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# RE: Wood-Framed Shearwall Compression Chords

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: Wood-Framed Shearwall Compression Chords
• Date: Wed, 14 Aug 2002 00:12:26 -0700

```Does your guru friend put 3 hold downs on a six foot long shearwall?

Are you allowed to use a perforated shearwall with that big an opening?
In standard wall design (not perforated) I think you would use the
reaction of half the opening directly on the end of the wall and
distribute the last 4 feet based on the tributary load above. For
seismic in one direction the you may have no overturning, bur the
opposite direction you will still have overturning. Now, whether or not
you want to put a hold-down on the end post carrying the big dead load
reaction from the header is dependant on how confident you are of the
uplift, and whether or not 2 extra hold-downs on the job are going to
kill the budget. I personally would put the hold-downs in if the
economics were minimal.

-gerard

-----Original Message-----
From: Haan, Scott M. [mailto:HaanSM(--nospam--at)ci.anchorage.ak.us]
Sent: Tuesday, August 13, 2002 3:52 PM
To: 'seaint(--nospam--at)seaint.org'
Subject: RE: Wood-Framed Shearwall Compression Chords

The panel sheathing is resisting the lateral forces and stuff behind the
wood panel carries gravity load, splices the panels together, splices
the
panels to the stuff above and below, and splices the panels to the
overturning anchors.

I've had one guru tell me the way to look at it is the gravity load goes
into the stud and into the foundation and using more than one panel
width
[4' tributary] to resist overturning is unconservative.

Say you have a 8'x40' long wall with 4 foot long panels at the ends and
30
feet contains wall openings. Question: For the perforated shear wall
method
can you use half of 40' feet of tributary dead load to resist
overturning at

Scott M Haan P.E.
Plan Review Engineer
Building Safety Division
Development Services Department
Municipality of Anchorage
http://www.muni.org/building
phone:907-343-8183
fax:907-249-7399
mailto:haansm(--nospam--at)ci.anchorage.ak.us

-----Original Message-----
Sent: Tuesday, August 13, 2002 10:48 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: Wood-Framed Shearwall Compression Chords

Dave,

wall. In the tension side, the weight is the resisting moment to
overturning and thus reduces the tension force ... but on the
compression side, the calculation is typically lumping this forces as an
additive force to the overturning. The intermediate studs obviously have
some capacity and take load ... however, the overturning component of
the downward compression is distributed based on the distance to the
neutral axis (or pivot point) of the wall - you could do an analysis
based on this method, but it's probably not worth the effort - there are
too many assumptions in shearwall design to begin with to try to get so
exact.

The other thing to remember with the compression design of the end post
post.

-gerard

-----Original Message-----
Sent: Tuesday, August 13, 2002 11:13 AM
To: seaint(--nospam--at)seaint.org
Subject: Wood-Framed Shearwall Compression Chords

Hello all,

I've got a copy of Donald Breyer's 3rd edition (I know there's a later
edition) for wood design and he describes the free-body diagram used to
determine the tension and compression chords of a shearwall.  If we
ignore reductions in the dead loads that the wall carries, a straight
use of the typical free-body diagram would indicate that the weight of
compression chord that is additional to the couple from the overturning
moment.  The FBD assumes no support below the wall between the ends,
thus simplifying to a two-reaction system.  This compression force comes
quickly during the check on the holdown, but I've always wondered if
this approach is overly-conservative for wood-framed shearwalls.  I
figure that the amount of "rocking" and realistic bearing of the wall
under a seismic event is difficult to quantify, so it's better/easier to
follow the FBD, but it still seems conservative.

Thanks,
Lane Engineers, Inc.
Tulare, Ca

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