Calculation of eigen-modes of a building

Hi all,

I am having issues with calculating the natural frequencies of a shear wall building. I wrote an old post where I had an issue with the interaction between the walls and the slab, however, @matttam helped me solve the problem by using the meshbrep component.

My model is acting like a solid object, however, when comparing the periods to the periods I get with RFEM I get results 10 times less. Also, on certain floorplans, I am experiencing large deformations in the z-axis which I have to limit by defining my slab as a rigid object. The large deformations I am experiencing are shown on the following image for the first mode (shouldn’t the majority of deformations be in the x-axis, not y, could also be because of large torsion?):

Depending on the mode I always have a large translation in an axis, in this case in the x-axis (1m) which I cannot solve. Another example (mode 3):

Drawing conclusions from the results something is wrong with my model. I am not sure if it is in the definition of the meshbrep component, the inputs are on the photo below:

I will attach the function and rhino object to the post:
Vinogradska.3dm (2.5 MB)
Natural (58.4 KB)

Any help is appreciated!

Hi @konstrukcije2020,
to me the model looks correct. The first Eigenfrequency lies at 14.2Hz which seems quite high. The large deformations in Z-direction appear at higher eigen-modes when the floor slabs start to vibrate. The first three eigenmodes are translations in horizontal direction as expected.
In your example you superimposed all eigenmodes in the ModelView-component - maybe this led you to the assumption that something is wrong.
The amplitude of the vibration modes is not determined by the eigen-mode calculation but by the way how the results are scaled.
– Clemens

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