This page explains how Clariti verifies anchor channels against shear failure modes according to EN 1992-4.
Overview
Three shear failure modes must be checked:
- Steel failure — Shear failure of anchor steel
- Concrete edge failure — Breakout toward a free edge
- Concrete pryout — Breakout on the back side of anchors
The governing mode depends on geometry, particularly edge distances and load direction.
Steel Failure in Shear
Equation
VRd,s = VRk,s / γMs
Where:
VRk,s = k₂ × As × fuk
| Symbol | Description | Source |
|---|
| k₂ | Reduction factor for shear | 0.6 (typical) |
| As | Stressed cross-section | ETA data |
| fuk | Ultimate steel strength | ETA data |
| γMs | Partial factor for steel | ETA (typically 1.0 for shear) |
Notes
- Shear steel resistance is typically lower than tension (k₂ = 0.6)
- Lever arm effects may further reduce capacity
- Product-specific values in ETA may differ
Lever Arm Effect
When shear acts with a lever arm (stand-off installation):
VRd,s = αM × VRk,s / γMs
Where:
αM = lever arm reduction factor
Concrete Edge Failure
When It Governs
Edge failure typically governs when:
- Shear acts toward a free edge
- Edge distance is less than ~10 × hef
- High shear loads relative to tension
Equation
VRd,c = V°Rk,c × (Ac,V / A°c,V) × ψs,V × ψh,V × ψec,V × ψα,V × ψre,V / γMc
Basic Resistance (V°Rk,c)
V°Rk,c = k₁ × dnom^α × √(lf/dnom) × √fck × c₁^1.5
Where:
k₁ = 1.7 (cracked) or 2.4 (uncracked)
dnom = nominal anchor diameter
lf = effective length under shear (≤ 8×dnom)
c₁ = edge distance in load direction
Reference Area (A°c,V)
A°c,V = 4.5 × c₁²
Actual area Ac,V reduced by:
- Member thickness limitations
- Spacing to adjacent anchors
- Corner effects (two edges)
Reduction Factors
Edge distance factor (ψs,V):
ψs,V = 0.7 + 0.3 × c₂/(1.5×c₁) ≤ 1.0
ψh,V = (1.5×c₁/h)^0.5 ≤ 1.0
ψec,V = 1/(1 + 2×eV/(3×c₁)) ≤ 1.0
ψα,V = √(1/(cos²αV + (sin²αV)/2.5)) ≤ 1.0
ψre,V = 1.0 (with edge reinforcement)
ψre,V = 0.7 (without edge reinforcement, narrow member)
Example Calculation
Given:
- c₁ = 150 mm (edge distance in load direction)
- c₂ = 200 mm (perpendicular edge)
- h = 300 mm (member thickness)
- fck = 30 MPa
- dnom = 10 mm, lf = 80 mm
- Cracked concrete
Calculate:
Reference area:
A°c,V = 4.5 × 150² = 101,250 mm²
Ac,V = Limited by geometry... (assume no reduction)
Ratio = 1.0
Edge factor (c₂ direction):
c₂/(1.5×c₁) = 200/(1.5×150) = 0.89
ψs,V = 0.7 + 0.3 × 0.89 = 0.97
Thickness factor:
1.5×c₁ = 225 mm < h = 300 mm
ψh,V = 1.0 (no reduction)
Basic resistance:
V°Rk,c = 1.7 × 10^0.5 × √(80/10) × √30 × 150^1.5
V°Rk,c = 1.7 × 3.16 × 2.83 × 5.48 × 1837
V°Rk,c = 153 kN
Design resistance:
VRd,c = 153 × 1.0 × 0.97 × 1.0 × 1.0 × 1.0 × 1.0 / 1.5
VRd,c = 99 kN
Edge failure is often the governing mode for shear toward edges. Always
check edge distances carefully and consider if reinforcement can be added.
Concrete Pryout Failure
When It Applies
Pryout governs for:
- Short, stiff anchors (hef < 60mm typically)
- Shear away from edges
- High concrete strength (concrete cone capacity is high)
Equation
VRd,cp = k × NRd,c
Where:
k = pryout factor
= 1.0 for hef < 60mm
= 2.0 for hef ≥ 60mm
NRd,c = concrete cone resistance (tension)
Logic
Pryout is related to concrete cone because the failure mechanism involves a concrete breakout on the opposite side from the shear load. The pryout factor k accounts for the different loading geometry.
Example
Given:
- hef = 50 mm
- NRd,c = 20 kN (from tension calculation)
Calculate:
k = 1.0 (since hef = 50 < 60mm)
VRd,cp = 1.0 × 20 = 20 kN
k = 2.0
VRd,cp = 2.0 × 20 = 40 kN
Pryout resistance doubles when embedment exceeds 60mm. This is a significant
threshold for anchor channel selection.
Shear Load Direction
The governing failure mode depends heavily on load direction:
| Direction | Likely Governing Mode |
|---|
| Toward near edge | Concrete edge failure |
| Away from edges | Pryout or steel |
| Parallel to edge | Steel (often), or edge if close |
| Oblique | Check all modes |
Governing Failure Mode
Utilization for each mode:
ηsteel = VEd / VRd,s
ηedge = VEd / VRd,c
ηpryout = VEd / VRd,cp
Governing mode = max(ηsteel, ηedge, ηpryout)
In Clariti
Shear verification displays:
- Load direction — Visual indicator of shear relative to edges
- Edge distances — All edge distances with critical values
- Mode breakdown — Each mode with utilization
- Governing indicator — Highlighted governing mode
- Expanded calculations — Full EN 1992-4 equations with values
The 3D view shows the shear vector and proximity to edges, helping you understand why certain modes govern. 
