Glossary · Snow and wind
Limit design snow load Sm
The snow load on the horizontal projection used for strength checks: S_m = γ_fm · S₀ · C under DBN V.1.2-2:2006.
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Definition
Section 8 of DBN V.1.2-2:2006 sets three design values for snow: limit, serviceability and quasi-permanent. The limit value is used for strength and stability, the ultimate limit states. Clause 8.2 defines it on the horizontal projection of the roof:
Sm = γfm · S0 · C, C = μ · Ce · CaltHere S₀ is the characteristic value, γfm depends on the mean return period, μ on the tilt, Ce on the operating conditions and Calt on the altitude. The serviceability value Se = γfe · S₀ · C (formula 8.2) uses the factor γfe and is applied to deflections.
Example: a 30° table in Kyiv
| Quantity | Value |
|---|---|
| S₀ (Annex E) | 1,550 Pa |
| γfm at T = 50 years | 1.00 |
| μ at α = 30° | 0.857 |
| Ce, Calt | 1 and 1 |
| Sm on the horizontal projection | 1,329 Pa |
| normal to the panel (× cos²30°) | ≈ 997 Pa |
With a 100-year service life γfm rises to 1.14, and for a flat surface (μ = 1) Sm becomes 1,767 Pa. A steeper table carries less: at 35° μ = 0.714.
How Solispec applies it
The engine computes Sm = γfm · S₀ · Calt · μ on the horizontal projection with Ce = 1 and converts it to the panel plane with cos²α. That load then goes into the rail, truss and joint checks. Rail deflection uses the serviceability value with γfe = 0.49 (η = 0.02).
Norms and clauses
- DBN V.1.2-2:2006, cl. 8.1–8.3, formulae (8.1), (8.2), (8.4)
Related terms
- Characteristic snow load S₀The weight of snow cover per 1 m² of ground exceeded on average once in 50 years; under DBN V.1.2-2:2006 Kyiv has 1,550 Pa.
- 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).
- Snow shape coefficient μThe conversion from ground snow to roof snow: μ = 1 up to 25°, 0 from 60°, linear in between (DBN V.1.2-2:2006, Annex Zh, scheme 1).
- Operating conditions factor CeThe snow load factor for clearing and melting; without data on how the roof is operated C_e = 1 (cl. 8.9).
- Altitude factor CaltThe correction for altitude: 1.4H + 0.3 for snow from 0.5 km, 2H for wind above 0.5 km, otherwise 1 (DBN V.1.2-2:2006).
- Reliability factor for the serviceability value γfeThe 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).
- 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.