Hi Jay Stress,

Just a short response to this inquiry/doubt:

<< As we check the frequency of the system in operating cases snubber remains inactive. Hence no restraint/stiffness being included in the system. Then how it is influencing the natural frequency of the system.>>

Natural Frequency is evaluated and corresponds to a CERTAIN STATUS of the restraints/supports. Under Normal Operating conditions (excluding dynamic actions and vibrations/cyclic excitation), Snubbers are indeed inactive/off.

However, under a dynamic load action (such as earthquake in your case), snubbers' restraints become active and they stiffen the piping system.

As pointed out above, when you define Dynamic Input Caesar II dynamic input processor, you must specify the Snubbers' restraints. Caesar II will consider those restraints (including their "finite" stiffness, as specified) in addition to the existing "permanent" support restraints, so that the dynamic response of the piping system will include the snubbers' restraints influence.

Dynamic analysis is quantifying ONLY the dynamic response of the System to the applied dynamic loads.

If you perform Response Spectrum analysis, for instance, and you need to superpose the Response Spectrum calculated support loads over an Operating Case loads, previously evaluated by the Static Analysis, then those Operating Loads are calculated "without" snubbers' action, while the Response Spectrum loads are quantified "with" snubbers' action included.

Therefore, if snubbers are actually installed in a piping system, and a Dynamic Modal Analysis is performed "without" snubbers (e.g. keeping snubbers inactive), then the Natural Frequency calculated is irrelevant for piping system dynamic behavior description, because Snubbers are actually part of the dynamic response.


Best regards,