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 tpagel 04-20-2010 10:26 AM

identifying joist species

The joist span tables I look at say you must know the species of wood to be able to calculate spanning properties correctly. Is there an easy way of identifying the species on 50 year old joists? Do I need to get a sample tested someplace, or are there any tricks to do it in the field?

 kwikfishron 04-20-2010 11:53 AM

199 Attachment(s)
What part of the country are you in?

Can you post a picture of the wood?

 tpagel 04-20-2010 12:06 PM

I am in Connecticut. Can't post a photo as I have not exposed the joists yet. This is my "next" project and i am trying to think ahead. Will post photos as soon as I am able. Thanks for your reply. Can you take a "guess" (I won't hold you to it) based on the region I live in?

 Yoyizit 04-20-2010 12:50 PM

Quote:
 Originally Posted by tpagel (Post 431019) Is there an easy way of identifying the species on 50 year old joists? Do I need to get a sample tested someplace, or are there any tricks to do it in the field?

To get the modulus, E, support an on-edge joist at each end, step in the middle, then post midspan deflection, total span, joist actual dims and your weight.
The violin makers say that old wood gets stiffer, so the E would increase.

Alternately, slice off a small piece with the grain, near the end of a joist [the IRC has rules for this] and do the same experiment with a lighter weight.

These values can be used to calculate the inputs for this link,
or it can be done with a hand calc. or on a spreadsheet, using the link formula for Wmax and solving for E.

I = [1/12] bh³ where b is the beam edge width and h is the height.
and
w = PL³/48EI so E = PL³/48Iw

Knowing E, you don't need to know what type of material it is, be it wood, steel, copper, concrete. . .

 Scuba_Dave 04-20-2010 03:25 PM

What are you trying to do ?

 tpagel 04-20-2010 03:51 PM

Trying to decide whether I will need to sister the joists below if I build out an attic level into living space. Right now, there are 2x8 joists at 12" O.C. spanning about 16'-3". I "think" that this may not be up to code, so I was going to take out the living room ceiling and sister all the joists with 2x8's glued and nailed with 3" nails about about 6" on center. I was going to have to take out the living room ceiling anyway for another reason, so that's not such a big deal, and it will also let me add acoustic insulation between the levels. I need to do the span calculation to know whether I really do need to sister the joists. What do you think? 2x8's? 12" OC? Good enough or needing support?

 Scuba_Dave 04-20-2010 04:02 PM

2x8 hem fir #2 grade 12" OC will span ~15' 7" 30psf
#1 gets you to 15' 10"
2x10's #2 grade will get you the span you need

Or add a support beam in the middle

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