Combined Gravity Load Capacity of a Non-Composite Metal Deck and Reinforced Concrete Slab 1

[jochav52802]

Hello All,

Regarding reinforced concrete slabs that are supported on non-composite metal deck, is it possible to use the combined gravity load capacities of both the slab and deck to determine what total gravity load the non-composite system can support?

Or should the deck only be looked at to confirm that it can support the weight of the deck,slab and construction live loads? If there's any extra remaining capacity, I'm wondering if it can be added to the capacity of the reinforced slab.

Thanks for your help!

 

[phamENG]

Short answer is no, you can't use the remaining capacity.

Long answer is sort of: Because it's non-composite, the deck and the concrete won't be working together like a composite system does. As a result, the only load sharing that occurs beyond the initial slab dead load occurs based on relative stiffness. The thing is, the concrete is generally going to be stiffer than the steel deck. By the time the concrete has deflected enough to make the load sharing meaningful, the concrete slab is probably too far gone. If you're in a market where material is really expensive and the serviceability requirements are low, you might be able to save something by trying to go that route. In most cases, though, there's no real savings to be gained from doing it and you'll just give yourself a headache if you try.

 

[jochav52802]

Thank you phamENG, your response makes sense.

Initially I had thought since the concrete is cast against the deck, they'll both engage right away once the concrete dries and live loads are applied, which is true. But because of the difference in stiffness, the deck won't contribute much of it's remaining capacity since the slab won't deflect enough to engage it.

Thanks for helping me think that relatively simple concept out!

 

[phamENG]

You're most welcome. It's often the simple stuff that gives us the most trouble, because we try to make it complicated.

 

[jochav52802]

I appreciate your graceful communication phamENG, it's a good example for this forum regardless of how simple-minded the question may be.