New RC frame on top of existing

[greznik91]

I m dealing with 2 existing RC frames. I have to design new RC slab on top of that.
Above that is another floor - another RC frames on top of existing (columns are 300 x 300 mm, spacing between them is approx. 3 m).

Im wondering is it ok to anchor rebars for new columns in new RC slab as shown below?
I dont think that rebars would be properly anhored if I drill holes in existing columns + epoxy them.

Also it would be hard to get sufficient anchor lenght (drilling) which is needed since it will be desingned as moment frame. I want to avoid drilling in existing columns since I dont want to demage existing reinforcement there.

 

[DETstru]

You need some kind of anchorage to the existing columns or beams. You have overturning and shear to resolve into the existing members. Either via the new slab or the new columns.

I'm not sure if you intend to do this, but it looks like you want to consider the bases of your new columns fixed. That's not really the case, especially if you only anchor them into the slab. That slab can rotate and isn't truly "fixed." Even if you epoxied the new column reinforcement into the existing columns it's not truly "fixed." That joint can rotate. If the loads are small, sure it's not much rotation, but it does rotate.

Do you have frames in both directions?