Which code are you referring to? In case it is the UBC code, STAAD calculates the time period from both Method A and Method B and will use the one that results in a higher base shear (or will use the lower of the two values). However, if it exceeds the limits as specified in equations 30-5 to 30-7, the effect of time period will not be noticed as the limiting values of base shear are not functions of time period.
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