THE PERFORMANCE OF CURVED FRP REINFORCEMENT FOR CONCRETE STRUCTURESCONCRETE STRUCTURES

Maurizio GuadagniniThanongsak ImjaiKypros Pilakoutas

Construction Innovation Research GroupDepartment of Civil and Structural Engineering

© 2007 The University of SheffieldWestern Bank, Sheffield S10 2TN, UK

The University of Patras, GreeceFRPRCS-8

Department of Civil and Structural Engineering

OutlineOutline

•Introduction

•Performance of bent FRP’s

•Experimental programme/results

•Conclusions

© 2007 The University of SheffieldWestern Bank, Sheffield S10 2TN, UK

The University of Patras, GreeceFRPRCS-8

IntroductionIntroduction

•End anchorages

•Element connectionElement connection

•Shear reinforcement

© 2007 The University of SheffieldWestern Bank, Sheffield S10 2TN, UK

The University of Patras, GreeceFRPRCS-8

IntroductionIntroduction

r ≥ 2r ≥ 2

Standardised shapes (BS8666)© 2007 The University of SheffieldWestern Bank, Sheffield S10 2TN, UK

The University of Patras, GreeceFRPRCS-8

Standardised shapes (BS8666)

IntroductionIntroduction

Typical ypGFRP

Typical steel

© 2007 The University of SheffieldWestern Bank, Sheffield S10 2TN, UK

The University of Patras, GreeceFRPRCS-8

Plastic strain induced by bending

IntroductionIntroduction

© 2007 The University of SheffieldWestern Bank, Sheffield S10 2TN, UK

The University of Patras, GreeceFRPRCS-8

Pre-bent FRP’sPre-bent FRP’s

•Thermosetting FRP’s:can only be pre-bent at the factory

•Thermoplastic FRP’s:could offer a valid solution for on-site bending of reinforcement

© 2007 The University of SheffieldWestern Bank, Sheffield S10 2TN, UK

The University of Patras, GreeceFRPRCS-8

Performance of bent FRP’sPerformance of bent FRP’s

The tensile strength of FRP bars can be largely reduced when subjected to a biaxial state of stressstate of stress

LongitudinaldirectiondirectionTransverse

direction

Premature failure at bent portion

© 2007 The University of SheffieldWestern Bank, Sheffield S10 2TN, UK

The University of Patras, GreeceFRPRCS-8

Performance of bent FRP’sPerformance of bent FRP’s

Design equation (JSCE)

50

60

70

σ b/ σ

max

(%)

α = 0.092

α = 0.05

30

40

50σ

α⎛ ⎞⎜ ⎟⎜ ⎟⎝ ⎠

= + ≤0.3bfb fu fu

b

rf f fdallowable stress in FRP links

0

10

20⎝ ⎠allowable stress in FRP links

r/t0 1 2 3 4 5 6

rb is the radius of the bend in the bar

© 2007 The University of SheffieldWestern Bank, Sheffield S10 2TN, UK

The University of Patras, GreeceFRPRCS-8

db is the nominal diameter of the FRP barffu is the design strength of a straight portion of the bar

Performance of bent FRP’sPerformance of bent FRP’s

α⎛ ⎞⎜ ⎟⎜ ⎟⎝ ⎠

= + ≤0.3bfb fu fu

rf f fd

Bend geometry

⎜ ⎟⎝ ⎠bd

- r/t

Composite make upComposite make-up- type of fibres

type of resin- type of resin- volume fractions

© 2007 The University of SheffieldWestern Bank, Sheffield S10 2TN, UK

The University of Patras, GreeceFRPRCS-8

Experimental programmeExperimental programme

GFRP thermoplastic strip (12x3mm)

Properties

Tensile strength (MPa) 720

Tensile modulus (GPa) 28( )

Ultimate strain (%) 1.9

Glass content (%v/v) 35Glass content (%v/v) 35

Density (g/cm3) 1.48

© 2007 The University of SheffieldWestern Bank, Sheffield S10 2TN, UK

The University of Patras, GreeceFRPRCS-8

Experimental programmeExperimental programme

Parameters (47 specimens)( p )- r/t (2 – 5)- embedment length (60mm, 145mm)g- tail length (tl/t = 5 – 15)- fcu (45MPa, 95MPa)

f t t t- surface treatment (smooth, sand coated)

© 2007 The University of SheffieldWestern Bank, Sheffield S10 2TN, UK

The University of Patras, GreeceFRPRCS-8

Type 2 Type 3

Experimental resultsExperimental results

42%

56%

300

400

ress

(MPa

)

f / f fu272529

28%200

str

21

23

0%

14%

0

100

0 4000 8000 12000 16000 200000%0

strain (με)

© 2007 The University of SheffieldWestern Bank, Sheffield S10 2TN, UK

The University of Patras, GreeceFRPRCS-8

Strain distribution in specimens Type 2

Experimental resultsExperimental results

42%

56%

300

400

f / f fu

ess

(MPa

)

2123 2725

29

28%200

stre

0%

14%

0

100

strain (με)0 4000 8000 12000 16000 20000

0%0

© 2007 The University of SheffieldWestern Bank, Sheffield S10 2TN, UK

The University of Patras, GreeceFRPRCS-8

Strain distribution in specimens Type 3

Performance of bent FRP’sPerformance of bent FRP’s

70%)

50

60

f / f fu

(%

JSCE

30

40

Type 2, SM, N

10

20

30Type 2, SC, NType 2, SM, HType 2, SC, HType 3, SM, N

/t0 1 2 3 4 5 6

0

10Type 3, SM, H

© 2007 The University of SheffieldWestern Bank, Sheffield S10 2TN, UK

The University of Patras, GreeceFRPRCS-8

r/t

A Macromechanical approachA Macromechanical approach

•Force equilibrium •Failure criterion2 2

2 1tr

σ σ=2 21 1 2 1

2 2 21 max 1 max 2 max

1σ σ σ σσ σ σ

− + =

© 2007 The University of SheffieldWestern Bank, Sheffield S10 2TN, UK

The University of Patras, GreeceFRPRCS-8

1,max 1,max 2,max

A Macromechanical approachA Macromechanical approach

•Predictive model

12

1,max 2

1

1 h h

σσ

β

=⎛ ⎞ ⎛ ⎞⎜ ⎟ ⎜ ⎟

21R R

β⎛ ⎞ ⎛ ⎞+ + ⋅⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠

1,maxσβ =

•Material testing

•Micromechanics2,max

βσ

=

( )2,max1

mc rmfk

σ σ= +

•Micromechanics

© 2007 The University of SheffieldWestern Bank, Sheffield S10 2TN, UK

The University of Patras, GreeceFRPRCS-8

kσ

A Macromechanical approachA Macromechanical approach

60

70

50

60

30

40

Type 2, SM, NType 2 SC N

10

20Type 2, SC, NType 2, SM, HType 2, SC, HType 3, SM, N

x= 90 MPa

β = 7

0 1 2 3 4 5 60

Type 3, SM, Hσ 2,max

© 2007 The University of SheffieldWestern Bank, Sheffield S10 2TN, UK

The University of Patras, GreeceFRPRCS-8

r/t

Final RemarksFinal Remarks

•The capacity of the bent portion is not only a function of its geometry

•Values of r/t > 3-4 guarantee theValues of r/t > 3-4 guarantee the development of 40% of the ultimate strengthstrength

•The macromechanical based model adequately captures strength degradation of bent bars

© 2007 The University of SheffieldWestern Bank, Sheffield S10 2TN, UK

The University of Patras, GreeceFRPRCS-8