Demolition part of Suspended Slab

[asixth]

Hi guys

I need to demolish part of a slab step. The step itself is located midspan of a two-way flat slab floor, so there is no top reinforcement that can be cut. I have determined that the slab will still have adequate capacity to transfer loads through the step.

The slab is suspended, so what is best practice to demolish the slab as shown? I would think to saw-cut it. What is the best procedure to specify?

 

[hokie66]

asixth,

I always worry about smooth stress transfer through steps like that, and thus always use a generous dimension between the top and soffit step, which is what the original designer did. So I am reluctant to change the profile.

But you asked how to do it, not whether it is acceptable to do so. I would have them make multiple longitudinal sawcuts, enough so that the strips can be easily broken off with hand tools. That way should prevent damage to the concrete which remains.

 

[rapt]

Personally, I would have had top and bottom reinforcement throught hat step, no matter where it occurs in the span! This would be even more important to me as the overlap length reduces!

 

[asixth]

hokie and rapt

thanks for your replies. I have had troubling finding good information that relates to set-downs in suspended slabs and the only reference material on the topic that I have been able to find is the steel reinforcing handbook published by SRIA. I understand that it is not ideal to provide set-downs in slabs because it limits the future flexibility of the slab.

The reinforcement handbook suggest that the thickness of the thickening should be a minimum of 1.5 times the thickness of the slab. For all set-downs I have been calling up 300 as the dimension of the thickening. This particular slab does have a thickening closer to 800 because it made the formwork easier.

How would I go about designing a slab setdown. My approach has been to assumed that the compressive forces in the top zone of the slab disperses at 45 degrees, so removing the slab will result in a slight alteration in the compressive stresses in the top zone because of the change in geometry.

I haven't been detailing top steel through set downs if it hasn't been required by the analysis. Is it common to provide top steel through set-downs even if it isn't required by the analysis?