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How to use the punching shear calculator

A flat slab round a column: what each input means, how to read the face and control perimeter checks, and when the engine designs punching links.

All guides Inputs Result Calc sheet Walk-through Mistakes

1. What the calculator does

The punching shear calculator checks a flat slab around a column for punching. It checks the shear at the column face against the maximum, then at the control perimeters away from the face, and if the concrete alone is not enough it designs the punching links in rings round the column. It takes interior, edge and corner columns, rectangular or circular, with drop panels, openings near the column and an unbalanced moment.

The code routes are SANS 10100, BS 8110, Eurocode 2 (EN 1992-1-1) and SANS 51992-1-1 (SA Eurocode, 2023 draft annex). The badge says it plainly: on SANS and BS the perimeters are at 1.5d per BS 8110 cl. 3.7.7 with the STATIX v_c; on Eurocode 2 they follow EN 1992-1-1 cl. 6.4.

Punching shear calculator header with the PASS badge — The header: PASS, with shear reinforcement governing, and the route badge naming the clauses.

2. The inputs, group by group

Input	What it means	Typical value
Code	The design code; it sets the perimeters and the v_c formula.	SANS 10100
Column	Shape, size c_x × c_y and position: interior, edge or corner.	400 × 400, interior
Slab	Overall depth h and cover to the outer bars; the engine works out d.	h 250, cover 25
Loads (ULS)	The factored column reaction V_Ed and, for the refined method, the unbalanced moment.	V 800 kN
β factor	The eccentricity factor: a code preset for the column position, or refined from the moment.	code preset
Materials	Concrete f_cu and link steel f_yv.	30 MPa, 450 MPa
Reinforcement	Top bars each way over the column; they set the steel ratio and so v_c.	Y16 @ 125 both ways

Punching shear inputs: code, column, slab, loads, materials and reinforcement — The inputs. The top bars over the column count: more steel, higher v_c.

3. How to read the result

The design result card lists the steps in order: effective depth d, the steel ratio ρ_l, the β factor, the stress at the column face against the maximum, the control perimeter u₁ and the stress there against v_c. If v exceeds v_c, the engine gives the shear reinforcement area and a layout suggestion (number of legs, rings and spacing).

Design checks summary and the design result card — Design result: d = 209 mm, face 2.75 / 4.11 MPa, u₁ = 4108 mm, v / v_c = 1.07 / 0.61 MPa, so links are needed: 20 × Y10 legs in 4 rings.

Read the face check first: if v₀ exceeds v_max, no links will help; the slab must get thicker, the column bigger or the concrete stronger. Then read u₁: the summary “3 pass · 2 need links” tells you the slab works only with the links designed. The badge names the governing check; anything the engine could not run shows as NOT CHECKED.

Column and slab sketch with the paid detail drawing note — The column and slab sketch. The full detail drawings are part of the paid plan.

4. Calc sheet and schedule

The result (pass / fail and utilisation) stays free for everyone. Every check with its clause, the calc sheet and the bending schedule are open to signed-in users. Sign in free: 3 designs a month (one calculator, open for 24 hours). Unlimited with a calculator pack.

The punching links have their own bending schedule. The card reads: “Sign in (free) to get the bending schedule of the punching links: 3 designs a month”, with CSV on a paid plan.

Bending schedule card for the punching links — The bending schedule card for the punching links.

Bending schedule panel to SANS 282 with project fields — The schedule panel (SANS 282) with the project fields that print on the schedule and the calc sheet.

5. A 2-minute walk-through

Open the calculator: a 400 × 400 interior column on a 250 mm slab with V_Ed 800 kN and Y16 @ 125 top bars.
Read the result: the face passes, but v at u₁ (1.07 MPa) is above v_c (0.61 MPa), so links are needed.
Change the slab to 300 mm and see whether the links go away.
Set the position to edge, then corner: β goes up and so does the stress.
Switch the code to Eurocode 2 and compare the perimeter at 2d.

6. Common mistakes

Interior position for an edge column. Edge and corner columns carry a bigger β and a shorter perimeter; the check is much harder.
Reaction without the slab self-weight. V_Ed is the factored column reaction from all the load on the slab, including its own weight.
Bottom bars as the top steel. The steel ratio for punching comes from the top bars over the column.
Openings ignored. An opening within a few slab depths of the column cuts the perimeter; enter it under More inputs.
Mixing routes. The SANS / BS perimeters and the Eurocode perimeters are at different distances; do not mix the numbers.

8. Learn more

Try it nowThe calculator opens with the walk-through inputs above. The result is free; sign in for the checks, calc sheet and schedule.
Open the punching shear calculator

A guide to using the calculator, not a design. Check every value against the current code and your own project, and have the design checked and signed by a registered professional engineer.

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