rebar at reentrant corner? (concrete over composite metal deck - exterior condition) 2

[Ben29]

The image below shows an exterior balcony comprised of air-entrained concrete reinforced with epoxy-covered WWF over composite metal deck. The metal deck switches direction at the corner. The yellow area has the deck running north-south, and the blue area has the deck running east-west. Assuming that this is monolithically poured, do you think that I need to provide rebar at the reentrant corner as shown?

 

[KootK]

I'd roll with whatever you specified originally. Serviceability matters but, for minor stuff, not more than your reputation I feel.

 

[Ben29]

The concrete pour for this balcony has been pushed off a few days due to weather conditions, which gives me more time to obsess over my details.

Thank you everyone for your help thus far.

Here are my specific questions:
After reading alot of posts on how cracking occurs in suspended slabs, I fear that we will have cracking at the 3 1/2" end. The owner is open to the idea of forming the slab edge as needed to provide a 4 1/2" slab at the left end. Of course I will have egg on my face if I encourage them to take this action, but would rather have the egg then to have them have a product they aren't happy with.

Per my vulcraft catalog, this deck is good for a superimposed live load of 220 psf (much much more than what I need), which is why I was comfortable going down to the 3 1/2" thickness at the low end.

[ul]
[li]Are the clear distances to the rebar OK?[/li]
[li][/li]
[li]Can I just tie the #4 bar to the WWF instead of introducing tie bars?[/li]
[li][/li]
[li]Do I really need to hook the end of the #4 bar? I am currently showing it unhooked.[/li]
Will these #4 bars do more harm than good? Will it be too heavily reinforced?
[/ul]

 

[hokie66]

Two comments, both too late for your project.

1) I would have sloped the beams and kept the slab depth constant. The slab does not cantilever, the beams do.

2) HDG steel is good, but the deck will have a much lower degree of corrosion protection.

 

[driftLimiter]

You want it to be developed on each side of your backstay support beam. It is doing nothing for you near the tip of the cantilever. Maybe just center the bars on the backstay beam?

Curious to see what others have to say about tieing it to the WWF.

 

[Ben29]

Hokie: The owner didn't provide the HDG steel anyway. His choice.

 

[Ben29]

drift: Thank you, I will make that change.

 

[jayrod12]

What sort of locale are we talking here? Because not having the HDG steel, and also following up on my comment above and Hokie's concern about the deck, this seems like a short lifespan structure. Between the rotting of the deck, and the corrosion of the steel, the owner will be lucky to get 15 years out of this.

 

[Brad805]

Unless you start talking about specific curing measures I think this is setup to crack. Any chance there is an arch membrane? If not, this will not work out well for very long.

 

[phamENG]

My biggest concern for resilience/longevity is at your bent plate. The steel underneath can be okay as long as you're a) not on the ocean and b) they maintain the paint that I really hope somebody spec'd. The deck may also be okay as long as it's maintained. I've seen deck used in a similar fashion - it failed in about 40 years but that was mostly a maintenance failure. Did you at least spec G90? Paint helps. Also not relying on salts to keep the balcony clear of snow/ice helps. (We're in a similar geographic region - about 4 hours apart, I think.)

But that bent plate....there's no keeping water out of there. Water will get in and will get trapped. It will freeze and spall the concrete. Probably better to have left that off and let them use temporary formwork for the edge. Hind sight. This is why I refuse to show metal pan stairs for exterior applications.

 

[Ben29]

I also spec'd out a neogard pedestrian traffic coating membrane on the concrete. Not sure if they will use it. They did not submit shop drawings for anything, even though I asked them 10 times, and my drawings state that they must be provided for my review/approval or I won't certify the structure.

 

[Ben29]

Brad: Were you referring to a traffic membrane?

 

[Ben29]

jayrod: This is in Maryland

 

[Ben29]

Should I tell them to attach formwork at the bent plate and pour the edge to 4 1/2"? Or should I just let them pour it per the detail?

 

[Brad805]

Ben, yes I would expect a finish of some sort. It is unlikely you will have a crack free cure, and the communication here does not sound stellar. Some owners are of the opinion that crack free concrete is the norm, and that is not the case.

I assume they were able to roll the C section to the radius specified or they cut it and re-welded as needed to make the curve. This might have been a case not to have a closure angle. It would be easy enough to build a wood closure for the straight segments and the curve. It sounds like it is too late for that. If the architect had spec'd a finish I would expect to see a flashing over the joint, and the finish would lap over the flashing. I agree with Pham where the water will go. I expect a gap will appear between the concrete and angle soon after curing, and that will grow as he described.

 

[phamENG]

The coating will help. Hopefully it will wrap over the edge, but I'm not sure how that product might adhere to the steel. Might need a sealant in the shrinkage gap.