In IBC, structural classification and earthquake design category depends on parameter, mapped spectral response acceleration at 1-S period (S1). When S1 is equal or greater than 0.75, the occupancy category I,II and III are assigned. The structure is also assigned to seismic design category E.
Structures located in regions where parameter mapped spectral response acceleration, S1 is equal or greater than 0.75, the occupancy assigned to them is occupancy category IV, also the structure is assigned following requirements of seismic design category F.
Other structures not categorized as E and F, are categorized depending on occupancy category and also in co-efficient design spectral response acceleration, SDS and SD1. The determination procedure of SDS and SD1 are as follows:
SDS stands for design spectral response acceleration at five percent damping at short period and SD1 stand for design spectral response acceleration at five percent damping at 1 second period.
SDS and SD1 determine as follows:
SDS =2/3X SMS (1)
SD1=2/3 XSM1 (2)
SMS= Maximum seismic spectral response acceleration taking into account for short period.
SM1= Maximum seismic spectral response acceleration taking into account for 1 second period.
SMS and SM1 are determined based on mapped spectral acceleration for respective periods. Dear reader we will discuss about determination of SMS and SM1 in our next post.
So we start with seismic design category E and category F, now what about category A, category B, category C and category D? Dear reader in our next part we will learn about these categories and also learn to assign category when mapped spectral response acceleration is less than 0.75; till then good bye.