@jay olleta
Code specify to use I*g/R value as initial scale factor.
But the simple way is to Initially take the scale factor equal to 1000.
Then run the analysis and check/compare the Static and dynamic base shear and update the scale factor accordingly.
If Static Base shear is greater than Dynamic Base shear, you will need to scale up the dynamic Base Shear
and if Static Base shear is less than Dynamic Base shear, you will need to scale down the dynamic Base Shear as follows:
New Scale Factor=1000*(Static Base Shear/Dynamic Base Shear)
See the UBC code pic attached for the minimum limit of reduction of elastic Response Parameters.