Response Spectrum Acceleration parameter

[tngv752]

I try to do the earthquake check of a tank based on a new standard API650 11th Edition. It's a lot different from the old standard.

I have a problem to understand the unit of spectral accerlaration parameter.

For example, "So" is the acceleration parameter at 0 second period, %g . It's meant that "So" is the max value =2.5 or 2.5g or 0.25 ???? ( g=9.81 m/s2)>

Say that earthquake in Australia
So=2.5g (T=0s) ????
Ss=2.5g (T=0.2s) ????


Thanks.