Seismic Analysis Parameters (Canadian Code NBC 2020)

The parameters of a structure seismic analysis depend on a seismic code used during the calculations of a structure influenced by seismic loads.

Select Canadian seismic code NBC 2020 in the New Case Definition dialog or click Parameters in the Analysis Type dialog.

To access the dialog:

1. Click Tools Job Preferences Design Codes.
2. In the Loads section select NBC of Canada 2020 from the seismic loads menu.
3. Click Analysis Analysis Types.

   The Analysis Types dialog opens.

4. Click New. The New Case Definition dialog opens.
5. Select Seismic, choose NBC of Canada 2020 and click OK.

   The Parameters dialog opens.

Code parameters

The code parameters for a seismic analysis according to NBC 2020 are defined as follows:

• Site classifications for ground (A, B, C, D, E, F) conform with Table 4.1.8.4.-A and 4.1.8.4.-B.
• Spectrum

You need to specify spectrum values Sa(0.2), Sa(0.5), Sa(1.0), Sa(2.0), Sa(5.0), Sa(10.0) in accordance to Article 4.1.8.1 for the site location.

It is possible to access official NBCC website: 2020 National Building Code of Canada Seismic Hazard Tool by clicking the button. This page allows to obtain values required for defining the spectrum and coefficient values based on basic data such as location and site soil class. To transfer the values from the spectrum definition table on the webpage to the definition table in the Robot Structural Analysis, the copy-paste operation can be used.

You may access and copy spectrum values in accordance to Article 4.1.8.1 - Sa(0.2), Sa(0.5), Sa(1.0), Sa(2.0), Sa(5.0), Sa(10.0) or additional values Sa(0.1), Sa(0.3). Spectrum values for a specific period S(Ta) is obtained by linear interpolation between these values.

• Coefficients:
  • IE (earthquake importance factor) conforms with table 4.1.8.5._A
  • Rd (ductility-related force modification factor) and Ro (overstrength-related force modification factor) factors conform with Table 4.1.8.9.
• Factors calculated for informative purpose
  • Factor PGA - Peak Ground Acceleration, as defined in Sentence 4.1.8.4.(1).
  • Factor PGV - Peak Ground Velocity, as defined in Sentence 4.1.8.4.(4).
  • Value of IE*Sa(0.2) and corresponding Seismic Category for Buildings according to Table 4.1.8.5-B
  • Value of IE*Sa(1.0) and corresponding Seismic Category for Buildings according to Table 4.1.8.5-B

In this dialog, you can also access and modify the Direction definition, Filters.

Click Base Shear to open the Base shear dialog. There you can select how to take account of the base shear force: calculate it according to the provisions of the seismic code 4.1.8.11.(3d ) or specify the value.

You can examine all the input parameters and base shear force distribution in the Calculation Notes (open Analysis > Calculation Notes > Simplified/Full Note)