I guess this is a support structure? Surface and underground police stations.
Seems like every building I make has something unique about it. When I was looking at the original artwork, I noticed that the surface police station is basically a "telescoped" version of the underground police station. I thought that was kind of novel, so I gave it a try.
The above ground structure has an elevated observation deck. This is to allow the workers to see over the top of tubes and neighboring buildings, as well as further out on the horizon. Since the underground version doesn't need to see as far, it doesn't need an observation deck. So the top portion of the structure is mounted directly to the top of base.
On one hand, this makes sense from the standpoint that modular/similar buildings are more efficient to produce. On the other hand, it wouldn't make any sense to have an actual retracting observation deck. The only time that would make sense is if there were weather disasters (similar to OP2), where the building needed to hunker down into a more survivable state.