Eigenvalue analysis after a short time history analysis

3DEC
1

Dear all,

I have this problem, but I am not sure if 3DEC allows to solve it by default.

I would like to know how the modal frequencies change while the model is accumulating damage. Therefore I would consider either two options:

A) performing an eigenvalue analysis, considering tangential or secant stiffness change, after only 2/3 seconds of a seismic input, therefore considering already some damage.

B) evaluating the natural frequencies while running the transient analysis, therefore per each time step.

I guess that the B) option is quite demanding and time consuming. But It would be great to hear your opinion.
Thank you in advance.

Best regards

Nicoletta

2

@jvlemos what do you think?

1 Like
3

The eigenvalue calculation in 3DEC is not directed to evaluate progressive damage, as it does not consider the tangent or secant stiffness for contacts at slip or beginning separation. The elastic stiffnesses are used until the sub-contacts are deleted, which typically happens only in advanced stages of damage.
I suppose it is possible to write a FISH function to assign stiffnesses to each sub-contact using some criteria for the effects of damage. This model would be only used to calculate the eigenvalues at a given stage, not for further cycling.

4

Thank you @jvlemos for your reply!