I am working on a piping system partially supported by "pendulum" supports (on the ground, each support is almost 5m long) and partially sitting on the steel structures (independent structures like piperack, valve platforms and etc). I understand that the acceleration created at the height of the piping sitting on the structures should be different than the ground acceleration and I probably have to make various time-acceleration spectrums. I just do not know how to add up the pendulum behaviours in the calculation. I wonder if anyone has a second thought on this matter. I have attached the drawing of a pendulum support for those who might not know what a pendulum support is.

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For those who may find this post a bit woolly: it is about performing a Seismic dynamic analysis.

Wouldn't it be simpler to include the steel in your CAESAR II model?

the structures where the piping system sits on, are relatively complex structures (all have stiffeners, bracing, stairways and etc.)
I tried to include the valve platform to the calculation and got totally different system reaction/results. Since I am no structural engineer, I can't make sure the model is correct though. I have attached the calculation below

thanks

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