Design of Slab for Lateral Loads

[cgseso]

I am currently designing a five storey steel structure using STAAD. I am planning to add the slab in the model (something I have never done before) to achieve diaphragm action. The lateral drift I am getting is so small and very little as compare to the maximum permissible drift as recommended by the code. Do I still need to design the slab for lateral forces? Or design for gravity is enough? Any thoughts?

 

[jayrod12]

You should still design the slab for the lateral. It's entirely likely that whatever depth and reinforcing that shakes out from the gravity design is sufficient for lateral, but you need to be confident of such.

 

[KootK]

The lateral drift I am getting is so small and very little as compare to the maximum permissible drift as recommended by the code.

Are you referring to the story drift or the relative lateral deflection of the diaphragms along it's length? The former would have no bearing on expected diaphragm forces.

If a diaphragm calcs out to be very stiff, then I think that it's valid to expect that it's flexural strength design would not be too taxing. The diaphragm shear connections to the collector elements might still be working hard though.

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.

 

[cgseso]

Thanks jayrod12 and KootK. I am now designing the slab for lateral loads/ diaphragm action. Though, I am not so confident about the detailing. Do you have nice reference for the connection details between steel beam and slab? How frequent should be the shear studs? And one more thing, our client would want the slab precasted. Thanks!

 

[KootK]

PCI’s Hollowcore design manual has some basic information as do some of the FEMA guides and a multitude of European publications. There are a lot of ways to make the connections and often it’s not studs. We’d need to know more about your situation to be of much help with that. Will you have a composite concrete topping? I mostly detest untopped concrete diaphragms.

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.

 

[jayrod12]

I agree with what Koot has written.

Another good reference for connection details would come directly from the manufacturers' literature. LaFarge I know has some typical details posted on their website.

Regarding composite toppings, the preparation required for the adequate performance is quite involved. This should be performed by an experienced contractor, we have had to have many toppings removed and reinstalled due to de-bonding of the topping from inadequate preparation. I do agree however with Koot's detest for untopped diaphragms, however there is a good publication on design of hollow core slabs put out by PCI titled "Manual for the Design of Hollow Core Slabs". This includes a full chapter on diaphragm design.