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Most real-world connections experience both tension and shear simultaneously. This page explains how Clariti checks the interaction between these load components.

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Why Interaction Matters

When tension and shear act together, the anchor capacity is reduced compared to either load acting alone:
Even though 10 kN < 20 kN (tension OK) and 10 kN < 15 kN (shear OK), the combined effect may exceed capacity.

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Interaction Equations

EN 1992-4 provides interaction equations depending on the failure mode being checked.

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Steel Failure Interaction

For steel failure (ductile mode):
This is a circular interaction — the most generous form.

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Concrete Failure Interaction

For concrete failure modes (cone, edge, pryout):

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Linear Interaction (Conservative)

For simplified checking:
This is the most conservative approach and always acceptable.

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Interaction Diagrams

The interaction equations define curves (or surfaces) in N-V space:
Points inside the curve: Design is adequate Points on the curve: Utilization = 100% Points outside: Design fails

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Which Mode to Check

Interaction must be checked for the governing failure modes in each direction: For mixed modes (e.g., concrete in tension, steel in shear), Clariti uses the more conservative interaction.

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Calculation Process

Clariti performs interaction checks as follows:

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Example Calculation

Given:
  • NEd = 12 kN
  • VEd = 8 kN
  • NRd,c = 20 kN (concrete cone governs tension)
  • VRd,c = 15 kN (concrete edge governs shear)
Check interaction (α = 1.5):
Design is adequate with 85% combined utilization.
Even if individual utilizations are moderate (60%, 53%), the combined utilization can approach limits (85%). Always check interaction for combined loading cases.

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Special Cases

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Tension-Only Connections

If VEd = 0:
For α = 1.5, this gives slightly lower utilization than the tension-only check. Clariti uses the governing (higher) value.

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Shear-Only Connections

If NEd = 0:
Similarly, shear-only connections use the direct shear utilization.

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Compression + Shear

When the axial load is compressive (toward concrete):
  • No tension failure modes apply
  • Compression improves shear capacity (friction)
  • Clariti may credit friction per EN 1992-4
Friction credit requires verification that compression is permanent and reliable. Conservative practice is to ignore friction benefit.

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Multiple Load Cases

Real connections may have multiple load combinations: Clariti checks interaction for each load case independently:
LC2 and LC3 fail — a larger channel or additional anchors needed.

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In Clariti

Combined loading verification displays:
  1. Interaction diagram — Visual plot showing design point
  2. Combined utilization — Overall pass/fail with percentage
  3. Component breakdown — N and V contributions
  4. Governing combination — Which mode pairing controls
  5. Load case comparison — Table showing all cases
The interaction diagram updates in real-time as you adjust loads or select different products, helping you find adequate solutions quickly.

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Key Takeaways

  • Always check interaction under combined loading
  • α = 1.5 for concrete modes, α = 2 for steel modes
  • Combined utilization can be high even with moderate individual utilizations
  • Check all load cases — different cases may govern
  • Compression can improve shear capacity via friction (use with caution)