Reinforcing in Flute of Concrete over Steel Deck - 1

[FusionDan]

Looking at combining the composite slab reinforcing (3@18" 1" clr. from top of slab) with Flute Valley reinforcing (#5@12" in flute, 1" clr. from bottom) into a Larger Diameter Welded Wire Reinforcing. Been looking for reasons why the EOR has bar in the flute, can anyone help guide me as to the purpose of the bars in the flute, and why they can't be brought up into the slab. 7.5" slab total thickness w/ 3" decking and 4.5" slab.

Thank you in advance!

 

[KootK]

I'd guess that the bars in the flutes are there to provide flexural capacity. That, likely because:

1) the composite deck alone is not enough or;

2) the slab is in a corrosive environment and cannot be relied upon for strength or;

3) Some aspect of fire protection prevents the composite deck from being considered reliable.

Moving the reinforcing significantly upwards will significantly decrease its contribution to flexural capacity.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[JedClampett]

This is a significant change. If I was the EOR, I'd be plenty ticked if you did this without asking.
Another reason that I would mention is that a lot of us old timers don't trust composite deck and always add reinforcing. And as the EOR, that's our design decision.

 

[FusionDan]

Jed,

Nowhere was it indicated no-one asked, which is exactly why the Eng-Tips community was approached.... simply doing my homework is all.

This is what seems to be going on; the EoR is using the composite decking merely as a form system (forklift loading is in play). So we are in T-beam design??? Been sorting through a pdf on T-beam design, trying to determine how substantial the As increase will be if I pull the reinforcing in the flute up. My hunch is this is not going to fly, but the labor impact of running a bar down a flute vs. moving the steel up into the flange area is substantial. There's hundreds of thousands of square feet.

Been reading through this...but its a little above my pay grade...[

https://www.slideshare.net/elixireros/t-beam-ultimate-strength-design

[/url]

 

[JAE]

I agree with KootK and JedClampett on both their comments.

If forklift traffic is anticipated, the EOR may have had concerns over the long term bond between deck and concrete - necessary for flexural strength.
By adding the bars, set in the deck valleys you create a very positive deck system, flexurally.

No T beam behavior here - the bottom bars in tension and the top band of slab in compression - no different than a typically reinforced concrete slab.
The deck flutes would all be in the tension zone of the cross section and thus ignored and assumed fully cracked at ultimate strength.



Check out Eng-Tips Forum's Policies here:
faq731-376

 

[Archie264]

What's "Hard Rock Concrete"?

 

[JAE]

Well there's Pop Concrete, Folk Concrete, R&B Concrete, Motown Concrete, etc.

Check out Eng-Tips Forum's Policies here:
faq731-376

 

[kipfoot]

The bars in the flutes make the slab stronger. If you put the steel higher, you make the slab weaker.

 

[wannabeSE]

Hard rock = normal weight

 

[Archie264]

Thanks. And I guess now I'll start calling the associated music "normal weight" music.

 

[TLHS]

This isn't an unusual detail in my experience. In fact, some decking manufacturers give you options for flute spacing so you can match whatever rebar spacing you want.

I'd normally do it somewhere we're I'm not convinced that the deck is going to be protected in the long term. For instance, most industrial installations I'll ignore the contribution of the deck, because they're normally not hidden away and aren't protected from corrosion. I've seen a whole lot of corroded industrial decking over the years. I might do the same in some outdoor applications.

You may also do it if there are constraints on slab thickness but extra bending strength is required.

 

[Sawbux]

I used to show rebar in the flutes of deck for pulp & paper projects. Corrosion usually made the steel deck disappear after awhile. Rebar was good insurance that it would stand up for a time after the deck was noticed as being missing.

 

[FusionDan]

Corrosion is not an issue. It's in a Retail facility.

Can anyone direct me to a calc example that determines reinforcing As?

 

[JAE]

If you ignore the deck, isn't it simply basic concrete slab/beam design procedures?

Check out Eng-Tips Forum's Policies here:
faq731-376

 

[TLHS]

Yes. It means that you're just designing the decking as a form.