Foundation Design

Punching shear check — Isolated Footing & Raft Foundation · ACI 318-25 · EC2 · IS 456:2000

Input Parameters

ACI 318-25 · kN-m
Foundation Type
Raft foundation: design shear Vu entered directly. Drop panel and edge/corner columns supported.
Slab Properties
mm
MPa
mm
mm
d = h − cv − db = 505 mm
Column
mm
mm
Loading
kN
kN·m
kN·m
Shear Reinforcement (optional)
Drop Panel (optional)
📋
Enter values and click Calculate.

Input Parameters

EN 1992-1-1 · kN-m
Foundation Type
Raft foundation: design shear VEd entered directly. Drop panel and edge/corner columns supported.
Slab Properties
m
MPa
m
m
d = h − cv − db = 0.530 m
%
%
Column
m
m
Loading
kN
kN·m
kN·m
Shear Reinforcement (optional)
Drop Panel (optional)
📋
Enter values and click Calculate.

Input Parameters

IS 456:2000 · kN-m
Foundation Type
Raft foundation: design shear Vu entered directly. Drop panel and edge/corner columns supported.
Slab Properties
mm
N/mm²
mm
mm
d = h − cv − db = 505 mm
Column
mm
mm
Loading
kN
Shear Reinforcement (optional)
Drop Panel (optional)
📋
Enter values and click Calculate.

📚 Design Background & Code References

Punching Shear in Foundations

A column punching through its foundation creates a truncated cone (pyramid) failure surface. The critical check is whether the shear stress on the perimeter of this cone — the critical perimeter — exceeds the concrete's capacity. Two foundation types are handled differently:

Isolated Footing

The upward soil reaction partially counteracts the column load within the critical perimeter area. The effective punching force is reduced:

Net Punching Force — All Codes
Vu,net = Pu − qu × Acrit
qu = Pu / (B × L)   [uniform upward pressure for concentric loading]
Acrit = area enclosed by critical perimeter (interior rect.: (c1+d)×(c2+d))
B × L = footing plan area. The net force can be significantly smaller than the column load — a key difference from slab punching.

Raft Foundation

For mat/raft slabs, the punching check is structurally equivalent to a flat slab. The design shear Vu is taken as the total factored column reaction (net of self-weight where accounted for in analysis). Drop panels may be used to locally increase the slab depth at columns and reduce the demand-to-capacity ratio.

Critical Perimeter

Location by Code
ACI 318-25 / IS 456:   d/2 from column face (rectangular outline for rect. columns)
EC2 §6.4.2:   2d from column face (rounded corners, radius = 2d)
For EC2 isolated footings, if the distance from column face to footing edge a < 2d (stocky footing), the control perimeter may be taken at a < 2d and the capacity is enhanced by the factor 2d/a (§6.4.4).

ACI 318-25 §13.4.4 Footing Punching — Governing Section

Footing two-way shear is governed by ACI §13.4.4, which references §22.6 for the capacity formulas. The critical section is at d/2 from the column face. The net upward pressure within the critical area is subtracted from the column load.

Net Punching Force — §13.4.4.1
Vu,net = Pu − qu × (c1+d)(c2+d)   [interior rectangular column]

ACI 318-25 §22.6.5.2 Shear Capacity — vc

The concrete shear capacity is the minimum of three expressions. Note: the size effect factor λs that applies to one-way shear (§22.5.5.1) does not apply to two-way (punching) shear for footings.

Three-Equation Approach (SI, MPa, mm)
vc1 = 0.17 · (1 + 2/β) · λ · √f'c
vc2 = 0.083 · (αs·d/bo + 2) · λ · √f'c
vc3 = 0.33 · λ · √f'c
vc = min(vc1, vc2, vc3)  ·  φVn = φ · vc · bo · d,   φ = 0.75
β = long/short column dimension; αs = 40 (interior), 30 (edge), 20 (corner); λ = 1.0 (normal-weight)

EC2 §6.4.4 Column Bases — Key Differences from Slabs

Net Applied Shear — §6.4.4(3)
VEd,red = VEd − ΔVEd   where   ΔVEd = qEd × Aenc
Aenc = c1c2 + 4d(c1+c2) + 4πd²   [interior rect., at 2d]
vEd = β · VEd,red / (u1 · d)
Stocky Footing Enhancement — §6.4.4(2)
If a < 2d:   vRd,c,enh = vRd,c × (2d / a)
a = distance from column face to footing edge (shortest direction)
At a = 2d the factor = 1.0, recovering the standard formula. For very stocky footings (small a), capacity increases significantly.
vRd,c — Same Formula as Slabs (§6.4.4 refs §6.4.2)
vRd,c = CRd,c · k · (100 ρl fck)1/3 ≥ vmin
k = 1 + √(200/d) ≤ 2.0  ·  CRd,c = 0.18/γc  ·  vmin = 0.035 k3/2 √fck

IS 456:2000 Cl 34.2.4 Two-Way Shear in Footings

Cl 34.2.4 explicitly states the net shear force for footing punching: the shear to be resisted is the net total upward force in the area outside the critical section (i.e., the column load minus the upward pressure within the critical perimeter).

Net Force — Cl 34.2.4
Vnet = Pu − qu × (c1+d)(c2+d)   [interior rectangular column]
τv = Vnet / (bo × d)  ·  bo at d/2 from column face
Permissible Shear — Cl 31.6.2
τc = 0.25 √fck   [N/mm²]
ks = min(0.5 + βc, 1.0)   where βc = short/long column dimension
Permissible: τv ≤ ks · τc

References

  • [1]
    ACI 318-25 — Building Code Requirements for Structural Concrete. American Concrete Institute, 2025. §13.4.4 (Footing two-way shear), §22.6 (Two-way shear strength), §26.5 (Spread footings).
  • [2]
    EN 1992-1-1:2004 — Eurocode 2: Design of Concrete Structures. CEN, Brussels. §6.4.4 (Column bases / punching in footings), §6.4.2 (Punching shear — slabs).
  • [3]
    IS 456:2000 — Plain and Reinforced Concrete — Code of Practice, 4th Rev. Bureau of Indian Standards, New Delhi. Cl 31.6 (Punching shear — flat slabs), Cl 34.2.4 (Two-way shear in footings).
  • [4]
    Wight, J.K. & MacGregor, J.G. — Reinforced Concrete: Mechanics and Design, 7th Ed. Pearson, 2016. Chapter 15 (Footings), §15-6 (Two-way shear in footings).
  • [5]
    Mosley, W.H., Bungey, J.H. & Hulse, R. — Reinforced Concrete Design to Eurocode 2, 7th Ed. Palgrave Macmillan, 2012. Chapter 11 (Foundations), §11.3 (Punching shear).
  • [6]
    Pillai, S.U. & Menon, D. — Reinforced Concrete Design, 3rd Ed. Tata McGraw-Hill, 2009. Chapter 14 (Footings), §14.8 (Two-way shear).
Disclaimer: For educational and preliminary design only. Verify all results with a licensed structural engineer.