Work out the seismic design resistance of an anchor failure mode for AS 5216:2021, with alpha_eq, alpha_gap and the DLS displacement reduction. Try it.
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About this Seismic Design Resistance of Anchors Calculator
This calculator works out the design resistance of an anchor or group of anchors in one failure mode for the seismic design situation, for a design to AS 5216:2021. The characteristic resistance of the mode is reduced by the seismic reduction factor α_eq and, in shear, by the hole clearance factor α_gap, then reduced again where the approval's displacement at the damage limitation state exceeds the one the design allows, and checked against the seismic design action.
- Structural engineer checks anchors for plant, services and non-structural elements in the seismic design situation, mode by mode.
- Seismic restraint designer compares single-anchor and group fixings and sees how the hole clearance and the displacement limit cut the resistance.
- Design checker confirms that each seismic resistance used in a report traces back to the approval data and the stated factors.
It is an engineering-grade CalcTree calculation, and repeating it for each failure mode gives a clear, auditable record of the seismic anchor design.
More info on Seismic Design Resistance of Anchors
Failure modes and anchors resisting
A dropdown selects the failure mode: steel in tension, pull-out, bond, concrete cone, splitting, steel in shear, pry-out or concrete edge. A second selects whether one anchor or two or more resist the action. Together they set the seismic reduction factor α_eq from a table on the page, and decide whether α_gap and the pull-out concrete strength factor ψc,eq apply.
Seismic resistance
The seismic characteristic resistance is the mode's characteristic resistance times α_gap and α_eq. The design resistance applies the capacity factor of the mode and, for pull-out, ψc,eq. For steel and pull-out the input is the approval's seismic value, for bond the resistance with the seismic bond strength, and for the concrete modes the ordinary characteristic resistance.
Displacement reduction
Where the approval's displacement at the damage limitation state exceeds the displacement the design allows, the design resistance is reduced in proportion. The reduction never raises the resistance. Tension displacements apply to the tension modes and shear displacements to the shear modes.
Scope and assumptions
The anchor must be qualified for seismic use in its approval, in the performance category the design requires. The page is for elastic design, where the anchors resist the seismic actions directly. The α_eq values follow EN 1992-4 Annex C and should be confirmed against the approval. Capacity design, blow-out, steel failure with a lever arm and combined tension and shear in the seismic situation are not covered.
Common Calculation Errors to Avoid
- Using static product data instead of the approval's seismic values for steel, pull-out and bond overstates the resistance.
- Applying α_gap to a tension mode is wrong. The hole clearance factor allows for the hammer effect under cyclic shear and applies to the shear modes only.
- Counting the wrong anchors sets the wrong α_eq. Count only the anchors that resist the action in the mode being checked.
- Leaving out the displacement reduction where the approval's damage limitation displacement exceeds the design limit gives a resistance the connection cannot deliver at that displacement.
- Checking only one mode misses the governing one. Repeat the check for every mode the static design covers.
Engineering templates
Common calculators
Design guides
FAQs
What is α_gap?
It is the hole clearance factor from the approval. It allows for the hammer effect of the gap between an anchor and its fixture hole under cyclic shear. A gap filled with mortar or a filling washer may allow a higher value where the approval says so.
Why does α_eq depend on the number of anchors?
The table of seismic reduction factors on the page gives separate values for one anchor and for two or more anchors resisting the action. For most modes the group value is the lower, so counting the resisting anchors correctly matters.
What displacement values should I enter?
Enter the displacement the design allows at the damage limitation state and the approval's displacement for the same state. Where the design sets no limit, enter the approval's value in both and no reduction applies.
Does this page check every failure mode at once?
No. It checks one mode at a time. Run it for each mode the static design checks, using the seismic action for that mode.
Is capacity design covered?
No. The page is for elastic design, where the anchors resist the seismic design actions directly. Capacity design sets the actions differently.
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