Question regarding Response Spectrum Analysis .

[lesgidis]

I am having a 2storey 3d structure which i have to solve with Response Spectrum Analysis , and since Opensees is unable to solve the model with the above method , i was wondering if there is a way to export the stiffness matrix , or the modals of the eigen analysis .
Thank you for your time .

[vesna]

There is no OpenSees command that returns stiffness matrix. Look at this example: http://opensees.berkeley.edu/wiki/index ... -bay_frame to see how you can get modal information.