Check anchor steel failure in shear with a lever arm to AS 5216:2021 Clause 7.2.2.3, with restraint and tension reduction. Open the template.
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About this AS 5216 Steel Shear with Lever Arm Calculator
This calculator checks the design steel resistance in shear of an anchor that bends across a stand-off, to AS 5216:2021 Clause 7.2.2.3 with the lever arm of Clause 4.2.2 and the verification of Clause 3.4.3. Where a fixture sits on a grout layer or levelling nuts, the shear acts some distance above the concrete, so the anchor works as a short beam and fails in bending well below its plain shear resistance.
- Structural engineer. Designing column base plates on levelling nuts or a grout pad, where the stand-off controls the anchor size.
- Facade or balustrade engineer. Checking post and bracket fixings that stand off a slab edge or wall on shims or packers.
- Checking engineer. Testing how sensitive the result is to the restraint assumption and the tension on the same anchor.
An elevation redraws with your inputs, showing the shear line, the lever arm down to the point of fixity and the bent shape of the anchor. It is an engineering-grade calculator on CalcTree that you can duplicate and adapt.
More info on AS 5216 Steel Shear with Lever Arm
Lever arm and restraint
Clause 4.2.2 sets the lever arm l_a from the shear line at mid-thickness of the fixture down to a point of fixity a_3 below the concrete surface, so it adds the stand-off e_b, half the fixture thickness and a_3, which depends on the anchor diameter. The restraint factor α_M reflects whether the fixture can rotate: a free fixture bends the anchor as a cantilever, while a restrained one bends it in double curvature and doubles the resistance.
Bending resistance reduced by tension
Eq. 7.2.2.3(2) reduces the approval's characteristic bending resistance M⁰_Rk,s by the ratio of the tension on the same anchor to its design steel resistance in tension. Where the tension alone uses up the steel, nothing is left for bending and the check fails.
Shear resistance and design check
Eq. 7.2.2.3(1) gives V_Rk,s,M as α_M times M_Rk,s divided by l_a. The capacity factor φMs from Table 3.2.4 or the approval gives the design resistance, checked against the design shear on the anchor under Clause 3.4.3, with a utilisation and a pass or fail result.
Common Calculation Errors to Avoid
- Assuming restraint without justification. The restrained case needs a fixture that genuinely cannot rotate, such as a nut tightened down on a stiff base plate held against rotation. When in doubt, take the fixture as not restrained.
- Measuring the lever arm to the concrete surface. The lever arm runs from mid-thickness of the fixture to a point of fixity below the surface, not just across the stand-off.
- Using the group's highest tension. The tension reduction uses the tension on the same anchor as the shear, the one with the highest shear utilisation, which may not be the anchor with the most tension.
- Applying a lever arm where none exists. A fixture bearing on the concrete, or on a bedding thin enough to treat as none, should be checked without lever arm.
- Forgetting a nut and washer at the surface. The point of fixity below the surface assumes the anchor is not clamped to the concrete by its own nut and washer.
Engineering templates
Common calculators
Design guides
FAQs
When is a lever arm needed in anchor shear design?
When the shear acts above the concrete surface, typically because the fixture stands off on a grout layer or levelling nuts. The anchor then bends, and AS 5216:2021 Clause 7.2.2.3 replaces the plain shear resistance with a bending-based one.
What is the restraint factor α_M?
It reflects the rotational restraint of the anchor at the fixture. A fixture free to rotate bends the anchor as a cantilever; a fixture restrained against rotation bends it in double curvature, which doubles the shear resistance for the same bending capacity.
Why does tension reduce the shear resistance here?
Tension on the anchor uses up part of its steel, so less is available for bending. Eq. 7.2.2.3(2) reduces the bending resistance in proportion to the tension on the same anchor.
Where do M⁰_Rk,s and the capacity factors come from?
From the anchor's approval for its size and steel. The page asks for capacity factors for steel failure in both tension and shear, since both are used.
Does this replace the tension and interaction checks?
No. Steel failure in tension, pry-out, concrete edge failure and the interaction of tension and shear are separate AS 5216:2021 checks.
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