Wind Depending on the Structure Height for Vertical Walls

Technical Article

The wind loads are regulated according to Eurocode 1 - Actions on structures - part 1-4: General actions - Wind loads. The nationally determined parameters of a respective country can be found in the National Annexes.

The application area of DIN EN 1991-1-4:2010-12 is specified for buildings and engineering structures with a height of up to 200 m. This limit may be extended with DIN EN 1991-1-4/NA:2010-12, NCI to 1.1 (2) due to the wind profile that is valid in Germany for structures up to a height of 300 m.

The division of a country's wind zones is generally done using a wind zone map. Due to the relatively coarse resolution of the wind zone maps, however, the correct allocation in the transition areas of individual zones is relatively difficult. Thus there are detailed determinations of the wind zones according to administrative borders that can be very comfortably taken into account, for example by using the Dlubal online service Snow, Wind and Seismic Zoning Maps.

To determine the velocity pressure qb for the respective building location, the following alternative variants apply according to DIN EN 1991-1-4/NA:2010-12, Annex NA.B.

Simplified Peak Velocity Pressures for Structures of up to 25 m Height

In this approach, the peak velocity pressure may be applied as a constant value across the building height for reasons of simplicity. The related velocity pressures are regulated in Table NA.B.3 for the wind zones 1 to 4 according to Annex NA.A. For structures with a height above 25 m and structures on the islands of the North Sea with a height of more than 10 m, the peak velocity pressure must be more precisely determined as per the equations (NA.B.1) to (NA.B.8) or according to NA.B.2.

Height-Dependent Peak Velocity Pressure in Normal Case

For building heights of more than 25 m above ground, the influence of ground roughness, which is i.a. determined by the vegetation and the building development, must be taken into consideration when calculating the peak velocity pressure with the equations (NA.B.1) to (NA.B.8) or according to NA.B.2.

The normal case according to DIN EN 1991-1-4 NAB.3.3 is divided into three different profiles:

  • inland areas
  • coastal areas (band of 5 km in width landwards as well as the islands in the Baltic Sea)
  • North Sea islands

Precise Method for Calculating the Peak Velocity Pressure with Influence of Ground Roughness

If the building location is topographically influenced to a large extent or if it is located near large inland waters, the peak velocity pressure must be determined according to NA.B.2.

The peak velocity pressures in flat terrain are divided via the terrain categories 1 to 4. If the classification in a terrain category cannot be determined with absolute certainty, the respective smoother and therefore more unfavorable terrain category must be selected.

Wind Load on Vertical Walls Depending on Building Height

As explained above, the simplified velocity pressure (approach 1) für structures with a height of up to 25 m can be applied as a constant value over the entire building height.

If one of the other two approaches is used, the velocity pressure may be applied in a graded manner across the height of the building in wind range D. For buildings with dimensions of b < h ≤ 2 ⋅ b, a lower strip with the height b and an upper strip with the height (h - b) is assumed.

For buildings with dimensions of h > 2 ⋅ b, a lower strip with the height b and an upper strip with the height (h - b) is assumed. The area in between is to be divided into an appropriate number of intermediate strips with the height hstrip.

Figure 01 - Graded Wind Load Over Different Building Heights

In RFEM and RSTAB, the grading of the velocity pressure on the wind range D for vertical walls when generating loads is fully taken into account.

Keywords

height-dependent wind load terrain category

Reference

[1]   Eurocode 1: Actions on structures - Part 1-4: General actions - Wind actions; German version EN 1991-1-4:2005 + A1:2010 + AC:2010
[2]   National Annex - Nationally determined parameters - Eurocode 1: Actions on structures - Part 1-4: General actions - Wind actions; EN 1991-1-4/NA:2010-12
[3]   Albert, A.: Schneider - Bautabellen für Ingenieure mit Berechnungshinweisen und Beispielen, 23. Auflage. Köln: Bundesanzeiger, 2018
[4]   Holschemacher, K.; Klug, Y.: Lastannahmen im Bauwesen, 2. Auflage. Berlin: Beuth, 2016

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