Isolation joint between floor slab and elevator shaft?

[GalileoG]

I am designing a two-storey structure. Steel moment frames in one direction and braced framed in another. Floor slab is composite deck with concrete topping. The structure will have a concrete elevator shaft that is quite eccentric to the centre of mass. The top of shaft is somewhere between the 2nd floor and the roof. I want to isolate the shaft from the 2nd floor slab to prevent torsional behavior given its undesirable eccentric location. However, in the moment frame direction, seismic deflection is about 4" after multiplying the elastic deflection with the ductility/over-strength factors. So, conservatively, I would need a 5" isolation joint. This seems quite significant. The 2nd floor concrete topping will be exposed (no floor finishing). How does one detail this isolation joint? Is this design approach reasonable? Thanks!

 

[Tomfh]

Why aren’t you connecting to the core?

 

[structSU10]

I agree with Tom - why not place bracing that works with the shaft and use it? Why is it concrete in this case? I could see masonry of even shaft wall with steel as required as they are likely cheaper especially if it only functions as a self supporting shaft.

 

[haynewp]

Unless there is a durability concern, I would push for shaftwall construction and get rid of the concrete core. Likely will save money.