ABSTRACT
This chapter deals with the confinement of reinforced concrete members under compression, such as columns, using fiber-reinforced plastics (FRP). In general, confinement acts to increase the compressive strength and ultimate compressive strain of concrete by creating a three-dimensional state of stress in the concrete. This increase in compressive strength and ultimate compressive strain of concrete leads to an increase in bending moment and rotational capacity of the concrete member under compression, which is of major importance for structures subjected to seismic action. In general, the increase in strength is much less significant than the increase in ductility. Recent earthquakes have shown again and again that many columns in existing buildings have insufficient transverse reinforcement leading to major damage of the columns or even collapse (Figure 16.1). The need to upgrade columns has become more and more evident (Priestley and Seible, 1995). Traditional external confinement techniques are steel jackets or hoops. However, steel yields at a tensile strain of only 0.002 and then exerts an almost constant confining pressure, whereas FRP shows an elastic behavior up to failure, usually at strains of more than 0.01. The confining action therefore increases continuously during loading. Furthermore, due to its lightweight, FRP is more convenient to apply and it is not prone to corrosion. In the last couple of years, the use of FRP to confine existing reinforced concrete columns has become increasingly popular for the reasons mentioned earlier. Experimental studies have shown, in fact, that the confinement of columns using FRP can be very efficient, especially for circular columns (Seible et al., 1997; Rochette and Labossière, 2000; Matthys et al., 2005; Gosh and Sheikh, 2007).
