Load combinations determine the design loads (NEd, VEd) that Clariti uses for verification. This page explains how loads are combined according to Eurocode principles.
Load Combination Framework
EN 1990 defines how actions (loads) are combined for structural design. These combinations produce the design loads input to Clariti.
Ultimate Limit State (ULS)
The primary design verification:
Ed = γG·Gk + γQ·Qk,1 + Σ(γQ·ψ0,i·Qk,i)
Where:
Gk = characteristic permanent action
Qk,1 = dominant variable action
Qk,i = other variable actions
γG = partial factor for permanent (1.35)
γQ = partial factor for variable (1.5)
ψ0 = combination factor
Serviceability Limit State (SLS)
For deflection and durability checks:
Characteristic: Ed = Gk + Qk,1 + Σ(ψ0,i·Qk,i)
Frequent: Ed = Gk + ψ1,1·Qk,1 + Σ(ψ2,i·Qk,i)
Quasi-permanent: Ed = Gk + Σ(ψ2,i·Qk,i)
Common Load Cases
Dead Load (G)
Permanent, constant loads:
- Self-weight of structure
- Fixed equipment
- Permanent fixtures
Factor: γG = 1.35 (unfavorable) or 1.0 (favorable)
Live Load (Q)
Variable loads from occupancy:
| Category | Example | ψ0 | ψ1 | ψ2 |
|---|
| A (Domestic) | Residential | 0.7 | 0.5 | 0.3 |
| B (Office) | Commercial | 0.7 | 0.5 | 0.3 |
| C (Assembly) | Public spaces | 0.7 | 0.7 | 0.6 |
| D (Retail) | Shops | 0.7 | 0.7 | 0.6 |
Wind Load (W)
Variable environmental load:
| Parameter | Value |
|---|
| ψ0 | 0.6 |
| ψ1 | 0.2 |
| ψ2 | 0.0 |
Snow Load (S)
Variable environmental load (altitude dependent):
| Altitude | ψ0 | ψ1 | ψ2 |
|---|
| < 1000m | 0.5 | 0.2 | 0.0 |
| > 1000m | 0.7 | 0.5 | 0.2 |
Temperature (T)
Thermal actions:
| Parameter | Value |
|---|
| ψ0 | 0.6 |
| ψ1 | 0.5 |
| ψ2 | 0.0 |
ULS Combination Equations
Equation 6.10 (General)
Ed = 1.35·Gk + 1.5·Qk,1 + 1.5·Σ(ψ0,i·Qk,i)
Equations 6.10a and 6.10b (Alternative)
Some National Annexes use:
6.10a: Ed = 1.35·Gk + 1.5·ψ0·Qk,1 + 1.5·Σ(ψ0,i·Qk,i)
6.10b: Ed = ξ·1.35·Gk + 1.5·Qk,1 + 1.5·Σ(ψ0,i·Qk,i)
Where ξ = 0.85 (typical)
Check your National Annex for which approach applies. Clariti accepts
factored design loads regardless of the combination method used.
Worked Example
Facade bracket supporting a cladding panel:
| Action | Vertical (Tension) | Horizontal (Shear) |
|---|
| Dead load Gk | 8 kN | 0 kN |
| Wind Wk | 0 kN | 12 kN |
| Live Qk | 2 kN | 0 kN |
Combination 1: Dead + Wind (Primary)
NEd = 1.35 × 8 + 1.5 × 0.7 × 2 = 12.9 kN
VEd = 1.5 × 12 = 18.0 kN
Combination 2: Dead + Live (Primary)
NEd = 1.35 × 8 + 1.5 × 2 = 13.8 kN
VEd = 1.5 × 0.6 × 12 = 10.8 kN
Design Loads
Both combinations should be checked. The governing combination may differ depending on which failure mode controls.
Load Direction Considerations
Tension vs. Compression
- Tension (away from concrete): Engages anchor capacity
- Compression (into concrete): May provide friction benefit
Shear Direction
- Toward edge: Concrete edge failure likely governs
- Away from edge: Pryout or steel may govern
- Parallel to edge: Direction affects capacity
Sign Convention
In Clariti:
- Positive NEd: Tension (anchor in tension)
- Negative NEd: Compression (toward concrete)
- VEd: Specify direction relative to edges
Special Situations
Seismic Loading
Seismic combinations per EN 1998:
Ed = Gk + AEd + ψ2·Qk
Where AEd = seismic action
Seismic design requires additional considerations per EN 1992-4
Annex C. Products must be qualified for seismic applications.
Accidental Loading
For accidental design situations (impact, explosion):
Ed = Gk + Ad + ψ1·Qk,1 + Σ(ψ2,i·Qk,i)
Where Ad = accidental action
Fatigue Loading
For cyclic loading:
- Reduced partial factors may apply
- Fatigue verification per EN 1992-4 Section 4.4
- Product-specific fatigue data required
In Clariti
Clariti expects factored design loads:
- Single load case: Enter NEd and VEd directly
- Multiple cases: Define several load cases, check each
What to Enter
| Input Field | What to Enter |
|---|
| NEd | Factored design tension (kN) |
| VEd | Factored design shear (kN) |
| Direction | Shear direction relative to edges |
Multiple Load Cases
For comprehensive verification:
- Create load cases for each combination
- Clariti checks all modes for each case
- Results show which case governs
- Export includes all cases
If unsure which combination governs, enter multiple cases. Clariti
will identify the critical one for each failure mode.
