# Wooden Shear Walls



## MOOK (Oct 6, 2010)

How do you determine if the wood shear wall needs blocking or not? and if it does need blocking, what is the typical size and spacing of the blocking?

Is there any thing in IBC or NDS codes about that?

Also, what is the typical size and spacing for blocking in diaphragms?

Thanks


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## kevo_55 (Oct 6, 2010)

Mook,

Typically, wood SW don't have blocking. Wood SW's have a top and a bottom plate, and then intermediate studs.

You could use them though. For example, if you wanted to lower the KL/d of the end studs you could add blocking for intermediate supports.

I hope this helps.


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## MOOK (Oct 6, 2010)

kevo_55 said:


> Mook,
> Typically, wood SW don't have blocking. Wood SW's have a top and a bottom plate, and then intermediate studs.
> 
> You could use them though. For example, if you wanted to lower the KL/d of the end studs you could add blocking for intermediate supports.
> ...


Thanks Kevo for your reply but what is the typical spacing for the intermediate studs to use Table 2306.3.1 IBC??

Kevo, do you have any thoughts for questions in my other thread SEAOC V.2??

Thanks again


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## mjbikes (Oct 7, 2010)

Thanks Kevo for your reply but what is the typical spacing for the intermediate studs to use Table 2306.3.1 IBC??

Kevo, do you have any thoughts for questions in my other thread SEAOC V.2??

Thanks again


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## kevo_55 (Oct 8, 2010)

Mook,

Sorry, I haven't had any time to take a look at your other SEAOC questions. I'll try to take a look at them today.

II do have one slight alteration of my wood SW answer though. If your SW is higher than a "standard" piece of plywood (say 8' tall), then you would need blocking. If you have a short SW, then the top and bottom plates are effectively your blocking.


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## McEngr (Oct 13, 2010)

kevo_55 said:


> Mook,
> Sorry, I haven't had any time to take a look at your other SEAOC questions. I'll try to take a look at them today.
> 
> II do have one slight alteration of my wood SW answer though. If your SW is higher than a "standard" piece of plywood (say 8' tall), then you would need blocking. If you have a short SW, then the top and bottom plates are effectively your blocking.



Sorry it's been too long for me to reply to anything. I've been overloaded with a 12000 sf house.

Anyhow, the shearwalls all come from the ICC Evaluation Service Report #1539. You can also add an additional 1.4 allowable increase if the wall is wind controlled. Kevo is right: I've never designed an APA-rated shearwall with blocking. In addition, Simpson or similar always has testing to back up their holdowns. The double stud, triple stud, or post for the shearwall end-couple will not control generally unless it is a balloon-framed wall (more than a single 10ft story).


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## dastuff (Oct 13, 2010)

I'll preface this by saying I don't use wooden shear walls at all in my line of work.

But back in the day, I was told blocking is used to help slow fire traveling through the walls (and obviously doubles as some lateral bracing)... Now I've never given much thought to this, but does that have any merit? Just wondering.


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## McEngr (Oct 13, 2010)

dastuff said:


> I'll preface this by saying I don't use wooden shear walls at all in my line of work.
> But back in the day, I was told blocking is used to help slow fire traveling through the walls (and obviously doubles as some lateral bracing)... Now I've never given much thought to this, but does that have any merit? Just wondering.


Yes. It's called fire blocking, but it has nothing to do with lateral design.


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## MOOK (Oct 13, 2010)

Thanks all

So are the values in Table 2306.4.1 IBC are valid for intermediate studs with spacing 16" or 24"?? how do you usually determine the spacing of the intermediate studs?


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## McEngr (Oct 14, 2010)

MOOK said:


> Thanks allSo are the values in Table 2306.4.1 IBC are valid for intermediate studs with spacing 16" or 24"?? how do you usually determine the spacing of the intermediate studs?


Yes.


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## *Ananda* (Nov 9, 2010)

I see that a lot of wrong anwers are posted here. Don't you guys and gals know the code sections about which you provide "answers"?

For a long time, wood shear walls require blocking, and their values are based on having blocking, see 2006 IBC Sec. 2305.3.3. I don't have the 2009 IBC with me, but I assure you, all shear walls require blocking except:

unblocked wood shear walls are now allowed and have design values for limited applications in the ANSI / AF&amp;PA SDPWS-2008 - Special Design Provisions for Wind and Seismic. I'm not sure if this is referenced in the 2009 IBC.

Size of framing is 2x minimum per 2006 IBC 2305.1.2.1. The shear wall tables require larger than 2x framing for certain high load (high nail) applications.

Spacing of intermediate studs (16" or 24") can be per 2006 IBC Table 2308.9.1 for conventional construction. For typical engineered construction, the spacing required depends on the load demands.

This is not true: "shearwalls all come from the ICC Evaluation Service Report #1539." Shear walls have been in all model building codes for many years (50+/-).

This is also not true: "The double stud, triple stud, or post for the shearwall end-couple will not control generally unless it is a balloon-framed wall (more than a single 10ft story)." Check the hold down framing demands on a high capacity double sided shear wall.


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## greatjohn (Nov 9, 2010)

Actually, both the stud spacing and the need for blocking shall be determined by structural calculation. For a one or two storey residential builing which houses one or two families, the conventional construction in IBC and IRC may be used; however, if any condition specified by the conventional construction cannot be satisfied, engineering design is a must. So you will see 2x6 or 2x10 with close spacing are used in multi-storey condos.


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## McEngr (Nov 9, 2010)

*Ananda*:

Do you talk to clients the same way that you talk to other engineers on this board? What are your credentials, sir? The blocking is only for panel edges... this is obvious and I don't think that was the intent of the initial question.


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## *Ananda* (Nov 9, 2010)

oops... figuring out the buttons here...


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## *Ananda* (Nov 9, 2010)

Ok, now I have my 2009 IBC. In the 2009 IBC, most wood shear wall provisions have been moved from the 2009 IBC to the 2008 AFPA SDPWS.

The first time in recent history that model codes permit unblocked wood shear walls is in the 2008 AFPA SDPWS Sec. 4.3.3 but is limited to shear walls with nails spaced not closer than 6" o.c. and has strength and stiffness reduction factors.

Otherwise blocking is required per SDPWS Sec. 4.3.7.

Perhaps semantics, but prescriptive conventional construction requirements specify "braced wall panels" not "shear walls". In the 2009 IRC, braced wall panel joints require blocking, or if not, then it is specified to increase bracing amounts by a factor of two, see 2009 IRC Sec. R602.10.8.

Yes, blocking (or framing) is for panel edges to transfer shear from one panel to another.

I realize my post might rub people the wrong way, but at some point wrongs answers need to be stated for what they are. I've provided references for my statements. I'm sorry to see these facts raise the call for my "credentials".


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