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ANALYSIS: Effective Diaphragm Thickness

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For a long time I’ve used the discussion in the SDI Diaphragm Design Manual (Larry Luttrell) as the basis for determining and “effective diaphragm thickness” to use in FE analysis. The shear rigidity of a corrugated steel deck is much less (typically an order of magnitude) less than a “flat plate” of the same thickness because of the edge conditions, the “warping” of the flutes, etc.


Thinking about this, I wonder if I’m still being a bit too simplistic, however. The discussion by Dr. Luttrell does not really address anything beyond shear distortion. For example, is it reasonable to expect that the axial stiffness (normal stiffness) in the direction of the deck span might be greater than the axial stiffness in the orthogonal direction? Qualitatively it seems to me that the direction orthogonal to the span might see stiffness nearer to the shear stiffness (because of the “flattening out” of the flutes, e.g.) whereas the normal direction is going to be closer to what a flat plate might see (the corrugations actually ADD area, though the edge fastening effect is still there, etc.)


I wonder if anyone has addressed this, and what your thoughts are.