NBC 2005 Wind Load Generation

Importance Categories and Factors

Input of importance categories in Table 4.1.2.1and calculation of factors in 4.1.6.1 has been implemented. The importance factor has been added to the equation for wind pressures in 4.1.7.1.

Importance Input

The Building use input in the Site Dialog has been changed to Importance category, the new categories have been implemented, and a full description of the categories from table 4.1.2.1 has been added

Reference Wind Velocity

Velocity pressure q in 4.1.7.1(4) has changed. It is now based on a probability of 1-in-50 year return period. It was previously 1-in 10 for CC, 1-in-30 MWFRS, and 1-in-100 for post disaster. These inputs have been removed from the Site Dialog. Only one input is now in the Site Dialog.

Default Reference Wind Velocity

The default reference wind velocity in the Design Settings can now be set via a dropdown list giving the design q for dozens of Canadian cities, taken from Appendix C of the NBC.

Exposure Factor C_e

A dropdown list has been added to the site dialog to allow selection of open or rough terrain.

The factor C_e has been changed according to from 4.1.7.1(5) has been implemented:

• (h/10)^0.2 but not less than 0.9 for open terrain (essentially the same as in NBC 1995 and Sizer 2002a
• 0.7(h/12)^0.3 but not less than 0.7 for rough terrain.

  Gust Factor C_g

The gust factor C_g from 4.1.7.1(6) has been implemented:

• Cg = 2.0 for main structural members (6a),
• Cg = 2.5 for C&C loads (6b)

  Gust Factor C_gi

An input field has been added to allow user input of the internal gust factor C_gi to allow for detailed calculations allowed for in 4.1.7.1(6) c

Internal Pressure Co-efficient C_pi

New internal pressure co-efficients C_pi have been implemented according to NBC structural Commentary I-31.

• For Category 1, the lower range has been changed from -0.30 to -0.15
• For Category 2, the range has changed from -0.7 to 0.7 to -0.45 to 0.3
• Category 3 is the same

  Low-rise Note 8 – Low-slope Windward Loads

In in the design results, log file, and load list in load input view, references to Note 9 regarding the splitting of windward loads on, low-sloped roofs has been changed to Note 8.

Low rise Note 5 Roof Slope Angle

Note 5 to Figure I-7 allows eave height as reference height for angles less than 7 degrees now, instead of 10.

Component and Cladding Reference Height

Note 5 regarding reference height based on roof angle has been removed for component and cladding wall design. The reference height shown in the diagram is always mean roof height.

Figure I-7 Procedure

We removed reference to “Medium-rise” and “All heights” when referring to this figure, and instead refer to it as the Fig. I7 procedure. The design code refers to it as a procedure for flat-roofed structures, but Shearwalls uses it for all roof types, as an alternative to the low-rise method for those structures that do not conform to the low-rise limitations.