Lisa.blue


Eurocode terrain category scanner software

Get now the terrain category actions on your building with Lisa.blue!

What is terrain category?

Table 4.1 from Eurocode 1 part 1-4
Terrain category z0 (m) zmin (m)
0 Sea, coastal area exposed to the open sea 0.003 1
I Lakes or area with negligible vegetation and without obstacles 0.01 1
II Area with low vegetation such as grass and isolated obstacles (trees, buildings) with separations of at least 20 obstacle heights 0.05 2
III Area with regular cover of vegetation or buildings or with isolated obstacles with separations of maximum 20 obstacle heights (such as villages, suburban terrain, permanent forest) 0.3 5
IV Area in which at least 15% of the surface is covered with buildings and their average height exceeds 15m 1.0 10

Other example: Table from french national annex
Terrain category z0 (m) zmin (m)
0 Sea or coastal area exposed to sea winds; lakes and water bodies covered by wind over a distance of at least 5km 0.005 1
II Open field, with or without a few isolated obstacles (trees, buildings, etc.) separated from each other by more than their height x40 0.05 2
IIIa Campaign with hedges, vineyards, grove, sparsely populated 0.20 5
IIIb Urban or industrial areas; dense grove; orchards 0.5 9
IV Urban areas with at least 15% of the surface is covered with buildings whose average height is greater than 15m; forests 1.0 15
  • The roughness length z0 is used to calculate the terrain factor kr.
  • The zmin height is the threshold below which no pressure reduction should be applied.
  • The terrain categories are evaluated by direction of the wind in a circle around the building. The radius R of the circle is defined in the national annex.

How to calculate roughness factor from terrain category ?

  • The terrain roughness to be used for a given wind direction depends on the ground roughness and the distance with uniform terrain roughness in an angular sector around the wind direction. Small areas (less than 10% of the area under consideration) with deviating roughness may be ignored.
  • When a pressure or force coefficient is defined for a nominal angular sector, the lowest roughness length within any 30° angular wind sector should be used.
  • When there is choice between two or more terrain categories in the definition of a given area, then the area with the lowest roughness length should be used.
  • The terrain factor is : kr = 0.19*(z0/(0.05*z0,II))0.07
  • The roughness factor is : cr = kr*ln(z/z0)

How to detect roughness effect on the wind pressure with Lisa.blue?

We have developped a wonderful scanner which automatically detect the terrain category for each sector of wind. If you subscribe you'l be able to use it, else you can manually set the terrain category with looking of the satellite photography. Then lisa.blue will calculate the peak velocity pressure you need to calculate your building.

Snow, Wind & Seism full report generated by Lisa.blue software

On this example, you can see that Lisa.blue detected roughness IV for the north (urban areas), and roughness II for the other sectors due to the proximity with the Seine river.

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