Structural Concrete Slab Reinforcement

[AKSherpa]

Friend of mine is building a house with a reinforced concrete slab for the roof that will also double as a driveway. Curious as to recommendations for steel reinforcement in the slab. It will be spanning multiple beams in one direction and a center support in the other. He has purchased structural decking to place the concrete onto. The support beams are spaced 6 feet in the short direction. Since it is a continuous style system it seems he will want reinforcement in both the top and bottom of the slab. Hoping to get some feedback on the typical way of placing reinforcement for this type of structural slab. Top and bottom bars? Min slab thickness if using double mat of #4's. Nelson stud spacing? Best method to connect Nelson studs, meaning should he drill holes in the structural decking to allow for welding the studs to beams or place the Nelson studs and then cut the panels to span between them? Any info appreciated, Thanks

 

[Ron247]

If your friend does not know how thick this roof will be, how did they size the beams that will support it?
I think your friend needs to hire a structural engineer. This sounds like a full design is needed not some guidance.

 

[Dowels93]

My recommendation is to look at hiring a local structural engineer who can evaluate the loads, load path, and reinforcement as necessary. It seems beyond the typical information you'd get from an online forum.

 

[AKSherpa]

I am not looking for design. I am looking for verification that my preliminary design consisting of a double mat of rebar is the best option before I put a lot of time into something that isn't standard method. I am PE capable of doing the design just looking for tips to get me started in right direction and help guide me.
Thanks

 

[radiocontrolhead]

Few resources:

verco deck catalog
AISC manual (for composite action design)

 

[BridgeSmith]

It sounds similar to a bridge slab, and that being the case, the AASHTO bridge design specifications would be the go-to reference.

 

[Dowels93]

Is it a composite or non-composite deck? Are you also planning on using the concrete in a composite system with the steel beams (unrelated to whether it is a composite deck)? What other loads might be added (i.e. shelving/racking if it's a garage, not just a driveway)? The slab thickness will be influenced by all of these, rather than just by the rebar you've selected.

In my area (Ontario, Canada), if a deck is non-composite, then the slab is reinforced top & bottom like a typical slab. If it is composite, then it'll be reinforced with rebar in the deck flutes and often a welded wire fabric to control cracking and provide capacity over the supports. I haven't seen any concrete on metal deck acting compositely with the beams, but I do know it is done, and the stud spacing will be determined by the degree of composite action required.

I'd recommend taking a look at Canam, Vulcraft, VicWest, and other deck manufacturers for their typical details & loading tables. A car also adds the concern of point loading (through the 4 tires), which may need a quick call to a manufacturer for more info. Some of this is regional though, and getting in touch with a local SE still wouldn't hurt.