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Re: URM

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Mark:

It's a little difficult to comment on your detailing of the 
frame-to-lintel connection, given the limited information.  

With regard to your questions regarding diaphragm boundary nailing, I 
would like to suggest that you may want see whether it is possible to 
nail your new edge blocking from above.  This commonly done, even in 
historic buildings.  The nails will yield much more effectively than 
the screws, which may break or pull out.  If you really have to use 
screws from below, you should try to put in enough of them that 
you're sure they'll remain elastic.  The diaphagm can still yield, as 
the UCBC intends, along a line parallel to the diaphragm boundary.  

--SKH

> Date:          Fri, 07 Nov 1997 10:17:17 -0800
> From:          Mark Baker <shake4bake(--nospam--at)earthlink.net>
> Reply-to:      seaoc(--nospam--at)seaoc.org
> Organization:  Baker Engineering
> To:            seaoc <seaoc(--nospam--at)seaoc.org>
> Subject:       URM

> I am working on a retrofit of a three story URM building. In detailing
> the connection of a new moment frame to the existing lintel element,
> frame placed within the open storefront of the building, I am concerned
> about the effectivenes of any shear transfer connection I make.
> 
> The existing lintel is presently being opened up so I will ultimately
> have more info about what is there but for now...
> 
> I can see a 13" wide 3/8" thick horizontal steel plate under the lintel
> with rivets. I am assuming this plate is the bottom flange of a built up
> member buried within the thickness of the 13" thick urm above.
> 
> I need to be sure that in plane loads from the wall above are going to
> transfer to this built up member if I  make connection between the new
> frame and existing 3/8" steel plate. Once this area is opened up I can
> access the capabilities of the existing assembly but for now I am
> interested in what others have come up against for this type of
> connection.
> 
> Secondly, I am making all my diaphragm to wall connections from below,
> the existing straight sheathing and hardwood flooring will remain
> intact. When installing new continuous blocking, tension ties and shear
> bolting, I am questioning the neccesity of providing new boundary
> nailing. Per the UCBC, the limitation of the shear connection capacity
> to the shear capacity of the diaphragm provides a connection strength
> that causes shear yielding in the diaphragm. Will any new boundary
> nailing compromise the shear yeilding mechanism of the diaphragm? Any
> new boundary nailing of existing sub floor to blocks would be done from
> below with a35's screwed into underside of sub floor.
> 
> Any comments would be appreciated.
> 
> Mark D. Baker
> Baker Engineering

Stephen K. Harris
EQE International
44 Montgomery St, Suite 3200
San Francisco, CA 94104