Design of a two-way slab - Reinforced Concrete with FRP Bars: Mechanics and Design - page 323

8.8 STEP 6—CHECK CRACK WIDTH

Crack width is checked using Equation (8-9) of ACI 440.1R-06. A crack
width limit, w lim , of 0.028 in. is used for interior exposure, while 0.020
in. is used for exterior exposure. The middle strip interior support is
considered.
Ratio of modulus of elasticity of bars to modulus of elasticity of concrete is

n f = 1.399

Ratio of depth of neutral axis to reinforcement depth, calculated per
Equation (8-12), is

k f = 0.122

Tensile stress in GFRP under service loads is

m
Amin d,d1 k
3

sMax

f: = = 21.928 ksi ⋅

fs

( )

f

⋅ ⋅ −

f f1f

2

Ratio of distance from neutral axis to extreme tension fiber to distance
from neutral axis to center of tensile reinforcement is

( )

t kmind ,d
mind ,d

−⋅

slab f f1f2

β :=

1k =1.263

( ) ( )

11

⋅ −

f1 f2 f

Thickness of concrete cover measured from extreme tension fiber to cen-
ter of bar is

d c := t slab - min(d f1 ,d f2 ) = 1.5·in.

Bond factor (provided by the manufacturer) is

K b := 0.9

The crack width under service loads is

2

2 f
E

s

fs 2 f_ts

w: = β ⋅ kd+ ⋅ =0.025 in Equation (8-9)ofACI 440.1R-06 ⋅

11 b c

2

f

The crack width limit for the selected exposure is

w lim = 0.028·in.