In EN-13480-3 Section A.2.1.6, it tells the analyst (when one is doing a response spectrum analysis) to choose a damping ratio dependent on the particular frequency of a pipe.Is it possible in AutoPIPE to have frequency dependent damping in a response spectrum analysis?
In the figure below, the response spectra applied to a small section of a pipe model would be dependent on that small section's modal analysis results.
For example, if there was one major mode of 10 Hz it would use the 5% damping spectra, if it was 20 Hz it would use the 2% spectra, and if it had two modes at 10 and 20 Hz with approximately equal participation factors, the results would be approximately a 50/50 combination of applying the 5% and 2% curves. If it had multiple modes with varying participation factors, it would be a very complex calculation.
AutoPIPE does not currently have a mode dependent damping but it does provide that variable damping suggested by ASME. Its a simple On / Off switch.
Please see the following AutoPIPE help sections for complete details:
1. Help > Contents> Contents Tab> Bentley AutoPIPE> Command Reference> Response Spectrum> N411
2. Help > Contents> Contents Tab> Bentley AutoPIPE> Reference Information> Analysis Considerations> Response Spectrum Analysis> Double Sum Method> N411 Damping
Either add N411 variable damping or not.
En13480 Piping calculations