Limitations (BS6399-2 Wind wizard)

Tekla Structural Designer
Modified: 5 May 2021
2024
Tekla Structural Designer

Limitations (BS6399-2 Wind wizard)

This page discusses the limitations to the wind wizard.

Throughout the development of the Wind Modeler extensive reference has been made to the References and we consider it advisable that you are fully familiar with these before using the software.

In addition, because wind loading is complex and its application to general structures even more so, it is essential that you read and fully appreciate the following limitations in the software:

Geometry

DANGER: You should seek specialist advice for building shapes that are not covered by the Standard - see Clause 1.1 of BS6399-2:1997.
  • Open sided buildings are beyond scope.
  • Free standing walls and sign boards are not considered.
  • Parapets and free-standing canopies are not considered.
  • Exposed members are not considered, for example lattices, trusses......
  • Barrel-vault roofs and domes are not considered.
  • Dominant Openings are not explicitly handled - Clause 2.6.2. However, you can use Table 17 to calculate the necessary Cpi values and manually apply to a loadcase or individual zone loads.

Loaded areas

The difference between the loaded area of wall panels and roof panels defined at the centre-line rather than the sheeting dimension is ignored.

Wind direction

  • All outward faces within 60 degs of being perpendicular to wind direction - loads applied as windward normal to face. All inside faces within 60 degs to wind direction - loads applied as leeward normal to face. All other faces considered as side.
  • Orthogonal wind directions at the definition of the user.

Beneficial loads

  • No automatic reduction is made for beneficial load. When you edit the Zone Load Data for a wind direction, having generated wind loadcases, there is an option to allow for beneficial loads.

Wind loading on wall panels

Automatic zoning applies to all wall panels subject to the limitations described below:

  • Wall panels that are more than 15° from the vertical are outside the scope - Clause 2.4.1.5.
  • The inset storey clause 2.4.4.2 b) is not implemented. You can edit the zones manually according to your engineering judgement to include zone E if you consider this necessary.
  • Wall panels of internal wells are not automatically identified - Clause 2.4.3.2a. You can manually edit the zones to apply the roof coefficient to the wall panels.

Wind loading on roof panels

  • Automatic zoning only applies to all triangular roof panels and quadrilateral roof panels that are not concave, i.e. all of the internal angles < 180°
  • The inset storey clauses 2.5.1.7 a) and b) are not implemented. In clause a) the software sets Hr and H equal conservatively. You are obviously able to edit the zones manually according to your engineering judgement to include the further zones indicated in Figure 18 should you consider this necessary.
  • It should be noted that in Table 8 for curved and mansard eaves, the zones start from edge of horizontal roof and not from the edge of the feature.
  • Special care should be taken for winds blowing on duopitch with slopes that differ by more than 5°. If the wind is blowing on the steeper slope (that is that the less steep slope is downwind of ridge), the downwind slope should be set to be a flat roof with mansard at eaves for this wind direction.
  • Mansard and Multipitch Roofs are not detected automatically, However, you can manually apply the relevant roof type, apex type and bay position parameters for each appropriate wind direction to match the requirements of Figure 22 and Figure 23 - see BS6399-2 Wind Zones.

  • Roof Overhangs are not explicitly handled. It is suggested that you should define two separate roof panels - one forming the overhang and the other covering the inside of the building. You can then define Cpi values manually to either have the same coefficient as the adjacent wall, (Clause 2.5.8.2 Small Overhangs), or as an open sided building (Clause 2.6.3).

Additional wind loads

There may be situations when you perceive a need to manually define loads that cannot be determined automatically. You can do this by defining additional wind loadcases to contain these loads and then include these with the relevant system generated loads in design combinations in the normal way.

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