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Re: Wood Moment Frame?

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Dan,

I completed a research report on this topic before I retired from APA -
The Engineered Wood Assn.  It is APA Report 156; I'm not sure if it is
published yet (15 months later).  :o(

>From your info, this application is feasible. It is similar to what we
wound up recommending for this loading condition. A similar design also
was proposed in 1976 by ATC (ATC-4), after the San Fernando earthquake.

The sheathing panel (plywood or OSB) is so rigid that there is virtually
no inflection point at mid-height, unless perhaps the sheathing is cut
in two pieces with horizontal blocking at mid-height. The allowable
design shear load as published in UBC tables should be reduced when the
wall aspect ratio (h/w) is greater than 2.0; recommendations are in the
report. Also, wall displacement should be checked in accordance with UBC
provisions in Chapt. 23 to verify end wall displacement is compatible
with other portions of the building, or can be accomodated by finish
materials.  This could be critical if stucco or brick or stone veneer is
used for exterior finish, but wood-based siding or similar is more
forgiving (e.g., can withstand more displacement without damage).

For a copy of the report, contact tom.skaggs(--nospam--at)apawood.org or
bill.baker(--nospam--at)apawood.org.

John Rose
APA (retired)
Tacoma, WA

Dan Goodrich wrote:

> I'm looking at a fairly simple garage.  Wood trussed roof,
> wood shear walls, etc.  The walls are 11 ft. high.  The
> front of the garage has a 16 ft. x 10 ft. door.  The panels
> on either side of the garage are only 2 ft. wide.  Total
> seismic shear on this wall line is 1200 lbs.  Seismic zone 3.
>
> The engineer of record shows the LVL header over the
> garage door extending to the end of the 2 ft. wide panels on
> either side of the garage.  He has holdown straps from the
> foundation to the holdown posts.  He also placed straps from
> the holdown posts to the LVL header at the top.  Something
> like a moment frame?
>
> He claims that since he is restraining the rotation of the shear
> wall at the top, then the inflection point is at mid-height of the
> panel.  Therefore, the panel height is only 5-1/2 ft., which
> doesn't violate the 3-1/2 to 1 ratio for shear walls required
> by the UBC.
>
> I don't agree with this, and told him so.  I think the panel height
> should be from the bottom of the header to the top of the
> foundation wall.
>
> What do you think?  Any kind of documentation on something
> like this?
>
> TIA,
> Dan Goodrich, P.E.
>
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