I have data
Ss=1.217,
S1 = .499
Fa=1.0, Fv=1.5, importance factor = 1.5
Sds(Damped design spectral response acceleration for short period)= 0.811

I did spectrum generation in Caesar as per IBC where the maximum value of acceleration is 0.3
While creating spectrum Caesar did not ask value for Sds.

Now my structural engineer says that the acceleration value should be Cs ( Seismic response coefficient) = Sds * I /R
which comes around 0.3 which is 1/3 of Sds

Now I want to input the g-acceleration as a uniform load U1.
Which value is correct for input Cs = 0.3 or should it be Sds?
I can see the shear force is calculated from Cs * weight.
Is Caesar expecting Sds as a input and doing the calculation of Cs internally for doing force calculation in dynamic analysis?

Hence by method of using uniform load acceleration is it doing mass x acceleration.
And by using dynamic spectrum analysis we are reducing the g acceleration by importance factor and response modification factor and getting lesser loads?




Thanks,

The CAESAR II IBC seismic spectrum generator creates a response spectrum for use in dynamic analysis. I believe your seismic response coefficient is used to create an "equivalent" static load. They should be related but I don't expect them to be the same.