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Wall of Windows
2

Wall of Windows

Wall of Windows

(OP)
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.





RE: Wall of Windows

With the first picture, the 5.125 X 12 glulam will probably fail in wind weak axis bending. lateral deflection will be a lot more too.

I much prefer the second option with the two full height columns taken to the roof diaphragm.

Mike McCann, PE, SE (WA)


RE: Wall of Windows

Option one lacks post continuity from foundation to roof diaphragm. You'd either need a monster girt at eave hight or you'd have to count on the specified strapping to moment connect the posts across the girt. Using the straps in this way would make me particularly nervous as the substantial load from the ridge girder will tend to promote stability problems.

Have I passed the quiz?

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

RE: Wall of Windows

(OP)
I made it too easy, I shouldn't have posted the wind load information on the first sketch.

With the 189 plf load on the glulam beam in its weak direction, neglecting any straps that may counteract this lateral load, even sistered with two 2x6 (top and bottom) I get the following:

fb = 4500 psi > Fby' = 2530 psi (CSI = 1.78) ======> NG

Also if the beam doesn't snap it will deflect 15.2 inches. Granted the wall may act as a web to some degree and resist this lateral deflection but I wouldn't count on it.

Then you take the vertical loads which will only make matters worse (hinging effect).

Hence Rev. 2 of the design... and I need to explain to the architect/designer why his wall of windows won't work.


RE: Wall of Windows

Could you run the two 6x6 posts through continuously, and get rid of everything else other than the eave hight girt and the shear walls?

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

RE: Wall of Windows

My biggest concern with option #1 (besides the obvious deflection issues with the Glulam) would be the connection at the two shear walls.
The load coming out of both ends of the Glulam would be in the range of 4,000+ lbf - not your average wind load.

A quick glance at your Second drawing (much better design in my opinion) gives me concern about the 2x12 rafters.
Tall gable end walls always need special concern for the lateral support at the roof decking.
I would frame the wall full height to the roof decking and attach a 2x4 or 2x6 ladder spanning at least 24" (your first roof truss / rafter past the wall), possibly 48" depending)
The Ladder framing runs at 12" OC. perpendicular to the wall with:
-nails to the roof decking to transfer lateral load to the diaphragm
-nails to the double top plates to transfer load to the ladder framing
-this allows you to cant out for overhang as well


See the attachment for a similar design I have done - pay attention to the lower right hand for the ladder framing detail

RE: Wall of Windows

(OP)
I see where you are going with this Signious. The 2x12 on edge will want to topple over without some blocking running perpendicular to the rafter.

How about something like this:



If more strength is needed put another 2x4 block in line with the outlooker to the next rafter (and strap tying the two together).

RE: Wall of Windows

(OP)
This will require a nailer on the inside wall for the ceiling sheetrock. Also the straps connecting the 2x12 Header (HD1) to the DBL top plate will require some additional blocking if the strap is on the inside (block as required).

RE: Wall of Windows

(OP)
The change in the posts shrunk my shearwalls slightly as well as increased the height. At 514 plf I'm going to sheath the interior and exterior of both shear panels and even though my allowable is 670 plf, and probably a little conservative, I welcome the additional margin of safety.

RE: Wall of Windows

(OP)
Is there any particular name you call the stubby 6x6 post that the glulam beam seats on?

RE: Wall of Windows

Reminds me of a King Post.

Mike McCann, PE, SE (WA)


RE: Wall of Windows

Depending on the size of it required a lot of times I would call it off as full bearing solid blocking down to the 2x12 header.

I think it's unlikely that you need the capacity of a 6x6 over a short height like that.

RE: Wall of Windows

(OP)
Probably not, but it does fit nicely.

RE: Wall of Windows

So does a 3 or 4 ply 2x6 created from the cut ends they will have lying around.

RE: Wall of Windows

@medeek

I usually just call it a cripple post / cripple stud (same as I call the studs below sills)

RE: Wall of Windows

(OP)
Alright, 4 ply 2x6 with a 1/2" ply spacer. No contractor is going to want to cut up a nice 6x6 post for such a small piece, I see your point. I think most contractors will take whatever shortcuts they can regardless of what the plans actually say.

RE: Wall of Windows

Hey Medeek,

off topic question: where abouts in the world are you, and what is the 'standard' lumber species you use. I see a lot of D.Fir being used, but where I am if you spec anything other than SPF you get a lot of angry calls

RE: Wall of Windows

@medeek;

Those are pretty extensive calcs and sketches. How are you making any money on these jobs?

RE: Wall of Windows

Kick-ass spreadsheets. I doubt Medeek does much of anything by hand more than once.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

RE: Wall of Windows

(OP)
I don't consider the calcs that extensive but the sketches are really for discussion points and my own education. I've never dealt with an exotic wall like this before so I'm chalking it up to "education and new skills". On this particular job I had to deal with custom portal frames and this wall, both of which have taken me over a week just to think through, research and discuss with other engineers on this site and over the phone, as well as by two additional text books. Tomorrow I meet with an old engineering friend of mine who has agreed to peer review the project, his services are not inexpensive either. So I've actually lost money on the job but I've gained much more, created two new computational tools, and now understand the methodology behind analyzing portal frames.

RE: Wall of Windows

(OP)
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.

RE: Wall of Windows

(OP)
Here is the basis geometry drawn up:

RE: Wall of Windows

(OP)
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.

RE: Wall of Windows

(OP)
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.

RE: Wall of Windows

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.

RE: Wall of Windows

(OP)
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.

RE: Wall of Windows

(OP)
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.

RE: Wall of Windows

(OP)
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.

RE: Wall of Windows

(OP)
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...

RE: Wall of Windows

(OP)
The updated detail:

RE: Wall of Windows

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.

RE: Wall of Windows

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.

RE: Wall of Windows

(OP)
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.

RE: Wall of Windows

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'

RE: Wall of Windows

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.

RE: Wall of Windows

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,

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