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Re: Three Sided Diaphragm (Cantilever Diaph)

[Subject Prev][Subject Next][Thread Prev][Thread Next] Aswin,

I would recommend you put in the moment frame at the front and not try to cantilever the diaphragm.  Still design the rear wall for 100% of the base shear, since when the moment frame deflects, the diaphragm will become a drag strut and transfer all the force to the rear wall.  You want the moment frame to help control the amount of deflection of the open side of the diaphragm.  I don't think you will be able to show that the diaphragm is rigid to transfer forces by rotation to the cross walls.  If you provide the moment frame, you don't need to have the horizontal truss.

If this is in L.A. you may be able to use an OMF, but with some additional restrictions on design.  E-mail off-line or call if you want to talk more about it.

Mike Cochran S.E.

In a message dated 3/25/2002 5:31:29 PM Pacific Standard Time, rangaswamy(--nospam--at)sha.coffman.com writes:


Hello:

On this one story 40' x 75' long CMU building, there are CMU walls on three
sides except one longi. side which needs to be left open.  (Imagine a pep
boys service center).  The roof consists of 1.5" metal deck  with no
concrete on top (running along longi. direction) supported at about 8' o.c
with steel joist. The steel joists are supported on the wall at one end and
at the open side there is a WF beam, which are supported by columns at
20'-30' o.c. There is a drag strut at this line which takes care of the
chord forces.

I would like to avoid a moment connection at this side. Rotation would
probably be an issue .  What is the max. length to width ratio for a metal
deck flex. diaphragm?

If the deck has sufficient shear capacity would that be sufficient or would
diagonals need to be provided to transfer the shear to the 3 outer wall. 

I am looking for some references and some hints on this  subject.

- Aswin
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