Hi, I have a structure (like tower) which is a staircase and lift shaft. I designed the structure as you can see at the link bellow but it seems that the period is really small ( 0.74sec for the first mode and 0.54 for the second mode which activates 60% of the mass) for such a slender type of structure.
Does this seems right to you??
I also added a slab foundation to the structure and I find that is very strange that for the same foundation (comb 16- seismic foundation) the base pressure is always possitive but at the results of the sattlements I have uplifting effects!!
f1=1.36Hz seems ok to me for this kind of structure. In my opinion your structure has many bracings so it isn't so slender...