contra-flexure and the diameter of the longitudinal reinforcing steel. The experimental

average plastic hinge length was found to be equal to approximately one half the diameter

or depth of pile section. Watson and Park (1994) performed similar tests on reinforced

concrete columns and used the same empirical equation proposed by Priestly and Park

(1987) for estimating the length of the plastic hinge.

 Budek et al. (2000) proposed an empirical expression for estimating the length of

the plastic hinge which was derived based on tests conducted on bridge drilled-shaft

reinforced concrete piles. The plastic hinge length in that expression was a function of the

pile/column diameter and the above grade height of the pile or column. The California

Department of Transportation also provides equations for the estimation of plastic hinge

lengths for use in the design of structures undergoing dynamic loading such as seismic

(Caltrans 2004(b)). For columns and type II shafts Caltrans requires using an empirical

equation based on the length of the column or shaft and the yield strength and the size of

the longitudinal steel reinforcement. For type one pile shafts/columns Caltrans requires

using a different empirical equation that is based on the diameter or the least dimension

of the pile shaft and the length of the pile shaft/column from the point of maximum

moment to the point of contra-flexure.

 Conclusions

 Based on the information obtained from the literature review of previous research

the following conclusions can be drawn:

* Testing has shown that when the CFRP composites are used as flexural reinforcement
 the elements generally behave in a non-ductile manner.

* Confinement of concrete using FRP wraps or jackets improves concrete ductility and
 strength. It was found that if enough FRP reinforcement is used to confine concrete its
 strength can be improved up to 150% and its ductility up to a factor of ten.