Wall of Windows 2

[medeek]

I've got a wall of windows on a gable end with possibly two methods of framing it (so far). Can anyone tell me what is wrong with the first picture? Note that 22 ft. of roof is tributary to to the glulam beam at the ridge (actually only half of that 11 ft is tributary to the gable wall). The load is the S + D, the dead load is approximately 50% of the total load.

 

[medeek]

The other end of MB1 will be hangered from a girder truss, the funny thing is I'm not seeing a Simpson Strong-Tie hanger for Glulam-to-Truss Girder connection.

 

[medeek]

Here is the basis geometry drawn up:

 

[medeek]

So I met with my mentor today and apparently there is a pretty significant flaw with the design drawn above. The two center posts really need to tie directly to the double top plate otherwise the out of plane bending load (wind) is going to cause problems at the post/header interface. The problem is I am trying to maintain approximately 6 inches between the window and the door so there is no additional room for more trimmers. My only other option I can see is to make these two columns continuous to the top plate and then hanger the top header (HD1) off of the 4x6 columns (P1). I was kind of hoping for a good solid wood-on-wood bearing so having to resort to hangers at this point feels like a cop-out but maybe that the direction I have to take with this.

 

[medeek]

Also after re-checking the numbers on a longer column height, now 15 feet instead of approx. 13.5" I decided that the posts on both sides of the door need to be something more substantial, so 3-1/2" x 5-1/4" Versa-Lam 1.7 2650 PSL.

 

[OldPaperMaker]

medeek,
If you go to the internet and type in "ilevel residential wall guide" that will take you to Weyerhaeuser's specifier's guide to walls that you have shown in your sketches and drawings. The guide has a lot of typical details that might help you in your design.

 

[medeek]

Thank-you for cluing me in on that publication. There tall wall is very similar to the construction I have. Made me realized I need to do one more check on the post lateral anchorage.

 

[medeek]

I just checked the deflection on the P1 columns and I have a L/d of 106, looks like in this case the deflection is the limiting factor and not the stress. Looks like I'll have to go with deeper posts (ie. 3-1/2 x 7-1/4) however that brings up the debate whether to leave the wall at 2x6 and have the posts bumping out or bring the whole wall to 2x8 so the wall is smooth.

 

[medeek]

Even with the IBC .7 reduction (.42 C&C) from footnotes of section 1604.3 I still get a deflection of 1.56" => L/d = 116 which is too much. I'm really starting to dislike tall walls at this point.

 

[medeek]

3-1/2" x 7" PSL Column => L/d = 267, Deflection .67 inches. That works. Note that I am using the C&C zone 4 for these calcs per the general direction given in the ilevel document above and also being that this framing is in the center of the wall and actually is in zone 4. I'm beginning to think that using zone 5 would be over conservative in most cases with regards to stud walls etc...

 

[medeek]

The updated detail:

 

[XR250]

I hear you on not liking tall walls. I did one recently that peaked at 29' and had brick veneer. Used 2x10's for the studs as the contractor did not want any steel.

 

[jayrod12]

I've done a bunch of tall walls. Once I exceed about 20' in height I almost automatically switch to 2x8 engineered studs. Especially because like Excel noted, they always seem to clad these walls in some sort of brittle finish.

 

[medeek]

Since the columns bump out of the wall at 7" they will probably end up framing it up as a 2x8 wall to keep the interior smooth, but that will be the homeowners call.

 

[Signious]

I like the idea of using joist hangers for the header - I do a lot of tall walls and hadn't considered it before.

As the youngins would say, 'Mad props, yo'

 

[jayrod12]

The only thing about using hangers (from my experience) is they have to make sure that the hanger installed has enough lateral capacity to transfer the wind loads to the columns.

Not often, but on occasion I have seen the contractor install hangers that did not have the published capacity required. One guy tried to use fence brackets.

Would it have ever been a problem? Unlikely, but I'm not one to argue with the published capacities.

 

[ChiefInspectorJeff]

Here are a few observation. Complex wood designs are usually not built per plan on the job.
How does the LVL receive lateral loads if the roof diaphragm uses the LVL as a chord or drag strut? Or use the whole roof as a diaphragm and strap the rafters to each other over the ridge.
Can you use balloon framing 6x6 post between the windows and use connectors to the roof boundary members.This eliminates the continuous header. You can use 2x6 plates in the strength plane as headers. For extra strength you can use buckets and blocking at the post bottoms. Since the end SWS carry the lateral loads the 6x6's are carrying gravity and wind force perpendicular to the wall,