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Re: Rolling Shear on Wood Nailer

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Larry-
The USDA Wood Handbook shows an ultimate value of about 300 lb/sq in for tension perpendicular to the grain (as commonly found in cross-grain bending).  These values are based on the testing of small clear wood specimens free of splits, shakes, checks and other seasoning defects.  For example, if a member has a split or shake, the effective section modulus can approach zero resulting in an infinite tension stress. 
 
The 1997 National Design Specification for Wood Construction (NDS1997) at Section 7.1.3, which is adopted by reference in the 2001 CBC as amended and which applies to the entire State of California, discourages use of connections inducing tension stresses perpendicular to the grain.  According to the Commentary to the NDS1997, the provision was first included in the 1944 edition, dropped in the 1948 edition when shear stress provisions were revised and re-introduced for eccentric connections in the 1982 specification.  To quote the Commentary: "It is to be emphasized that no tenison design values perpendicular to the grain are given in the Specification (See Commentary for 3.8).  This is because undetectable ring shake and checking and splitting that may occur as a result of drying in service make it impractical to establish reliable, generally acceptable values of the property."
 
Larry, it would seen that your condition is quite analagous to the detail Nels describes below.  I would concur with Nels recommendation to rip the nailer flush with the beam flange.
 
Regards,
Bill Cain, S.E.
Berkeley CA
 
 
 
-----Original Message-----
From: Nels Roselund <njineer(--nospam--at)att.net>
To: seaint(--nospam--at)seaint.org
Sent: Mon, 28 Mar 2005 07:59:42 -0800
Subject: RE: Rolling Shear on Wood Nailer

Larry,

It's called cross-grain bending.  I don't believe that you'll find any
design values.  Many So. CA cities do not allow it.  Seismic damage that has
led to partial roof collapse was attributed to cross-grain bending.  The
damage occurred in wall anchor details in which the wall-anchor load-path
was: concrete or masonry wall, to anchor bolt, to ledger, to nailed plywood
sheathing [no direct connection of anchor bolt to framing, or a too flexible
connection of anchor bolt to framing].  The condition you are having to
solve seems much more benign.  Nevertheless, could you rip the nailer flush
with the beam flange before installing the hangers?  

 
Nels Roselund, SE
South San Gabriel, CA
njineer(--nospam--at)att.net

-----Original Message-----
From: lrhauer(--nospam--at)earthlink.net [mailto:lrhauer(--nospam--at)earthlink.net] 
Sent: Monday, March 28, 2005 7:27 AM
To: SEAOC
Subject: Rolling Shear on Wood Nailer

Does anyone know if there is a value for "rolling shear" in wood, (or I
guess you could call it "shear perpindicular to the grain")? I have a job
which is under construction and uses long span premanufactured wood roof
trusses sitting on a 4x nailer atop a wide flange beam, (perpindicular to
the trusses). My detail shows the truss bearing clips sitting on the top of
the nailer with the nailer edge flush with the flange of the beam, (typical
detail). However, in construction they somehow didn't get the wide flange
beam exactly straight, so that they want to "hang" the 4x nailer over the
edge of the beam flange about 1" to pick up the truss reaction.

I am reluctant to do this since I can find no value in the NDS for this type
of shear and have always been under the impression it is not good to do
this.

Anyone know of a value for "rolling shear", or any other advice like "make
them do it right"?

Thanks in advance,

Larry Hauer SE



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