The use of FRP (fiber reinforced polymer) in concrete structures
is becoming increasingly popular. FRP has two major applications:
(1) shear strengthening and provision of confinement to improve
the seismic performance of concrete columns and beam-columns
[1–3]; and (2) repair and retrofitting to restore or even increase
the strength capacity of concrete members in old buildings [4–6].
Among the various applications, the provision of FRP confinement
to the potential plastic hinge zones in concrete columns can substantially
increase both the strength and ductility of the concrete
columns, and is thus particularly useful. Hence, the effectiveness
of FRP confinement has been an active research topic for many
years. However, the behavior of FRP confined concrete is still not
fully understood and there are still no comprehensive design
guidelines for the provision of FRP confinement.
To study the axial stress–strain behavior of FRP confined concrete,
a large number of FRP confined concrete columns have been
tested for evaluating the effects of using various types of FRP [7–9],
the FRP confining stiffness [10–12], the FRP fiber orientation
[13,14], and the concrete strength [15–18]. Since the confining
stress and lateral strain in the concrete are inter-related and both
would vary with the axial strain during application of loading, test