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Ridge Vent - Shear Transfer Product? 1

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DayRooster

DayRooster

Structural
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Jun 16, 2011
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Has anyone used this product before? It seems to make sense and be a reasonable compromise for architectural ridge vents. Are there any other products that are similar? Or are engineers still just ignoring the discontinuity at continuous ridge vents?

 
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Thanks for the reference. Ive been blocking under each sheathing edge, clipping the blocks together, and coring holes through them to provide equivalent ventilation
 
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DayRooster said:
Or are engineers still just ignoring the discontinuity at continuous ridge vents?
Click to expand...

That one for me.
 
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Assuming the ridge joint/rafter to ridge connection is properly designed, it's no more discontinuous than any other aligned sheathing joint. You can only stagger in one direction, so they align one way or another.
 
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phamENG said:
Assuming the ridge joint/rafter to ridge connection is properly designed
Click to expand...


....except nobody designs that :)
 
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XR250 said:
....except nobody designs that :)
Click to expand...

True, but that's because there's really no need. When load is parallel to the ridge, shear is (usually) zero there if the load is uniform and the roof section under consideration is symmetrical. When perpendicular, you're dealing with a horizontal shear which is very small GREATEST at mid depth. (Sorry...seems my brain got inverted this morning.)

So in really funky, asymmetrical roof systems the ridge may land in a spot worthy of deeper consideration. But in a 'traditional' and simple roof, the ridge is almost always in a low stress area.
 
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phamENG said:
When perpendicular, you're dealing with a horizontal shear which is very small at mid depth.
Click to expand...
Wait, isn't that where it would be greatest?. Though in the grand scheme of things, probably not much.
 
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Additional points based on the additional comments by others:

1) A ridge vent joint is kind of like an unblocked, aligned joint as phamENG mentioned but with two primary differences.

a) a greater than normal gap between the sheathing boundaries.

b) lack of weak axis flexural continuity across the supporting framing.

2) I agree with XR250 about the horizontal shear being at a maximum at mid-depth for the perpendicular case. Really, it's the same at all vertical locations when we use the shear panel assumption.

3) Nobody really expects wind load to be even remotely uniform so I also don't favor the assumption of near zero shear stress at the ridge for the parallel case. At the least, I'd think one would provide 25% of the maximum demand at all locations, similar to what is done with steel joists.
 
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I think this all supports my belief that houses really act like a series of connected three-sided buildings. Don't need no shear continuity or chords.
 
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Yep...I was very wrong there. Thanks for calling me out.

XR - you're probably right about the behavior. We should have a modular house built and not connect the two halves together and see how it works! Could be a fun experiment, but we'd probably need to do it the big NIST laboratory.
 
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The first step is admitting to it. Honestly I don't have a solid answer to it yet either. Just one of those areas that I think about it randomly...
 
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phamENG said:
XR - you're probably right about the behavior. We should have a modular house built and not connect the two halves together and see how it works! Could be a fun experiment, but we'd probably need to do it the big NIST laboratory.
Click to expand...
I mean, each half seems to hold up fine traveling at 70mph down the road..
 
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I believe that I once saw something in APA that said that gable roof may have the ability to operate as two halves. I think it was APA documentation but it did not have any calculations to back it (which is one of my pet-peeves). The came was that un-blocked wood diagrams were capable of transferring the chord forces through the wood sheathing only. But again, up to what limit and show me the research. At this point we know it is possible but have no clue what the capacity and safety factors are for this condition.
 
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XR - remove the temporary bracing and see how that goes. I take your point though - houses (particularly when properly constructed) are more robust than many give them credit for.

DayRooster - if you find it, please share.

 
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phamENG said:
XR - remove the temporary bracing and see how that goes
Click to expand...

Did not realize they used that.
 
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DayRooster - looks like the lead author is an active faculty member at Washington State. You could reach out to him and see if he can get you a copy.

XR - all the ones I've seen in transit have had the open side covered, usually with plastic, so I can't see exactly what's there. But there is something preventing the plastic from being drawn in. Whether that's some sort of x bracing or reusable shear panels I don't know.
 
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What baffles me is that this is such as common design that you think APA would address the discontinuity in a clear manner. Instead of me having to go to the library of Congress to find the presidential book of secrets so I can find out that the research paper on split unblocked wood diaphragms is printed on the back of the Declaration of Independence. But here we are again and it looks like I have to go full Nicolas Cage to try and track down some research on this topic…
 
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I'm actually surprised Simpson hasn't come up with a $20 per foot solution to this issue.
 
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