Nodal load and Change in Modal Periods

[hlayssi]

Hello,

I was curious to know why any applied load, either point load at nodes or eleload along the element length, leads to change in the period of the structure.
I am comparing the periods with Etabs and OpenSees and it seems the periods in opensees are changing with any change in the loads.
Does opensees count these loads as Mass?

Thanks,
Hamed

[vesna]

These loads do not have any influence on the mass. However, if the load it large enough to induce damage in nonlinear elements, this may change the stiffness and as a consequence the period.