Diaphragm Design for Dutch Gable Wood Roof

[KootK]

Per the sketch below, I'm trying to work out shear transfer through a dutch gable wood framed roof. I've been considering it as three discrete, connected diaphragms:

1) The hip roof segment at the left end.
2) The main gable roof in the middle.
3) The hip roof segment at the right end.

The trouble is this: conceived this way, diaphragms one and three have aspect ratios of about 8:1 (sketch is poorly scaled). That's a no go per North American wood codes which usually limit diaphragm aspect ratios to around 4:1. I'm having a hard time seeing a away around this.

The only workaround that I've come up with is to consider all three diaphragms, and the vertical plywood at the gable trusses, as a single diaphragm. Basically, I take the five diaphragm surfaces -- three horizontal-ish and two vertical -- and fold them out flat in the east west direction. Then I use that fictional diaphragm for calculating deflections and aspect ratios. My logic for this is that all of the sub-diaphragms are shear connected to one another and jointly span between two drag elements (shear walls) at the far ends. Thus, one diaphragm for all intents and purposes.

Anybody buy this? Got a better idea? Please advise. There is some irony in the fact that, two decades ago, I was the truss guy framing out five or so of these roofs a month. Luckily, I wasn't the EOR and I had no concept of lateral loads whatsoever. A little less lucky for society I suppose.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[XR250]

@Excel: I see where you're headed and I agree: no failures and lots of data points. Still, I have to find some reasonable narrative here regarding load path. It'll be equally problematic for wind the other way.


FWIW, has anyone EVER observed a failure in ANY roof diaphragm? I have seen sheathing and rafters pulled of the roof, tall walls pushed in, garage doors ripped put, but never and shear failure of a roof diaphragm. I was even doing some work at a large strip mall recently and a roof edge angle did not even exist - no attachment at all from the metal deck to the 50 ft. long exterior masonry wall (one central i-beam diode bear on the wall). I don't even know if the bar joists are fastened down. The building has survived at least one strong hurricane unscathed.

 

[KootK]

I came across the same situation at a retail facility earlier this year Excel. The consequences for poor diaphragm design seem to be so non-existent that it's hard not to feel as though I'm wasting my time with it.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.