Introduction - Strengthening Design of Reinforced Concrete with FRP - page 4

concentration at the plate or sheet tip. Once cracking starts at an angle, it
changes to a horizontal crack parallel to steel reinforcement at the level of
primary steel because the steel stirrups inside the beam arrest the inclined
crack. The FRP and the entire concrete cover delaminates (e.g., Arduini,
Tommaso, and Nanni [1997], Beam A3 and A4).

4. Plate or sheet debonding along the interface plane due to the intermedi-
ate crack mechanism typically after yielding of primary steel reinforce-
ment when the flexural cracks widen. The horizontal crack occurs along
the adhesive layer or parallel to it within the concrete cover. This failure
mode is especially applicable to beams with end U-wrap anchorage, thus
delaying failure in item 3 (e.g., Arduini, Tommaso, and Nanni [1997],
Beam B3).

5. Concrete crushing failure for over-reinforced beams or cover delamination
failure in beams with short FRP plates prior to primary steel yielding (e.g.,
Fanning and Kelly [2001], Beam F10).

Shallow beams may also be strengthened with near-surface-mounted (NSM)
bars. This strengthening reinforcement is typically made of FRP bars or FRP tape
inserted in near-surface cut grooves and then sealed with resin adhesive that fills the
groove surrounding the bar or tape, as shown in Figure 1.3 (Rasheed et al. 2010).
FRP in this application behaves similarly to externally bonded FRP plates and
sheets. However, failure modes are typically limited to

1. FRP rupture after yielding of primary steel.

2. Concrete crushing after yielding of primary steel.

3. Concrete crushing before yielding of primary steel

CFRP strips (1
per groove)

CFRP stirrups
(1 layer)

16 in.

CFRP strips (2
per groove) 2
in. c/c

NSM stainless
steel (3 # 4
bars)

2.5 in. each

2 in.

(a) (b)

FIGURE 1.3 Strengthening identical beams with (a) CFRP tape and (b) NSM bars.