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Site Class
You choose a site class from A to F from ASCE 7 11.4.3, determined using the soil analysis procedures in Chapter 20 of ASCE 7. It is used in Tables 11.4-1 and 11.4-2 to determine site coefficients Fa and Fv
Chosen by Default
Use this box to indicate that Site Class D was chosen as the default site class because soil properties were not known, as per 11.4.3. If it is checked, then a a minimum value of 1.2 is now applied to the site coefficient Fa as per 11.4.4. This changes the value of Fa for SS = 1.0, 1.25, or 1.5. This box is only active if Site Class D is selected.
No Velocity Measurements
Use this box to indicate that Site Class B was chosen through site investigations without site-specific velocity measurements. It is active for Site Class B, only. If it is checked, then the values of Fa and Fv are set to 1.0, regardless of S1 and SS , as per 11.4.3.
Seismic Design Category
This is a non-editable text box giving the Seismic Design Category, from A to F. It is recalculated by the program whenever you change another input that affects the design category – the Site Class, the Risk Category, and the values of Ss and S1. In this way, you do not have to wait until a design is done before knowing the design category, which can affect other modeling decisions