Hi Jay,

I agree with Mariog. If I'm not mistaken, the harmonic, response spectrum and Time History Analysis are all dependent on the Modal Analysis (natural frequency). There is Direct Integration Time History analysis which maybe not depend on natural frequency if I'm not mistaken, but most software utilize the Modal Time History analysis which breaks the system into individual modes of vibration and combine them together to get the total response.

Any other opinion is highly appreciated. Just correct any misleading statement I've made.

Cheers!!