At 10:20 AM 6/23/2002 -0700, Randall Young wrote:
>The ceiling joists in my attached garage (which I use as my shop) are 2x6
>beams on 4' centers (yes, 48" centers) that span roughly 24' between the
>walls. Obviously the original intent was only to hold the walls together,
>but the previous owner laid some plywood down and my wife and I loaded the
>space up when we moved in. By now I'm not sure what all's up there, but
>it's probably mostly books. Last night I looked up and realized that one of
>the beams is broken ! It's cracked about 3/4 of the way through and has
>sagged until it appears the load is actually being carried by some 8'
>fluorescent lights ! (I wouldn't have believed you could bend a fluorescent
>tube that far without breaking it.)
>
>My thought is to jack the beam up until it's horizontal, then lay a 16' 2x6
>on each side (one resting on each wall) and run bolts through all three 2x6.
>(I'd have to seriously disassemble the house to get a new 24' beam in
>there.) Any comments on the flaws in my plan, or a better way ?
>Suggestions on how big and how many bolts to use ?
My garage has a 24 foot span. It uses 2x12 microlams on 1 foot centers.
The room above uses pre-engineered trusses built out of 2x4s and metal
connectors on 2 foot centers. The loads on the different floors is different
of course, but the point I'm trying to illustrate is that it takes a lot less
material to build a truss compared to a span.
I'd look at pre-engineered trusses as inspiration for your repairs. I wouldn't
bother sistering a 2x6. I'd think in terms of triangles rather than long
spans.
A truss uses more metal connectors and a lot less wood.
I couldn't find a picture that shows a simple pre-engineered roof truss,
but here's
a website that shows how complex the problem can be!
http://www.woodtruss.com/index1.html
It looks like the industry term is METAL PLATE CONNECTED WOOD TRUSS
If you want to be an amateur engineer, I think you start with a "free body
diagram"
or some such and get mathematical! Wish I could offer more help but I majored
in Philosophy.
Steve Shipley
Seattle, WA.
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