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Re: stacked joist members

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Only if there is some sort of identifiable / reliable / verifiable shear  transfer  across that interface.

Otherwise you've got 2 - 2x4's  :(

Years ago on a research project we need  2x12 redwood floor deck material to model an historic structure......kinda hard to find in the 1990's.

So made our 2x12's from 2 2x6's that we ripped to width.  We used a biscuit joiner & wood glue to assemble our 2x12.

To make sure that we really had a sound member, we cut up some sample & did a direct shear test.

Our "built up" 2x12 failed through the original material......both glue lines remained intact.   :)

More recently for my own amusement, I glued 2 4x4 together to create an approx 4x8.

No fancy prep,  just hand wire brushed the interface & applied some SIKA epoxy injection gel,  no clamping, just wiggled them together & let them set.

I tested it in 4 point bending and again.....failure was in the wood not the bond.

The members weren't great, cracks, checks, knots......the calc'd demand (at failure load) on the glue bond was ~175 psi.    The bond proabably would have gone much higher if the wood hadn't cracked.

If you cannot see the mating line perhaps they were glued up?

cheers
Bob



On 3/22/07, IRV FRUCHTMAN < ifaeng(--nospam--at)yahoo.com> wrote:
Dear List:
I've just seen floor joists comprised of two members
(each 1¾ " x 3 ¾" ) stacked on their narrow edges in
an old house being renovated. The entire floor (joist
span 12', o/c=16")  is made up of these joists. They
don't appear to be fastened and the mating line
between members is hard to detect.  Can this
arrangement be considered as a single 1¾ " x 7½ "
member?
Thanks,
Irv




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