The program allows you to use the approximate fundamental period approximated Ta according to the ASCE 7 12.8.2.1, Eqn. 12.8-7
Ta = 0.02 (hn)0.75
This value appears as the defualt value in the Site Dialog input for T, and you can override it with one you have calculated using deformation analysis by unchecking the "Calculate T" button. It is possible to specify a different T in each force direction
The program also computes the maximum allowable T according to Table 12.8-1 and warns you if the value you have input exceeds it. The period T is used for the following
maximum limit on the seismic response coefficient Cs in Equations 12.8-3 and 12.8-4. Cs appears in equation 12.8-1 used in proportion to the calculation of seismic base shear V . T appears in the denominator of the expression, so the larger the T the lower the seismic base shear limit.
rules in 11.6 whereby the value of short-term response acceleration parameter SDS alone is used to determine the Seismic Design Category, rather than using the one-second parameter SD1 as well.
