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I’m doing some structural engineering calculations for remodeling my 1926 house. There are no grade stamps on any of the old joists, I don’t think they had grading back then, so what numbers should I use for Extreme Fiber Bending Stress and Modulus of Elasticity? Would it be reasonable to assume that they’re no worse than the lowest grade currently allowed by code, #2 Doug fir?
Thanks —
— J.S.
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Replies
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John - If I were doing it I would play it pretty conservatively and use maybe Fb=750 psi (repetitive member) and E=1,200,000. More important perhaps is how they were framed (notched over ledgers?) and how they might have been compromised (6 x 3/4" holes in a row?, bug damage? checks?) over time. They are probably full 1 5/8" right? They are probably pretty hard to cut too.
Jeff
*I assume you are talking about 2x10's?I would rate it as No. 2 NonDense.Extreme Fiber Stress in Bending "Fb" = 950 1090Tension Parallel to Grain "Ft" = 550Horizontal Shear "Fv" = 90Compression Perpendicular to Grain = 480Compression Parallel to Grain "Fc" = 1400Modulus of Elasticity "E" = 1,400,000But that is just my way less than humble opinion. That is definitely underrating it, but I haven't seen it. That may be using too conservative a figure. But at least it is a safe figure.Billy
*Jeff --Thanks for the numbers. They're pretty close to what I've been guessing, #2 Doug fir for permanent loading has Fb = 810 psi, and E = 1,300,000.The joists are actually in very good shape, not notched, and they ran the electrical stuff between them and then down and through the wall studs. This is from the days of the brace and bit, all the holes in the lumber were put there by muscle power.I've opened up an exploratory hole in the ceiling alongside the interior bearing wall, and there's no insect or dry rot damage, and very few knots. The 2x10's are a full 2" by 9 1/4".The place is in very good shape, the problem is giving Building & Safety some numbers and calculations that they'll be comfortable with.-- J.S.
*John - You're welcome. I'm surprised about the full 2", though. If it comes down to a serious question of species, did you know that you can send a wood sample off to our erstwhile federal government and (for free) they will analyze it and tell you the species? I've used the service to determine flooring species in a 250-year-old building.If anyone is interested, I'll post the address. It does take awhile - no surprises there, right?Jeff
*Don't know where you're at but you might check out your grading association. In the northeast it'shttp://www.nelma.org. They have a brochure with those specs for various species including hemlock and ungraded lumber.
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I'm doing some structural engineering calculations for remodeling my 1926 house. There are no grade stamps on any of the old joists, I don't think they had grading back then, so what numbers should I use for Extreme Fiber Bending Stress and Modulus of Elasticity? Would it be reasonable to assume that they're no worse than the lowest grade currently allowed by code, #2 Doug fir?
Thanks --
-- J.S.