No, base acceleration is set only according to available codes, i.e. Concrete Centre (2006), SCI P354 Design of Floors for Vibration and AISC DG11: Floor Vibrations due to Human Activity.
But in case of SCI P354 and AISC DG11 base acceleration is a constant value and response factor is proportional to 1/base acceleration so it is very easy to convert it to different base acceleration value.
In case of Concrete Centre (2006) Design Guide it is more sophisticated because in case of resonant response the base acceleration is a function composed of 3 different branches for 4 Hz < fh < 8 Hz and moreover the overall response factor is calculated as SRSS of response factors for harmonics. But in this case it is possible to use detailed results for harmonics from Diagrams of Footfall analysis in RSA - see the attached screen capture. This data can be output to for instance MS Excel to be processed using arbitrary base accelerations.
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