Determining timber species and grade 1

[DCStructures]

I'm working on some existing row houses. They have typical rowhouse layout with timber beams and masonry walls. I can measure the timber beams but there is no indication of the grade or species of the beams. I need to verify the capacity of these beams. Is there a rule of thumb or general guideline regarding timber species/grade? The beams in some of the row houses are dressed but in other row houses they are rough-sawn. The row houses were all built between approximately 1900 and 1940 and are located in Washington, DC and Baltimore, MD. Any advice you have is much appreciated.

 

[RHTPE]

Reach out to the American Forest & Paper Association / American Wood Council. I have found them very helpful at providing old versions for allowable design stresses. Just make sure your analysis & design methods are appropriate for the time.

You could also attempt to obtain a number of samples and have them tested to determine the values, but keep in mind that things changed dramatically after the In-Grade testing program wound down.


Ralph
Structures Consulting
Northeast USA

 

[SlideRuleEra]

Go to the US Department or Agriculture, Forest Products Laboratory, Center for Wood Anatomy Research, website at the link below.

"...the Center identifies wood for industries, museums, universities, other government agencies, and the general public..."

On the right side of the web page there are instructions on where to obtain a "Wood ID Kit" to have wood samples evaluated.

http://www.fpl.fs.fed.us/research/centers/woodanatomy/

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[manstrom]

I've looked into it myself. It IS possible to have a sample tested, but it is expensive and not exact.

Even if you do have the species, how do you know the allowable values from 1920? I don't think it was standardized back then.

You could have a specimen load tested, then throw on some safety factors and go from there. But that is also expensive.

I typically make an assumption SPF, HF, DF or so and run with that. I try not to re-analyze something if it doesn't show signs of distress. If it's broke, fix it. If it's not deflecting now, leave it alone. If you are adding weight, add new members.

There is a very good chance that the rowhouse was not engineered and some contractor pulled the size out of a chart, or just grabbed what was cheap. I did a site visit on a wood apartment building in DC from the 20s. The whole floor was sagging. We got to the bottom floor and found a wood transfer girder had completely failed - snapped and fell about a foot. It had been like that for years.





When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.

-R. Buckminster Fuller

 

[MacGruber22]

my $0.02: As manstrom mentions, you can usually get away with not testing, sampling, etc. if your building occupancy is not changing to one requiring greater than 40 or 50 psf live load. Also, you can usually tell very quickly whether you have No. 2 or better once you have a feel for the grading requirements (slope of grain, knot size/location). The first question is 'what stresses do you need?". No. 2 lumber from the time period you mention will yield you allowable bending stresses of at least 800 psi and bending modulus of 1,200 ksi or more. If your demand stresses aren't more than that, and the wood is in great visual condition, it probably works all day long. Also, if available, you can get some insight by measuring the deflection of existing members that have been under a permanent dead load for many years. Then work backwards to find what long-term modulus would have been required to obtain that deflection.

Search Google for this text: A Grading Protocol for Structural Lumber and Timber in Historic Structures

There you will find some general basics.

And here is a grain slope template and template for recording knots in case you decide you want to try it out.

https://drive.google.com/file/d/0B_U7QFqf8S_-UUNvODZQeDVLZm8/view?usp=sharing

https://drive.google.com/file/d/0B_U7QFqf8S_-ajNCUExWTXNmRXc/view?usp=sharing

"It is imperative Cunth doesn't get his hands on those codes."