Concrete · Slabs & post-tensioning

Two-way slab calculator

Moments in both directions for a rectangular slab simply supported on four edges.

Standard: AS 3600 Cl 9 · Grashof–Rankine strips

Inputs in the worked example

The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.

Diagram for the worked example

Strips share load by equal mid-span deflection: wx = w r⁴/(1 + r⁴), wy = w/(1 + r⁴), r = Ly/Lx
Mx = wx Lx²/8 = 18.5; My = wy Ly²/8 = 8.24 kNm/m
dx = D − c − db/2 = 149 mm; dy = dx − db = 137 mm
Conservative for slabs with held-down corners or continuity (AS 3600 Table 6.10.3.2 coefficients give lower moments).

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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.