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Wood Shear wall 3

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Vrpps EIT

Vrpps EIT

Structural
Aug 21, 2018
58
Hi All,

Attached a pic of wind load on a wood frame. If individual joists and studs are designed as a portal frame (like beam & column) with structural connections capable enough to withstand the lateral push and uplift at the bottom. Then can I eliminate the need to check the end wall overall shear at east & west walls as they are the only walls in the direction parallel to the wind? or am I missing something that I need to check the end wall shear capacity for the load "w" multiplied by 80' and split it to each of them?

Thank you!
 
 https://files.engineering.com/getfile.aspx?folder=835600f8-2996-48c3-aa81-995403a4e3fb&file=Scan001_(3).jpg
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Out of curiosity, what type of structure is LxWxH 80x4x2?

At the ratio you are providing to get the loads to the end walls 80/4 = 20 you do not comply with wood diaphragm provisions. So something will need to be done in-between the end walls if you plan on using a wood framed plywood roof.

Proving that connection works will not be easy. Modeling the structure in software will not be easy as well. Why not just provide a diagonal every few feet to take out the wind loads?

 
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VrappsEIT -

You're talking about creating a wood moment frame, right? I'm not sure that is expressly forbidden by the code. But, cross grain bending in the connection makes it very difficult to do practically.

The closest that I've come to creating a wood portal frame is by using kicker braces instead. I would not choose to do the type of frame that you are proposing if it were a project I was working on.
 
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I agree with SteelPE that intermittent diagonals would be sensible and much more economical than connections required to provide adequate frame action.

Expecting a 4' wide diaphragm to span 80' is unrealistic. It would be much too flexible.




BA
 
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SteelPe
It's a roof parapaet to be mounted in a strange situation and the end wall shear load is 5kips and a unit shear force (5/4) which is 1.25 kip per feet of shear wall panel required. Yes a 3/4 ply wood be used for roof sheathing
 
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Again, you can't distribute the load over that long of a diaphragm. I think blocked diaphragms of wood have a maximum aspect ration of 4 for wind loads, you have 20, so it's not even close. If this isn't accessible to anyone just put in 2x diagonals every stud and be done with it. The cost to add the 2x can't be too much.
 
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Thank you! Steel Pe it makes sense to have diagonals in between, you would put them alternate directions right? between one and the other
 
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I don't think a diagonal is required on every stud. Maybe every eight or ten feet would be okay.

No need to reverse diagonals if they work for stress reversal, but reversing them is okay if you prefer.

BA
 
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1x4 let-in diagonal bracing members were used in the past, but only for bracing during construction. Not to be used to resist long term code forces.

Mike McCann, PE, SE (WA, HI)


 
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A 2x4 every 8 or 10 feet ain't going to break the bank!

BA
 
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BAretired said:
I don't think a diagonal is required on every stud. Maybe every eight or ten feet would be okay.
Click to expand...

I agree, but I was just going by what you typically see in lt guage shop drawings. They typically put diagonals on every stud. "But they don't typically have a diaphragm on top of the parapet!" I understand, it would probably easily work at every 8'-10' but then again, you are concentrating the loads on the supporting structure every 8'-10'. The load needs to go somewhere, and it would be more likely for a structure the parapet attaches to to support the loads if they were evenly distributed.
 
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Every 8 or 10 feet is evenly distributed, but if you want to say every third stud or every four feet, that is up to you. We should not speculate on what the parapet attaches to.

BA
 
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Vrapps EIT:
Pay some special attention to how these little 2’ x 4’ at 16” o/c frames are detailed and integrated with the main exterior wall framing and sheathing and the main roof joists/trusses and you could preassemble 61 to 64 of them on the ground at a cutting and fit-up station. Every forth frame (or some such) would include a diagonal member/brace for the lateral loading. Some simple lt. gage hardware might make the connections to the main roof and structure for lateral and uplift loads. If there are trusses on the job, you might get the truss guys to make these little frames for you. In some places you can also rent a small portable press for toothed stl. nailer plates.

Edit: While it may seem like overkill, if you use 2x6 studs, you can frame the studs and the horiz. 2x roof piece in one plane and still leave outer/upper corner notches (1.5 x 3.5” ea. corner) for two 2x4 continuous longitudinal framing members on the parapet system for sheathing nailing at the corners.
 
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Pre-fab trusses all day long in my neck of the woods.

c01_wl0u08.jpg
 
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KootK:
Thanks for the sketch Koot, that’s about what I had in mind, one of a few dozen minor variations, depending on his exact conditions.
 
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OP said:
Then can I eliminate the need to check the end wall overall shear at east & west walls as they are the only walls in the direction parallel to the wind?
Click to expand...

Are the walls perpendicular to the direction of wind, or parallel as stated?
 
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Thank you everbody for the suggestions its really helpful.
 
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retired13,

They are parallel to the wind and 80' apart. If using the KootK braces at 4' o/c or 8' o/c, the end walls are not resisting much wind load.

BA
 
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The end walls will be parallel to wind direction
 
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I got it. Thanks. Your original assumption is correct, if you can make a moment frame out of the joist and studs. Then the end walls will see very little load.
 
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