How does ideCAD control two-way slab design limits according to ACI 318-19?
The minimum slab thickness is controlled and reported automatically according to Table 220.127.116.11 for flat slabs.
The minimum slab thickness is controlled and reported automatically according to Table 18.104.22.168 for beam-to-slabs.
For nonprestressed slabs not satisfying 8.3.1, immediate and time-dependent deflection is calculated according to 24.2 and is not exceed the limits in 24.2.
h = overall thickness, height, or depth of member, in.
ln = length of clear span measured face-to-face of supports, in.
fy = specified yield strength for nonprestressed reinforcement, psi
αfm = average value of αf for all beams on edges of a panel
Minimum slab thickness
There are two different slab thickness limits according to flat slab and beam-to-slab.
Flat slab thickness limit
For nonprestressed flat slabs having a maximum ratio of long-to-short span of 2, overall slab thickness h is not less than the limits in Table 22.214.171.124 and is at least the value in a and b if the calculated deflection limits of 8.3.2 are not provided:
a) Slabs without drop panels = 5 in.
b) Slabs with drop panels = 4 in.
Note: Deflection is determined with a reduced modulus of rupture fr= 5√f’c for fy exceeding 80 000 psi.
Without drop panels
With drop panels
Beam-to-slab thickness limit
For nonprestressed beam-to-slabs, overall slab thickness h provides the limits in Table 126.96.36.199 if the calculated deflection limits of 8.3.2 are not provided.
Minimum h, in
Calculated deflection limits
According to 8.3.2, immediate and time-dependent deflections are determined in accordance with 24.2. Deflections should not exceed the limits in 24.2.2 for nonprestressed slabs not provided 8.3.1, nonprestressed slabs without interior beams spanning between the supports on all sides and having a ratio of long-to-short span exceeding 2.0, and prestressed slabs.
Reinforcement strain limit in nonprestressed slabs
It’s automatically designed according to Strength Reduction Factors per ACI 318-19 with ideCAD.