RC foudation slab - edge thickening bellow columns

[greznik91]

Hello!

I'm dealing with a concrete structure (walls and RC frames). Foudation slab is 300 mm. Since I have some columns with pretty large forces at the edge of the slab (punching shear) I have been thinking to make RC slab thicker (450 mm)in area bellow columns.

What is the proper way to change thickness?

Is it ok to change the thickness over a short distance (as shown in attached image) or should this distance be longer?

I havent done this before so I hope for some sugestions.

Thanks, regards


Green - columns,
Red - punching shear lines,
Yellow - opening in the slab

 

[HTURKAK]

Perimeter stiffening of the raft with 1500 mm width is OK. But, the remaining thick. 300 mm is questionable.. could be OK for single storey , flexible superstructure ..

Will you provide more info for the structure? ( no. of storeys, dimensions , etc)...??

 

[milkshakelake]

Looking at your section, if you've done all the calculations correctly, it depends on the economics in your area. In my area, it's cheaper and more conservative to extend the footing. The foundations will cost about 1% more but your liability will be around -5% less. 5x benefit for something that nobody will argue about.

I agree with @HTURKAK that 300mm is questionable. It can't support much in terms of punching shear.