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