Seismosoft | Earthquake Engineering Solutions

hi everyone,

i m trying to understand why is the eigenvalue analysis result show a stable and constant cumulative masses values at 71.151765% with almost no change after the forth mode of vibration in x-axis direction , but reach a 93% in y - direction in the same mode of vibration.

please help me answering this question.

regards;

I may be misinterpreting your question, but it doesn't seem out of the ordinary. Can you plot the mode shapes and see if, in fact, they make sense.

hi huffte ;
pleasure hearing from you again; what i m trying to say is that i need to capture 90 percent of the structure mass which is in my case seems impossible in the x-axis .
here is the Cumulative Masses result with its associated mode of vibrations:

1- https://drive.google.com/file/d/0BzZ5tJ ... sp=sharing
2- https://drive.google.com/file/d/0BzZ5tJ ... sp=sharing

and this is the total base reaction resulting from implementing the static analyses:

https://drive.google.com/file/d/0BzZ5tJ ... sp=sharing

Hi zthaer. Perhaps you simply need to solve for more modes. It is certainly possible that a significant portion of the mass could be effective at a period less than 0.087 seconds. Why don't you try increasing the number of eigenvalues from the default of 10 to, say 15 or 20 and see how much the x-direction mass participation increases? Of course, it is always a good idea to plot and animate your mode shapes to see if everything makes sense, and if not, then why.

dear huffte;
what is the way to eliminate such unexpected mode shape?
ive just increase the number of eigenvalues but still got the same number each time.

Hi Zthaer,

Increase the number to eigenmodes to a really large value, e.g. 50. You might alos need to change the eigensolver algorith (from Lanczos to Ritz or the opposite)
Regards,
Seismosoft Support