Composite Slab Diaphragm Design
Composite Slab Diaphragm Design
(OP)
For a fully composite steel floor system, how do you typically determine diaphragm capacity?
SDI publishes composite deck diaphragm design values based on welded metal deck connections and an unspecified amount of lightweight or normalweight concrete above the deck. This is a little questionable to me. Shouldn't the thickness of the concrete be a parameter? As well as the fact that there are shear studs present? I get the impression that the methodology here relies solely on the contribution from the metal deck.
Is there any reason why you can't simply argue that you have a concrete diaphragm based on the thickness of concrete above the flutes and design per the ACI shear provisions. That seems a lot more realistic.
Thoughts??
SDI publishes composite deck diaphragm design values based on welded metal deck connections and an unspecified amount of lightweight or normalweight concrete above the deck. This is a little questionable to me. Shouldn't the thickness of the concrete be a parameter? As well as the fact that there are shear studs present? I get the impression that the methodology here relies solely on the contribution from the metal deck.
Is there any reason why you can't simply argue that you have a concrete diaphragm based on the thickness of concrete above the flutes and design per the ACI shear provisions. That seems a lot more realistic.
Thoughts??






RE: Composite Slab Diaphragm Design
RE: Composite Slab Diaphragm Design
Also, I still don't understand why they say the support fasteners are 5/8" puddle welds (see attached table)? Wouldn't the shear studs be the support fasteners?
RE: Composite Slab Diaphragm Design
RE: Composite Slab Diaphragm Design
RE: Composite Slab Diaphragm Design
Unless I am mistaken, you do not need shear studs to make a "composite" slab only.
RE: Composite Slab Diaphragm Design
RE: Composite Slab Diaphragm Design
RE: Composite Slab Diaphragm Design
If the values for 2.5" work, then you are done, otherwise you need to calculate the diaphragm value for the actual thickness using the diaphragm design guide (3rd edition found here: http://www.sdi.org/manuals.htm). Actually I have found that Hilti DF diaphragm program is an excellent tool for calculating these capacities (they let you use puddle welds vs. hilti products for comparison: http://
Of course it changes depending on the strength of the concrete - take a look in ACI - there is a LW reduction factor for shear in reinforced concrete as well.