tall exterior wall framing

[calculor]

just curious what other engineers do in the following situation; 4 storey wood frame building with two storey atrium along the outside wall. Opening in the diaphragm is 28ft long x 12ft wide. I'm considering two options, running an lvl beam 28 ft long spanning between walls and designing for weak axis bending due to wind load or framing the wall with long studs for full height. Anybody have an other solutions?

 

[dik]

I've used LVL's and PSL's for framing tall walls with openings and Simpson type hangers for connecting the horizontal members. Sort of like a floor tilted up...

Dik

 

[woodengineer]

I have used that detail for small sections, but not for a 28' long run. I suggest balloon framing that area. Depending on the plate height and exterior finish (i.e. brick facade)you may choose 2x8's or LSL wall studs. In some cases where I have had large expanses of 20' wall heights, I incorporated masonry in those areas.

Todays clients want larger and more frequent openings with volume space. It sure makes wood framed construction difficult.

Good Luck!

woodengineer

 

[calculor]

I have seen projects where the wall was has been framed similar as though the diaphragm were not removed (platform framing without the diaphragm at the second floor). Can't seem to get my head around how this could possible handle the combined wind and gravity loading. I assume the wall studs are pinned at the rim joist and the rim joist has to spliced and therefore not spanning continuous between walls.

 

[dik]

The vert members can run full height (balloon framing?)... the advantage of using LVL, PSL or whatever. CWC has an excellent article on tall walls in *.pdf format.

Dik

 

[structuralaggie]

What ever works. My gut feel is that baloon framing would be the best. It depends how tall the wall is, how wide your studs are, and of course how large your wind load is. I have found steel tubes may have to be used if thickness of the wall isn't there. Also, I have convinced architects to add a porch with low roof on the exterior wall. This will support the wall at the first level plate height. All of the sudden no special framing is required.

 

[planitarch]

agree with structuralaggie......With regard to tall wall or 2-story wall framing, a horizontal steel tub 'belt' at mid height, tied to a corner steel column usually works.

Even easier, if the architect allows it, try thickening the wall. Vertical 2x6 LVL at 16" o.c. or 2x8 @ 16" o.c. should work. Even with large expanses of glass I've got 2x8 @16"o.c. studs to work...

 

[csd72]

Calculor,

Do you have axial loads on this wall? What happens when your LVL deflects (say 2")under wind load and your studs are no longer vertical. This will cause 2nd order effects in your wall.

Best to try and make 8" full height studs work, that is what I have done in the past. if you are stuck at 6" wall thickness try LVL studs.

I have had builder build it as if there was a floor there and I told them to pull it down and rebuild it as full height studs.

regards
csd