Design of a T-beam - Reinforced Concrete with FRP Bars: Mechanics and Design - page 266

7.6.2 Case 2—Midspan
Following the same approach discussed for Case 1, the minimum reinforce-
ment ratio required for bending can be selected. Because this section is at
midspan, a T-section is considered. The effective reinforcement depth is

−− φ

f_bar

d:hc =⋅ 26 in.f2

= f2 c

2

The gross-sectional area is

A c2 := t slab ·b eff + b w ·(d f2 - t slab ) = 764·in. 2

The longitudinal reinforcement ratio required for bending is

M 1

A

u2

ρ : ⋅ = 0.00419

=

f_ − req_bend2

− β

1

c2

0.65 f ⋅ ⋅ d 2 ⋅ 0.15d

fu f2 f2

The minimum reinforcement ratio is computed per Equation (8-8) of ACI
440.1R-06:

4.9fpsi
f

⋅

′ ⋅

bd, 300psi
f

( )

c

2

A: min ⋅ bd ⋅ = 1.706 in ⋅

=

f_min2 w f2 w f2

fu fu

A
A

f_min2

ρ : = 0.002233

=

f_min2

c2

The design reinforcement ratio required for bending is taken as

ρ f_bend2 := max(ρ freq_bend2 , ρ f_kmin2 ) = 0.004189

Reinforcement ratio required for creep-rupture stress check: For the case
of GFRP reinforcement, the limitation to the creep-rupture stress could be
governing for the design. The bending moment to consider for the creep-
rupture stress check is obtained for the combination DL + 0.20 LL, as
shown:

w .20w
w

+

D LPos

M: M ⋅ = 143.8ftkip ⋅ ⋅

= 2_creep0 s2

SPos

The limit stress is

f ff_creep = 12.8·ksi