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Snow, wind and seism zones for a building place
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Zones for snow, wind and seism

Snow zones and wind zones are specified on maps provided in the national annexes to the Eurocode 1.
Seism zones are specified on maps provided in the national annexes to the Eurocode 8 or in national legal texts.

What is a snow zone ?

Each country has set characteristic snow loads on the ground for each portion of its territory. The division is usually specified in the national annex of Eurocode 1 part 1-3.

What is a wind zone ?

Each country has set fundamental value of the basic wind velocity for each portion of its territory. The reference velocity corresponds to the average wind velocity over 10 minutes, measured at 10m above ground level on an 'open country' site with a return period of 50 years. The division is usually specified in the national annex of Eurocode 1 part 1-4.

What is a seismic zone ?

Each country has set reference peak ground acceleration on type A ground for each portion of its territory. The type A ground has a stratigraphic profile like rock or other rock-like geological formation, including at most 5m of weaker material at the surface. The division is usually specified in the national annex of Eurocode 8 part 1-1.

How to calculate snow on your building site ?

First, you need to calculate the value of snow on the ground at the relevant site :

Then, you can take into account the annual probability of exceedence by calculating the ground snow load with a return period equivalent to the design working life of your building.

Why calculate peak velocity pressure by wind direction ?

The wind direction is to be considered for several reasons :
  • First, the high velocities of wind are observed more frequently in certain direction sectors; the directional factor accounts for this by authorizing a reduction when the wind comes from a direction where the probability of occurrence of strong winds is less.
  • On the other hand, the orography and the roughness of the terrain generally vary with the direction of the wind.
  • Finally, the pressure or force coefficients depend on the direction of the wind relative to the construction.

How to calculate peak velocity pressure by wind direction ?

For the calculation of wind actions, only a few wind directions are considered; for example the normal directions to the facades in the case of buildings.

To accurately determine the peak velocity pressure, you will have to take into account many parameters such as :
  • the wind zone according to the map taken from the national annex to the Eurocode 1 part 1-4.
  • the directional factor cdir.
  • the annual probability of exceedence by calculating the basic wind velocity vb with a return period equivalent to the design working life of your building.
  • the roughness factor cr(z), to take into account the effect of the environment (vegetation / urbanization).
  • the orography factor co(z), to take in account the effect of terrain relief.
Then you can calculate the wind peak velocity pressure:
  • qp is the pressure in newtons per square meter (N/m2).
  • Iv(z) is the turbulence intensity, at height z, defined as the standard deviation of the turbulence divided by the mean wind velocity.
  • ρ is the air density in kilogram per cubic meter (kg/m3).
  • ce is the exposure factor: , with the basic velocity pressure

How to calculate wind velocity from pressure ?


Do I need for seismic analysis ?

In cases of very low seismicity, the provisions of Eurocode 8 need not be observed.
It is recommended to consider as very low seismicity cases either those in which the design ground acceleration on type A ground, ag = γI . agr, is not greater than 0.39m/s2, or those where the product agS is not greater than 0.49m/s2.
The seismic zones, the agr values and the chosen method may be found in national Annexes or in the law specific to each country. §3.2.1(5)

(Description of type A ground: Rock or other rock-like geological formation, including at most 5m of weaker Inaterial at the surface)

Example of results given by the software

See the features of Eurocodes Zoning
Available in English/French, otherwise «Google Translate»!

B1 - Localization

French flag
6.9511° , 43.4979°
1019565m , 6274536m
Large map that shows the building's position to determine snow, wind and seism zones
Simple map that shows the building's position to determine snow, wind and seism zones
06590 Théoule-sur-Mer, Provence-Alpes-Côte d'Azur

B2 - Elevations

Elevation map to calculate orography factor
Coordinates 6.9536°
43.4972°		 6.9455°
43.4994°		 6.9455°
43.4994°		 6.9368°
43.5019°
Elevations 9m 244m 244m 54m
Obstacle effective height H 235m 190m
Slope actual length Lu / Ld 698.4m 754.4m
Slope angle Φ 33.7% 25.2%
Horizontal distance site/top x 483.1m
Elevation at the place of construction 58m

B3 - Building

common structure
50years
8.0m
15°

B4 - Terrain categories

Terrain map
Sectors 1 2 3 4
Categories IIIb 0 0 IIIb
Radius R of the angular sector : 300m

C1 - Snow NF EN 1991-1-3/NA (may 2007) + A1 (july 2011)

A2 (sk,0 = 0.45kN/m2)
MANDELIEU-LA-NAPOULE,ALPES-MARITIMES (06)
sk,58m = 0.45 kN/m2

s50ans = 0.45 kN/m2

sad = 1.0kN/m2

C2 - Wind NF EN 1991-1-4/NA (march 2008) + A1 (july 2011) + A2 (september 2012) + A3 (april 2019)

2 (vb,0 = 24.0m/s)
THEOULE-SUR-MER, ALPES-MARITIMES (06)
3
Sectors 1 2 3 4
Sector definition from 330° to 60° from 60° to 150° from 150° to 240° from 240° to 330°
Fundamental value of the basic wind velocity vb,0 24.0m/s
Shape parameter K 0.2
Exponent n 0.5
Annual probability of exceedence p 0.02
Probability factor cprob 1.0
Directional factor cdir 1.0 0.85 0.85 1.0
Basic wind velocity vb 24.0m/s 20.4m/s 20.4m/s 24.0m/s
Reference roughness length z0,II 0.05m
Roughness length z0 0.5m 0.005m 0.005m 0.5m
Terrain factor kr 0.223 0.162 0.162 0.223
Height above ground z 8.0m
Minimum height zmin 9.0m 1.0m 1.0m 9.0m
Roughness factor cr(z) 0.645 1.193 1.193 0.645
Obstacle type isolated hills
Exposure type - upwind - downwind
Factor depending on the type and dimensions of the obstacle s max 0.0 0.8 0.0 0.8
Orography factor* co(z) 1.0 1.235 1.0 1.112
Mean wind velocity vm(z) 15.5m/s 30.1m/s 24.3m/s 17.2m/s
Turbulence factor kl 0.923 1.0 1.0 0.923
Standard deviation of the turbulence σv 4.943m/s 3.299m/s 3.299m/s 4.943m/s
Turbulence intensity Iv(z) 0.319 0.11 0.136 0.287
Air density ρ 1.225kg/m3
Exposure factor ce(z) 1.347 3.84 2.774 1.55
Peak velocity pressure qp(z) 475.1N/m2 978.9N/m2 707.1N/m2 546.7N/m2
Peak wind velocity for Serviceability Limit States vp(z),SLS 100.3km/h 143.9km/h 122.3km/h 107.6km/h
Peak wind velocity for Ultimate Limit States vp(z),ULS 122.8km/h 176.3km/h 149.8km/h 131.7km/h
* The orography factor is calculated for a well individualized obstacle (an emergent zone compared to a general ground without marked relief)

C3 - Seism Code of the Environment - Article D563-8-1 (09/01/2015) + JORF n°0248 of 24/10/2010 text N°5

2 (0.7m/s2)
Theoule-sur-Mer, Alpes-Maritimes (06)
A seismic analysis may be required for this building. You can check if your building is concerned on LEGIFRANCE.