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RE: Premanufactured wood trusses without diagonal

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Make sure they have analyzed for any unbalanced loading that may occur.  A 
Vierendeel panel as you are describing at midspan will usually look ok with 
a uniform load because the loading near midspan is maximum moment (i.e., 
high chord forces which the chords will probably handle), low shear on the 
truss (little shear force to take in the chords).  If the loading is 
unbalanced, the shear load rises (the chords may not be able to handle this 
shear) and they often don't work well.  Under the unbalanced load 
condition, deflection can sometimes be a problem, due to flexure of the 

Christopher Wright's suggestion of requiring them to show you free body 
diagrams at the panel is excellent (if they can't do it, they probably just 
have a technician running the program with little, if any, engineering 
review), but don't accept just a uniform load condition because it probably 
doesn't control.

Bill Cain, S.E.
Oakland, CA

-----Original Message-----
From:	AnandNene(--nospam--at) [SMTP:AnandNene(--nospam--at)]
Sent:	Thursday, October 29, 1998 8:05 AM
To:	seaint(--nospam--at)
Subject:	Re: Premanufactured wood trusses without diagonal

I am reviewing a truss submittal where the truss manufacturer has used a
rectangular panel in the truss in the center to make room for duct and some
light equipment.  When I asked about the moments in the members around the
rectangular panel, I was told that the program is designed to handle panels
without diagonals and that the interaction equation shows the effects of 
and bending forces.  When asked about the ability of the connector plates 
transfer moments, I was told that an ICBO report would be faxed to me.

I would like to know if others have reviewed trusses like this and what
comments they have.


Anand Nene, S. E.
Consulting Structural Engineers
1624 Franklin Street, Suite 1200
Oakland, CA 94612-2824

Tel: (510)-893-3464
Fax: (510)-893-3466


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