Concrete slab on Composite Steel Deck Design

[Perception]

Hello everyone,

I am getting into composite floor system design, and I have a quick question about utilizing the Vulcraft steel decking catalog.

1. Are the concrete slabs in the composite tables capable of carrying the superimposed live loads allowed for the deck? I saw that Vulcraft listed the SDI requirements for the slab design, but I wasn't sure if the slab design had been checked in the actual deck design tables. I assume the slab is "ok" provided the reinforcement (welded wire reinforcement) and span length requirements in the table are used, but I'm not sure.

2. For areas without simple loading or negative moment regions, what is the general practice for designing the slab? Do people design per ACI 318 and put rebar in the slab, or do people try to follow SDI and find the capacity of the slab with the decking as positive moment reinforcement (negative would obviously have to be ACI)?

Thanks

 

[KootK]

1) You should be working from Vulcraft load tables that clearly indicate the superimposed load capacities for various scenarios.

2) My first stop will usually be to ignore negative bending for strength and work out a uniform load that I feel is equivalent to the non-uniform load being considered. That way I can just stick with the tables. My second stop will be to use the deck for positive moment and conventional RC concrete provisions for negative moment if I need it. Positive moment rebar is really a last resort for me unless I'm considering the deck sacrificial for some reason (corrosive environment etc.)

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.

 

[Perception]

Great answer for the second question.

For the first question I am referring to the bending of the slab between two adjacent beams. I see that the Vulcraft manual accounts for the appropriate load cases to design the decking, but I wasn't sure if a properly design concrete slab was inherent in the superimposed load capacities. Would any slab design be necessary if everything fell under the span and loading conditions in the table? Also assuming that the slab thickness and wire reinforcement that corresponds to the superimposed load capacity was used.

Thanks

 

[KootK]

Most decking manufactures will supply you with two sets of tabulated capacities:

1) The bare deck on its own. This is used to asses the deck's capacity to support wet concrete and construction loads.

2) The deck working compositely with the concrete. This is for checking your final, in service condition.

If that doesn't clear things up, consider posting the table that you're using here for review.

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.

 

[Perception]

Just to update this thread, I called Vulcraft and they told me the following information:

- In their values for superimposed live loads, the slab had been checked to be properly designed between adjacent beams. They check the slab for bending, shear, and deflection assuming that the metal deck acts as tension reinforcement for the slab. Provided that the span being considered is simply supported with no negative moment, the only thing left to design for the slab is the shrinkage and temperature steel.