Steel fibres to improve structural performance of...

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Steel fibres to improve structural performance of reinforced

concrete members

Ass. Prof. I. KOVÁCS University of Debrecen

Hungary

” SteelFibres to Improve Structural Performance of Reinforced Concrete Members” by Prof. György L. Balázs TU Budapest and Ass. Prof. Imre Kovács UD

Prof. Gy. L. BALÁZS

University of Technology and

Economics Budapest

Hungary

„Structural Concrete and Time” fib Symposium La Plata Argentina September 28. – September 30. 2005

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Steel fibre reinforced concrete

Plain concrete Steel fibre reinforced

concrete

Aggregate

Steel

fibres

Cement



3

Observations

Dℓ

F

Tension

Compression

Dℓ/ℓ

s

Dℓ

F

Dℓ

ℓ

F F

Increasing fibre content




4

D D

F

F

d

F

d

F F

Observations

Bending

Effect of local force





5

Use of SFRC in a cross section

Concrete

Fibre reinforced concrete

Steel fibre

reinforcement in

concrete members

Steel fibre reinforcement in reinforced concrete and

prestressed concrete members

Reinforcing bar

Prestressing



6

Use of SFRC in a cross section

Steel fibre reinforcement in the end

block region of prestressed member

Steel fibre reinforcement in repair and

strengthening of concrete members



7

Series of reinforced concrete beams

Hooked-end

steel fibres 0 V% 0.5 V% 1.0 V%

No stirrups A1 A2 A3

6/240 A4 A5 A6

6/120 A7 A8 A9

No stirrups

6/240

4/240

150

1800 mm 100 100

6/120

4/120

216

216

216

F

F

F F

F

F

Crimped

steel fibres 0 V% 0.5 V% 1.0 V%

No stirrups B1 B2 B3

4/240 B4 B5 B6

4/120 B7 B8 B9


Reinforcing details


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Failure loads and failure modes Crimped steel fibres

D&D® ~ 30/.5

1.0 V%

Fu=44.7kN

0.5 V% Fu=33.6kN

SHEAR FAILURE

COMBINED FAILURE

fc,cube = 48.80 MPa fsp,cyl = 2.81 MPa

fc,cube = 47.16 MPa fsp,cyl = 4.13

MPa

Hooked-end steel fibres

Dramix® ZC 30/.5

NO STIRRUPS Fu=24.2kN

1.0 V%

Fu=35.0kN

0.5 V% Fu=29.0kN

NO FIBRES SHEAR FAILURE

SHEAR FAILURE

SHEAR FAILURE




A1

A2

A3

Fu=21.6kN



B1

B2

B3

NO STIRRUPS

NO STIRRUPS

NO STIRRUPS

NO STIRRUPS

NO STIRRUPS



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D&D® ~ 30/.5

1.0 V%

4/240 Fu=45.7kN

0.5 V%

4/240 Fu=44.3kN

SHEAR FAILURE

BENDING FAILURE



MPa


Dramix® ZC 30/.5

6/240 Fu=35.7kN

1.0 V% 6/240 Fu=35.0kN

0.5 V% 6/240 Fu=35.1kN


SHEAR FAILURE

BENDING FAILURE




A4

A5

A6

4/240 Fu=27.5kN


fc,cube = 42.70 MPa fsp,cyl = 1.60 MPa B4

B5

B6



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D&D® ~ 30/.5

1.0 V%

4/120 Fu=45.0kN

0.5 V%

4/120 Fu=46.6kN

SHEAR FAILURE

BENDING FAILURE



MPa


Dramix® ZC 30/.5

6/120 Fu=37.4kN

1.0 V% 6/120 Fu=36.6kN

0.5 V% 6/120 Fu=35.0kN

NO FIBRES BENDING FAILURE

BENDING FAILURE

BENDING FAILURE




A7

A8

A9

4/120 Fu=35.2kN


fc,cube = 42.70 MPa fsp,cyl = 1.60 MPa B7

B8

B9



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Crack development

20kN - RC-B7 - 4/120 - 0V% D&D® 30/.5

0.00

0.04

0.08

0.12

0.16

0.20

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Position of crack, x [mm]

w [

mm

]

n = 22, w = 1.450 mm

wm= 0.066 mm, sm= 78 mm

20kN - RC-B9 - 4/120 - 1.0V% D&D® 30/.5

0.00

0.04

0.08

0.12

0.16

0.20

0 200 400 600 800 1000 1200 1400 1600 1800 2000


w [

mm

]

n = 30, w = 1.030 mm

wm= 0.034 mm, sm= 58 mm

B7 B9


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Crack development ” SteelFibres to Improve Structural Performance of Reinforced Concrete Members” by Prof. György L. Balázs TU Budapest and Ass. Prof. Imre Kovács UD


0.00

0.04

0.08

0.12

0.16

0.20

Cra

ck

wid

th,

w [

mm

]

2000180016001400120010008006004002000


RC-B9 - 4/120 - 1.0 V% D&D® 30/.5

Fu = 45.0 kN

Bending failure

30 kN

0 kN

F F

fc = 47.16 MPa

fsp = 4.13 MPa

0.00

0.04

0.08

0.12

0.16

0.20

Cra

ck

wid

th,

w [

mm

]

0 200 400 600 800 1000 1200 1400 1600 1800 2000


RC-B7 - 4/120 - 0 V% D&D® 30/.5

Fu = 35.2 kN

Shear failure

30 kN

0 kN

F F

fc = 42.7 MPa

fsp = 1.60 MPa

B7 B9

13

r

rm kk.s

2125050

r

rm kk.s

2125045

r

rm kk.s

2125040

Plain concrete

0.5 V% steel fibre content

1.0 V% steel fibre content

Proposal for crack spacing

Crack width

smrmk sw



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Crack spacing and crack width


20

30

40

50

60

70

80

90

100

0 5 10 15 20 25 30 35

Force, F [kN]

Me

an

cra

ck

sp

ac

ing

[m

m]

EC2 (No steel fibres)0.5 V% fibre content (Proposal)

1.0 V% fibre content (Proposal)No steel fibre (Measured)

0.5 V% steel fibre (Measured)1.0 V% steel fibre (Measured)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0 5 10 15 20 25 30 35

Force, F [kN]

Me

an

cra

ck

wid

th [

mm

]

EC2 (No steel fibres)

0.5 V% fibre content (Proposal)

1.0 V% fibre content (Proposal)

No steel fibre (Measured)

0.5 V% steel fibre (Measured)

1.0 V% steel fibre (Measured)

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Conclusions ” SteelFibres to Improve Structural Performance of Reinforced Concrete Members” by Prof. György L. Balázs TU Budapest and Ass. Prof. Imre Kovács UD

Failure modes and failure loads

1) Steel fibre reinforcement can effectively be used to improve

shear capacity of plain concrete in beams made with no

stirrup reinforcement.

2) If reinforced concrete beams contain the required amount of

conventional shear reinforcement, hence fail in bending, the

addition of fibre does not considerably increase the failure

load.

3) With sufficient amount of fibres the failure mode could be

changed from shear failure to bending failure.

4) Steel fibres do not only increase shear capacity but also

provide substantial post-peak resistance and ductility in

conventional reinforced concrete members


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Conclusions ” SteelFibres to Improve Structural Performance of Reinforced Concrete Members” by Prof. György L. Balázs TU Budapest and Ass. Prof. Imre Kovács UD

Cracking behaviour

1. Steel fibres in concrete beams provide uniformly

distributed cracks.

2. More cracks developed in beams containing steel fibres

than in case of beams made of plain concrete and

consequently smaller crack spacing was observed.

3. Significant reduction of average crack width was observed

by the use of steel fibres.

4. Cracking characteristics was not significantly effected by

the type of fibre.

5. A modification to the crack spacing formula by EC2 was

developed in order to consider the effect of steel fibres.


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Structural application of model


ARCHI STAT LTD.

Architectural & Structural Design Bureau

Nyiregyháza, Hungary

Zsolt KASSAI DLA architect

Imre KOVÁCS PhD structural engineer

FREE SHAPE SENDWICH SHELL

HOUSES

Egerszalók, HUNGARY

Patented building technology for

sendwich shells


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Steel fibres to improve structural performance of reinforced

concrete members

Ass. Prof. I. KOVÁCS University of Debrecen

Hungary


Prof. Gy. L. BALÁZS

University of Technology and

Economics Budapest

Hungary


THANK YOU FOR YOUR KIND ATTENTION!

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