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RE: Cantilevered Wood Diaphragm -Reply

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Of course the perpendicular walls provide no support for the load in the
longitudinal direction.  However, if the loading becomes eccentric (and
it will) the "beam" (diaphragm) will have to rotate.  Rotation causes
movement perpendicular to the load, and this movement is restrained by
the perpendicular walls.

All of the longitudinal load goes to the longitudinal walls, but any
eccentricity is resisted by the perpendicular walls.


Charles F. Espenlaub, III, P.E.
Martin-Espenlaub Engineering



-----Original Message-----
From: Roger Turk [mailto:73527.1356(--nospam--at)compuserve.com]
Sent: Wednesday, October 18, 2000 10:54 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: Cantilevered Wood Diaphragm -Reply


Charles Espenlaub wrote:

>>But if that 56' beam were 150' deep and were braced against rotation
by
perpendicular shear walls at 30'-40' o.c., should you now be worried??


Charles F. Espenlaub, III, P.E.
Martin-Espenlaub Engineering<<

But, of course!  Those shear walls are analogous to pinned end beams
that are 
contributing to the loading of the 56' long beam and provide no support
for 
the 56' long beam.  For loading parallel to the longitudinal shear
walls, the 
perpendicular shear walls provide no restraint or support.  In fact, the
mass 
(weight) of the perpendicular shear walls contribute to the loading of
the 
diaphragm, and hence, the load to the supports (longitudinal shear
walls).  
(Other than providing lateral support for beams/girders, how much does
floor 
framing contribute to the bending and shear capacity of beams and
girders 
when designing for gravity loads?)

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

-----Original Message-----
From: Roger Turk [mailto:73527.1356(--nospam--at)compuserve.com]
Sent: Tuesday, October 17, 2000 10:46 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Cantilevered Wood Diaphragm -Reply


Just thoughts:

For lateral forces acting in the long direction:

If I had a beam 56-feet long, and supported only by two supports 6-feet
apart 
at the center of the beam, I would be worried, very worried.

No, there is nothing in the code that would prevent me from doing it,
but 
common sense tells me that it is not the prudent thing to do, no matter
what 
the arithmetic says!

A. Roger Turk, P.E.(Structural)
Tucson, Arizona