avril stéphane , vautrin alain, ferrier emmanuel, hamelin patrice, surrel yves

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A full-field optical method for the experimental analysis of Reinforced-Concrete beams repaired with composites.

AVRIL Stéphane, VAUTRIN Alain, FERRIER Emmanuel, HAMELIN Patrice,

SURREL Yves

A full-field optical method A full-field optical method for the experimental analysis of for the experimental analysis of

Reinforced-Concrete beams Reinforced-Concrete beams repaired with composite repaired with composite

materialsmaterials

Comp-Test, Châlons en Champagne, 28-30 January, 2003

http://www.univ-lyon1.fr/corpsucbl.htm

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Rehabilitation of damaged Reinforced-Concrete infrastructures

Composite sheets are bonded onto concrete.

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Shear and flexural strengthening

Flexural deficiencies: a CFRP plate is bonded onto the bottom of the beam.

Shear deficiencies: GFRP “U-jackets” bonded onto the the lateral surface.

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Efficiency of flexural strengthening

Are vertical cracks bridged by the CFRP plate ?

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Application of the grid method in the area of interest.

Solution: a full field optical method

x

y

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Bridging of shear cracks by the GFRP U-jackets:

Cracks are not visible.

Efficiency of shear strengthening

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x

y

Solution: still the grid method ?

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The light intensity reflected by the grid writes:

I = I0 [ 1 + f (]

Principle of the grid method

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p

U-1(x,y)

Undeformed grid :

(x,y)

Undeformed grid :

Deformedgrid :


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resolution 5 µm

spatial resolution 2 mm

p = 1 mm

p)y,x(U=)y,x(Δ xπ2φ


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Strain field measurement

resolution 150.10-6,

spatial resolution 10 mm.

25 x 30 strain sensors,

Numerical differentiation by fitting the best plane of 5 x 5 pixels subimages of displacement fields.

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Detection and characterization of cracks

Ux : x

y

Discontinuities

Ux (µm)

Abscissa (pixels)

Crack width

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Example of a crack width investigation

ZOOM

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Application to shear behaviour

x

y

Cracks are detected from displacements fields measured with the grid method.

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Mechanical behavior without composite

Crack openings can be decomposed in two parts:

- mode I,

- mode II.

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Mechanical behavior after strengthening

Strain yy :

Strain xy :

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Modeling of shear cracks

Mode I : Shear strains xy

Mode II : Tensile strains yy Debonded area

Crack under the composite sheet

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Initiation and propagation of peeling failure

Strain xy :

Enlargement of strain concentration areas

6,954,962,980,99

-0,99-2,98-4,96-6,95

xy(x10-3)

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Interest of full-field measurements

The size of strain concentration areas is an indicator for anticipating peeling failure in RC beams strengthened in shear with a GFRP U-jacket.

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Conclusions

The grid technique is a suitable method for evaluating crack bridging in concrete structures repaired with composites:

- crack widths are measured over a whole field area,

- cracks can also be detected under a composite reinforcement bonded onto cracked concrete.

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Perspectives

Application of the grid method to real infrastructures.

Use of other full-field optical techniques which do not need to deposit grids.

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Acknowledgements

The authors wish to express their appreciation to the Région

RHÔNE-ALPES for its financial support to the project:

“Rehabilitation of civil engineering structures with composite

materials : modeling of repaired cracked beams”.

avril stéphane , vautrin alain, ferrier emmanuel, hamelin patrice, surrel yves

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