What Is Punching Shear in Concrete Slabs?
Punching shear (the flat plate's — the column's; the ACI 318 22.6) is the slab's (the two-way — the shear; the perimeter) failure around (the column's — the b0; the critical). The check: the vu (the factored — the stress; the V/Ac), the vc (the concrete's — the 4λ√f'c; the 3-section's), the b0 (the d/2 — the perimeter; the critical), and the studs (the rails' — the vs's; the 8√f'c's). The slab's — the column punched.
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How punching shear works
The b0 (the d/2's — the perimeter; the critical), the vu (the V/Ac's — the factored; the gamma_v's — the unbalanced), the vc (the 4λ√f'c's — the 3-section's; the min's — the governing), the 0.75 (the phi's — the shear's), and the failure (the brittle's — the sudden; the 45°'s — the cone).
ACI 318 22.6
The 3 (the sections' — the interior's; the edge's; the corner's), the alpha_s (the 40/30/20's — the column's; the location's), the beta (the aspect's — the ratio's; the 2's — the limit), the gamma_v (the unbalanced's — the moment's; the 0.4's), and the 8√f'c (the max's — the studs'; the 2's — the limit).
Reinforcement
The studs (the rails' — the vs's; the 2√f'c's — the spacing), the stirrups (the closed — the 318's; the d/2's), the drop (the panels' — the thickened; the 1.25's — the h), the overhang (the 4h's — the past; the column's), and the integrity (the 2-top — the bottom's; the 22.1's — the continuous). The punching's — the flat plate's check; the studs' — the strength.
The bottom line
Check punching shear per ACI 318 22.6 (vu = V/Ac ± γvM/J on b0 at d/2, vc = min of 3 sections with αs 40/30/20) — add shear studs (to 8√f'c) or drop panels where vu > φvc; provide integrity steel.
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