Summing shear capacities

[pthorley]

2305.3.8 allows shear capacities to be added when applied to both faces of the wall. Does the limitation of 350 plf apply to each face separately? In other words, can I go up to 700 plf without requiring 3x members?

 

[JAE]

Yes, I believe that you can simply double the shear capacity if you sheath both sides equally.

 

[pthorley]

Yes, I agree, but would a shearwall sheathed on both sides with a capacity of 700 plf require 3x by members as noted in footnote (i) table 2306.4.1? Does the 350 plf limit before requiring 3x members apply to the total wall or to each face of the wall?

Thanks

 

[JAE]

Please specify the code you are using.

In the IBC 2000, Table 2306.4.1, footnote h. indicates that "Where panels are applied on both faces of a wall and nail spacing is less than 6 inches o.c. on either side, panel joints shall be offset to fall on different framing members. Or framing shall be 3-inch nominal or thicker and nails on each side shall be staggered".

 

[pthorley]

Sorry IBC 2003

Yes (h) describes the option of 3x members or offset panels for wall applied to both faces and less than 6" nailing.

I am in a mostly "D" SDC so (i) also applies.

If I have a 240 plf on each face (not less than 6" nailing) the total allowable would be 480 plf. But (i) says that if I go over 350 plf (ASD) then I need 3x members and joint sill plate nailing staggered. Or does the 350 limit apply to each face separately.

Thanks

 

[JAE]

I don't have IBC 2003 handy - anyone else out there in Eng-Tips Land?

 

[pmkPE]

What community has adopted the IBC 2003?

 

[pthorley]

Every city in Northern Utah has adopted IBC 2003 (IRC 2003) as of Jan 1 04.

 

[CTruax]

The 350 limit is for the wall total, not each side.
The increase to 3x allows less potential for sole plate splitting.

 

[damstructural]

And to avoid splitting 2x's when nailed from both sides, especially the boundary members. You'd never even see it with ply on both sides. Good practice to go 3x's for this case, even if it weren't in the code.

 

[pthorley]

Thanks, your comments are very helpful. I understand the splitting issue especially with tight boundry nailing such as 2" or 3" OC. But in certain circumstances you can go up to the 350 plf limit with 6" OC boundary nailing. Footnote (h) in table 2306.4.1 IBC 2003 says that if you apply panels to each side and the nailing is less than 6" OC then you have to offset the panel edges from inside to outside so that the boundary nailing does not occur on the same stud otherwise you have to go to 3x members.

Sorry to beat this to a pulp, but (h) implies that you can use 6" OC nailing on each side and not use 3x. Also, I am typically referring to 2x6-framed walls. With the 1 3/8” (8d) fastener penetration on a 2x6 would seem to be potentially less damaging than a 2x4.

By the time you apply to both sides and possible stagger the panel edges it is probably easier and cheaper to just go to 3x members.

Thanks,

 

[EPSTR]

This is a geat thread, I too have been hesitant with my interpretation of the code (IBC)...
I agree that the code reads such that 2x members are acceptable given the staggered attachment on opposite sides. This clearly reflects a concern that the studs may split with the increased nailing patterns.
nonetheless 2x's are OK the way I read it.
My question is whether or not a dbl 2x stud will serve as an appropriate alternate to the 3x. Is there a particular condition that this idea does not account for? I agree that the an increase in the stud thickness improves shearwall rigidity.
BUT... In our area builders see 3x and ask, "what is that?"

Thanks