composite floor deck on ribbed concrete

[barnugget]

Anyone come across a condition where a concrete composite deck is placed on top of an existing ribbed concrete deck? The corrugated composite deck wil span perpendicular to the concrete ribs (one way joists). The existing slab between the ribs is a little less than 3" in some areas and the new deck is to be for observation. I was hoping to use the composite deck to increase the effective depth of the reinforcement and strengthen the floor systems. The composite deck will be made of lightweight concrete and only 3-1/2" thick. The existing deck spans 19' and has 6" ribbed slabs at 36" on center with a pan depth of 8" and slab of 3". Calculations of additional deck and live load superimposed are good for shear and flex. Do I need a special connection for shear transfer to the deck? Any one with experience using this type of application? Would a cellular type deck be better?

 

[DaveAtkins]

I don't believe you will get composite action between a concrete filled steel deck and the one way joist system it sits on. It sounds to me like you are just adding dead load on to the existing joists.

DaveAtkins

 

[jjeng2]

I dont think this is a good idea. Theoretically you would have to drill and epoxy dowels thru the slab and into the ribs and hook them into the new slab to get composite action between the ribs and new deck. I dont see a way other than drilling and epoxying dowels all over the place to get the slabs to work together. This is all just theoretical, as I would not use this approach and it would require testing and detailed calcs. If you want to reinforce the slabs only and the ribs are ok, try steel angles under the slab from rib to rib or some sort of CRFP reinforcement under the slab. I had to locally reinforce a similar slab for a crane installation and put a network of steel under the area. This approach may not work on a one way slab subjected to uniform psf load though. Consider busting out the slab only and pouring a new, thicker slab on top. Need to connect to ribs though. Have done this on deteriorated parking garages. Also, if it can handle the dead load, throw a lwt reinforced topping slab over whats there and bond it to the ex slab. Disregard contribution of ex. slab though. I wouldnt count on them working together.

 

[phdunn]

The ACI Code 318 has a section on composite construction, using concrete on concrete. I would leave out the metal decking, use the existing concrete as form, roughen the existing concrete, add a good epoxy adhesive (Sika makes several) Follow ACI 318 to see if you need to add dowels.