Prefabricated FRP Jacketing
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Another category of the composite retrofit method can be called as prefabricated (procured or preformed) FRP jacketing system, where the FRP composites are formed prior to retrofitting a column. Two types of prefabricated E-glass Fiberglass pultruded profiles composite jacketing systems,shown in Figure 3, for retrofitting and repairing reinforced concrete columns were investigated at the University of Southern California (Xiao et al. 1997, 1999; Ma and Xiao 1999). The prefabricated FRP shells are made either continuously to form a multi-layer roll like coil or cut into individual single-layer cylindrical shells with a longitudinal slit. During retrofit of a column, the shells are opened and clamped around the column. Thixotropic, two-part, urethane adhesive is applied to bond the shells to the column surface and between the layers to form a jacket. The slits of the individual shells are staggered to avoid the concentration of weak seams. Nine half-scale bridge column models were tested in the studies, which validated the efficiency of the prefabricated jacketing systems and resulted in design methods. Recently, over 3,400 columns in the bridges of Yolo Causeway, west of Sacramento, California, were installed with the prefabricated jacketing (Xiao et al. 2000), as shown in Figure 4. To date, the project is perhaps the largest commercial application of FRP jacketing for seismic retrofit in North America.
Other types of prefabricated jacketing systems include half circles or boxes (Nanni and Norris 1995; Ohno et al. 1997). Teng and Lam (2002) discussed a CFRP jacketing, where the prefabricated shell is used as both forming
the additional concrete to alter the original rectangular columns into elliptical shape and then as jacket.