Shear Transfer at Stud Walls

[EngSD]

I have a 50'x 200' gabled building where the roof purlins are running parallel to the perimeter shear wall below in the 200' direction. The purlins span between glulam beams spaced at roughly 20' o.c.. The contractor wants to place the purlins on top of the glulam beam in which case transferring the diaphragm loads into the shear wall becomes a problem because of the gap. See attachment as this will hopefully help clarify my problem.

I am wondering if I need to treat the end purlin as a drag strut and then transfer my force at the glulam beam support locations or if there is another way to transfer the diaphragm loads.

Thank you for any help.

 

[EngSD]

I noticed the attachment I included needs to be rotated 90 degrees. It is a section cut at the perimeter wall between the glulam roof girders showing how the roof purlins and diaphragm are above my shear wall.

 

[JAE]

I think I would be inclined to extend the wall sheathing vertically up to the roof sheathing instead of angling it outward as your sketch shows.

The easiest way to transfer the roof diaphragm shear down the wall sheathing is via a common blocking along the wall length into which both roof and wall sheathing can be connected.

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[EngSD]

I am not sure running the wall sheathing up vertically helps me as the purlins are angled in correlation with the roof slope so there wouldn't be anything to attach the wall sheathing to. Unless I am not seeing the solution.

 

[msquared48]

Just fab in a nailer at the roof to catch the wall sheathing. Carpenters need to earn their money somehow!

Mike McCann, PE, SE (WA)

 

[JAE]

See attached for an idea:


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[jayrod12]

How tall is your Glulam? Does it sit on top of the wall plates or on a column below the wall plates?

I would be extending my wall continuously up to the underside of sheathing if it's the latter as opposed to JAE's stubby wall.

Or as msquared mentioned, just have them cut a sloped piece to tack onto the last purlin that allows for the wall sheathing to be fastened to it.

 

[msquared48]

JAE:

Good detail, but I would also add transverse full depth blocking between the rafters @ 4' OC to support the short pony wall and control the knuckle joint created by not extending the stud wall to the roof sheathing.

Mike McCann, PE, SE (WA)

 

[EngSD]

The glulam columns are usually about 24" deep and it sits on a built up column below the wall plates.

 

[CBSE]

JAE:

Why build a pony wall when you could just run the studs up full height? The rest would work out fine. See attached, I just did a project like this a few weeks ago.

 

[msquared48]

CBSE:

The OP says the plate needs to be where it is.

Mike McCann, PE, SE (WA)

 

[EngSD]

The reason the contractor wants the plate where it is would be so that the studs are a standard 12' height. Obviously I can require them to extend the wall like what was shown by CBSE but I would like to be accommodating if I can justify the load path.

Wondering what people think of treating the last purlin as a drag strut and transferring the load at the glulam support location where the double top plate frames into the side of the glulam (see attached). I would have some weak axis bending in the beam but could detail it to handle the load.

Thoughts?

 

[CBSE]

What's the distance between the top plate and the under-side of the sheathing? May be able to get a shaped engineered rim board to work instead of the pony wall.

 

[RFreund]

If you can resolve the "rollover" forces you might be able to transfer the shear through the glulam.

EIT

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[KootK]

With a 20' glulam spacing it's worth remembering that you'll either need to run the walls up to the diaphragm or provide a wind girt at the top of the wall. That may chance the calculus of your contractor's preference. If not, the girt will brace the hinge in JAE's detail.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.