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

​
Why Interaction Matters

When tension and shear act together, the anchor capacity is reduced compared to either load acting alone: 
Individual capacities:
  Tension only:  NRd = 20 kN
  Shear only:    VRd = 15 kN

Under combined loading:
  If NEd = 10 kN and VEd = 10 kN
  Are we safe? We need to check interaction.
Even though 10 kN < 20 kN (tension OK) and 10 kN < 15 kN (shear OK), the combined effect may exceed capacity.

​
Interaction Equations

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

​
Steel Failure Interaction

For steel failure (ductile mode): 
(NEd/NRd,s)² + (VEd/VRd,s)² ≤ 1.0
This is a circular interaction — the most generous form.

​
Concrete Failure Interaction

For concrete failure modes (cone, edge, pryout): 
(NEd/NRd)^α + (VEd/VRd)^α ≤ 1.0

Where:
  α = 1.5 for anchor channels (EN 1992-4)

​
Linear Interaction (Conservative)

For simplified checking: 
NEd/NRd + VEd/VRd ≤ 1.2
This is the most conservative approach and always acceptable.

​
Interaction Diagrams

The interaction equations define curves (or surfaces) in N-V space: 
        N/NRd
          │
     1.0 ─┼─────────╮ ← Circular (α=2, steel)
          │          ╲
          │           ╲
          │            ╲ ← α=1.5 (concrete)
          │             ╲
          │              ╲ ← Linear (α=1)
          │               ╲
     0.0 ─┼────────────────┼─── V/VRd
          0              1.0
Points inside the curve: Design is adequate Points on the curve: Utilization = 100% Points outside: Design fails

​
Which Mode to Check

Interaction must be checked for the governing failure modes in each direction:
Tension ModeShear ModeCheck Interaction
Concrete coneConcrete edgeYes (α = 1.5)
SteelSteelYes (α = 2)
Concrete conePryoutYes (α = 1.5)
PulloutSteelYes (mixed)
For mixed modes (e.g., concrete in tension, steel in shear), Clariti uses the more conservative interaction.

​
Calculation Process

Clariti performs interaction checks as follows: 
1. Calculate all tension utilizations
   ηN,steel = NEd / NRd,s
   ηN,cone  = NEd / NRd,c
   ηN,pull  = NEd / NRd,p
   etc.

2. Calculate all shear utilizations
   ηV,steel = VEd / VRd,s
   ηV,edge  = VEd / VRd,c
   ηV,pry   = VEd / VRd,cp

3. Find governing modes
   ηN,gov = max(ηN,steel, ηN,cone, ηN,pull, ...)
   ηV,gov = max(ηV,steel, ηV,edge, ηV,pry)

4. Check interaction for governing combination
   ηcombined = ηN,gov^α + ηV,gov^α

5. Also check other critical combinations
   (e.g., steel-steel, cone-edge)

​
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): 
Tension utilization:
  ηN = 12/20 = 0.60

Shear utilization:
  ηV = 8/15 = 0.53

Combined utilization:
  ηcombined = 0.60^1.5 + 0.53^1.5
  ηcombined = 0.465 + 0.386
  ηcombined = 0.85 ≤ 1.0 ✓
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.

​
Special Cases

​
Tension-Only Connections

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

​
Shear-Only Connections

If NEd = 0: 
ηcombined = 0 + ηV^α = ηV^α
Similarly, shear-only connections use the direct shear utilization.

​
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.

​
Multiple Load Cases

Real connections may have multiple load combinations:
Load CaseNEdVEd
LC1: Dead + Live10 kN5 kN
LC2: Dead + Wind15 kN12 kN
LC3: Dead + Seismic8 kN18 kN
Clariti checks interaction for each load case independently: 
LC1: ηcombined = 0.50^1.5 + 0.33^1.5 = 0.54
LC2: ηcombined = 0.75^1.5 + 0.80^1.5 = 1.37 ✗ FAILS
LC3: ηcombined = 0.40^1.5 + 1.20^1.5 = 1.57 ✗ FAILS
LC2 and LC3 fail — a larger channel or additional anchors needed.

​
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.

​
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)