Design of a two-way slab - Reinforced Concrete with FRP Bars: Mechanics and Design - page 306

8.3.2 Concrete properties
The following concrete properties are considered for the design:

f ′ c := 5000 psi Compressive strength

ε cu := 0.003 Ultimate compressive strain

145 1bf
ft 3

ρ=

:

Density

1.5

⋅

ρ
⋅

Compressive modulus of elasticity

0.5 c

E: 33 psi = f ′

c c

− 3

1bf ft

E c = 4074·ksi Computed as indicated in ACI 318-11

0.5

f: 7.5psi = ⋅ f ′ Concrete tensile strength

ct c

f ct = 530·psi Computed as indicated in ACI 318-11

The stress-block factor, β 1 , is computed as indicated in ACI 318-11:

0.85 if f ′ = 4000 psi

c

f
1000 psi

′

c

β= : 1.05 −⋅ 0.05 if 4000 psi<f ′ < 8000 psi =0.8

1 c

0.65 otherwise

8.3.3 Analytical approximations of
concrete compressive stress-strain
curve—Todeschini's model
Compressive strain at peak:

1.71 f
E

⋅ ′

c

ε= : =0.0021

c0

c

Compressive stress at peak:

f"
psi

c

σ= ": 0.9 ⋅

c