Flexural Strengthening of Beams and Slabs - Strengthening Design of Reinforced Concrete with FRP - page 98

350 mm 350 mm

600 mm

600 mm

10 mm

40 mm

FIGURE 5.10 Example 5.7 showing the alternative FRP design details.

A =ρ×= bd 125.23 mm

2

f f

A
nt

125.23
20.17

f
f

b == × = 368.32 mm > 350 mm

f

20.17 × × +× = 350 b 0.17 125.23

f

b = 36.7mm 0mm ≈

f
Either wrap the two layers 10 mm up the sides or add a 40-mm partial layer to the
soffit, as shown in Figure 5.10.
The effective depth of the wrapped CFRP layers in the second alternative is

600.17 ××+× ××

×

350 0.34 2 595 10 0.34

d f = = 599.89 ≈ 600 mm O.K.

350 0.34 + ×× 2100.34

5.4.2 b rittle C ruShing oF C onCrete
This is the failure mode in which concrete reaches the limit of useful compressive
strain of 0.003 before yielding of tension reinforcement (i.e., ε s < ε y ). It is not a desir-
able failure mode because it does not involve a warning sign at failure. Therefore,
ACI 440.2R-08 reduces the ϕ factor to 0.65 to make this failure mode less likely to
occur. It is not an anticipated failure mode, but it is allowed by ACI 440.2R-08. This
section will show that this failure mode, which is admissible for a heavily reinforced,
heavily strengthened section, is not practical to consider.

5.4.2.1 Flexural Strengthening of a Singly Reinforced Section
Strain compatibility:

dc
c

ε= 0.003

(5.34)

s

dc
c

−

f

ε= 0.003 −ε ≤ε

(5.35) fe bi fd