90% of Mass Participation

Question:

Hello,

In the model that I have attached, please let me know how to change parameters of Eigen Value analysis to achieve 90% mass participaton which is necesarry to seismic issues.

We could change frequencies number to 200, but calculation is slow, do you have any other ideas ?

Regards,



Answer:


Hey,

Actually the plate modelling would create many local modes and thats causing this issue.  There are 2 ways around this.
1)  Use the plate stiffness scale factor to make the plate very rigid for eigenvalue analysis.  Boundary change assignment feature would have to be used so that this is done only for eigenvalue and no other analysis.
2)  The easier way, use the Ritz vector method.

With that, 90% modal mass participation is obtained.  The modified model is attached.  Kindly let me know if any further assistance would be required.

Regards,
Nandeep
Technical Manager, MIDAS


Hallo,

thank You for the answer. Could You please give us some more leads how to follow the first method ?

Best regards,


Hello,

The first method is causing some change, but not enough to lead to 90% participation.
So, either springs would have to be provided at bottom slab, which can be activated only for eigenvalue analysis or Ritz vector method could be used.  Personally I wouldn't recommend the point spring approach since it would also cause many reactions for RS analysis.

Regards,
Nandeep
Technical Manager, MIDAS
Creation date: 10/17/2018 10:49 PM (dklee@midasit.com)      Updated: 10/18/2018 8:20 AM (dklee@midasit.com)
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Model 3.mcb
Model 3.zip