Two-Way (Punching) Shear at Interior Column
Two-way (punching) shear check at an interior rectangular column supporting a flat slab or footing per ACI 318-19 Section 22.6, under concentric load (no unbalanced-moment transfer). Locates the critical section at d/2 from the column face, computes the concrete two-way shear strength as the governing minimum of the three Section 22.6.5.2 expressions, applies the two-way size-effect factor λs, and compares the factored punching demand against the design strength. Fully customizable.
What this calculates
Average effective depth (d), critical perimeter (bo) and critical-section shear area at d/2, column aspect ratio (βc), size-effect factor λs = √(2/(1+d/10)) ≤ 1, the three Section 22.6.5.2 stress terms governed by βc, αs, and the basic 4·√f'c term, the nominal two-way shear stress (vc) and strength (Vc), the design strength (φVc, φ = 0.75), and the punching demand-to-capacity ratio (Vu/φVc).
Inputs
Column side in one direction
Column side in the other direction
Overall slab (or footing) depth
Clear cover to flexural reinforcement (ACI 20.5.1.3)
Slab flexural bar (sets effective depth)
Specified compressive strength of concrete
Net factored shear transferred to the column
40 interior / 30 edge / 20 corner (ACI §22.6.5.3)
Outputs
Average effective depth of the two reinforcement directions
Critical-section perimeter at d/2 from the column
Two-way size-effect factor √(2/(1+d/10)) ≤ 1
Design two-way shear strength with φ = 0.75
Punching demand-to-capacity ratio — must be ≤ 1.0
Methodology
Per ACI 318-19 Section 22.6 (two-way shear, strength design). The critical perimeter bo = 2(c1 + d) + 2(c2 + d) is taken at d/2 from the column face per Section 22.6.4.1. The concrete two-way shear stress vc is the minimum of: 4·λ·λs·√f'c, (2 + 4/βc)·λ·λs·√f'c, and (2 + αs·d/bo)·λ·λs·√f'c per Section 22.6.5.2, where βc is the column aspect ratio and αs = 40 for interior columns (Section 22.6.5.3). The size-effect factor λs (Section 22.5.5.1.3) reduces vc for thick members — a code change the legacy three-term form omits. φ = 0.75 for shear (Section 21.2.1). Excludes moment transfer, shear studs, and edge/corner columns.
Code References
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