Home / Tools / ACI 318-19 Two-Way Slab (DDM) C · Concrete

ACI 318-19 Two-Way Flat Plate — Direct Design Method (§8.10)

Checks the Direct Design Method limits, computes the total static moment M_o, distributes it to end and interior spans (Table 8.10.4.2) and to column and middle strips (Tables 8.10.5.1–8.10.5.5), and sizes the strip reinforcement with the 0.0018A_g minimum.

Panel and slab

ℓ₁ (direction of analysis) ft

ℓ₂ (transverse) ft

Column c₁ in.

h in.

Average d in.

f′c psi

f_y psi

Superimposed dead psf

Live psf

Exterior edge

Edge beam β_t

DDM limits (8.10.2)

Spans in each direction

Successive span difference / longer

Column offset / span

Results

q_u · ℓ_n · DDM applicable—

M_o = q_uℓ₂ℓ_n²/8—

Column / middle strip width · s_max—

Location	M (kip-ft)	CS share	M_cs	M_ms	A_s,cs (in.²)	A_s,ms (in.²)

ACI 318-198.10.2 (limits), 8.10.3.2 (M_o), Table 8.10.4.2 and 8.10.4.1 (longitudinal distribution), Tables 8.10.5.1, 8.10.5.2, 8.10.5.5 (column strips), 8.10.6.1 (middle strips), 8.4.1.5 (strip width), 8.6.1.1 (A_s,min), 8.7.2.2 (spacing). Clause numbers only.

VerifiedStructurePoint two-way flat plate example (DDM): M_o, span and strip moments and column-strip steel reproduced to the example's rounding. The DDM coefficients have been unchanged since ACI 318-95.

Preliminary calculation tool. Final design requires the full text of ACI 318 and review by a licensed PE. This tool follows ACI 318-19, the edition referenced by the 2021 and 2024 IBC; ACI CODE-318-25 was published in January 2025 and is expected in the 2027 IBC (changes include development length equations and seismic provisions).