Glossary · Snow and wind
Reliability factor for the serviceability value γfe
The multiplier for serviceability loads (deflections): at η = 0.02 snow 0.49, wind 0.21 (Tables 8.3, 9.3 of DBN V.1.2-2:2006).
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Definition
Limit states of the second group — deflections, vibrations, cracking — are checked against the serviceability load, not the limit one. DBN V.1.2-2:2006 provides a separate factor γfe for it, which depends on η, the share of time during which the serviceability condition may be violated (cl. 8.12, 9.15).
Se = γfe · S0 · C, We = γfe · W0 · C| η | γfe, snow (Table 8.3) | γfe, wind (Table 9.3) |
|---|---|---|
| 0.002 | 0.88 | 0.42 |
| 0.01 | 0.62 | 0.27 |
| 0.02 | 0.49 | 0.21 |
| 0.05 | 0.28 | 0.14 |
η is set by the structural design codes or by the design brief. For mass construction both clauses allow η = 0.02.
Example: Kyiv
For a flat surface in Kyiv the serviceability snow load is Se = 0.49 · 1,550 ≈ 760 Pa, half the limit value. For wind at 2 m in terrain type II: 0.21 · 370 · 0.7 ≈ 54 Pa before the aerodynamic coefficient. The gap to γfm explains why a rail can pass on deflection and fail on strength, or the other way round.
How Solispec applies it
The Solispec engine applies γfe in the rail deflection check: the combination G + γfe · S + 0.9 · γfe · W↓ with γfe = 0.49 for snow and 0.21 for wind (Tables 8.3, 9.3, η = 0.02). Strength checks use γfm.
Norms and clauses
- DBN V.1.2-2:2006, cl. 8.12, 9.15, Tables 8.3, 9.3, formulae (8.2), (9.2)
Related terms
- Reliability factor for the limit value γfmThe multiplier on S₀ and W₀ that depends on the mean return period T: 1.00 at 50 years, 1.14 at 100 years (Tables 8.1, 9.1).
- Limit design snow load SmThe snow load on the horizontal projection used for strength checks: S_m = γ_fm · S₀ · C under DBN V.1.2-2:2006.
- Limit design wind load WmThe wind load used for strength checks: W_m = γ_fm · W₀ · C, where C covers aerodynamics, height, topography and dynamics.
- Mean return period TThe period in years over which a load is exceeded once on average; γ_fm depends on it (Tables 8.1, 9.1 of DBN V.1.2-2:2006).
- DBN V.1.2-2:2006 “Loads and actions”: what matters for a solar plantNorms explained
Solispec’s calculation is preliminary: for a design it has to be checked by an engineer. The values and clauses follow the current editions of the norms on the date of the page.