Core Wall - Raft Stability Check?

[JackEngTip]

Hi guys,
I have a structure that has a basement. If I use the ground floor as base, do I still need to check raft-soil stability under wind and earthquake?
Thank you.

 

[Trenno]

Need much more info. Perhaps a sketch too.

I assume you meant to say you've modelled the lateral stability elements to ground floor only in your analysis model. That approach may be fine for prelim analysis, but in reality I suspect your lateral system won't transfer at ground and will continue down to the basement. In any case, yes the basement raft will need to be checked against all loads, including lateral wind/EQ.

While you're at it, have a read of this article - I think you'll find it ties in with what you're looking at.
Backstay Effect Article

 

[JackEngTip]

Thanks for your reply Trenno.

The structure is a multi-storey apartment with one basement. There is a 300mm Thick concrete slab on the ground floor (no openings near the core). The lateral load will be resisted by the lift core.

It is a prelimary design and I am wondering if I can take the restraint of ground floor into consideration when it comes to the stability design of the raft that supports the lift core. The lift core carries no much gravity loads P*, and if I dont take the ground floor slab into consideration, which means I will apply the whole base overturning moment M* caused by the wind and earthquake for the stability design of the raft, the equvailent eccentricity e = M*/P* will be very large, which requires a very big raft foundation for the core wall.
Just like the article that you mentioned, The overturning moment on the basement (raft) will be reduce if I take the ground floor as a pin or spring support. So what is your normal pratice on this? Use the whole overturning moment on the raft stabilty design?

Thank you.