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Re: Wood Truss Rafter Center Uplift

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Richard Lewis wrote:
> I am designing two story motel type structure which has a interior center
> corridor.  It will be constructed of wood framing.  The roof will have metal
> press plate truss rafters at 2'-0" o.c.  The bearing walls for the floor
> framing are the exterior longitudinal walls and the interior corridor wall.
> I am trying to decide whether to clear span the roof rafters to the exterior
> walls (50 ft. span) or use the interior corridor bearing walls.  My concern
> is "Roof Truss Uplift" at the corridor due to fluctuations in the moisture
> content.  My options would be to clear span the building and detail the
> corridor/truss connection to allow the uplift to occur without picking up the
> partition, or to break the truss into two pieces and simple span to the
> corridor.
> What are your suggestions?
> Perhaps someone from WTCA can give some advise also?
> Rich
> __________________________________________________
> Richard Lewis, P.E.
> Missionary TECH Team
> rlewis(--nospam--at)
> The service mission like-minded Christian organizations
> may turn to for technical assistance and know-how.
 An additional thought: if you "ignore" the interior walls, how will you
deal with the large deflection at center span?  At L/240 deflection a
50' span deflects 2.5", that's an awful lot for sheet rock to move.  My
point is, the trusses will bear on those walls, even if you don't intend
them to.  Think relative rigidity as well.  If the walls are stiffer
than the trusses, the walls will take the load.  You can design for 2.5"
of movement, but it won't be easy.

Jake Watson, E.I.T.
Salt Lake City, UT