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new RC slab with existing columns 1

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n3jc

n3jc

Civil/Environmental
Joined
Nov 7, 2016
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189
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SI
Im dealing with a new concrete slab that is 120 mm thick.
Slab is supported on existing walls and on new masonry wall that is made between existing RC columns (300 x 300 mm)
Im wondering should I:

OPTION 1: anhor (rebars) new slab in the middle to the existing columns. I would use very small diameter of anchors/rebars so columns wont be affected much

OR

OPTION 2: dilatate new slab from existing columns (20 mm of insulation between slab and column)


What do you guys think? what is better. I know that a slab capacity is not problematic since spans are small and it is supported, but what about cracks between columns and edges of a new slab?


kov_rjwixc.png
 
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Your new slab will shrink the most in the long direction (parallel to the long walls). I like your option 2 of separating the slab from the columns, if they are not needed for support. Put some diagonal reinforcing in the re-entrant corners of the slabs near the column block-outs to help control cracking there.
Dave

Thaidavid
 
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Can you use a rebar locator to find the column bars and core drill through the existing column to install 'through dowels' assuming the column is small... and use 1/2" flexcel to isolate the slab on three sides from the column?

Dik
 
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I see no reason to connect it to the columns. All your gravity and lateral support comes from the walls.
 
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DETStru: Correct... I thought there were beams between the column... just isolate around the columns...

Dik
 
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I ll isolate.
thanks for help!

 
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