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Re: Vierendeel truss in wood

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Rick:

Ah, but I am the engineer for the "glulam" manufacturer, so to speak.  I
am now working for a timber framer/structural insulated panel manufacter,
but we end up supplying/doing more than just traditional timber (which is
usually oak or solid DougFir with traditional jointery [i.e. mortese and
tenon]).  So, I am now doing the final detailing for the shop drawings for
a truss that an architect dreamed up (I don't think that there is a
structural engineer on the job).

Regards,

Scott
Adrian, MI

On Wed, 8 Sep 2004, Rick Burch wrote:

> Scott,
> It sounds like you are planning on doing the glulam truss design and
> detailing yourself, which is different from how I have seen it done
> around here (SC), but I know things are done differently in different
> areas.  Here, for an architecturally exposed truss, I specify the
> profile of the truss, the web configuration, the desired member sizes,
> some information about the appearance of the connections, and then the
> glulam supplier has their engineer design the truss and its connections
> and they provide sealed shop drawings for review.  I like this method a
> lot, since the connections can get quite intricate where trusses frame
> into other trusses at hip and valley conditions.  Those guys make these
> things fit together for a living so they are quite good at it.
>
> That being said, one time an architect asked me if we could do a glulam
> Vierendeel truss, so I called the glulam supplier that seems to get most
> of the glulam jobs around here (Unit Structures) and asked them.   They
> came back with the answer:  "Absolutely not!"
>
> That was the end of that.   We wound up going with steel Vierendeel
> trusses clad in steel studs and gyp board.
>
> My trusses had a much longer span than yours however - about a hundred
> feet down the length of a church sanctuary.  It seems that your 32' span
> and small tributary width could almost be handled by the two chords
> acting as beams (ignoring Vierendeel truss action).  This would probably
> show up in your analysis model - even if you fix the joints, the chords
> would probably carry the great majority of the load as bending members
> since their stiffness is so much greater than your webs.
>
> Rick Burch
> Columbia, SC
>
>
>
> Scott Maxwell wrote:
>
> >I have project where the architect would like to create/use a Vierendeel
> >truss out of timber/glulam members.  I thought that I would get others
> >thoughts as my gut is not giving me the "warm fuzzies" (I am in the
> >process of creating a model to determine what kind of moments I would
> >dealing with at the connection of the vertical members to the top and
> >bottom chords, so I only have my gut at this point).
> >
> >The configuration proposed is basically comprised of two 15" deep by 5
> >1/8" wide glulams as the top and bottom chord.  At three places along the
> >span there are three vertical timber members that are spaced about 6" or
> >so apart (i.e. three locations of three vertical members each).  The
> >connection of the vertical members (9 members total in groups of three) is
> >done by way of a vertical row of two bolts/pins.  The vertical members are
> >about 4" to 6" wide (don't totally recall and don't have the drawings
> >right in front of me).  The span of the truss is on the order of about 32
> >ft.  The truss is carrying about 6 foot (horizontal projection of 12/12
> >roof) tributary width of stick framing roof joists.  The ground snow load
> >will likely be on the order of 25 psf.
> >
> >Now, I know wood is not really that great for "moment connections".  But,
> >I also know that there will be some rigidity there from how this will be
> >put together.  I am just not completely sure how much I can count on (and
> >don't know yet how much I will really need until I run the model).
> >
> >Oh, likely DougFir...if it matters.
> >
> >Any thoughts?
> >
> >Thanks,
> >
> >Scott
> >Adrian, MI
> >
> >
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