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RE: removing partition walls:

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Very true, however if the assumption is that the shear is transfered to the
exterior walls by the diaphragm then it is fairly easy to see if the
capacity of the diaphragm and exterior walls meets the demand. From my
experience on investigating interior shearwalls after Northridge - in one
case a wall was sheathed both sides with plywood, HD20's at each end of the
wall and a gigantic foundation to resist uplift. The wall was located in the
center of the home so it probably took 50% of the lateral load. When we
opened up the ceiling we found that the wall stoped at the ceiling joists
and never connected the 3' to the roof diaphragm.
Not to argue the point with you, but most shearwall failures are not related
to improperly designed walls - even if gypsum was used for the full 150 plf
each side - the majority of failures came from improper connection of the
materials to the studs (stucco failures) or improper connection of the
shearwall to the diaphragm above.
I assumed that the post was originally refering to old homes built prior to
1960 where construction inspection was not necessarily a standard practice.

Dennis


Dennis Wish PE

|-----Original Message-----
|From: John Buchanan [mailto:jjb(--nospam--at)scruznet.com]
|Sent: Wednesday, March 11, 1998 6:10 PM
|To: seaoc(--nospam--at)seaoc.org
|Subject: RE: removing partition walls:
|
|
|At 05:16 PM 3/11/98 -0800, Dennis Wish wrote:
|>This is an interesting question because it assumes that the original
|>structure was desiged with consideration to the interior partitions to
|>resist shear. I would doubt that to be the case unless you can verify the
|>connection of the interior partition which was removed to check it's
|>connection to both the foundation and roof (or floor diaphragm) above.
|
|
|
|>My guess is that if the interior wall is gypsum or plaster, it was not
|>considered in the lateral analysis - if one was even performed. I would
|>assume that, if shear was checked, the shear transfers would occur at the
|>exterior partitions. Therefore, I might disregard the interior partitions
as
|>being anthing but dampers for the diaphragm.
|
|I would be carefull here. In the mid eighties I worked for a structural
|engineering firm
|in which gypsum shear walls were used quite a lot. especially in large
|development
|projects.
|
|Also the interior gypsum walls will act to dampen the acceleration of the
|structure during a seismic event and they provide a certain amount
|of redunant shear resistance.
|
|
|
|John Buchanan
|
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|