RC building software model.

[Sthprad]

Hi Everyone,

I analyzed the 30 storey plus 5 basement car park using RC building software. The core wall start from basements 5 to roof. In addition to this, additional three shear wall is added to meet the AS3600 drift requirement. This addition shear walls are 8m long starts from Level 1.
From the output result the shear and bending moment on these additional shear walls are very big for dead load only compare to wind and earthquake. Are these high internal forces resulted due to p-Delta effect or because of level 1 slab being transfer?

 

[Agent666]

I'd say with the level of information you have provided, it could be virtually anything. More detail of the exact configuration, loading, behaviour is required to get any meaningful response. Maybe reread your question and see if you could answer your question based on what you've told us if you knew nothing about at all about your building... I don't mean to be rude at all but you'll be more likely to get an answer if you provide sufficient information to diagnose the issue you are seeing.

 

[MIStructE_IRE]

This worries me..

 

[Settingsun]

You're on the other side of the world, MIStructE_IRE. Spare a thought for the locals.

 

[Retrograde]

Maybe your transfer slab is not stiff enough causing it to rotate - throwing moment into the wall. What software are you using? Did you do a construction stage analysis?

 

[Sthprad]

Retrogarde the transfer slab is 1m thick PT slab. I performed 2nd order analysis using RC building software of Inducta package. For DL only max deflection is 12mm which is 3 times more compare to wind. But the transfer slab will have 10mm deflection for longterm combination once the slab is designed as PT. In Rc model, I even increase the slab stiffness factor and tried run again the result is same. In my opinion, this high internal forces resulted from p-delta effect once the transfer slab sink by 12mm. Is it ok to go with this structural system. I have attached the structural configuration please see the attachment.

 

[Retrograde]

A 1,000mm slab does not sound anywhere near thick enough to transfer out a shear wall in a 30 story building. I would expect you would need at least 1,500mm (depending on the spans) just to transfer the vertical loads.

 

[calvinandhobbes10]

You ask is it ok to go with this structural system. No, as it is the irregular layout needs improvement in my mind. You also dont seem to yet understand the load path sufficiently. Take time, study it, and you probably need to get your supervisors to help. Wouldnt be surprised if youre right about the sag causing the moment, but now you have a reversed dead load moment tugging on disphragms above that is countered by the shear-core. Not a wise move in my mind.

Fortunately, you have negotiated a great deal of walls in the upper floors. Trade back some of those to get some columns under every free tip of your discontinuous shearwalls. Cannot emphasize this enough. Columns under wall ends. Don't let the transfer slab, whatever thickness it is, do all that rotational lifting. If you do this i bet you will find that you dont need all those interior drift walls because of the immensely reduced base rotation of those transfer walls, which reduces story wind drift (a lot). Architect might like less walls in his new flats. Basement parking garages dont need to be column-free, they never are. Plus, as you have mentioned, this avoids the added long term creep deflection in transfer slab that will sag all 30 floors above, which appears to be at the feature face of the tower nonetheless.

Your building looks kind of square-ish. Is wind drift an issue in the east-west direction?

Please take pains to get this design right. You sound rushed to arrive at a solution. Study it, chew on it. Dont be afraid to ask the architect for more structure where you need it.

Good luck!