What this calculator does
A mechanical anchor rarely fails by pulling its own steel out. It fails by tearing a cone of concrete out of the slab — and then the bar’s own tensile strength caps what you actually have. Both limits are calculated here, because an anchor sized on concrete pull-out alone is silently limited by its steel.
How to use it
- Enter the anchor diameter and its effective embedment depth.
- Enter the concrete cone bond stress and cone-area factor for your concrete and edge condition — this tool has no code table and picks no value.
- Enter the anchor steel area, yield strength and the partial safety factor you are designing to.
- Read the governing failure: if the steel governs, a deeper hole will not help you; a bigger bar will.
Governing formula
N_concrete = c · π · d · L · k Where:
-
c= Concrete cone bond stress, N/mm² -
d= Anchor diameter, mm -
L= Effective embedment depth, mm -
k= Cone area factor
Derived Equations:
N_steel = A_s · f_y / γ_M0 N_design = min(N_concrete, N_steel) Worked example — 16 mm bar, 100 mm embedment, moderate bond
The figures below were produced by running this page's own engine with the example inputs (Anchor diameter (mm), Effective embedment depth (mm), Concrete cone bond stress (N/mm²), Cone area factor (–), Anchor steel area (mm²), Steel yield strength (N/mm²), Partial safety factor (steel) (–), Number of anchors (no)). If the calculator returns something different for the same numbers, that is a bug, not a rounding difference.
| Design capacity per anchor | 22619 N |
|---|---|
| Governing failure mode | concrete cone |
| Concrete cone capacity | 22619 N |
| Steel tension capacity | 87391 N |
| Total for the number entered | 22619 N |
| Concrete ÷ steel ratio | 0.26 – |
| What this means | The concrete cone governs at 22.6 kN per anchor, so increasing the embedment depth will raise the capacity. The steel has 87.4 kN available as spare. |
- The cone surface is π × 16 × 100 × 3 ≈ 15,080 mm².
- At 1.5 N/mm² that gives about 22.6 kN of concrete pull-out.
- The steel gives 201 × 500 / 1.15 ≈ 87.4 kN, far more.
- The concrete cone governs, so a deeper embedment would raise the capacity.
Assumptions & limitations
Engineering calculation. Concrete cone pull-out and steel tension checked separately, with the weaker failure mode reported so the limit is explicit.
- The concrete cone bond stress and cone-area factor are YOUR inputs. They depend on concrete strength, cracking, edge distance and install condition; this tool holds no code table and selects no value.
- No code clause, edge-distance reduction, spacing reduction, group effect or load eccentricity is applied. A group of anchors is simply multiplied up, which is NOT a group capacity.
- Static tension only. Dynamic, seismic, sustained and sustained-plus-cyclic loading are not assessed, and dynamic anchors typically need a lower design resistance.
- The default bond stress and factor are illustrative example values, not code or manufacturer data. Confirm them against your concrete and your anchor’s test data before using a capacity.
This tool supports professional engineering work; it does not replace a sealed design. Confirm every result against the applicable standard and a licensed engineer before it is built.
References & standards
- BS EN 1992-4 and ACI 318 — anchorage and concrete breakout provisions, as the framework behind the two failure modes.