FRP Concrete Confinement

 Confinement of concrete is not a new concept but rather has been practiced for

many years. Confinement of concrete can be achieved by wrapping the concrete,

therefore providing resistance in the hoop direction of a concrete element in compression.

A concrete element loaded in compression in addition to the displacement in the direction

of the applied compression load it also displaces in the hoop direction (the direction that

is perpendicular to the applied load) due to the Poisson effect. If the concrete is

unconfined the expansion developed in the hoop direction will eventually result to the

failure of the concrete element. On the other hand, if a concrete element is confined, a

confining pressure develops which restrains the hoop direction expansion and therefore

prevents the failure of the concrete element until a different mode of failure occurs. This

has two primary effects on the behavior of the concrete element. First it increases the load

at which the concrete element fails and secondly increases the amount of displacement

required to produce failure. As a consequence of the second effect the concrete element

can dissipate higher amounts of energy, which makes it more ductile, compared with the

unconfined concrete element.

 Abdel-Fattah and Ahmad (1989) tested 3 x 9 in. (the unsupported length was 6 in.)

concrete cylindrical specimens confined by steel rings spaced at 0.5 in. with the cylinders

exhibiting highly ductile behavior. Mei et al. (2001) tested 4 x 8 in. cylinders with a steel

sleeve on the outside. Axial compressive load was applied only to the concrete core. The

improvement to the concrete properties was apparent with concrete properties further

improving with an increase to the thickness of the steel sleeve.

 When fiber reinforced polymer (FRP) materials became widely available in the

civil sector, they started replacing steel as external confinement reinforcement. One of the