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?

 

[Just Some Nerd]

Typical detail over here is to provide trimmers at every re-entrant corner as a blanket rule, so I'd be providing a couple of bars there just in case.

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Why yes, I do in fact have no idea what I'm talking about

 

[dik]

Unless you have a highrise where you may have several bits of this framing, I'd put top reinforcing equal to half the span for a fixed end condition, concentrated in an area about 1/6 the span in both directions, adjacent to the reentrant corner. I would dispense with the diagonal bars.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[hokie66]

Reinforcement will not be enoug to stop or control a crack there. It needs a joint, forming a straight crack.

 

[Ben29]

hokie: that is what I am afraid of. But we don't put sawed control joints in an elevated slab, right? Also, the only logical place for a construction joint would be over the top of the beam.

 

[phamENG]

Ben - you already have a joint. Since you're using composite deck and changing the direction, you have a pair of one way slabs meeting at that line. There's really no need for flexural stresses to be transferred there. I would make it a construction joint or a formed control joint. Saw cutting will be difficult to get right at the beginning and end next to a wall and on a free edge with a terrifying drop on the other side.

 

[Ben29]

pharm: Hot damn, you are right.

 

[phamENG]

blind squirrels and nuts, Bern.

 

[jayrod12]

...Bern.

I see what you did there, and I like it.

Now, onto the topic of discussion, this is an exterior slab that you're relying on the composite steel deck as part of the capacity? Or is the steel deck sacrificial formwork?

Where I am, steel deck is never used in exposed conditions except as formwork, we would not rely on it as a truly long term structural solution.

 

[KootK]

1) I feel that we need to recognize that is not a re-entrant corner in the "serious" sense because the balconies will, presumably, be laterally attached to a main building diaphragm that will restrain the balcony slabs from flexing in the manner that typically does harm to re-entrant slabs.

2) In the context of #1, I recommend just some "detailing" crack control reinforcing at the corner, similar to what JSN recommended.

 

[KootK]

If it were me, I'd be inclined to span the deck perpendicular to the building face wherever possible and then use a control joint layout as shown below. I feel that the good stuff that you might get with the control joints will offset the efficiency hit occurring as a result of a lack of continuity in the slab.

 

[KootK]

A you currently have your deck spans set up, I would expect you to be inviting some cracking at the locations shown in green below. My feeling on this is that the natural action for the deck slab is for it to be a cantilevered element spanning perpendicular to the building face. Setting things up this way would probably mean running top steel everywhere to reinforce the cantilever.

 

[Ben29]

kOOTK: Well hindsight is a dish best served cold and the deck is already installed (pouring tomorrow). I will note that I never received shop drawings for this, despite my pleading for them. So who knows what direction they actually installed the deck.

I do have a heavy wire mesh specified. 4x4 - 4/4

The only reason I know they are going to pour this tomorrow is because I got a text message over the weekend asking me how often they should install control joints and whether they could be saw-cut. I never planned on having control joints.

 

[KootK]

I never planned on having control joints.

Well, that's a feather in your contractor's hat then. It takes a village.

 

[Just Some Nerd]

Didnt notice the smaller cantilevers at first glance - would agree with Koot's suggestion that the decking should have spanned perpendicular to the building rather than alongside it.

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Why yes, I do in fact have no idea what I'm talking about

 

[Ben29]

ugh.....

 

[KootK]

It'll probably be fine. There's been no point in time at which I would ever have allowed a version of myself from five years prior design anything. Yet everything... is fine.

 

[Ben29]

Thanks KootK
It was a full 21 months ago that I actually designed this. I'm marginally smarter now.

 

[Ben29]

Ok, so they are telling me the deck is already installed. Should I have them add bars perpendicular to the building face that extend through the cantilevered ends? Currently I just have the WWF.

They told me they are pouring today.

Should I have them cut control joints where Koot showed the cracks would occur (in green)?

 

[Ben29]

I reviewed my details again and I am showing rebar at the slab edge. Now I just need to call up the contractor and make sure he installs them.