a Mbrace (Wabo). b Tyfo (FyFe). c Replark (Mitsubishi).

a Mbrace (Wabo). b Tyfo (FyFe). c Replark (Mitsubishi).

system. Such applications are termed "bond-critical" applications. In the case of axial compressive strengthening where the role of the strengthening system is to confine the lateral expansion of the cracked concrete the interface bond is not as critical as long as the FRP strengthening system is in intimate contact with the concrete and is wrapped around the concrete continuously so as to provide a confining pressure with appropriate hoop stiffness and strength. Such applications are termed "contact-critical.'' It is important to note, however, that in either type of system the polymer resin still plays a critical role in the FRP composite in transferring load to the fibers and protecting the fibers. A poorly applied sheet or fabric having a low fiber volume fraction (<20%) and a relatively thick (uneven thickness) polymer layer with large void content (>3%) will not provide a durable FRP strengthening system even though the amount of fiber placed in the wrap may be according to design requirements.

Since most FRP strengthening systems depend on the curing of polymer adhesives or resins at ambient temperature in the field, the glass transition temperatures of these components maybe quite low (120 to 180°F). Since the effectiveness of the strengthening system depends to a great degree on the stiffness of the adhesive or resin used to bond the FRP composite, to the concrete, an FRP strengthening system can be severely degraded at even moderately high temperatures (~120°F). In certain cases where the fibers are sufficiently anchored away from the region subjected to the high temperature the FRP strengthening system may still be effective (Meier 1995). Designers should always be aware of the transition temperature of the FRP composite or adhesive they are using in a design. In the event of fire the integrity of an FRP strengthening system may be severely compromised in a short time. Test methods for FRP strips and sheets are provided in JSCE (2001) and ACI 440.3R-04 (2004).

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