Introduction - Strengthening Design of Reinforced Concrete with FRP - page 2

strengthening and repair need to be implemented. One of the earliest techniques
for repair and strengthening of concrete members, dating back to the mid-1970s,
involved the use of epoxy-bonded external steel plates (Dussek 1980). However, in
the mid-1980s, durability studies revealed that corrosion of external steel plates is a
restrictive factor for widespread usage of this technique in external exposure (Van
Gemert and Van den Bosch 1985).
A revolutionary advancement in the technique of external strengthening
occurred when Meier replaced external steel plates with external carbon FRP
(CFRP) plates in 1987. FRP is resistant to corrosion and has high strength-to-
weight and high stiffness-to-weight ratios that provide efficient designs and ease
of construction. FRP also has excellent fatigue characteristics and is electro-
magnetically inert. Accordingly, it is a viable replacement to steel in external
strengthening applications. Since 1987, research in FRP strengthening tech-
niques has developed an extensive volume of literature proving the effective-
ness of the application. The ACI 440 Committee on Fiber Reinforced Polymer
Reinforcement has twice reported on state-of-the-art advancements (ACI 440R-
96; ACI 440R-07 2007). The same committee has produced two design docu-
ments for FRP externally bonded systems for strengthening applications (ACI
440.2R-02; ACI 440.2R-08 2008). The technology has matured to the point that it
can be introduced to the structural engineering curriculum through the develop-
ment of courses and textbooks.

1.3 BEHAVIOR OF STRENGTHENED REINFORCED
CONCRETE BEAMS IN FLEXURE
Shallow beams are typically strengthened in flexure by externally bonding FRP
plates or sheets on the tension face or soffit of the member, as shown in Figure 1.1.
The fibers are oriented along the beam axis in the state-of-the-art application.

FIGURE 1.1 Strengthening the soffit of inverted reinforced concrete beam with CFRP.