The category A, category B, category C and category D are more severe design category and can be categories according to Table 1 and Table2.
|Table 2. Seismic design category for 1-S period response acceleration|
Now we will learn about structures located in regions when S1<0.75. In this case we can use table 1 when following all are applicable:
A. Approximate fundamental period of structure in each orthogonal direction (each of two)
Ts and Ta are determined as per 11.4.5 and 128.2.1 of asce7.
B. Fundamental period of structure in each orthogonal direction (each of two) that are used to determine story drift<Ts
C. Seismic response co-efficient is determined as per ASCE-7
R=Response modification factor
I=Occupancy importance factor
D. Diaphragms in structure are rigid. For flexible diaphragms distance between vertical element≤40ft.
In IBC a simplified procedure for seismic design also provided when seismic design category will be determined as per ASCE7.