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How to Determine Seismic Design Category, IBC (Part-2)

Dear reader we were discussing about earthquake design category according to International Building Code. We have learned how to categorize structure to seismic design category E and category F. We will know discuss about rest category A, category B, category C and category D.


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.
Seismic design category for short period response acceleration
Table 1. Seismic design category for short period response acceleration

Seismic design category for 1-S period response acceleration
Table 2. Seismic design category for 1-S period response acceleration
We can easily understand that table 1 is based on response acceleration at short period and table 2 is based on response acceleration 1 second period.


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)

Ta<0.8Ts

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

Seismic response co-efficient
SDS =As per Part-1

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.

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