Old Wood Members 1

[msquared48]

Does anyone have any data on any research performed on any aloowable stress increases permitted for wood, take Douglas-Fir for example, that is in the order of 80 to 100 years old? Specifically shear, deflection and bending allowables over what was originally allowed. I realize that codes and allowable stress tables were non-existant for the most part that long ago. Nevertheless, I ask the question.

The reason I ask is that on one occasion, years ago, I came across an old wood wall that had the interior and exterior sheathing removed during a remodel. The interior hadbeen lath and plaster and the exterior horizontal wood siding. I had designed a cantilever steel beam with a backspan, 3:1 as I recall, to support the roof and floor and was using dead load bearing from the wall to help with the cantilever deflection. Well, believe it or not, the wall with the sheathing removed actually created a point load to the tip of the cantilever, and arched to a point at least 10 feet into the backspan, not providing the anticipated dead load to the backspan. As a result, there was more deflection than designed for and a diagonal strut had to be added to support the cantilever. Totally unanticipated.

The point is here that the wall assembly, independent from the siding and lap and plaster interior, had a memory, behaving more like a Vierendiel (SP?) truss than a bearing wall - never could spell this. The nails into the hardened wood were creating a moment connection of sorts as near as I can figure.

Also, considering the fact that nails must be predrilled into this material to avoid them from bending, it seems that there must be some measurable increase in allowables that could be documented with age. This data could really help in remodel applications if allowable.

Mike McCann
McCann Engineering

 

[csd72]

Mike,

Very good question. The timber used in these would not only have been older, better quality timber but would also have been seasoned over the years in the dry interior environment.

In the past I have usually allowed a higher stress on old timbers than for new to allow for this, but it relies heavily on judgement.

I can only think that you would need to get it stress tested in field to get a true indication.

Maybe at the following conference they would have better ideas:

http://www.asce.org/files/pdf/seminars/Design and Reno of Wood.pdf

 

[JKW05]

There is some info in the 1923 "Carnegie Pocket Companion" for timber design from that era starting on page 288. This is available at sliderule's website:

http://www.slideruleera.net/

Heading: Miscellaneuous

 

[msquared48]

WoW!

Sliderule has a great website - he must be almost as old as I am!

Thanks for the lead for the old values, but recent destructive tests on the 80 to 100 year old timber of some of the most common structural species would be very helpful.

I'll check out that conference too. Thanks.

Mike McCann
McCann Engineering

 

[SlideRuleEra]

msquared48 - Glad that you are finding my website useful. If the "48" in your handle stands for the year you were born (1948), then I have you beat by one year (1947).

Here are a few papers from the Forest Products lab that may help:

"Properties of Lumber & Timber Recycled From Deconstructed Buildings"

http://www.fpl.fs.fed.us/documnts/pdf1999/falk99b.pdf

"Stress Grading of Recycled Lumber and Timber"

http://www.fpl.fs.fed.us/documnts/pdf1999/falk99d.pdf

"Evaluation of Lumber Recycled From An Industrial Military Building"

http://www.fpl.fs.fed.us/documnts/pdf1999/falk99a.pdf

http://www.SlideRuleEra.net

 

[msquared48]

Yup. Ya got that right. You ex CIA or something?

I did use a slide rule too. Graduated from the UW in '70.

Mike McCann
McCann Engineering

 

[msquared48]

You used a Pickett - metal? I used the same thing in high school. In college I used a bamboo K&E.

Slang is "slipstick" for the younger crowd.

Mike McCann
McCann Engineering

 

[concretemasonry]

K&E - mahogany in 1963 (nicer "holster").

Also, a circular in my pocket, when I did not want to look like an engineer with my pocket protector full of pens.

 

[SlideRuleEra]

I really liked the all metal Pickett. Had give it a complete bath in the sink about once a month to keep it clean. Then apply a tiny dab of Vaseline to the slide.

http://www.SlideRuleEra.net

 

[sundale]

I do not know the IBC equivalent reference, but the old '97 Uniform Code for Building Conservation (UCBC) has some very good information on this topic. Table A-1-D Allowable Stresses for Existing Materials (p.25) says that Douglas Fir wood can use stresses allowed for #1 D.F. and may use the typical stress increases.

Appendix UCBC-3 Allowable Stresses for Archaic Materials (p.201)lets you assume select structural grade for stresses and goes further to permit a 125% bump for shear stresses above typical code values.

The code writers have given a nod to the strength of old growth wood that was typically used in these older structures.

Does anybody know the IBC equivalent to the UCBC?