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Two-Way Slab — Direct Design Method

Minimum thickness, total static moment M0, span distribution (interior / exterior) and column-strip vs middle-strip moments per ACI 318 DDM.

Inputs

m (in design direction)
m (perpendicular)
mm
kPa
kPa
MPa
0 if no beams
Method & assumptions
  • wu = 1.2D + 1.6L (kPa).
  • M0 = wu·ℓ2·ℓn² / 8.
  • Interior span: 0.65 M0 negative @ supports, 0.35 M0 positive @ midspan.
  • Exterior span (no edge beam): exterior neg = 0.26, positive = 0.52, interior neg = 0.70 of M0.
  • Column strip width = 0.25·min(ℓ1,ℓ2) on each side of column line. Strip distribution per ACI Table.
  • Min thickness h: per ACI 318 Table 8.3.1.1, dependent on fy and ratios.

Results (per design direction strip)

Min thickness hmin (≈)
Factored Load wu
Total Static Moment M0
Column Strip Width
Middle Strip Width

Moment Distribution

SectionTotal (kN·m)Col. StripMid Strip