[Univ of Cambridge] [Dept of Engineering]

Fracture of concrete-CFRP bond

by L. Arthur


The theoretical gain in flexural strength of a reinforced concrete beam strengthened with FRP plate is enormous, however researchers have observed new types of failure that limit this gain.  These observed failures are most often brittle in nature and involve delamination, edge peeling and interior debonding of the FRP plate.  These occur at loads significantly lower than the theoretical ultimate load of a strengthened beam.  Thus, an understanding of these failure mechanisms must be sought to safeguard against their occurrence.

Many researchers have concentrated on the use of the strength and the finite element methods to analyse these local failures of the concrete-FRP bond. These methods require knowledge of the details of the crack tip and the surface characteristics but these are not known in normal applications.  The present study uses the Hutchinson fracture model together with the compatibility of the strains and changes in length along the unbond surfaces.  Based on the Hutchinson fracture model, the present study assumes that flaws exist, and looks at whether these flaws can aid propagation of interior debonding or edge peeling with a given energy release.  The model also is used to investigate whether debonding or edge peeling would occur first and which would dictate the ultimate failure of plate bonded beams.  Finally, the unbonded length under any given loading conditions was determined.

The model was coded into a computer program using Matlab.  For a given load condition, the energy release rate, strains, stresses in various components of the strengthened beam and the unbonded length were the output of the program.  A parametric study was conducted and the result revealed that the thickness of the plate dictates, to some extent, the type of local failure that would occur with a given load condition.  It was concluded that interior debonding failures that initiate from the constant moment region are likely to occur before the other types of local failure since the energy release rates are higher in that region.

[Cambridge University | CUED | Structures Group | Geotechnical Group]

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