Bond behaviour of FRP bars in concrete.

This thesis investigates the bond behaviour of Fibre Reinforced Polymer (FRP)
reinforcing bars in concrete elements both analytically and experimentally.
Two series of experiments were conducted. In the first series, more than 100
cube specimens were tested in direct pullout. The mode of bond failure of FRP bars in
the pullout tests was found in most cases to differ substantially from that of deformed
steel bars. Within this series the parameters that influence bond development were
examined. The bond strengths developed by CFRP and GFRP bars appear to be very
similar, and just below what is expected from deformed steel bars.
In the second series of experiments, nine beams were tested in four-point
bending to examine the bond splitting behaviour of FRP single anchorages and splices.
CFRP bars develop higher bond splitting strength than respective GFRP bars, which
contradicts the findings of pullout tests. The lower elastic modulus of GFRP bars is
thought to play an important role to their lower bond splitting strength. For this reason,
the suitability of the cube tests for measuring the bond strength ofFRP bars for practical
purposes is questioned. Spliced bars appear to develop similar bond splitting strength to
single bar anchorages. The distribution of bond stresses along the anchorage length and
the effect of flexural cracks on the bond development were also examined. The thesis
also discuss other parameters that influence bond splitting such as transverse
reinforcement, concrete cover, and support action.
An analytical study was conducted to enhance further the understanding of the
bond behaviour of FRP bars. Both the pullout and beam tests were modelled by using
FE packages. Non-linear springs describing the bond behaviour of short embedment
lengths were chosen and used for predicting the behaviour of longer embedments. The
influence of flexural cracking was also considered in the case of beams. The analytical
results showed a good correlation with the respective experimental.
Finally, some important issues regarding the design of anchorage lengths for
FRP reinforcing bars were addressed and a method of working towards the formulation
of design recommendations is suggested.