Multi-Story Wood Shearwalls

[dengebre]

We have several wood building projects ranging from 3-5 stories. Due to high lateral forces, many shearwalls are required especially within the interior of the building. The question posed to this fine forum is how to handle the shear transfer from one wall segment to the segment at the next floor below (the walls in question are interior demising walls and are contiguous within their vertical plane). Our solution was to have the sheathing be continuous through the height of the shearwall. Unfortunately, that prevents the floor framing from bearing on top of the wall (the floor framing is perpendicular to the wall for these shearwalls). A horizontal nailer could be nailed to the face of the shearwall to support the floor framing, but the contractor thought we were insane.
The floor framing is 12"-24" deep depending upon the floor. There is a gap between the floor diaphragm and the shearwall below if the floor framing must bear on top of the wall. We are arguing that SOMETHING has to be provided to transfer the shear across this gap (sheathing, blocking, bracing, etc.) and to prevent rolling of the floor framing. What is typically done to transfer the shear across this gap?

 

[csd72]

Have a look at this:

http://www.structuremag.org/Archives/2008-4/C-Prac Sol-Commins-Apr-08.pdf

 

[JAE]

Here are a couple of sites to review on this topic:

http://www.strongtie.com/products/highwind/str.html

http://www.strongtie.com/products/ats/techinfo/design-ex.html

An APA Shear wall Design Guide (must register – but free):

http://www.apawood.org/level_b.cfm?content=app_com_shear

Also look here for a listing of some free publications on shearwalls (scroll down):

http://www.awc.org/Publications/download.html

 

[dengebre]

It is definitely a good article but appears to address mainly with the transfer of the C/T force and not the shear force (I did not read the whole thing to be honest). However, the detail provided in the article does show solid blocking to transfer the shear force to the next segment below. The issue we are facing is a gap up to 24" due to the floor framing interupting the shearwall. Thanks!

 

[dengebre]

Thanks JAE. The figure for the Simpson CTD33 (your second link from the top) shows graphically the situation. Simpson specifies "solid blocking" in order to transfer the shear across the gap and prevent rolling of the floor framing. This blocking would have to occur between each floor framing member if those members are to sit on top of an interior shearwall. What is typically used for this blocking (some type of rim board, sheathed studs, etc.)? Our investigation of the available literature yielded a plethura on holddowns and transferring the T/C force, but is ambiguous as a whole on the detailing for the shear force transfer.

 

[csd72]

Have you thought about fire seapration requirements between these units? This may also dictate what you available options are.

 

[KBVT]

dengebre - For interior partition shear walls, a common solution to this problem where the floor joists are continuous across the bearing wall is to place truss blocking between each floor joist. Have the truss manufacturer design the shear transfer (truss) block for a shear force equal to the capacity of the lower wall on your plans and you should remain relatively conservative.

 

[dengebre]

KBVT

1) Excellent idea for trusses! For my own education, is this a "truss block" an actual truss that fits in between the floor trusses?
2) What if the floor is LVL's?

Thanks!!

 

[haynewp]

I was going to suggest the same regarding the shear transfer truss. I have used these before and they fit in between the main floor trusses. You might could also use blocking and metal straps between the floor trusses to transfer the shear, but I expect the pre-made truss would be a lot easier.

You should be able to use some of the details that are in the links above that show solid blocking if the floor uses LVL's.

 

[DaveAtkins]

I have also used 1" thick plywood as blocking in the past.

DaveAtkins

 

[dengebre]

Everyone - Thank you very much for the excellent responses. I am adding this to the thread for future searchers of this forum:

Some excellent illustrative examples are shown in Thor Matteson's book "Wood-Framed Shear Wall Construction". Figures 23-25 on page 30 show exactly the problem I was trying to describe. The best solution is to introduce "truss frames" (Fig. 25) in between the floor framing (aka, the truss blocks described above). An alternate to that, but allegedly not as good, is to use blocking (Fig. 24). Bottom line is that something MUST be provided to transfer the shear from the floor diaphragm across the gap into the wall sheathing.

 

[MightyPirate]

I have a similar situation only I have a roof truss that cantilevers 6' beyond the bearing/shearwall. Thus, there is a 3' gap between the top of the shearwall and the top of the truss.

Now, for the roof diaphragm to work correctly the shear has to come out of the sheathing and go into the wall. To do this there has to be some blocking. So, do I need full depth blocking or will just blocking the compression chord allow me to use the trusses to transfer the shear from the sheathing to the plate?

 

[tedamiao]

We use panel blocking to transfer shear. Basically it is four pieces 2x member to form a rectangular shape with sheathing on it. This panel blocking shall be put between floor joists or floor trusses on top of shear wall and under floor sheathing.

 

[KBVT]

You can do as tedamioa detailed which is basically a 3' high shear wall which you can determine allowable loads from the IBC tables, or you can design a panel with a diagonal from corner to corner going into tension or compression depending on the direction of the shear. Either method would work fine.