This page explains how Clariti verifies anchor channels against tension failure modes according to EN 1992-4.
Overview
Four tension failure modes must be checked:
- Steel failure — Fracture of anchor or channel steel
- Concrete cone failure — Breakout of concrete cone
- Pullout failure — Anchor pulls out without cone formation
- Concrete splitting — Splitting of concrete member
Each mode has characteristic resistance (NRk) reduced by partial factors (γM) to give design resistance (NRd).
All verifications follow the same format:
Where:
- βN = Utilisation ratio (shown as percentage)
- Nᵃₑd = Design tension force on anchor (from force distribution)
- NRd = Design resistance for the failure mode
A utilisation ≤ 100% means the design is adequate for that failure mode.
Steel Failure — Anchor in Tension
This failure mode occurs when the tension load exceeds the tensile strength of the anchor shaft, causing it to fracture.
Equation
Parameters
| Symbol | Description | CPRO38 | CPRO50 | CPRO52 | Source |
|---|
| NRk,s,a | Characteristic tensile resistance of anchor | 27.1 kN | 42.4 kN | 71.7 kN | ETA Table C1 |
| γMs | Partial safety factor for steel | 1.85 | 1.85 | 1.85 | ETA Annex C1 |
Design Resistances
| Channel | NRk,s,a (kN) | γMs | NRd,s,a (kN) |
|---|
| CPRO38 | 27.1 | 1.85 | 14.6 |
| CPRO50 | 42.4 | 1.85 | 22.9 |
| CPRO52 | 71.7 | 1.85 | 38.8 |
Worked Example
Given: CPRO50 channel, anchor tension Nᵃₑd = 13.90 kN
Step 1: Look up characteristic resistance
- NRk,s,a = 42.4 kN (from ETA Table C1)
Step 2: Apply partial safety factor
NRd,s,a = 42.4 / 1.85 = 22.92 kN
βN = 13.90 / 22.92 = 0.61 = 61%
Steel Failure — Channel Connection
This mode checks the connection between anchor and channel (the weld or mechanical connection).
Equation
NRd,s,c = NRk,s,c / γMs,ca
Parameters
| Symbol | Description | CPRO38 | CPRO50 | CPRO52 | Source |
|---|
| NRk,s,c | Characteristic resistance of connection | 28 kN | 32 kN | 76 kN | ETA Table C1 |
| γMs,ca | Partial safety factor | 1.8 | 1.8 | 1.8 | ETA Annex C1 |
Steel Failure — Channel Bolt
The T-bolt connecting the load to the channel must also be verified.
Equation
Bolt Characteristic Resistances
| Bolt Size | CPRO38 | CPRO50 | CPRO52 | Source |
|---|
| M10 | 40.6 kN | — | — | ETA Table C7 |
| M12 | 45.7 kN | 59 kN | 59 kN | ETA Table C7 |
| M16 | 101.7 kN | 109.9 kN | 109.9 kN | ETA Table C7 |
| M20 | — | 145.2 kN | 145.2 kN | ETA Table C7 |
Concrete Cone Failure
Equation
NRd,c = N⁰Rk,c × (Ac,N / A⁰c,N) × ψs,N × ψre,N × ψec,N / γMc
Basic Resistance
N⁰Rk,c = k × √fck × hef^1.5
| Symbol | Description | Cracked | Uncracked | Source |
|---|
| k | Cracking factor | kcr,N | kucr,N | ETA Table C2 |
| Channel | kcr,N | kucr,N | hef (mm) |
|---|
| CPRO38 | 7.8 | 11.1 | 72 |
| CPRO50 | 8.1 | 11.6 | 99 |
| CPRO52 | 8.7 | 12.4 | 151 |
Area Ratio
The reference cone area assumes unlimited concrete:
Where scr,N = 3 × hef
The actual area Ac,N is reduced by:
- Proximity to edges
- Overlap with adjacent anchors
- Member thickness limitations
Reduction Factors
Edge distance factor:
ψs,N = 0.7 + 0.3 × (c / ccr,N) ≤ 1.0
ψre,N = 0.5 + hef/200 ≤ 1.0 (without supplementary reinforcement)
ψre,N = 1.0 (with supplementary reinforcement)
ψec,N = 1 / (1 + 2eN/scr,N) ≤ 1.0
Pullout Failure
Equation
NRd,p = NRk,p × ψc,p / γMp
Characteristic Resistances
| Channel | Cracked NRk,p (kN) | Uncracked NRk,p (kN) | Source |
|---|
| CPRO38 | 13.6 | 19.0 | ETA Table C2 |
| CPRO50 | 18.4 | 25.8 | ETA Table C2 |
| CPRO52 | 32.2 | 45.1 | ETA Table C2 |
Pullout resistance is product-specific and determined by testing. Clariti uses certified ETA values directly.
Concrete Splitting
When It Applies
Splitting must be checked when:
- Member thickness h < hmin (specified in ETA)
- Edge distance c < ccr,sp
- Spacing s < scr,sp
Minimum Member Thickness
| Channel | hmin (mm) | Source |
|---|
| CPRO38 | 100 | ETA Table B1 |
| CPRO50 | 130 | ETA Table B1 |
| CPRO52 | 185 | ETA Table B1 |
Equation
NRd,sp = N⁰Rk,c × (Ac,N/A⁰c,N)sp × ψs,N × ψre,N × ψec,N × ψh,sp / γMsp
ψh,sp = (h / hmin)^(2/3) ≤ 1.0
Safety Factors Summary
| Failure Mode | Symbol | Value | Source |
|---|
| Anchor steel failure | γMs | 1.85 | ETA Annex C1 |
| Anchor channel connection | γMs,ca | 1.8 | ETA Annex C1 |
| Channel lips | γMs,l | 1.8 | ETA Annex C1 |
| Tension bolt | γMs2 | 1.87 | ETA Annex C1 |
| Channel flexure | γMs,flex | 1.15 | ETA Annex C1 |
| Pullout | γMp | 1.5 | ETA Annex C2 |
| Splitting | γMsp | 1.5 | ETA Annex C2 |
| Concrete cone/blowout | γMc | 1.5 | ETA Annex C2 |
Governing Failure Mode
Clariti determines the governing mode automatically:
ηsteel = NEd / NRd,s
ηcone = NEd / NRd,c
ηpull = NEd / NRd,p
ηsplit = NEd / NRd,sp
Governing mode = max(ηsteel, ηcone, ηpull, ηsplit)
In Clariti
Clariti displays tension verification as:
- Summary — Overall tension utilisation and governing mode
- Breakdown — Each mode with its utilisation percentage
- Expanded view — Full calculation with all intermediate values
- ETA references — Source data for traceability
All factors and their values are shown with the equation that generated them, allowing full verification of the calculation. 
