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Re: Garage Door Detail

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everyone eems concerned about the frame on either side of the door opening.
 What about your diaphragms?  Does the roof diaphragm have anchorage to the
rest of the structure?  Are the boundaries sufficiently fastened?  Is there
a need to cross tie the ceiling or use it for a diaphragm?  Why not use the
two side walls and the back wall?  The load is resisted by the stiffest
path.  Is that path adequately tied and anchored?  Do the engineering and
let the code be your guide!!
Thanx, Mark Scott SE

----------
> From: Charles Greenlaw <cgreenlaw(--nospam--at)speedlink.com>
> To: seaoc(--nospam--at)seaoc.org
> Subject: Garage Door Detail
> Date: Sunday, February 08, 1998 10:40 PM
> 
> You have described....
> 
> >a garage door detail,
> >which consists of a GLB spanning the garage opening, supported by two
very
> >narrow (16" min) walls, which are sheathed on two sides. The ply
sheathing
> >is nailed to the GLB in a grid pattern.  Tiedown straps are added
between
> >the GLB and the walls, with HD's as the footing.
> 
> >What we are doing is creating a wood moment frame. Is this wise?? If
wood,
> >over time, shrinks, or takes on a permanent deflection, wouldn't the
nails
> >lose their shear resistance capacities?
> >
> >Talk to me, people
> >
> >Kate O'Brien, P.E.
> >Simi Valley, CA
> __________________
> Others have said:
> 
> >As far as I know, the Code does not recognize the existence of plywood
> >"frames." 
> 
> > It goes without saying that the owner must
> >be made fully aware that this is not code-approved construction. 
> 
> >Assuming that this detail is meant to be a portal frame!
> __________________
> I say:
>         Of course it is a portal frame. Same as always, only right side
up.
> The familiar way is inverted, with an indifferently detailed concrete
beam
> in the ground and two plywood columns sticking up, depending on
hold-downs
> for most of their moment connection. This is true even if these plywood
> columns are wider than the 2:1 ratio now touted as the panacea for most
of
> their shortcomings.  
> 
>         While the building code does not expressly provide a methodology
for
> rigid frames of wood, it has done very little more for customary wood
shear
> wall construction, especially in matters of their moment connections. 
> 
>         The code, by its own terms, does not purport to discriminate
against
> uncommonly used ways of assembling commonly used materials to satisfy
> code-specified loading conditions and serviceability expectations. (See
Sec.
> 104.2.8 in the '94 ed.)  The P.E.Act in this state defines the work of a
> professional engineer, in part, as "creative" (Sec 6701). The code gives
an
> all-purpose requirement for every engineered design: "a rational analysis
in
> accordance with well-established principles of mechanics." (Sec. 1603.1) 

> (It's amazing how often urgently-enacted code changes fail to admit of
any
> rational analysis-- a spectacle most easily seen while serving on a
change
> -perpetrating committee.) 
> 
>         This interesting design problem appears to be amenable to use of
> conventional statics and strength of materials. It has been for me,
anyway,
> and in too many permutations to remember. APA has useful but
seldom-invoked
> strength values in their Plywood Design Specification. Nail "slip" values
in
> UBC Standards show a non-linear stress/strain relationship and lots of
> resistive value beyond the loads corresponding to allowable shear wall
> shears. Understressing this nailing offers disproportionate advantage in
> reducing the nail slip component of assemblage deflection. And who says
you
> are limited to 2x studs or a single row of nails?  
> 
>         Due caution is among the design tools also. As mentioned by many,
> envisioning the effects of moisture change and the effects of play,
> slippage, and deformation in the connections would be essential. Effects
of
> workmanship on the components is another important consideration. There's
a
> host of things to discover and deal with, but isn't that what our
education
> and training was supposed to equip us to do?  Isn't that ability part of
> being a professional?
> 
>         The next several years are going to be entertaining, as the 2:1
> ratio limit goes into effect, and results in all sorts of creative
> circumventions and evasions, for better or otherwise.  Too bad no fixes
or
> mitigations for 3.5:1 ratios were allowed.  Kind of like controlling Teen
> Pregnancy only by demands for abstinence, which few will obey, and you
won't
> allow condoms.  
> 
> Charles O. Greenlaw, S.E.     Sacramento  CA
> 
> 
>