Flat Plate / Slab Calculator, ACI 318-19

What it checks

The module designs the two-way punching shear capacity of flat plate or flat slab members at interior, edge, or corner columns. It applies the strength design method per ACI 318-19 §22.6, evaluating the critical section located at d/2 from the column face. The sequence of checks begins with determining the governing concrete shear strength Vc, followed by the calculation of the punching shear demand ratio.

Inputs

Geometry - Column location (interior, edge, or corner), column dimensions c1 and c2 (in), slab overall thickness h (in), and clear spans ln1 and ln2 (ft).
Material - Concrete compressive strength f'c (psi) and lightweight concrete factor λ (1.0 for normal weight, 0.85 for sand-lightweight, 0.75 for all-lightweight).
Reinforcement - Concrete cover to bottom reinforcement (in) and estimated bar diameter for effective depth calculation (in).
Loads - Factored shear Vu (kips) from tributary load and factored unbalanced moment Muv (kip·ft) for interior column moment transfer.

What it reports

Governing Vc - The minimum of the three concrete shear strength expressions from §22.6.5.2a, b, and c, reported in kips.
Design Shear Strength - The product of the strength reduction factor φ (0.75) and the governing Vc, reported in kips.
Punching DCR - The ratio of factored shear Vu to the design shear strength φVc, indicating the demand-to-capacity ratio.
Average Shear Stress - The average shear stress vu at the critical section, reported in psi.
Moment Transfer Stress - The additional shear stress due to unbalanced moment Muv, reported in psi for interior columns only.
Combined DCR - The demand-to-capacity ratio including the effects of moment transfer, reported for interior columns.
Minimum Thickness - The minimum slab thickness h_min per Table 8.3.1.1 for slabs without beams, reported in inches.
Thickness Verdict - A boolean indicator confirming whether the input slab thickness meets the minimum thickness requirement and is at least 5.0 inches.

Code references

The engine cites ACI 318-19 §22.6 for two-way punching shear calculations. It references §22.6.5.2a, §22.6.5.2b, and §22.6.5.2c for the concrete shear strength expressions, and §21.2.1 for the strength reduction factor. The minimum slab thickness check follows Table 8.3.1.1 for slabs without beams.

Limits

The module assumes the slab is without beams for the minimum thickness check. The unbalanced moment input is used only for the interior column moment-transfer stress check and is ignored for edge or corner columns. The module does not calculate the required area of shear reinforcement such as stud rails or shearheads; it only reports the demand and capacity to determine if such reinforcement is necessary. Results are engineering aids; the engineer of record is responsible for the design.

This module ships in the desktop app

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