Mass Participation in modal analysis in each frequency

Hi,
can anyone suggest me how to extract Mass Participation in modal analysis in each frequency in CAESAR II in terms of kg or N.
Is it possible to extract for individual frequency?.

In other software like caepipe it can be easily extract, similarly can we extract in Caesar also ?

Hi,

Just curious why you want to know the mass participation in terms of kg or N?

I usually look in terms of percentage for mass participation, showing what modes have high participation, which can be potentially excited by a vibration source (e.g., surge/waterhammer, pressure pulsation, FIV, seismic, etc.). From there, dynamic analysis will be performed making sure that all potential modes are captured, normally from 80% to 90% (with "include missing mass" is toggled on).

Warm Regards,

thanks for your valuable response

as you said usually mass participation will be in terms of percentage i agree,
but from the mass participation factor can I calculate the effective mass participated on each mode ?.
I found in the CAEPIPE & PEPS are giving the effective mass details for each mode of frequency.


Please refer the attachment (output from CAEPIPE & PEPS)

Hi,

Not sure also, but if you get the effective mass, where it will be used?
Because my understanding is, we will use this mass participation as an indication which mode will participate more in the dynamic response. I haven't used yet the effective mass as a real value, when performing dynamic analysis.

Anyway, what type of dynamic analysis are you performing (time history, response spectrum, harmonic or modal analysis)?

hi, thank you Borzki,

As of now i am doing Response spectrum analysis.

why i asked regarding this, because our customer is asking to include effective mass details in the report.
and i have checked the reports of other software there I found below

Effective mass = (mass participation factor)^2
Included mass = (Effective mass/Total mass of the piping system)X 100

but if i follow the same procedure in my model, it is not matching with the included mass
Please put your suggestion, mean while i will also search regarding this


Regards,
Pradeep

I understand your situation. I need to scrutinize it more to understand why it's needed as part of the report.

Normally, I don't do response spectrum analysis in my previous projects. I just have some fundamental understanding of the concept (that the piping system is like a shaker table consists of different oscillators which can be excited by source such as earthquake, the response of each oscillator to excitation, will be combined by certain combination method to get the total response of the system). My understanding is that as long as your input is correct in Caesar II for mass & stiffness and you have break the long lines to shorter segments for better accuracy of mode shape and the input for spectral curve is correct, I think you should be ok, considering you have captured sufficient mass participation and missing mass included in order not to miss potential modes that can be excited by the source.

But of course, satisfaction of the customer should be priority. It's a great opportunity for you to prepare such report and maybe if it will be part of your job often, so better understand customer requirements and maybe you can present it the other way to convince your customer that your report is reliable.

Maybe other forum members who are experts in this field and have been doing this type of report regularly can share to you how to answer your customer satisfactorily.

Cheers!!

We are all in the same page in this case.

Warm Regards,