Bond between reinforcement and the adjoining concrete has been extensively studied, and it
is confirmed that the use of deformed bars is essential for composite behavior of reinforced
concrete (RC) structures. But since bond between the longitudinal bars and concrete results
in concentration of damage at a specific localized interval of longitudinal bars where the
local buckling occurs, Takiguchi et al. (1976) suggested mitigating this concentration of
damage through unbonding of the longitudinal bars from concrete at plastic hinge zone.
Kawashima et al. (2001) conducted an experimental study on RC columns reinforced with
different lengths of unbonded bars at the plastic hinge zone. It was noticed that the failure of
concrete was much less in the unbonded column than standard column, and strain on
unbonded bar was less than that on the reinforcement of standard column. Recently, to
improve the seismic performance of RC members, it is highlighted in the study of Pandey
and Mutsuyoshi (2005) that reducing bond strength between the longitudinal bars and
concrete has a favored effect on the failure mode, shear capacity and ductility of RC bridge
piers: failure mode at ultimate state is changed from shear to flexural and shear strength and
ductility are increased.
In the performance-based design approach, the design is primarily focused on meeting a
performance objective, which is in line with a desired level of service (Floren et al., 2001,
Priestley et al., 2007). For instance, new seismic design philosophies for bridges recommend
that important bridges subject to massive earthquakes should be able to sustain the expected
maximum lateral force in the inelastic stage with limited damages. To achieve this aim,
structure should realize the existence of post-yield stiffness, damage level should be limited,
and its permanent deformations (residual deformations) should be smaller than a specified
limit; and all these indices are essentially dependent on the composite behavior of RC
structures. On the other hand, the studies of Kawashima et al. (2001) & Pandey and
Mutsuyoshi (2005) revealed the importance of reducing concrete-to-steel bond to mitigate
the concentrated damage in the plastic hinge zone.
In the last two decades, civil engineers and designers have attempted to develop and adopt
new forms of materials that would assist in the building of stronger, larger, more longer