Yes that 1.66 Hz is from experiments and 8Hz is for simulation I did in ANSYS.
For the experiments a solid base was used to connect the structure with the shaking table which I have not included in my model because the primarily objective of the base is to excite the structure I guess. Do you think this matters? You can see in the picture I pointed the rigid base while I ignored this and directly applying excitation at column face.
One more thing is reported by the author an "artificial mass" which is not explicit described and I could not understand what that means. It is mentioned that the have used a certain artificial mass. Do you have idea on this? and if yes How one can apply an artificial mass in WB?