I can find absolutely nothing in the text and commentary of the
1999 ACI 318 that suggests that section 21.7, "Structural
Diaphragms and Trusses," is applicable to the concrete over metal
deck. What concerns me is the fact that all references are to
monolithic diaphragms or topping-slab diaphragms on precast
Buckling, as referenced in the commentary for 21.7.2, may be a
problem for thin (3" or so) concrete over metal deck. I'd expect
topping on a precast panel, or concrete joist/waffle systems, to
behave differently than "topping" on a metal deck, so the 21.7.4
minimum thickneses may not be enough.
BTW, I'm aware of the SDI manual's take on this...I need more
capacity (ultimate shears on the order of 10,000 plf or more).
I'd appreciate any thoughts on this subject.
D a v e E v a n s , P . E .
T N H, I n c .