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

About this AS 5216 Pull-out Failure Calculator

This calculator checks the design pull-out resistance of a post-installed mechanical anchor to AS 5216:2021 Clause 6.2.4, against the tension on the highest-loaded anchor. Pull-out is the anchor being drawn out of its hole, by slip of the expansion or undercut mechanism, before the concrete around it breaks out. The approval gives the pull-out resistance at a reference concrete strength, and the page scales it to the actual strength.

• Structural engineer. Checking expansion or undercut anchors for a bracket or base plate, where the product's pull-out value often governs over the concrete cone.
• Site or remediation engineer. Assessing anchors in existing concrete of a different strength from the approval's reference, with the strength factor applied consistently.
• Product specifier. Comparing mechanical anchors on their approval data for cracked and uncracked concrete.

All approval inputs are kept visible next to the result, which makes the check easy to review. It is an engineering-grade calculator on CalcTree, ready to duplicate into a project.

More info on AS 5216 Pull-out Failure

Inputs

You enter the characteristic pull-out resistance N_Rk,p exactly as the approval tabulates it at its reference strength, the concrete strength exponent from the approval, f′c, the capacity factor φMp and the design tension on the highest-loaded anchor. N_Rk,p, the exponent and φMp should all be for the concrete condition, cracked or uncracked, that the design assumes.

Concrete strength factor

AS 5216:2021 gives no equation for N_Rk,p. The approval supplies it, along with the adjustment for concrete strength. The page computes ψc as the ratio of f′c to the approval's reference strength raised to the approval's exponent, and multiplies the approval value by it to get the resistance at the actual strength.

Design check

The capacity factor φMp from Table 3.2.4 or the approval, 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

• Applying the strength factor twice. Enter the approval's value at its reference strength, not one already adjusted for f′c. The page applies ψc itself.
• Extrapolating ψc. The strength factor is only valid within the range of concrete strengths the approval covers.
• Using uncracked values by default. Take N_Rk,p for cracked concrete unless the concrete is shown to stay uncracked under the design loads.
• Using this for bonded anchors. Bonded anchors fail by combined pull-out and concrete failure, which is a different check.
• Installing outside the approval. The resistance assumes embedment, edge distance, spacing and member thickness at or above the approval's minimums.

FAQs

What is pull-out failure of a mechanical anchor?

The anchor slips out of its hole because the expansion or undercut mechanism lets go, before the concrete around it forms a cone. It is a product-specific failure mode, so the resistance always comes from the anchor's approval.

Why does the page scale the approval value?

Approvals tabulate N_Rk,p at a reference concrete strength. The strength factor ψc, with the exponent from the same approval, adjusts it to the actual f′c. Where the approval gives no increase with strength, the exponent is zero and the value is used unchanged.

Is this check for headed cast-in anchors?

No. This page is for post-installed mechanical anchors. Cast-in headed anchors have their own pull-out equation in AS 5216:2021 and a separate CalcTree template.

Does the page cover seismic or fatigue loading?

No. Seismic and fatigue actions need the reduced resistances the approval gives for them. Steel failure, concrete cone failure and splitting are also separate checks.