Hi colleagues

I have diferents loads on snubbers by stactic and dynamic analysis.... which one should I consider to select this element (snubber)?

Thanks

Consider the total load (static + dynamic load) (e.g. Normal Ope, W+T1+P1 + Surge Load, F1) to size the snubber.

Warm Regards,

Thank you BORZKI.

Do you know why this happens? I meant, The loads on the snubbers are big in static analysis and so low in dynamic analysis.

I am using the same sismic sprectre for both... In static I extract the U vector and in dynamic I use the values table.

I think that the dynamic analysis is the real situation.

Thanks

Your example is seismic. Are you using response spectrum analysis and comparing it to static equivalent?

For simple models, this two approach may have approximately similar results.

Take note that response spectrum considers the natural frequency of the piping system (each mode have a certain participation to the overall result) which is not considered in the static equivalent.

If you have the data for response spectrum curve, then it is best to use this approach. Just take note that the your "% mass included" must be high enough and the "include missing mass" is active. Maybe this is the reason why your dynamic load is low.

A common specification asks that at least 90% of the overall seismic response comes from modal terms not the static load. Increase the frequency cut-off to capture more modal response.

Just check this in your analysis and compare again the results.

Cheers!!

In "equivalent static", have you considered the maximum on spectrum or the value readable on spectrum vs. the fundamental period/ frequency of your system (are they different/ have they the same value)?

Hi MARIOG

Yes... I have made that consideration... They have the same value.

Thanks

You can try a simple piping configuration and compare the results.
Say a cantilever beam fixed in one end and free on the other. Sharing your CII file will help also to check the way you set up the model and see if the difference in results makes sense.

Warm Regards,

ok, you need also to work with same "I" and "R" in both cases.
For your case, making a dynamic analysis by combining modal SRSS, the values on spectrum corresponding to second, third, etc modes may be on the linear ascending part of spectrum (usual such part of spectrum is constructed between ag and 2.5ag). As an extreme improbable case of "minimum" in dynamic calculation, let's say they correspond (all) to "ag" on spectrum and their effective mass participation is 50%. In this case a SRSS with the first mode 50% subject to 2.5ag is something as 1.34ag vs 100% mass subject to 2.5ag in "equivalent static". Of course such "demonstration" is ridiculous in terms of calculation, but my conclusion is that I would be suspicious if your wording " big in static analysis and so low in dynamic analysis" means something greater than a ratio of 2...2.5 to 1.

The above written may be valid when working with one spectrum, not when you apply spectra on three directions (and make equivalent static with a rule like 100-40-40).