Modal time history analysis

[jfhuang]

Hello everyone, does anybody know how to do a linear modal time history analysis in OpenSees? This will be useful in understanding the dynamics of the structure and modal contributions. I know we can do a response spectrum analysis but a time history is more of what I need. Thanks a lot for the inputs.

[kesavapraba]

Hi, I am not aware of any direct method available in OpenSees. However, you can still achieve it by some custom TCL script or extenal numerical platform, like MATLAB and Python. After developing your model, you can obtain mass and stiffness matrices as well as modal properties (frequencies and mode shapes) from OpenSees. With these information, you can write the model from physical into modal coordinates and then you can conduct time history analysis on each SDOFs and subsequently back assemble the response in physical coordinates - any structural dynamics book can help to understand this step. Please note that STKO also provides Python API in post-processing, you can explore this possibility to assemble the responses of SDOFs.

[jfhuang]

Hi, I am not aware of any direct method available in OpenSees. However, you can still achieve it by some custom TCL script or extenal numerical platform, like MATLAB and Python. After developing your model, you can obtain mass and stiffness matrices as well as modal properties (frequencies and mode shapes) from OpenSees. With these information, you can write the model from physical into modal coordinates and then you can conduct time history analysis on each SDOFs and subsequently back assemble the response in physical coordinates - any structural dynamics book can help to understand this step. Please note that STKO also provides Python API in post-processing, you can explore this possibility to assemble the responses of SDOFs.

Hi Prabakaran, I was trying to figure out whether there is a more convenient way of doing it instead of performing modal decomposition and mapping between nodal DOFs and mass/stiffness/damping matrices myself externally. Thanks for the response and suggestion!

[kesavapraba]

Yes, I understand that. We can have an answer if any of our forum members has an experience in it.

[STKO Team]

No, OpenSees only has direct integration analysis