Design of a two-way slab - Reinforced Concrete with FRP Bars: Mechanics and Design - page 324

“OK” if ww
“Not good”otherwise

≤

lim

Check_Crack1:=

Check_Crack1 = “OK”

8.9 STEP 7—CHECK DEFLECTIONS

Maximum long-term midspan deflection is checked. The maximum allow-
able deflection is l/480.
The gross moment of inertia is

( ⋅

3

1ftt
12

slab

4

I:= = 512 in ⋅

g

The cracking moment is

2f ⋅ I

ct g

M = =5.657 kipft ⋅ ⋅

cr

t

slab

The cracking moment per unit width is

2f ⋅ I kipft

ft

⋅

ct g

m = =5.657 ⋅

cr

slab (

)

t ⋅ 12in

Because the service bending moments are smaller than the cracking
moment, the section remains uncracked and the gross moment of inertia
may be used to calculate the deflections.
From the finite element analysis the following results can be obtained:

Δ DL := 0.10 in. Delection due to dead

loads only

Δ LL := 0.09 in. Delection due to live loads

only

ξ := 2 Multiplier for time-

dependent deflection at
5 years (ACI 318-11)

λ := 0.60ξ = 1.2 Reduction parameter,

Equation (8-14b) of ACI
440.1R-06

Δ LT := Δ LL + λ·(Δ DL + 0.20·Δ LL ) = 0.232·in. Long-term deflection

1
480 =0.6in

1

∆ := ⋅ . Deflection limit

limit