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Snow, wind and seism zones for a building place

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- What is a snow zone ?
- What is a wind zone ?
- What is a seismic zone ?
- How to calculate snow on your building site ?
- Why calculate peak velocity pressure by wind direction ?
- How to calculate peak velocity pressure by wind direction ?
- How to calculate wind velocity from pressure ?
- Do I need for seismic analysis ?
- Example of results given by the software
- Get the zones for a localisation using Eurocodes Zoning !

What are the Eurocodes ?

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- Eurocode 1 - Actions on structures

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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.

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

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.

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.

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.

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

- depending on the snow zone in which the building is located, according to the map taken from the national annex to the Eurocode 1 part 1-3.
- taking into account the effect of the elevation.

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.

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.

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 c
_{dir}. - the annual probability of exceedence by calculating the basic wind velocity v
_{b}with a return period equivalent to the design working life of your building. - the roughness factor c
_{r(z)}, to take into account the effect of the environment (vegetation / urbanization). - the orography factor c
_{o(z)}, to take in account the effect of terrain relief.

Then you can calculate the wind peak velocity pressure:

- q
_{p}is the pressure in newtons per square meter (N/m^{2}). - I
_{v(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/m
^{3}). - c
_{e}is the exposure factor: , with the basic velocity pressure

- v is the velocity in kilometers per hour (km/h).
- q is the pressure in newtons per square meter (N/m
^{2}). - ρ is the air density in kilogram per cubic meter (kg/m
^{3}).

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, a_{g} = γ_{I} . a_{gr}, is not greater than 0.39m/s^{2}, or those where the product a_{g}S is not greater than 0.49m/s^{2}.

The seismic zones, the a_{gr} 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)

See the features of Eurocodes Zoning

Available in English/French, otherwise «Google Translate»! ## B1 - Localization

## B2 - Elevations

## B3 - Building

## B4 - Terrain categories

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

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

^{*} 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

Available in English/French, otherwise «Google Translate»!

6.9511° , 43.4979°

1019565m , 6274536m

06590 Théoule-sur-Mer, Provence-Alpes-Côte d'Azur

1019565m , 6274536m

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 L_{u} / L_{d} | 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 |

common structure

50years

8.0m

15°

Sectors | 1 | 2 | 3 | 4 |
---|---|---|---|---|

Categories | IIIb | 0 | 0 | IIIb |

Radius R of the angular sector : 300m

A2 (s_{k,0} = 0.45kN/m^{2})

MANDELIEU-LA-NAPOULE,ALPES-MARITIMES (06)

s_{k,58m} = 0.45 kN/m^{2}

s_{50ans} = 0.45 kN/m^{2}

s_{ad} = 1.0kN/m^{2}

2 (v_{b,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 v_{b,0} | 24.0m/s | |||

Shape parameter K | 0.2 | |||

Exponent n | 0.5 | |||

Annual probability of exceedence p | 0.02 | |||

Probability factor c_{prob} | 1.0 | |||

Directional factor c_{dir} | 1.0 | 0.85 | 0.85 | 1.0 |

Basic wind velocity v_{b} | 24.0m/s | 20.4m/s | 20.4m/s | 24.0m/s |

Reference roughness length z_{0,II} | 0.05m | |||

Roughness length z_{0} | 0.5m | 0.005m | 0.005m | 0.5m |

Terrain factor k_{r} | 0.223 | 0.162 | 0.162 | 0.223 |

Height above ground z | 8.0m | |||

Minimum height z_{min} | 9.0m | 1.0m | 1.0m | 9.0m |

Roughness factor c_{r(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^{*} c_{o(z)} | 1.0 | 1.235 | 1.0 | 1.112 |

Mean wind velocity v_{m(z)} | 15.5m/s | 30.1m/s | 24.3m/s | 17.2m/s |

Turbulence factor k_{l} | 0.923 | 1.0 | 1.0 | 0.923 |

Standard deviation of the turbulence σ_{v} | 4.943m/s | 3.299m/s | 3.299m/s | 4.943m/s |

Turbulence intensity I_{v(z)} | 0.319 | 0.11 | 0.136 | 0.287 |

Air density ρ | 1.225kg/m^{3} | |||

Exposure factor c_{e(z)} | 1.347 | 3.84 | 2.774 | 1.55 |

Peak velocity pressure q_{p(z)} | 475.1N/m^{2} | 978.9N/m^{2} | 707.1N/m^{2} | 546.7N/m^{2} |

Peak wind velocity for Serviceability Limit States v_{p(z),SLS} | 100.3km/h | 143.9km/h | 122.3km/h | 107.6km/h |

Peak wind velocity for Ultimate Limit States v_{p(z),ULS} | 122.8km/h | 176.3km/h | 149.8km/h | 131.7km/h |

2 (0.7m/s^{2})

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.