AS 5216:2021: Pull-out Failure of Headed Anchors in Tension

About this AS 5216 Headed Anchor Pull-out Calculator

This calculator checks the design pull-out resistance of a cast-in headed anchor to AS 5216:2021 Clause 6.3.4, against the tension on the highest-loaded anchor. A headed anchor carries tension by bearing of its head on the concrete above it, and pull-out failure is that concrete crushing locally, so the anchor draws out before a concrete cone breaks away. The resistance is the bearing pressure the concrete can take times the bearing area of the head.

• Structural engineer. Checking headed studs and cast-in bolts in footings, plinths and embedded plates, where a small head can govern before the cone.
• Precast engineer. Choosing a head size or washer for lifting and connection inserts cast into panels.
• Detailer or shop drawing reviewer. Confirming that a nut and washer used as a head gives enough bearing area.

A section and plan of the head redraw with your inputs, showing the bearing pressure and the bearing area. It is an engineering-grade calculator on CalcTree that you can duplicate and link to the other AS 5216 checks.

More info on AS 5216 Headed Anchor Pull-out

Head bearing area

The bearing area A_h is the head less the shank. For a round head the page works it out from the head diameter and the shank diameter. For any other head, such as a hexagon head or a nut and washer, you enter the bearing area net of the shank directly.

Bearing factor and concrete condition

Clause 6.3.4 gives N_Rk,p as the bearing factor k2 times A_h times f′c. The bearing factor depends on whether the concrete is cracked or uncracked, and the page selects it from your concrete condition input.

Design check

The capacity factor φMp from Table 3.2.4, including any installation safety factor, gives the design resistance. It is checked against the tension on the highest-loaded anchor under Clause 3.4.2, with a utilisation and a pass or fail result.

Common Calculation Errors to Avoid

• Counting the shank in the bearing area. Only the annulus of the head outside the shank bears on the concrete. Using the full head area overstates the resistance.
• Assuming uncracked concrete. The bearing factor is higher for uncracked concrete. Use cracked unless the concrete is shown to stay uncracked under the design loads.
• A head that is too flexible. The equation assumes the head, or nut and washer, is stiff enough to spread the load over its whole bearing area. A thin washer may not.
• Stopping at pull-out. Steel failure, concrete cone failure, splitting and, near an edge, blow-out are separate checks that can govern a headed anchor.

FAQs

How does pull-out of a headed anchor differ from a mechanical anchor?

A headed anchor's pull-out resistance comes from an equation in AS 5216:2021 Clause 6.3.4, based on head bearing area and concrete strength. A post-installed mechanical anchor takes its pull-out resistance from its approval instead. CalcTree has a separate template for each.

Can I use a nut and washer as the head?

Yes. Choose an entered bearing area and give the area of the washer that bears on the concrete, net of the shank. The washer must be stiff enough to spread the load over that area.

Why does cracked concrete matter for headed anchor pull-out?

The bearing factor k2 is lower in cracked concrete, so the resistance falls. The page applies the factor that matches your concrete condition.

Which other checks does a cast-in headed anchor need?

Steel failure, concrete cone failure, splitting and, near an edge, blow-out are separate AS 5216:2021 checks. Impact, fatigue and seismic actions are not covered by this page.