Seismic load as rotation

[Boniek]

Dear all,

I've found strange behaviour during time-history analysis of simple cantilever.
After seismic analysis with load as a rotational acceleration I get bending moment as shown in picture (non-zero moments at the top of the structure, and change in sign in the middle node).
This does not happen when I am not including stiffness proportional damping.
I would appreciate any help.

https://onedrive.live.com/redir?resid=1 ... lder%2cspf

Best regards.

[huffte]

Hi Boniek. The behavior is entirely due to the fact that the acceleration has been applied as a rotation, which is rather unusual. But perhaps you are studying the effects of rotational accelerations as opposed to the usual translational accelerations. I cannot speak to whether or not the rotational nature of the load should produce this effect. Perhaps in the same way that a translational acceleration would produce a shear at the top of the column, a rotational acceleration would produce a moment in the top of the column in addition to the reversal noted at the joint between elements. I hope this helps. Best of luck on your work.

[Boniek]

Dear Tim Huff,
Thank you for response. I will consider this also. But it appears more to be more like numerical issue rest comparing rest of the results of the model.