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Spectral Response Accelerations Sa(T)
Damped spectral response accelerations Sa(T =0.2), Sa(T= 0.5), Sa((T=1.0), Sa(T= 2.0),Sa(T= 5.0) are input, where T is the period in seconds. These values are specific to the geographic location of the building site.
The default values for new files are those appropriate to the city chosen from a list of dozens of Canadian cities in the Design Settings. When a city is chosen, the response factors are taken from Appendix C of the NBC and Table J-2 of the structural commentaries for that city.
These are measured in units of gravitational acceleration g.
Site Coefficients F(T)
Site co-efficients F(T) are determined from in Tables 4.1.8.4.-B to -F for periods T from 0.2 to 5.0, based on the value of PGAref and the Site Class. For Site Classes A-E, these cannot be changed except under special circumstances, and are shown for your information.
For Site Class F, and for other site classes under certain circumstances, the F(T) values not found in the corresponding tables. Instead, according to the notes to these tables referring to NBC 4.1.8.4 (6) , site-specific geotechnical investigation and dynamic site response analysis shall be performed to determine their values. Therefore, these inputs become active when Site Class F is selected, or under those other circumstances to allow you to enter the coefficients so determined.