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b
0.85
f
c
´
ε
cu
ε
f
(0)= 0
ε
f
(1)= 0
h
ε
f
(2)= 0
ε
f
(3)= 0
Figure 9.5
Pure compression.
b
ε
cu
0.85
f
c
´
ε
f
(0)= 0
σ
c
(
x
)
ε
f
(1)= 0
0.8c
c = h
ε
f
(2)= 0
ε
f
(3)= 0
Figure 9.6
Neutral axis at the lowest level of fibers.
contribution of the FRP reinforcement is still null because the section is
fully compressed.
The combined nominal axial and moment capacities, P
n
and M
nx
, for
β
1
= 0.8 are
P
=
0.85
f
′
bc
(0.8 )
n
c
(9.4)
Mf bc
h
=
0.85
′
(0.8 )
⋅
−
0.4
c
nx
c
2
Condition 3: neutral axis depth h ≥ c ≥ c
bal
.
The cross-section failure
is controlled by concrete crushing when the neutral axis depth is situ-
ated below the balanced location (c ≥ c
bal
), which can be computed as
follows:
ε
ε+ε
cu
c
=
d
(
N
−
)
(9.5)
bal
f
f
cu
fd
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