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New CLT slab supported on existing RC columns

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n3jc

Civil/Environmental
Nov 7, 2016
187
SI
Hi,
I'm dealing with the existing residental building with the masonry and concrete walls 300 mm thick and the RC frames in the ground floor that support existing concrete slab.

RC columns are 300x300 mm and are reaching 5 m above the RC slab - they are supporting existing roof beams at the top.

I'd like to add another floor above existing one.
The new slab will be CLT (140 mm thick cross laminated timber slabs) supported on the steel frames.

My question is would you support/fix new steel beams directly on existing RC columns (as shown in the attached image) since they are 5,00 m above existing slab and are acting as cantilever that is 5,00 m tall?

New CLT slabs will be connected to all bearing perimeter walls.

That way RC columns are laterally supported since CLT slabs is acting as diaphragm in case of the seismic forces.
But when I've done seismic analysis I got large bending moments in existing concrete columns at the height of the new floor( probably due to the new floor displacements?).

Would it be better idea to completely seperate new CLT floor from existing columns?



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Pretty much exactly as you've shown, but likely with more anchors into the column.
 

I would suggest ;

- Check for flexible diaphragm condition. The CLT slab may be modelled assuming flexible diaphragm .

- Check the modelling of steel beam- RC column connection. Assign both ends pin .

- Provide more info . regarding the applicable code , seismicity etc. to get better responds..






Use it up, wear it out;
Make it do, or do without.

NEW ENGLAND MAXIM


 
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