Permeability

Opening the Snow/Wind Load dialog and clicking the Permeability tab displays the following dialog.

The dialog box is used to define the permeability of structure walls. Wall permeability has a direct effect on generating coefficients of wind pressure inside a structure. When you select an option its diagram displays in the upper-right corner of the dialog..

The dialog is divided into the following 4 fields with groups of specific options.

• The Internal pressure coefficient Cpi option is at the top of the dialog. The value of the internal pressure, Cpi, can be defined in 3 ways:
  • Closed structure (Cpi = 0) - When selected, single cases (Cpi=0) are generated without considering negative pressure (-) and positive pressure (+) in a building. All the options in the dialog are unavailable.
  • Automatic - When selected, the Cpi value is generated based on the permeability value.
  • Manual - When selected, you can manually define the Cpi value in the Pressure (+) CpiS and Pressure (-) CpiD fields. All the options in the dialog are unavailable.
• In Permeability of side walls field specifies the left and right side wall permeability. Permeability is always expressed in %. For a completely open wall, the permeability value is 100%; whereas, for a completely closed wall, it is 0%.
• In Permeability of front and rear walls field specifies the front and rear wall permeability. Permeability is always expressed in %.

  For a completely open wall, the permeability value is 100%; whereas, for a completely closed wall, it is 0%.

• The Doors field has the following options:
  • Left side - When selected, the door is located on the left-side wall of the building. The permeability value for this wall can be specified in the field on the right.
  • Right side - When selected, the door is located on the right-side wall of the building. The permeability value for this wall can be specified in the field on the right.
  • Front - When selected, the door is located in the front wall of the building. The permeability value for this side can be specified in the field on the right.
  • Rear - When selected, the door is located in the rear wall of the building. The permeability value for this side can be specified in the field on the right.