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RE: Flexible diaphragm

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Bill,
Is the existing building also masonry (and if so is it Unreinforced
masonry)? Are you using the elevator core to resist shear in an effort
to retrofit the building?

Here is my experience from Unreinforced Masonry retrofit:
1. I have considered all interior masonry walls as connected to the
diaphragms.
2. If the masonry existed, the diaphragm would contribute shear based
upon its capacity of the connection. You may reference the Uniform Code
for Building Conservation Appendix Chapter 1 for Unreinforced Masonry
bearing wall systems.
3. If new wall was designed to drag as much diaphragm capacity as was
required by the calculated demand. 
4. The diaphragm was required to be connected to the masonry wall to
control the mass of the wall out-of-plane. Although I have not
calculated this for some time, it used to be based on about 30% of the
weight of the tributary width of the wall connected at each level and no
less than 200-plf (this has gone up in the latest code but I don't have
a reference in front of me.

In summary, the diaphragm will connect to control out-of-plane loads at
the minimum (tension). If the diaphragm is supported by the wall, then
there will be a shear transfer and the distribution of shear through the
building should be adjusted with this in mind.

There is a great deal of information on this - including design
methodologies for historic buildings. What is important here, in my
opinion, is if you are dealing with an Unreinforced Masonry building in
a high risk area (zone 3 of 4).

Sorry - I guess I've been away from this so long that this may seem more
confusing than helpful.

Dennis S. Wish, PE
California Professional Engineer
Administrator - The Structuralist.Net
Website: 
http://www.structuralist.net
 
Professional Forum: 
http://www.structuralist.net/cgi-local/yabb/YaBB.cgi
 


-----Original Message-----
From: Bill Marczewski [mailto:bmarczewski(--nospam--at)pndast.com] 
Sent: Wednesday, December 05, 2001 4:19 PM
To: SEOC Engineering Forum
Subject: Flexible diaphragm

I have a condition in an existing historic building where we may add
concrete or masonry core walls for an elevator system.  The building has
a
wood floor system, which I am assuming to be a flexible diaphragm.  This
question may be a "no brainer" for many of you but here it is:  Is there
any
problem with a flexible diaphragm transferring load into a rigid wall
system.  I only have previous experience with rigid floor systems
transferring load into concrete/masonry shear walls.  Thanks in advance.

Bill S. Marczewski
Peratrovich, Nottingham & Drage, Inc.
Engineering Consultants
Scow Bay Trading Building, 399, 31st Street, Suite A
Astoria, Oregon  97103
503-325-1250 Main; 503-325-9789 Fax
Office Locations: Anchorage, Seattle, Juneau, Astoria, San Francisco
www.pnd-anc.com/; bmarczewski(--nospam--at)pndast.com
NOTICE: This communication may contain privileged or other confidential
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information. Thank you.



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