When you say the excitation is in the y axis, is that in the plane of the ground or is that vertical?
Please insert an image into your reply showing the coordinate frame of the model in ANSYS.
Is the y axis of the table the same as the y axis of the model in ANSYS? If not please insert another image showing the coordinate frame of the table.
Since you have a physical structure mounted to a table, the table is being driven by an input signal. The input signal could be a Sine Sweep. That means there is an amplitude A and the frequency sweeps from a low value to a high value. It would be good to know these numbers.
The first thing you should do is run a Modal analysis on your building frame. What is the frequency of the first mode?