Introduction - Reinforced Concrete with FRP Bars: Mechanics and Design - page 3

but hollow and other shapes are available. Bars cannot be bent after resin
curing: Bends must be incorporated during manufacturing. A bar surface
deformation or texture, such as wound fibers, sand coatings, and sepa-
rately formed deformations, is induced so that mechanical bonding is devel-
oped between FRP rebars and concrete. The longitudinal tensile strength
of FRP rebars is bar size dependent [11] due to a phenomenon known as
“shear-lag.” The lower cost-to-performance advantage of glass over carbon
fibers makes glass FRP (GFRP) rebars preferable in conventional concrete
members. However, for special requirements, carbon FRP (CFRP) rebars
may be the ideal choice.
Internal FRP reinforcements are also available in multidimensional
shapes [10] with the most common being prefabricated, orthogonal, two-
dimensional grids. Multidimensional FRP reinforcements can also be fab-
ricated on-site by hand placement and tying of one-dimensional shapes [9].
To minimize uncertainty in their performance and specification, several
standards development organizations have developed consensus-based test
methods for the characterization of the short- and long-term mechani-
cal, thermomechanical, and durability properties of FRP reinforcements.
The recommended test methods are based on the knowledge gained from
research results and literature worldwide. The first document that intro-
duced test methods for FRP rebars was “Recommendation for Design and
Construction of Concrete Structures Using Continuous Fiber Reinforcing
Materials,” which was published in 1997 by the Japan Society for Civil
Engineering (JSCE) [12]. ASTM International and the Organization for
Standards (ISO) offer standardized test methods related to the use of FRP
composites in structural engineering. Model test methods for FRP bars
are recommended by the American Concrete Institute (ACI) in document
440.3R, “Guide Test Methods for Fiber-Reinforced Polymers (FRPs) for
Reinforcing or Strengthening Concrete and Masonry Structures” [13],
effective since 2004. Testing procedures have also been developed by the
Canadian Standards Association (CSA).
1.3 FRP REINFORCED CONCRETE
Over the past two decades, laboratory tests have demonstrated that FRP
bars can be used successfully and practically as internal reinforcement in
concrete structures. The role of industry/university cooperative research
became key in transferring the use of internal FRP reinforcement for con-
crete from the laboratory to the field. To date, reinforcing bars made of FRP
have gained acceptance as internal reinforcement in concrete structures.
The mechanical behavior of FRP rebars differs from the behavior of
conventional steel rebars. FRP composites are anisotropic, linear, and
elastic until failure and are characterized by high tensile strength only in