A_d = ordinate of the design spectrum defined in Section 1
W = the weight of the building including the permanent and variable loads given in  Sections 2
u = the greatest of the values given by:

N = number of levels
T = fundamental period
T* = period given in Table 1
In any event the value shall not be below the minimum seismic coefficient given in Section 3

Ductility Factor
The maximum values of the ductility factor D for the different types of structures and design levels are given in Fig. 2.