Design of a column - Reinforced Concrete with FRP Bars: Mechanics and Design - page 346

The strength reduction factor is

( )

ε j, N1

2

−

f3 f

0.65 if 1.15 − ≤ 0.65

ε

fu

( ) ( )

ε j,N1

2

− ε j,N1

2

−

f3 f f3 f

1.15 − if 1.15 − ≥ 0.65 ∧ 1.15

ε ε

()

fu fu

φ j:

= 3

( )

ε j,N1

2

−

f3 f

− ≤ 0.75.

ε

fu

( )

ε j,N1

2

−

f3 f

0.75 if 1.15 − ≥ 0.75

ε

fu

The equations for computing the axial strength, the bending moment,
and the phi-factor are shown above, and are functions of the neutral axis
depth represented by the factor j.

9.5.4 Point 4—Balanced conditions
Neutral axis depth is

c 4 := c bal = 3.9·in.

ε cu = 0.003

c 4 = 3.9 in

ε fu = 0.01

Concrete compressive strain distribution is

ε

cu

ε (x): x

=

c4

c

4

The strain in FRP reinforcement is

ε ε

( ) ( ) () ()

cu cu

⋅ cdi if − ⋅ cdi − ≥− 1.05 ε

4 f 4 f fu

c c

()

ε

i:

4 4

=

f4

ε

( )

()

cu

0if ⋅ cdi − ≥ 0

4 f

c

4