peteroznewman
Subscriber

A Harmonic Response is the correct analysis to obtain the acceleration Amplification factor from the Frequency Response result.  It is usually faster to use a Modal analysis and drop a Harmonic Response analysis on the Solution cell of Modal to create a mode superposition harmonic response analysis.

A Frequency Response Function (FRF) is obtained from a sweep of frequencies of a harmonic (sinusoidal) input vibration. In the figure you show, it looks like one of the modes is near 25 Hz.

A seismic vibration input to the base of a structure is not a harmonic input so you don’t get an FRF output. You get what you show in your other thread.