There are (and were) several types of timber that come from Oregon, see "Information on Oregon Wood Species". Suggest having tests made on small samples to determine what species were used. Actual load tests on samples are even better... if possible.

Nineteenth century data on some timber properties does exist but tests were just being developed so some results may seem odd by today's standards. The most accessible records are in the Trautwine's Civil Engineer's Pocket Book series (tests make before 1888). There will be some data on spruce, but most interest at that time was southern pine and oak.

Other sources are 19th & early 20th century engineering "Pocket Books". I cataloged a number of these pocket books on my website: Link. In particular, see the pages 184 thru 190 of the 1893 Carnegie Pocket Companion. (It summarizes the 1888 Trautwine data.)

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...and keep in mind that old wood may have different current properties than it had when the structure was first erected.

Testing some pieces, as SRE mentions, would be a good approach.

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As usual SRE is a hell of a resource!!

Within Australia, "Oregon" was (i.e. hard to obtain now in Australia) Douglas Fir.

For clear grain DF in that era, probably looking at 1600 to 1800 psi in bending. Have it tested though as suggested.

Mike McCann, PE, SE (WA)

Hi All,

I am very appreciative of all this information and at the very least it will give me enough information to relate the timber to the closest likely strength within the Australian Standard. I will review all of this information with relish and digest! Slide Rule Era, as per usual you have useful information for just about everything!

JAE - with respect to your comments, do you mean the properties have changed due to degradation i.e. rotting or that I should consider the usual load duration/creep effects? I have a condition survey that states that the timber is in excellent condition so am not accounting for any degradation over time.

One of my colleagues mentioned that it is likely that the timber imported from the USA back them was felled from 'natural growth' forests which would likely be stronger than the farmed timber used nowadays given it's slow growth. I am not so sure about this as I imagine that by 1880 the USA would have been growing Oregon by the forest loads given it's worth back then. Any thoughts?

I will try to send a photo of the final scaffold installation for your interests, as scaffold goes, it is about as sexy as it gets!

I think your colleague is correct. In 1880, they were cutting down big trees, with not much thought to reforestation. The Douglas Fir timber in good condition would be high grade stuff. The only problem Australia has had with "Oregon" timber in recent years is a fad by some architects to use the material in exterior environments. It is not durable in that type use.

I think Mike McCann's guess of allowable bending stresses is in the ballpark, with about 75% of that for compression parallel to grain.

I wasn't referring to rotting (either wet or dry rotting) but more to age embrittlement. I honestly don't have the document or copies of the information at hand but many years ago I read and was led to understand that as wood ages it gets less ductile, so to speak, and more abrupt failures in the wood can occur. The wood fibers dry out over time and fractures can begin to occur through the matrix of the grain.

I saw an example of this at Offutt AFB in Bellevue, NE, a several years ago where they had old wood trusses (flat rough sawn bottom chords and glue laminated arched top chords).
These trusses spanned over a large space (originally used for construction of bombers back in WWII). The bottom chords had numerous splits - very tight jagged things at several bolted split-ring joints. The trusses were very high above the floor and in the winter the upper reaches of the space was kept very warm and very dry.

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Here is a USDA Forest Products Lab paper on the aging effect that JAE discusses:
"Evaluation of Recycled Timber Members"

Results happen to relate to Douglas Fir which is likely relevant to the project.

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