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Re: Garage door detail

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Subject: Garage door detail

>...1997 (many of you may also have gotten it).  It is 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.

>My initial thoughts on this are:

>We could resolve the moment at the GLB/wall connection by distributing the
load to the nails in the grid pattern (this was a basic statics problem in
school). The nails would all be in shear.

We could determine the uplift force by resolving the moment into a couple
(another basic statics problem). We could use standard Simpson products (or
equal) for the straps and holdowns.

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

Assuming that this detail is meant to be a portal frame!

The main shrinkage will be across grain.  The glulam and the plywood should
show little shrinkage.  The amount of nail grip loss will therefore be
minimal.  If that is considered a problem then allow for it in the treatment
factors Kt or Kst.

I have a problem with the base detail.  With such a short "wall" the moment
transfer to the foundation is going to be relatively high.  The detail as
shown would not adequate for the moments possible.  Alternatively the lower
connection should be detailed as a "pinned" condition.  Also, serious
anchors may be needed into the foundation and the glulam connection
depending on the load accumulation at this joint.

In order to reduce the load(s) to such a portal, consideration of the
supported floor to act as a diaphragm might work.

Thor Tandy  P.Eng
Victoria  BC