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RE: Ridge beam/joist analysis

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: Ridge beam/joist analysis
• From: "Craig & April" <csmleko(--nospam--at)bellsouth.net>
• Date: Mon, 28 Jun 2004 20:43:14 -0400

```I sure appreciate all the input...thanks to everyone...this is a great
resource for a guy working solo. In sum I have a vertical reaction that
induces axial load (due to pitch) in the joist. I will carry all the axial
load as tension at the ridge connection, which should eliminate lateral
thrust (besides ridge deflection).

The hump I can't seem to get over is a statics problem of analysing the
joist tension load. The camp will be 28' square, 3' roof overhang (17'
horizontal load on joist), 10:12 pitch, and 60lb/ft2 total roof (vertical
only for now) load. For analysis I turned the joist horizontal. At specified
pitch the actual length of joist 22.13', with the wall bearing point 3.91'
in from one end. Cosine 39.8 * 60 lb/ft2 gives my 'w' acting normal to the
joist (46.1 lb/ft2)...this times trib spread over total length of joist is
what I will use for bending and shear. Sine 39.8 x 60 x trib for tension.

The problem in a nutshell is that my normal partial vector result (using
46.1 and actual length) is the same (619.3lb at wall/400.7lb at beam) as my
original analysis of the full gravity load on pitched (shorter) joist.
Shouldn't it be smaller as it is only a component of the actual gravity
load? At the same time it seems intuitive that reducing the load and
stretching the joist by these amounts would result in what I'm getting.

No reply ok, you can still come visit me at the Northern Michigan Looney
Farm. I'll be the guy scratching his head with a confused look on his face
mumbling something about "vector...mmmm...span...lateral...".

Craig

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