Dear sir/madam,
I have two questions about damping in dynamic analysis:
1) Is it correct to use Rayleigh damping with HS Small model (using hysteretic damping), what should be the upper limit not to cause overdamping?
2) According to the manual, i used appropriate target frequencies and applied an average 2% rayleigh damping ratio to soil layers and results are too much different from the case without Rayleigh damping. In additioın, if i don't use rayleigh damping, there is an amplification/noise in acceleration graph and it continues like input motion continues at the end of the analysis. What could be the reason for this situation?
Thanks and best regards.
Dear Nuri,
1) It's correct to use Rayleigh damping together with HSsmall model, because the HSsmall model doesn't damp the very small amplitudes. Some people already add the Rayleigh damping during the seismic event, other people prefer to have the seismic event with just HSsmall and no Rayleigh damping, and then after the seismic event add a Dynamics phase without seismic load but with Rayleigh damping to damp out the residual accelerations. Both systems work.There is no fixed upper limit, it depends on how much damping is in the HSSmall parameters. In practice something in the order of 0.5-1% Rayleigh damping is used. If you would opt for the second method as described above, you could calibrate the amount of Rayleigh damping on how fast you would like to dissipate the residual accelerations.
2) You mean 2% Rayleigh damping on top of using HSsmall? I would say that is quite a lot. Try using less Rayleigh damping ....Apart from that I don't really understand your question. You're saying that without Rayleigh damping you have residual motion (which makes sense without the damping) and with 2% damping the results are quite different, which also make sense since you added a lot of damping .So what is exactly your question?With kind regards,
Dennis Waterman
Answer Verified By: Nuri Taştekin