Hold Down for Wood-Framed Shear Walls 1

[Sanira]

Suppose you have a very long wood shear wall. In reality, the long shear wall is divided into a number of panels at shop for installation at site. How do you guys analyse the overturning of shear wall for chord forces and hold down design? Do you divide and analyze the walls separately or do you analyze one long shear wall? Or do all the wall segments act as one long wall as they are connected together by top wall plate? Thanks.

 

[Guest090822]

Sanira - I'm not following the question. Are you looking at a temporary condition or final condition?

 

[Sanira]

TheRick109- I am talking about the final condition.Suppose you have a long shear wall but that shear wall is fabricated in shop into different pieces of wood panels. How do you splice those panels at the field for all the pieces to act as a one single shear wall? I believe the upper plate of the top plate provides splice at the top. But how about the bottom plate? How are they spliced?

 

[jayrod12]

The top plate does need to be connected such that they all move the same amount. The bottom plate does not. The floor diaphragm does the splicing for you.

 

[JoshPlumSE]

Honestly, you can do it either way. It's mostly a matter of where you put your hold downs.

I suppose there is a related question that you might be getting at. Is the there a code limit (or a practical limit) in length vs height ratio for a single wood shear wall?

I'm not sure about that one.

 

[Celt83]

If you treat it full length and they are panelizing the walls make sure they leave room to provide lapped sheathing in the field. You don't really get true rigid body motion out of the wood shear wall so everything is reliant on complete load path from chord to chord.





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[JoshPlumSE]

Celt makes a REALLY good point. I wasn't thinking about prefab wall sections the way the OP described. You definitely want to do something to get force transfer between individual panels.

 

[molibden]

You need to connect panels vertically with bolts or screws. You need to figure out shear flow between panels. Top plate doesn't really do anything here. If not, you need to treat walls as separate. But that is not economical. Longer wall is stiffer and stronger than more short walls. As far as holddowns go, if you connect panels properly it acts basically as one wall with holddown on both ends.

 

[jayrod12]

I think without top plate continuity, the walls have a chance to rack as individual pieces before the connection between panels is engaged IF no sheathing splice is provided across the joint as Celt83 indicated.

 

[Sanira]

Thanks you everyone for your response. Celt83, JoshPlumSE, jayrod12 - But what if the sheathing is itself prefabricated along with the wall studs.I have got shop drawings from the wood panel fabricator where this is the case. In this case, I suppose we need to go as molibden suggests i.e. To connect panels vertically between the end studs with bolts or screws. Any other thoughts?

 

[msquared48]

If the sheathing stops at the panel splice joints, then you will need to nail the panels together at the studs.

And, yes, the top plate is a tension link and should be treated as such. The top plate is essential for the wall to work as one long wall.

If the wall is long enough with enough dead load, you may not even need any hold downs.

Mike McCann, PE, SE (WA, HI)

 

[jayrod12]

I'm not a fan of just nails between adjacent studs to provide a stiff enough connection between panels. I'd be tempted to consider each panel segment as an individual shear wall subject to it's own racking. Therefore I'd be making sure that the connection at each end of each segment were adequately connected to below.

I really just fear the fastener slip will allow the wall segments with no true holddowns to lift. Nails are not sufficient.

 

[Celt83]

if the sheathing stops then I'd treat them as individual panels and add hold downs to each panelized segment.

My Personal Open Source Structural Applications:

https://github.com/buddyd16/Structural-Engineering

Open Source Structural GitHub Group:

https://github.com/open-struct-engineer

 

[msquared48]

If the plywood extended beyond the end stud by 3/4 to 1.5”, then the nailing could make the connection satisfactorily, limiting the number of hold downs. The plywood at the other of the panel could be recessed to accept the plywood from an adjacent panel. Would take some coordination and planning, but doable.

Mike McCann, PE, SE (WA, HI)

 

[jayrod12]

Another option would be to leave the last stud space unsheathed on each side, then on site someone just had to infill the pieces. Theres going to be a guy on site doing minor framing and sheathing anyway.

 

[molibden]

What we basically do, is we connect end studs with bolts/screws and design them for shear flow sv,0,d.

 

[Sanira]

molibden - What is sv,0,d ?

 

[molibden]

sv,0,d is design shear flow between sheathing and timber frame on the perimeter of wall segment.
You can calculate it as sv,0,d = Fh,d / L, where L is length of the wall and Fh,d is design horizontal force.