Cantilver slab to be poured later 4

[canstructural]

I have a situation ,where as per site requirements, cantilver slab of about 9ft will be poured later in the construction.

Please see the attached sketch and provide your opinion, is it possible to pour as one of the options. I am just wondering that there is no monolithic joint at the junction.

I can ask for bottom rebar to make continuous at support, if it requires to be.

Appreciate for your kind suggestions.

 

[jike]

As long as you can transfer shear and tension, you should be OK. I would ask for 3" bearing. I would also extend bottom bars to lap with.

 

[JAE]

Attached is what I would do.

Use a little larger ledge.
Use supplemental bottom dowels to use for shear friction (even though you have a ledge).
Hook the outer wall bar parallel to the wall.

 

[canstructural]

Thanks a lot for quick reply, i would make 3" min. bearing and keep the bottom dowels from slab.

 

[seny]

continues bottom bars or dowels.
could consider increasing of amount of bottom reinforcement.

 

[JAE]

I would also suggest looking at cambering up the forms on the cantilever a small bit - if this is exterior be careful you don't over camber and negate any required slope for drainage.

There will be some initial downward slip that I think would be more than that found in a monolithic placement.

 

[JedClampett]

A slick way to do this is with Richmond Dowel Bar Splicers (

http://www.daytonconcreteacc.com/a06_Threaded Splicing5_D-101-A.html).

That way you don't have the bars projecting out.
I'd also thicken the slab just a bit. ACI says to use a slab thickness of at least L/10 for a cantilever and yours is less than that. I'd round up to 12 inches thick, either on the thicker side or for a constant thickness slab.

 

[rapt]

I would be worried about corrosion inm the joint. There will be a weakness there and long term corrosion will be bad.

I would also use continuous bottom reinforcement.

 

[rowingengineer]

I would also be concerned about corrosion, you could consider using corrosion resistant reinforcing.


Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that them like it

 

[msquared48]

Two things and both in the 18' backspan:

1. I would make the top steel continous, and

2. Make sure the bottom steel is also sized for the no cantilever condition too. I would put at least 20 psf construction LL on the backspan too for this condition.

Mike McCann
MMC Engineering

 

[80smetalfm]

canstructural,

-Extend bottom bars in form of dowels say by 40xbar diameter min.
- Ensure face is scabbled prior to next pour.
- Cover might be an issue so dont ignore as it drastically reduces your effective depth.

______________________
Aussie brand RAPT is the best for slender rc columns!!

 

[BAretired]

I would remove the shear key and place the joint at the middle of the wall. The bottom steel should be extended to lap with the bottom steel of the cantilever.

I agree with Mike that top steel should extend throughout the backspan.

BA

 

[canstructural]

Thanks for your valued input.
See attached sketch with modifications to suit.

This is a 2 story structure, condition stated repeat at two levels, level one is interior at top with bottom of slab exposed to freezing and other at roof with expososed from top.

 

[BAretired]

Looks good to me.

BA

 

[canstructural]

Thanks for your sincere support.

 

[80smetalfm]

she looks good!

________________________________
Use RAPT for Slender RC Columns

 

[msquared48]

Take out the 9' min dimension in the upper sketch as it does not apply any moe.

Mike McCann
MMC Engineering

 

[BAretired]

Actually, you don't have to carry all of the top reinforcement across the backspan. If you decide to carry 50% of it through, then the 9' dimension could refer to the fifty percent of bars cut off. Without doing any calculations, that would seem reasonable to me.

BA

 

[hokie66]

I trust there is a membrane on the roof slab.

 

[canstructural]

yes, we can terminate 50% of steel at half the span, i was thinking to keep the option 2 with tapered cantilever slab and want to terminate 50% of top there at midspan of cantilever too.
Top rebar arrangement would look like: [] is support cantilver wall.

[]--------------------[]---------
[] -----------[]---------------- []--------------------[]---------
[] -----------[]----------------
hokie,
yes there would be a membrane at roof.