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 ,fam@civil.queensu.ca

(613) 533-6352

Check out ACI Committee 440 ……..…. ask for J…