Punching Shear Checker (ACI 318-19)

How the check works

The critical section is taken at d/2 from the column faces (22.6.4.1): four sides for an interior column, three for an edge column and two for a corner column. The factored shear stress combines direct shear Vu/(bo·d) with the part of the unbalanced moment transferred by eccentric shear, γv·Mu·c/Jc, in both directions (8.4.4.2.3). γv = 1 − γf, with γf = 1/(1 + (2/3)√(b1/b2)). The concrete capacity is the least of the three expressions in Table 22.6.5.2, multiplied by the new size-effect factor λs.

ACI 318-19 changes

• Size effect: λs = √(2/(1 + 0.004d)) ≤ 1 reduces vc for slabs with d over about 250 mm.
• Minimum slab steel (8.6.1.2): where vuv > φ0.17λsλ√f′c, provide As,min = 5·vuv·bslab·bo/(φ·αs·fy) over a width bslab = c2 + 3h.
• Stirrups: λs may be taken as 1.0 when Av/s ≥ 0.17√f′c·bo/fyt (22.6.6.2).

Worked example

Interior 500 × 500 column, 250 mm slab (d = 210 mm), f′c 35 MPa, Vu = 650 kN, Mu1 = 60 kN·m, Mu2 = 30 kN·m. b1 = b2 = 710 mm, bo = 2840 mm, so vuv = 650 000/(2840 × 210) = 1.090 MPa. With γv = 0.40 and Jc = 5.12 × 10¹⁰ mm⁴, the moment terms add 0.166 + 0.083 MPa, giving vu = 1.340 MPa. λs = 1.0 (d < 250 mm), vc = 0.33√35 = 1.952 MPa, φvc = 1.464 MPa ≥ 1.340 MPa: OK without shear reinforcement (92% used).

Limits

• Rectangular columns, no openings near the column and no drop panels or capitals.
• Prestressed slabs (22.6.5.5) and headed shear studs are not covered.
• The stress is checked at the critical corner using the larger distance c for each direction (conservative for edge and corner columns).

FAQ