)'cf Light weight ( = 41 MPa)'
cf
Con
fined
stre
ngth
(M
Pa)
0
10
20
30
40
50
60
70
80
FS-n
w
F-nw
RS-
nw
R-n
w
FS-lw
F-lw
RS-
lw
R-lw
Normal weight ( = 22 MPa)'cf Light weight ( = 41 MPa)'
cf
Con
fined
stre
ngth
(M
Pa)
ControlControl ControlControlFreezeFreeze--ThawThaw
+ Sustained load+ Sustained loadFreezeFreeze--ThawThaw
+ Sustained load+ Sustained load
ANALYSISANALYSIS&&
DESIGNDESIGN
Classical Lamination Theory Classical Lamination Theory -- ULFULFFRP / constitutive relationships
x y 1
21θ
1
2
2θ
C TT
Ex
Classical lamination theoryProgressive & ULF approach
Input:Input:1E 2E 12υ 12G θ[ ]
K=1
n
Output:Output:xE yE[ , …...]
Ey
Strain ( x 10-3)
Stre
ss (M
Pa)
0 5 10 15 20 25 30
350
300
250
200
150
100
50
0
Predicted
Experimental
Failure of [-88]5 layers
Failure of [+8]4 layers
+8o
- 88o
60%40%
Flexural AnalysisFlexural Analysis
M =
ψ =
concrete
c
Tf
Cf Cc
stresses
shell
Tc
d2 yd x2
ψ =
y
y = ψ dx dx =
ψ1
Moment - area method
- Equilibrium- Strain compatibility Layer Layer -- by by -- layer / cracked section analysislayer / cracked section analysis
For = ε M & ψ = ??
ε
ψ
strain
M = ?=
ccε
Rσ
uR uR
uR
Rσ
ccε
uR
Use radial displacement compatibility to estimate the confining pressure:
=uR( ) tube ( ) coreuR
Rσ = ?Radial
cc
c
c
s
cR
EtER
ευ
υσ−
+= 1
Only the core is loaded:
cc
c
c
s
scR
EtER
)( ευ
υυσ−
+
−= 1
Core and tube are loaded:
Axial Load Analysis & ConfinementAxial Load Analysis & Confinement
Failure Criteria Failure Criteria
hoop tensile strength
axial compressive
strength
(tension)
at failure
xσ
( )uxx σσ =
( )uxσxσ
bi-axial stress failure envelope
yσ(Comp.)
(tension)xσ
( )uxx σσ <at failure
yσ( )
uyσ
stress path(Tsai-Wu)
0
500
1000
1500
2000
2500
3000
3500
4000
4500
0 20 40 60 80 100 120 140 160
t = 2 mmSmall Small ““ee””
Large Large ““ee””
1:91:91:11:19:19:1
Axi
al L
oad
(kN
)
Bending Moment (kN.m)
(Axial : Hoop)
300 mm
D/t = 152
‘‘Beam Beam –– ColumnColumn’’ AnalysisAnalysis
Fibre Ratio
Sample Design Charts Sample Design Charts –– UnreinforcedUnreinforced CFFTCFFT
0
50
100
150
200
250
300
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1
Curvature (1/m)
Mom
ent (
kN.m
)
10.7 in.
12.7 in.
14.4 in.
16.5 in.
FOS = 2
FOS = 1.5
FOS = 3
0
50
100
150
200
250
300
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1
Curvature (1/m)
Mom
ent (
kN.m
)
10.7 in.10.7 in.
12.7 in.12.7 in.
14.4 in.14.4 in.
16.5 in.16.5 in.
FOS = 2FOS = 2
FOS = 1.5FOS = 1.5
FOS = 3FOS = 3
Moment-curvature design charts of the composite piles in bending
0
1000
2000
3000
4000
5000
6000
7000
8000
0 0.002 0.004 0.006 0.008 0.01 0.012
Axial strain (mm/mm)
Axi
al lo
ad (k
N)
14.4 in.
16.5 in.
FOS = 1.5
FOS = 2
FOS = 3
12.7 in.
10.7 in.
0
1000
2000
3000
4000
5000
6000
7000
8000
0 0.002 0.004 0.006 0.008 0.01 0.012
Axial strain (mm/mm)
Axi
al lo
ad (k
N)
14.4 in.14.4 in.
16.5 in.16.5 in.
FOS = 1.5FOS = 1.5
FOS = 2FOS = 2
FOS = 3FOS = 3
12.7 in.12.7 in.
10.7 in.10.7 in.
Axial load - strain design charts of the composite piles
0
1000
2000
3000
4000
5000
6000
7000
8000
0 0.002 0.004 0.006 0.008 0.01 0.012
Axial strain (mm/mm)
Axi
al lo
ad (k
N)
14.4 in.
16.5 in.
FOS = 1.5
FOS = 2
FOS = 3
12.7 in.
10.7 in.
0
1000
2000
3000
4000
5000
6000
7000
8000
0 0.002 0.004 0.006 0.008 0.01 0.012
Axial strain (mm/mm)
Axi
al lo
ad (k
N)
14.4 in.14.4 in.
16.5 in.16.5 in.
FOS = 1.5FOS = 1.5
FOS = 2FOS = 2
FOS = 3FOS = 3
12.7 in.12.7 in.
10.7 in.10.7 in.
Axial load - strain design charts of the composite piles
0
1000
2000
3000
4000
5000
6000
7000
8000
0 50 100 150 200 250 300 350 400 450
Axi
al lo
ad (k
N)
Bending moment (kN.m)
14.4 in.
16.5 in.
12.7 in.
10.7 in.
Balanced condition
0
1000
2000
3000
4000
5000
6000
7000
8000
0 50 100 150 200 250 300 350 400 450
Axi
al lo
ad (k
N)
Bending moment (kN.m)
14.4 in.14.4 in.
16.5 in.16.5 in.
12.7 in.12.7 in.
10.7 in.10.7 in.
Balanced condition
Axial load – moment interaction charts for composite piles
0
1000
2000
3000
4000
5000
6000
7000
8000
0 50 100 150 200 250 300 350 400 450
Axi
al lo
ad (k
N)
Bending moment (kN.m)
14.4 in.
16.5 in.
12.7 in.
10.7 in.
Balanced condition
0
1000
2000
3000
4000
5000
6000
7000
8000
0 50 100 150 200 250 300 350 400 450
Axi
al lo
ad (k
N)
Bending moment (kN.m)
14.4 in.14.4 in.
16.5 in.16.5 in.
12.7 in.12.7 in.
10.7 in.10.7 in.
Balanced condition
Axial load – moment interaction charts for composite piles
Sample Design Charts Sample Design Charts –– RReinforced CFFTeinforced CFFT
0
10
20
30
40
50
60
70
80
0 0.5 1 1.5 2 2.5
Curvature (m -1)
Mom
ent (
kN·m
)
Rebar Rebar ReinfReinf. Ratio. Ratio -- Varied from 0 to 4.8%Varied from 0 to 4.8%
0
10
20
30
40
50
60
70
80
0 0.5 1 1.5 2 2.5
Curvature (m -1)
Mom
ent (
kN·m
)
Rebar Rebar ReinfReinf. Ratio. Ratio -- Varied from 0 to 4.8%Varied from 0 to 4.8%
4.8%
0%
3.2%
1.6%
0.3%
0102030405060708090
0 0.5 1 1.5 2
Curvature (m-1)
Mom
ent (
kN•m
)Tube Laminate StructureTube Laminate Structure ––
Varied from 3 Hoop:1 Axial to 1 Hoop:3 AxialVaried from 3 Hoop:1 Axial to 1 Hoop:3 Axial
0102030405060708090
0 0.5 1 1.5 2
Curvature (m-1)
Mom
ent (
kN•m
)Tube Laminate StructureTube Laminate Structure ––
Varied from 3 Hoop:1 Axial to 1 Hoop:3 AxialVaried from 3 Hoop:1 Axial to 1 Hoop:3 Axial
1H:3A
1H:1A
3H:1A
Concrete StrengthConcrete Strength -- Varied from 25 to 75 MPaVaried from 25 to 75 MPa
0
10
20
30
40
50
60
70
0 0.5 1 1.5 2 2.5
Curvature (m-1)
Mom
ent (
kN·m
)
Concrete StrengthConcrete Strength -- Varied from 25 to 75 MPaVaried from 25 to 75 MPa
0
10
20
30
40
50
60
70
0 0.5 1 1.5 2 2.5
Curvature (m-1)
Mom
ent (
kN·m
)
75 MPa
25 MPa
Closing Remarks Closing Remarks …………..Fundamental research on Fundamental research on CFFTsCFFTs is well is well establishedestablished……. Mechanics & behavior are . Mechanics & behavior are now very well understoodnow very well understood……
For some products design charts readily For some products design charts readily availableavailable…….. No .. No ‘‘single simple equationsingle simple equation’’like conventional RC (at least not yet)like conventional RC (at least not yet)…………..
What is needed is more field What is needed is more field applicationsapplications…….Engineering community .Engineering community needs awareness, encouragement & needs awareness, encouragement & realization of system & advantagesrealization of system & advantages
AcknowledgementsAcknowledgements
All my Graduate StudentsAll my Graduate Students
ISIS CanadaISIS Canada
Lancaster CompositeLancaster Composite
VDOTVDOT
QueenQueen’’s Universitys University
Virginia TechVirginia Tech
Thank You ,Thank You ,[email protected]
(613) 533-6352
Check out ACI Committee 440 ……..…. ask for J…
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