BS6399-2 Wind Zones

Tekla Structural Designer
Modified: 8 Mar 2019
2024
Tekla Structural Designer

BS6399-2 Wind Zones

At the end of the Wind Wizard..., the system creates default zones for all the walls and roof panels for each of the defined wind directions.

If any errors have occurred in this process, a red cross appears next to Pressure Zones in the Project Workspace.

Basic Geometry

The basic building geometry is assessed as follows:

  • Reference Height (Hr) - is taken as the difference between highest point on wall or roof panel and ground level.

  • Wall height (H) - is taken as the difference between highest and lowest points on the wall panel.

    These definitions apply to wall panels without parapets and the actual parapets. Wall panels with parapets above them will take their highest point from the parapet. See the diagram below.

  • Roof height (H) - is taken as the difference between highest point on wall or roof panel and ground level. This definition does not handle the upper roof of inset storey but is conservative and only affects the scaling dimension, b - see Clause 2.5.1.7.
  • The Building Breadth, B is calculated from the smallest enclosing rectangle around the whole building (considered over all roof and wall panels only) for the given direction. You can override the calculated value in case the Tekla Structural Designer model does not include the whole building.

Wall Zones

Wall Type

We assess each wall panel to determine if it is a windward, leeward or side wall. We classify the type of wall dependent on q:

  • θ ≤ 60 deg - Windward,
  • θ ≥ 120 deg - Leeward,
  • Other walls are classed as Side.
Windward walls Windward walls have a single zone and Table 5 is used with interpolation for D/H.
Leeward walls Leeward walls have a single zone and Table 5 is used.
Side walls Side walls are assessed for recesses (narrow or wide), irregular flushed faces, downwind re-entrant corners. In all cases, side walls have the relevant number of zones. Table 5 is used.

Roof Zones

Roof zones are automatically generated where possible for each wind direction. In essence each roof panel is assessed in its own right based on its properties. The interconnectivity of touching roof panels is not generally considered.

Direction

Internally the roof slope vector (line of maximum slope) is determined from the normal vector, with its direction always giving a positive slope angle, i.e. the roof slope vector must always point up the slope.

We calculate the angle between the wind direction and projection of roof slope vector onto horizontal plane ( q in range -180° to +180°).

Automatic Zoning

Automatic zoning normally only applies to all triangular roof panels and quadrilateral roof panels that are not concave, that is that all of the internal angles < 180°. However, additionally, it only applies to Hip Gable roofs if they are triangular, and Hip Main roofs if they are quadrilateral. Further, Downwind Slope Hip Gables must not have 2 upwind corners.

Dimensions

All zone dimensions are specified in plan.

Flat Roofs

See BS 6399 Clause 2.5.1, Figure 16 and Table 8.

Monopitch Roofs

See BS 6399 Clause 2.5.2.3, Figure 19 and Table 9.

Duopitch Roofs

See BS 6399 Clause 2.5.2.4, Figure 20 and Table 10.

Hip Gable

See BS 6399 Clause 2.5.3, Figure 21 and Table 11.

Hip Main

See BS 6399 Clause 2.5.3, Figure 21 and Table 11.

Mansard Roofs

If you manually set the connected roof types to Mansard, then the program will correctly identify the special cases in BS6399 Figures 17c, 22a and 22b, and use the correct tables and values. See BS 6399 Clauses 2.5.1.6.2 & 2.5.4

Multi-bay Roofs

We allow you to interpret BS 6399 Clause 2.5.5 and Figure 23 as you think appropriate and manually define the roof types and sub-types accordingly. You also have the ability to manually set the multi-bay position for each roof panel for each wind direction:

  • Not Multi-Bay - for this wind direction (conservative default),

  • Upwind Bay - first bay of many for this wind direction,

  • Second Bay - for this wind direction,

  • Third or more Bay - for this wind direction.

Where the reduction applies, the values of all coefficients are reduced according to Table 12.

Non-Automatic Zoning

Where automatic zoning does not apply, the system creates a single zone covering the entire roof as follows:

  • Flat - B,

  • Monopitch - B,

  • Duopitch - B for upwind, A for downwind, B for side,

  • Hip Gable - B for upwind, B for downwind, D for side,
  • Hip Main - B for upwind, A for downwind, D for side.

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