Wood Species/Strength Determination 3

[kxa]

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.

 

[JAE]

I'm assuming northeast USA? There are lots of fine engineers from all over the world here.

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.

 

[NHstructural]

I believe this is the place in Wisconsin that JAE is refering to. I have never used their services.

http://www2.fpl.fs.fed.us/WoodID/idfact.html

 

[dicksewerrat]

Get a belt sander and sand off just enough to see the grain. Take good picture and bring to a lumber yard. Walk aroound the lumber and compare. In the 20's most of the structural lumber was Douglas fir. or other fir heartwood.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[kxa]

Thank you all. I am in the process of checking the actual loads on the beam and so far, it looks like the Fb>1000 psi. I guess in the old days even the quality of wood was better. Thanks again.

 

[jheidt2543]

I have had the U.S. Forest Products Lab in Madison, WI identify wood species in the past ( see link above). I took a small coupon sample by using a "hole saw" in a drill bit and cutting about 1/4" thick x 1" dia. sample out, put it in a zip-lock baggie with a note describing the wood member it was taken from. I got results back in less than a week - although, that might have been their slow season. They identified the species of wood and the moisture content.

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.

 

[msquared48]

In the Northeast back in the 20's, with a red tint, it could be a Red Oak. Is the grain real tight?

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

 

[SlideRuleEra]

In the 1920's wooden members were designed "based on the working stresses adopted by the American Railway Engineering Association". See pages 290 thru 299 of "Carnegie Pocket Companion - 1923" which can be downloaded from this page of my website

http://www.slideruleera.net/miscellaneous.html

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net