composite steel deck + regular slab connection 1

[serrojo]

Hi to All!

I have found a difficulty finding an example of joint between a regular plain slab and a composite slab.

The problem is that I need to create this joint in an unusual place (middle of the span), we are trying to figure out the solution to cast in-situ slab over prefabricated bathroom pods. Unfortunately we don't have to much space between the top of the pod and the bottom of the slab (say about 35cm).

So I am thinking of using a permanent formwork, and just leave it there. Maybe a steel deck would do the job, but I need to figure out how to support one end of the deck.

Any ideas/ suggestions/ warnings would be much appreciated.

Thanks in advance,


MSc. Eng. Serguei Joa
Structural Engineer
Bouygues Batiment International, Cuba.

 

[phamENG]

What's going on the to the right? That slab would have to be continuous or fixed at the next support.

Why not run the steel deck the whole width of the bay?

 

[serrojo]

Hello phamENG,

Thanks for replying,

Yes, the slab is continuous on the other end, the scheme is a continental frame for residential apartments, so the span is about 7.5m by 7m, too much for the deck, the idea is to support the patch of "formwork only" deck, i would keep same reinforcement and pour in one go each slab.

Sounds fair? But don't seem to find much details like this, so maybe it is not recommended or some other reason not to use.

Thank you.

MSc. Eng. Serguei Joa
Structural Engineer
Bouygues Batiment International, Cuba.

 

[phamENG]

Well you'll need shoring anyway, right? Why not run the deck all the way, use temporary shoring where you can, and support the ends of the deck on a steel angle or something that fits into your system. If the slab is designed to span the whole way already, then you maintain continuity and the steel deck becomes disposable after the concrete has cured. Remove the shores and you're good to go - leave the deck there if you can't remove it.

 

[serrojo]

Thank you phamENG,

It is very helpful.

Have a great day.



MSc. Eng. Serguei Joa
Structural Engineer
Bouygues Batiment International, Cuba.

 

[HTURKAK]

What are the dimensions of the plain slab and bathroom slab? Apparently , the bath room slab with composite deck and top level has a depression ...Without knowing the plan dimensions, the options on the table are, İ) convert the adjoining plain slab to composite slab, İİ) Provide drop beam at joint(s) with plain slab İİİ)Convert the composite deck to plain slab..

 

[serrojo]

Thank you @HTURKAK

please have a look at the scheme.

I think it is good enough, though a bit of waste as the deck is not considered collaborating, just permanent formwork on top of the Bathroom POD.

Thanks for the time, to look at my issue.

MSc. Eng. Serguei Joa
Structural Engineer
Bouygues Batiment International, Cuba.

 

[phamENG]

serrojo - I think there's a little confusion with your statement "joint between a regular plain slab and a composite slab."

To clarify, no part of the slab is actually composite, correct? The metal deck is just form work. (I've talked to plenty of engineers who mistakenly interchange the two - there's composite steel deck where the deck and the concrete work together and steel form deck where the steel deck at most carries the slab dead load and the slab carries all of the live and post-slab dead load alone.)

 

[serrojo]

@phamENG.

Spot On!

The aim is just to ease the execution part of the solution, as we have no clear height between the Pod's Top and the Bottom of the slab to be cast, I am not expect it to work as composite in any part.

Slab is 225mm thick and the recess is 50mm. I have designed the slab with the recess, and it works just fine!

thanks.

MSc. Eng. Serguei Joa
Structural Engineer
Bouygues Batiment International, Cuba.

 

[phamENG]

Hmm...I have another idea. What's the pod's top made of? Can it support the weight of wet concrete? If it's going to be essentially cast into this building no ability to remove it anyway, just pour the concrete on top of it.

I say this because metal deck has a trade-off - you're effective slab thickness is reduced due to the flutes. If you have enough meat from the top of the top flutes to the top of slab, you're good. But if you "need" the full depth (bottom flute to top of slab), you won't get it with metal form deck.

 

[serrojo]

Yes, I agree that the shape of the deck reduces the overall thickness.

But we plan to drop it's level to allow the needed thickness of slab over the deck.




MSc. Eng. Serguei Joa
Structural Engineer
Bouygues Batiment International, Cuba.

 

[HTURKAK]

Dear serrojo (Civil/Environmental);

I do not look to web everyday and moreover, we are at very different time zones..After looking to the sketch, i will suggest ; delete composite deck, and use similar RC slab having thickness 175 mm for the bath and 225 mm for the remaining area. Just provide 50 mm depression at top for bath area..

 

[serrojo]

Thank you @HTURKAK

That is exactly the idea, But a regular formwork is not working over the bathroom pod, to be installed, so I am looking to put some permanent formwork (sacrificial).

MSc. Eng. Serguei Joa
Structural Engineer
Bouygues Batiment International, Cuba.

 

[HTURKAK]

I could not see the reason why you do not install after formwork remowal..so , you will not need metal deck or sacrifial formwork..

 

[serrojo]

Hello,

It is required to put the bathroom POD before casting the upper slab, so no shoring is possible, as there is bathroom POD.

MSc. Eng. Serguei Joa
Structural Engineer
Bouygues Batiment International, Cuba.