shear wall sheathing

[structuralnerd]

How high does the plywood sheathing need to extend for a shear wall on a wood framed wall? To the bottom chord of the truss? To the top chord of the truss? Reasons?

 

[csd72]

To the roof diaphragm, whatever level that is at.

csd

 

[DaveAtkins]

It typically extends to the top of the shear wall, which is at truss bearing level. This brings up the valid concern of "rolling" of the trusses, because the roof sheathing is several inches above this level. Some engineers add blocking between the trusses to prevent this rolling effect. I typically don't worry about a gap between the roof sheathing and the top of the shear wall of less than a foot.

DaveAtkins

 

[structuralnerd]

Is the only need to bring the sheathing to the top of the truss to prevent rolling? Is there a need for shear force transfer at all? I have a situation where I don't think it can reach all the way to the roof diaphragm.

 

[SperlingPE]

You need a complete lateral load path.
Are you talking about shear walls on the exterior of the building where the trusses bear? Or other shear wall?

 

[structuralnerd]

I'm talking about an exterior shear wall on a non load bearing wall....parallel to the truss.

 

[DaveAtkins]

There should be some sort of "gable end truss" (or monoslope top chord end truss) on top of the end wall. The sheathing should cover this end truss and extend up to the roof diaphragm. There may be some 2 X 4 outriggers cantilevering over the end truss, preventing the sheathing from extending to the roof sheathing, but this is not a big deal. If you have outriggers and are concerned, add blocking between the outriggers.

DaveAtkins

 

[structuralnerd]

Why does the sheathing have to cover the truss though? Isn't the truss designed to take the shear into the bottom chord, which in turn is connected to the top plate of the wall studs?

 

[JAE]

Isn't the truss designed to take the shear into the bottom chord,

Not usually unless the engineer of record requires it. Most trusses are designed solely as gravity components and any lateral load brought through the truss is not provided for in the "standard" truss designs unless the design plans require it....even then I'd wonder if they would do it as I don't think the typical truss software that is used provides for that sort of loading.

So usually you use sheathing or other means to provide the complete load path required.

 

[haynewp]

I have specified metal stud endwall trusses to be used as shear trusses and calculations were submitted by the manufacturer supporting this. I dealt with NUTRUSS and I remember they also had square shear trusses to be used along the sidewalls that were perpendicular to the roof trusses to get the shear from the diaphragm into the cmu walls (I had a sizeable overhang at these walls and the diaphragm was a couple of feeet above the top of the shearwall). But my shear loads for this building were not very large.

 

[msquared48]

The shearwall sheathing should extend to the top of the shearwall double top plate on which the trusses bear. The blocking between the trusses prevents rollover of the trusses. The edge nailing of the roof sheathing is connected to the blocking and other mecnanical connectors connect the blocking to the wall double top plate. Hence, the full vertical load path.

Mike McCann
McCann Engineering

 

[haynewp]

Of course my post above has absolutely nothing to do with wood trusses.

Is this a gabled truss above the endwall?

 

[msquared48]

If it is an endwall truss scenario - I agree with JAE.

Here, too, the SW sheathing must extend to the roof diaphragm. This is not to say though, that if it cannot continue above the wall top plate in one continuous line, that another section of the truss be sheathed and nailed off to transfer the same force with the double top plate serving as a drag link between the two respective sections of the shear walls. Is this your situation?

Mike McCann
McCann Engineering

 

[structuralnerd]

I guess I should back track... First off, are end wall truss typically placed flush with the outside face of the exterior stud wall? My situation is that I have a couple steel columns that interrupt the continuity of the shear wall diaphragm and they stick out beyond the outside face of the stud wall. Trying to keep a continuous diaphragm, I was thinking to place the plywood on the inside face of the stud. However, the wall sheathing would then need to end at the bottom chord of the truss because the truss is not flush with the inside face of the wall. I was thinking since I have told the truss manf. to design the truss for a certain plf of shear force, I'd be safe. Now I'm thinking that may not be true??

However, if that is not possible, and I need to keep the sheathing on the outside face, do I need to put some hold downs on either side of the columns to transfer the potential over turning forces? I also have a steel beam interrupting the diaphragm, but I have the connection detailed so the studs can transfer the shear through the beam via bolts.

Sorry this is getting so long, but if the shear wall sheathing runs all the way to the roof diaphragm, is there even a need for a special shear connection between the bottom chord of the truss to the top plate of the stud wall?

Thanks everyone for your help!

 

[CJJS]

The sheathing may run all the way up the gable truss, but, often times the sheating does not lap the joint between the gable truss and the top plate. That is, the gable end truss may be sheated in the shop. If this is the case there needs to be a minimum connection between the truss and the top plate to transmit the horizontal shear to the top plate.

 

[msquared48]

Yes, the truss end wall is placed with the outside flush to the outside of the exterior wall.

You will need a minimum of double studs on either side of the pipe column with strap holddowns.

Is the endwall truss interrupted by the pipe column too?

Interrupted or not though, you will need strap holddowns from the truss to the two studs below on each side of the pipe column. That way you can sheathe the outside of the truss rather than the inside.

Mike McCann
McCann Engineering

 

[structuralnerd]

Yes, the truss is interrupted as well by the columns. If I can sheathe both sides of the wall and can keep it constant on the inside face, can I avoid doing the hold downs?

 

[msquared48]

Unless the wall sees a lot of dead load, I doubt you can avoid the holddowns. Endwalls do not usually carry much dead load. Do an overturning check and find out what the uplift is. Count your roof trib dead loadplus the wall dead load too in your calcs.

Strap holddowns should be all you need and they can be installed vertically on either the inside or outside of the end wall.

Mike McCann
McCann Engineering