Glossary · Snow and wind
Altitude factor Calt
The 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).
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Definition
The city table and the zoning maps give S₀ and W₀ for lowland conditions. For sites in the mountains DBN V.1.2-2:2006 introduces an altitude factor, where H is the height above sea level in kilometres:
сніг / snow: Calt = 1,4·H + 0,3 (H ≥ 0,5 км), Calt = 1 (H < 0,5 км)вітер / wind: Calt = 2·H (H > 0,5 км), Calt = 1 (H ≤ 0,5 км)Both formulae are meant for mountainous terrain. The norm calls the snow version approximate and on the safe side. Where snow surveys or wind observations exist for the site, the value is derived statistically and Calt = 1 is used.
Examples
Kyiv lies below 0.5 km, so Calt = 1 for both snow and wind. For a plot in the Carpathians at 800 m: snow Calt = 1.4 · 0.8 + 0.3 = 1.42, wind 2 · 0.8 = 1.6. Snow on such a plot is 42 % above the table value for the nearest city, and wind 60 % above. The snow factor is continuous: at exactly 0.5 km it equals 1.
How Solispec applies it
In Solispec the altitude is an input in metres (in the constructor and in the snow and wind calculator). The engine divides it by 1000 and applies formula (8.5) to Sm and formula (9.4) to Wm. An empty field means Calt = 1.
Norms and clauses
- DBN V.1.2-2:2006, cl. 8.10, formula (8.5); cl. 9.10, formula (9.4)
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.
- Characteristic wind pressure W₀The mean wind pressure at 10 m height exceeded on average once in 50 years; Kyiv has 370 Pa under DBN V.1.2-2:2006.
- 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.
- Snow and wind zonesThe zones of maps Fig. 8.1 and 9.1 of DBN V.1.2-2:2006; for calculations the S₀ and W₀ values in Pa from the city table are easier to use.
- 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.