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RE: Wood truss

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-----Original Message-----
From:	Ed.Haninger(--nospam--at)fluordaniel.com 
[SMTP:Ed.Haninger(--nospam--at)fluordaniel.com]
Sent:	Thursday, July 31, 1997 4:42 AM
To:	seaoc(--nospam--at)seaoc.org
Subject:	Wood truss

     I have a wood truss design that I would appreciate feedback 
on.  This
     truss is to be used for roof support on a barn.  It uses 
2x4's (flat
     side out) for chords and diagonals with OSB "gussets" 
nailed on both
     sides.  The trusses have a 20 foot span, 4:12 side slope 
and spaced at
     24" on center.  The nails are to be driven and "clinched" 
(bent over
     on the far side).  With the double shear on 10d nails I 
need 6 nails
     per member on the largest loaded connection.  Some 
connections are not
     concentric, so this number would go up.

     Things I was wondering about:
        1) Will OSB work OK vs. plywood in this application?
        2) What is the recommended nail spacing and edge 
distance?
        3) Any other special considerations for gusset size?
        4) What is the best way to brace the bottom chord for 
wind uplift?

     Ed Haninger
     ed.haninger(--nospam--at)fluordaniel.com

[Dennis S. Wish PE]  Ed, I have done on one job out in the 
desert where I had to justify a "job built" truss similar to 
what you describe. So that I understand better, are the chords 
bending in their strong direction? In other words when viewed in 
section is the width of the chords 1.5" or 3.5"? The truss I 
analyzed used 2x6 top and bottom chords with no diagonals. The 
truss was basically a rafter tied system where the bottom chord 
was in the same plane as the top chord and died into the framing 
at the bearing wall. A plywood gusset was used on both faces and 
nailed off with 8d or 10d nails.
The only way I could get the connection to work was to make sure 
that the bottom chord was continuous over the twenty feet. The 
problem was the tension in the bottom chord which either 
exceeded the nailing on the existing gussets.
Go for the bottom chord and check tension to verify if nailing 
will work.
I also suggested that in the renailing process, the contractor 
pull each plate and glue it back in place - can't hurt and 
provides that much more strength to the connection.

On final thought. I don't think I could have ever proved the 
truss to be adequate if the bottom chord was not continuous - 
depending on dead load, the tensions gets pretty large for a 
simple gusset.

I'm not an admirer of OSB, however I loose this fight all the 
time to contractors that want to save money. The code values 
support it's use so I guess it can be used wherever plywood 
works provided you take care of it and keep it out of weather 
(rain etc). It must be adequacy sealed to preserve it from 
deterioration when exposed.

Simpson makes a Hurricane strap - H7 or MTS which is a Twist 
type strap that nails to the double plate and goes over the top 
chord of the truss. Depending upon the eave dimension and the 
amount of open structure, these are good insurance at 4'-0" on 
center.

Hope this helps some.
Dennis Wish PE