Wood Species/Strength Determination
Wood Species/Strength Determination
(OP)
I am involved in evaluating wood joists and girders in an old house in the northeast and would like to know if there is anyway (w/o testing) to identify the wood type or assume a reasonable strength for them. The house was built in the late 20’s and the joist sizes are 3x8 and the girder 5.5x8 inches. Was there any type of NDS design table at the time? The wood color is dark brown and slightly reddish. Any assistance is appreciated.






RE: Wood Species/Strength Determination
No NDS back in the 20's.
My older engineering mentors (from the 40's) used to simply use 1000 psf for the allowable stress.
One thing you can do is take samples and send them off to a lab (I think there is a lab in Wisconsin that does this) and they can tell you what the species of tree is, but not an allowable stress.
A testing lab in your area could take a sample and test for modulus of elasticity and for ultimate stress in bending. That might get you able to compare with current lumber tables and use an appropriate "equivalent" grade of lumber.
Short of all that, you could do a limited load test on the floor (per IBC) and see what sort of capacity you have, or measure deflections to again get an estimate of E.
RE: Wood Species/Strength Determination
http://www2.fpl.fs.fed.us/WoodID/idfact.html
RE: Wood Species/Strength Determination
Richard A. Cornelius, P.E.
WWW.amlinereast.com
RE: Wood Species/Strength Determination
RE: Wood Species/Strength Determination
For design values, I could then go to older text books and find the values used at the time of construction. You can also use current values for comparison.
RE: Wood Species/Strength Determination
From the dimensions, sounds like you could be dealing with a material that may have been logged and milled on site.
In lieu of sending a sample to a lab for testing, some jurisdictions will accept a value two stress grades less than that determined by a visual inspection, if you can locate a reputasble professional who can do that for you. I know that works here.
Mike McCann
MMC Engineering
RE: Wood Species/Strength Determination
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