Wood trusses with large heel height 1

[ntattose]

I am designing a wood framed building with a monoslope roof. The heel height of the
truss at the high side is about 48". In the past I have used shear frames between trusses
to transfer the shear down to the top plate and into the shearwall. How do others handle this?
The trusses are spaced at 24" o/c, can these verticals be sheathed with plywood and treated like
a shearwall?

 

[driftLimiter]

Yes you can extend sheathing up the heel and use the truss like studs, just need to carefully detail shear transfer from the roof to the wall then down. I usually just use truss blocking (your calling this shear frames) and specify the shear load to the truss manufacturer.

In either scenario you want to consider the overturning as well and think about how the forces get resolved over the 48" lever arm. The truss blocking can be connected to the trusses on the vertical edges and resist the overturning in a distributed way. Worth thinking about either way because your truss blocking would be pretty slender H/W ratio.

Other thing to consider if your using shear ply, is how that panel aligns with other shear panels below, does it increase the height of your shear walls or does it just sit on top of them?

 

[dik]

...and make sure you lap the sheathing so the 48" width is not always at the line of the double top plate...

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[XR250]

In either scenario you want to consider the overturning as well and think about how the forces get resolved over the 48" lever arm. The truss blocking can be connected to the trusses on the vertical edges and resist the overturning in a distributed way. Worth thinking about either way because your truss blocking would be pretty slender H/W ratio.

The OT only exists at the end of the run of trusses as it resolves itself internally between trusses.

 

[driftLimiter]

The OT only exists at the end of the run of trusses as it resolves itself internally between trusses.

Agreed, and better yet the end OT force is only equivalent to the OT force of a single bay of the blocking.

 

[Gopher13]

Attached is a photo from a building designed +/- 5 years ago. Trusses spaced at 2 feet o.c., 6 foot overhang, roof sheathing 2.5 feet above top of masonry wall. "Blocking Panels" were placed between each truss above the wall.

 

[ntattose]

That's a good example where blocking (shear) frames are required, and the
truss ends cannot be used as shearwall.

 

[DaveAtkins]

That looks like very robust blocking between trusses. It looks like it was supplied by the truss manufacturer, which surprises me.

DaveAtkins

 

[ntattose]

I always require the truss supplier provide the sheer frames.

 

[Gopher13]

Yes, supplied by truss manuf. as listed in the spec.

 

[RontheRedneck]

As a truss supplier, I hate the shear frames. They're expensive and difficult to install.

I'd rather see the shear transfer with the sheathing on the end verticals. Or some diagonal bracing.

 

[BAretired]

I don't think shear frames are needed in every truss space, but the EOR might want them spaced periodically along the wall, rather than just at the ends.

BA

 

[XR250]

@Ron,

Why are they difficult to install and expensive?

 

[RontheRedneck]

@XR250:

They're expensive because there are a lot of pieces and a lot of plates in a small area. Two TC, two BC, 2 verticals and one diagonal web = 5 pieces. And 4 pairs of plates.

They're hard to install because lumber is imperfect. No truss is exactly 1.5" thick. The saws can't cut pieces to an absolutely perfect length.

So let's say the bracing frame BC and TC are cut a bit short and the truss is lumber is a bit thin - You have a gap.

If the TC and BC are a bit long, at least they can be trimmed. But they almost never just drop in place easily.