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RE: 2, 3 & 4 ply trusses

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The two ply trusses can be nailed together with no problem.  The three ply
trusses may be able to be nailed together if the girder truss is loaded from
both sides.  The three ply trusses may need to be bolted together depending
on the loading condition and the four ply trusses definitely should be
bolted together.  Assuming that each of the plies is the same profile and
therefore the same stiffness, if a three ply truss is loaded from one side
only, then the connection of the 1st ply to the other two plies must be such
that it can transfer 2/3 of the load to the remaining two plies.  The
calculation is similar for both 2 and 4 ply trusses and depends on the
loading condition, but the calc isn't that difficult.  I try to avoid 4 ply
trusses whenever possible, but when required I always bolt them together.

>From the WTCA publication HIB-91, the tolerance for trusses out of plumb is
the lesser of D/50 or 2", where D is the truss depth, and the tolerance for
bow the lesser of L/200 or 2" where L is the span length between bearing
points.

Hope this helps.

Albert J. Meyer, Jr., P.E.
Martin Engineering
238 North 22nd Street
Philadelphia PA 19103-1004
(215) 665-8570
(215) 561-5064 Fax


-----Original Message-----
From: David Williams [mailto:dwilliams(--nospam--at)snydereng.com]
Sent: Friday, February 22, 2002 2:17 PM
To: seaint(--nospam--at)seaint.org
Subject: 2, 3 & 4 ply trusses


I'm supposed to look at some wood trusses in a one-story wood-frame office
building under construction.
There are several 2, 3 and 4 ply girder trusses that have apparently not
been installed properly.  The framer
who installed the them did not nail the plies together per the truss
manufacturer's recommendations.
Now that the trusses are in place, the architect and contractor who has been
hired specifically to fix
the problems want to know if the chords and webs can be nailed or
thru-bolted without taking the trusses
down.  The truss manufacturer hasn't been much help (and I don't blame them
since they already did their job.)
I assume the recommended nailing is to carry the required shear between
plies so they all act as a unit.
I think the 2-ply and possibly even the 3 ply trusses can still be clamped
and nailed per the manufacturer's
schedule, but am particularly interested in the 4-ply truss. Is there any
reason thru-bolts wouldn't work if
designed properly?

Second issue, one of the 4-ply girder trusses (54' span)has been installed
such that the top chord is "wavy".
The architect says at least 12" side to side variation, possibly 18".  This
concerns me.  How much side-to-side
variation is tolerable?

Thanks in advance.

David L. Williams, P.E.
Vice-Pres., Snyder Engineering, Inc.
409 Vandiver Drive, Bldg. 5, Ste 203
Columbia, MO  65202
(573)449-9177


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