Buckling of Arched Sections of Corrugated Roof Deck

[Corn]

I am looking for information that would help me determine the span increase in a corrugated metal roof deck that could be afforded by its installation across bowstring trusses. The transverse curvature due to the wrap of the panel around the radius of the arch will clearly increase the moment of inertia of the section. The local web crippling or crushing at the supports will not be increased, so that will still have to be checked and may govern, but there should be a significant increase in the span capability of a roof panel due to the radius. In "Aircraft Structures" ISBN 0-07-049196-8, Peery and Azar present an equation (11.67) proposed by Kanemeitsu and Nojima that predicts the critical buckling stress of unstiffened sheet metal cylinders with a term that has a value proportional to the 1.6 power of the sheet thickness divided by the radius. This is about the kind of effect I expect, but I have not found more applicable gudance. Anyone got a clue for me?

 

[14159]

If there's nothing in the AISI NASPEC 2001, then I wouldn't increase the strength for this effect. I'd also think of called Vulcraft or some other deck mfr to get opinions. They think about this stuff a lot more and a lot deeper than the rest of us.

The deck comes in fairly narrow sheets that will have displacement compatibility sheet-to-sheet (from lap fasteners) but not full composite action. This has always led me to think of the curvature of an individual panel rather than the large curved roof section. When I look at it for an individual panel near the top of the roof, the idea of increasing the section property by a wide margin isn't so appealing. Granted, this is the lower bound behavior, but full composite action for a big curved roof is the upper bound. My opinion is that there are enough questions that I'd rather go with the lower bound.

I've never looked really hard at this because it's already possible to span roof deck far enough to make me nervous about the proposition.

I'm sure the eng-tips community would appreciate it if you tell the results of your research.

DBD

 

[Corn]

DBD,
Thanks for your thoughts. I like the idea of examining, analyizing, and/or testing the lower bound. I agree that a single-span single-sheet at the top of the arch would represent a lower bound. The single sheet approach is especially appropriate because the corrugated form of the sheet limits transverse stiffness to a small fraction of the axial capability. Even a single sheet might not behave as you might think. I've often thought a transverse strap or two, one on top, one below would extend the span capability a lot for the money. And to paraphrase Vince Lombardi- "Cost isn't everything, its the only thing".