The material properties are orthogonal and isotropic (neglecting residual stresses from forming!); however, the mechanical properties vary significantly between longitudinal and transverse directions. Longitudinal buckling is "column-like" with significant capability, while the transverse is "accordion-like" with less capacity.
Any guidance as to where one can obtain values for deck shear strength parallel to the flutes ? Most of the published tables that I have seen for steel deck diaphragms seem to cover the more conservative case of diaphragm shear perpendicular to the flutes.
From what I have been able to gather from Vulcraft's Research Department, it doesn't matter what direction the load comes from because a deck won't fail in direct compression, it fails in shear along the 45 degree plane. This is why the G' and the published shear values don't matter for deck orientation, because the shear still fails it along the diagonal.
dougantholz,
exactly....if you remember your Mohr's Circle exercises, shear on a small segment involves the same dual couple on both orthogonal directions. It doesn't matter which "direction" the shear is in because shear really doesn't have a direction.
If you refer to axial stiffness, as Ron indicates, for forces parallel to the corners of stamped indentations shows far bigger stiffness thatn transversally to them, due the ability to behave accordion-like.
Now there'is some interest and even some examples built of webs made of deck-like material, but for such applicaiton it seems the stamped indentations run invariably vertical, since this must also preserve better the shear rigidity available. Laying them horizontal would make web crippling too sure, since the flanges wouldn't have support under the applied loads, and overall transversal shape of the built-up shape would be soon lost.
I am not completely sure I understand why you would even be considering using the deck in a transverse direction. From a building engineering perspective, you would normally put a concrete topping and mesh on steel decking in say composite slabs and would ignore the steel decking capacity completely. this would gove you local diaphragm action. In a lightweight steel roof you would ignore the steel decking and use transverse beams/purlins diagonal bracing to resist significant lateral loads. Crinkly tin does not have significant structural capacity in a transverse direction to span. Hope this helps.
A three sided box where your deck is subject to rotation. I would still try to analyze it to determine the effective shear in the diaphragm. If you determine the shear along each of the three shearwalls (or braces or whatever) you end up with a pair of force couples. One couple is the resultant shearwall shear for the pair of parallel walls which are perpendicular to the lateral force. The other couple is made up of the one shearwall shear and the resultant lateral force. These, roughly speaking, seem to create natural shear forces between the couples which can be used to design.
I tried to download the Hilti diaphragm program last week but when I tried to run it, it gave me an error about a missing file.
Thanks everyone. My question may be silly but I want to know if what I am modeling is accurate. I am looking at a three sided box, where the aspect ratio is about 2:1 (where one of the short sided ends is open). I want to know what the deflection at the open end is. And I want to know the deck response to the load.
My theory is: That if I load the deck in an orthagonal direction, I get shear along the 45 deg. plane. If then you are asking the deck to rotate as well in order to resist the 3-sided box, then some of the deck will be in compression/tension parallel to the flutes, and some will be in comp/tension perpendicular to the flutes. The loading perpendicular to the flutes will control since this value is much lower (rationally) than deck in the other direction. My question is what is that value and how would I find it.
Back to my other quesiton, does anyone know how to calculate the deflection of the 3-sided box?
My suggestion is that you model explicitly the folded shape by at least membrane elements, this should capture well the behaviour. You can even yourself make this way the analysis on some assumptions for different sizes of boxes and then adjust orthogonal rigidities that match the more complete models.
dougantholz - I guess I don't see how the deck would ever accordian on you. The deck is typically connected to the underlying roof joists or beams which are spaced at a fairly close distance and extend perpendicular to the flutes. As the roof diaphragm is loaded, the roof joists take the true axial load and the deck only serves in shear. For the deck to accordian, it would have to slip across the supporting joists, which cannot occur as they are fastened and the joists do not deflect axially to any great extent.
