Glossary · Snow and wind
Peak velocity pressure qp
A Eurocode term from EN 1991-1-4:2005 (cl. 4.5): wind pressure including gusts; DBN V.1.2-2:2006 uses W₀ and C_h instead.
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Definition
If you read a mounting manufacturer’s documentation or a foreign calculation, it almost certainly uses qp(z), the peak velocity pressure at height z. Clause 4.5 of EN 1991-1-4:2005 defines it as the pressure including the mean velocity and short-term fluctuations. The recommended rule is Expression (4.8): qp comes from the basic velocity pressure qb multiplied by the exposure factor ce(z), which depends on height and terrain roughness. A National Annex may set its own rule.
qp(z) = ce(z) · qbHow it relates to the DBN
DBN V.1.2-2:2006 takes another route. The starting quantity is W₀, the mean (static) pressure component at 10 m with a 50-year period (cl. 9.6). Height and terrain enter through Ch from Table 9.01, and the fluctuating part, for structures with a period over 0.25 s, through the dynamic factor Cd (cl. 9.13). For low, stiff structures such as solar tables Cd = 1.
So a qp from a European calculation cannot simply replace W₀ · Ch: the two belong to different systems with different inputs and factors. What can be compared is the end result, the force on a panel or a support.
For Kyiv under the DBN at 2 m in terrain type II: W₀ · Ch = 370 · 0.7 = 259 Pa.
How Solispec applies it
Solispec computes design wind loads under the DBN: Wm = γfm · W₀ · Ch · Calt. From EN 1991-1-4:2005 the engine takes only the panel force coefficients (Table 7.6) and the position of the resultant (Figure 7.16). The snow and wind calculator shows Wm = γfm · W₀ · Ch · Calt at the building height — the same DBN value as in the designer’s report.
Norms and clauses
- EN 1991-1-4:2005, cl. 4.5, Expression (4.8)
- DBN V.1.2-2:2006, cl. 9.6, 9.9, 9.13
Related terms
- 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.
- Height factor ChThe wind correction for height above ground and terrain type, Table 9.01 of DBN V.1.2-2:2006: 0.7 at 5 m and 0.9 at 10 m for type II.
- 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.
- Aerodynamic coefficient Caer (cf)The multiplier turning wind pressure into force on a shape; for panels Solispec takes c_f from Table 7.6 of EN 1991-1-4:2005, as cl. 9.8 of the DBN allows.
- Terrain type I–IVThe wind classification of a structure’s surroundings under cl. 9.9 of DBN V.1.2-2:2006: from open water (I) to dense urban areas (IV).
- 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.