Step 1: Determine the zip code of the site under consideration. STAAD will automatically find the latitude and longitude of the location, thereby, deriving the Ss and S1 values

Alternatively, if zip code is unknown, then the latitude and longitude may be provided.

You may also manually input the value of Ss and S1 mentioned in equation 11.4.1 of ASCE 7-05 by calculating the same.