Randall Young wrote:
>Thanks for the thoughts, Peter.
>
>
>
>>The cracked appears, from your post, to be 6 feet from the wall.
>>
>>
>
>My apologies, the break is actually near the center.
>
No apologies necessary, I should have understood 3/4 through meant
across the board, not along the board. It does change things
dramatically. What you are suggesting will make a strong joist than before.
>I would really try to get a full length joist up there. You should be
>able to bow a 24 foot joist enough to get it up there. Lay the joist
>flat, not on edge, on one wall. Have a big friend hang on the center of
>the beam while you raise the other end into place. Once up there twist
>the joist to put it on edge.
>
>
>
>Good thought, but there are shelves and cabinetry in the way. I'm really
>hoping to avoid having to tear them out and rehang them. Also, if my
>envelope hasn't slipped a digit, you're talking about deflecting the center
>of the beam by roughly 20" (to shorten a 24' beam by 3"), which strikes me
>as enough to possibly break it, and more deflection than I would expect from
>my heaviest friend <g>
>
I'll bet you can bend the joist enough. A 24' joist laid face up will
bend considerably under its own weight. Wood has to bend or light
breezes would snap trees.
>
>
>>Rather than bolt which would compromise the strength of the joists, I
>>would use wood glue to laminate the sister joist in place. Wood glue is
>>stronger than wood and bolt holes would compromise the strength of the
>>joist.
>>
>>
>
>I'll agree glue is stronger than wood, but I'm not convinced that in this
>case it would result in a stronger joint. Glue will concentrate the force
>at the face of the beam, while the bolts will distribute it through the
>beam. Wood is weakest in tension, so it will start breaking right at the
>glue surface and continue across the joint. The clamping force of the bolts
>will also result in significant friction at the face, likely nearly as
>strong as the glue.
>
Wood expands and contracts with the seasons. If you bolt them together
in the summer, they bolts will be loose in the winter. You'll have to
tighten them. Wood also compresses. When summer comes the swelling will
crush the wood only to be loose again the next winter. This means at
some time the loads will be focused at the bolts and there will be no
friction. Gluing would avoid problems with movement and distribute the
load. Consider this, a clear span joist 24 feet long can only use
engineered, laminated lumber.
However, consider gluing and bolting.
>
>Thanks
>Randall
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