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Re: Ridge beam/joist analysis

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Thanks Nels, you saved me  the time typing as I was going to say what you
said. It should be noted that we are assuming that this ridge beam is a beam
and not a ridge board. The beam must be capable of supporting the load for
the given span. A single 2x12 spanning 30' does not constitute a beam but is
a ridge board.

Rand


----- Original Message ----- 
From: "Nels Roselund, SE" <njineer(--nospam--at)att.net>
To: <seaint(--nospam--at)seaint.org>
Sent: Monday, June 28, 2004 1:24 PM
Subject: Re: Ridge beam/joist analysis


> Craig,
>
> The ridge beam allows you to assume that the wall and the ridge support
the
> gravity-loaded rafter with reactions that are vertical only.  If W is a
> gravity load, it acts vertically -- no matter how you analyze the rafter,
> whether analyzing it with strictly vertical loads, or resolving the
vertical
> gravity load into components perpendicular and parallel to the plane of
the
> rafters, the result will be vertical reactions onto the ridge and the
wall.
> If that is not the answer you get, brush up on statics and keep trying.
>
> If W is a wind load, the analysis becomes a little more complicated and
will
> involve the two sloping planes of the roof as a two diaphragm planes.  In
> determining how the joist reactions are resolved, base your analysis model
> on the assumption that the wall and ridge resist only vertical loads and
the
> each of the diaphragm planes resist loads only in its plane.
>
> Nels Roselund
> Structural Engineer
> South San Gabriel, CA
> njineer(--nospam--at)att.net
>
> | > -----Original Message-----
> | > From: Craig & April [mailto:csmleko(--nospam--at)bellsouth.net]
> | > Sent: Sunday, June 27, 2004 4:42 PM
> | > To: seaint(--nospam--at)seaint.org
> | > Subject: Ridge beam/joist analysis
> | >
> | > Any thoughts on the conventional knowledge(?) that a structural ridge
> beam
> | > eliminates all lateral thrust at the exterior joist bearing walls? I'm
> | > designing a timber camp roof with a 10:12 pitch. Looking at the joist
> | > member
> | > as it will exist in the structure, (i.e. pitched) the loads are
> obviously
> | > vertical at beam and wall. However, in order to do an exact analylsis
of
> | > the
> | > joist, I applied the 'w' load (reduced for actual longer span) at the
> | > appropriate angle to a horizontal joist. An axial load exists as the
> | > result
> | > of the partial vector. This seems to indicate tension in the joist (if
> | > supported from beam) or compression (if supported at walls)...which is
> | > contrary to what I thought I knew. Anyhow, I hope I'm wrong because
> | > developing the lateral restraint would be tough at 8x8 timber walls...
> | ****** ****** ********
> |
> |
> |
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