AS 5216:2021: Combined Tension and Shear Interaction of Anchors

About this Anchor Tension and Shear Interaction Calculator

This calculator checks an anchor or group of anchors under combined tension and shear to AS 5216:2021 Section 8. It takes the utilisation ratios from the separate tension and shear checks and combines them twice: once for steel failure, and once for the concrete modes, by the power form of Eq. 8.2.1(1) or the linear form of Eq. 8.2.1(2).

• Structural engineer closes out an anchor design once the individual failure modes are done, with the governing steel and concrete ratios in one place.
• Design reviewer sees at a glance which interaction governs and whether the design relied on the power or linear form.
• Fixings specialist runs quick sensitivity checks on how much tension a connection can take for a given shear ratio.

The page is an engineering-grade CalcTree calculation with every step visible, and it sits at the end of the AS 5216 anchor checks as the final verification.

More info on Anchor Tension and Shear Interaction

Inputs

The four inputs are ratios of design action to design resistance from the separate checks of Clause 3.4.2 in tension and Clause 3.4.3 in shear. The steel ratios come from steel failure in tension and in shear, the shear one the larger of without and with a lever arm. The concrete tension ratio is the largest of the concrete modes in tension, and the concrete shear ratio the larger of pry-out and concrete edge failure. A selector chooses the concrete interaction form.

Steel failure interaction

For steel failure the tension and shear ratios combine as the sum of their squares, which must not exceed one.

Concrete failure interaction

For the concrete modes AS 5216:2021 gives two forms: a power form with exponent 1.5, Eq. 8.2.1(1), and a linear form, Eq. 8.2.1(2), which the page writes as a utilisation. By default the page applies both and keeps the lower utilisation; Power only or Linear only applies one form for a design that has to follow a stated one.

Scope

The page combines results; it does not compute them. Each failure mode must pass on its own as well. The seismic design situation and supplementary reinforcement designed to carry the tension or shear are not covered.

Common Calculation Errors to Avoid

• Using the steel shear ratio without a lever arm when the fixture has a stand-off understates the steel interaction. Take the larger of the two.
• Combining ratios from different load combinations gives an interaction that no real load case produces. All four ratios must come from the same combination.
• Taking the concrete ratio from one mode only can miss the governing case. Use the largest concrete tension mode and the larger of pry-out and edge failure.
• Entering percentages instead of decimals inflates the result. Enter each ratio as a decimal.
• Treating a passing interaction as the whole check overlooks the individual modes, which must each pass on their own.

FAQs

Why are steel and concrete checked separately?

Steel and concrete fail differently under combined load, so AS 5216:2021 Section 8 gives a different interaction for each. Steel uses the sum of the squared ratios, and the concrete modes use the power or linear form.

Which concrete form should I use?

By default the page applies both and keeps the lower utilisation. Choose Power only or Linear only where the design has to follow a stated form.

What if the anchors carry only tension?

Enter zero for the shear ratios. The interaction then reduces to the tension ratio, which must already pass on its own.

Can the steel and concrete ratios come from different anchors?

Yes. The steel ratios are those of the most highly loaded anchor, and the concrete ratios those of the governing concrete mode, which may be for a different anchor or group.

Does this apply to seismic design?

No. The seismic design situation is not covered by this page.