Log Building Member Grades and Design Values

I am working on a log home project and I just discovered that there are grades and design values distinct and seperate from those published in the NDS that are used just for "Structural Members Used in Log Building." I am aware of ASTM D3957 which is a guide to establishing the grades. I have not been able to find who the grading rules writing agency is or who publishes the design values for the established grades in the commonly used log species. Any information would be greatly appreciated.
Thank You
P.S. Would these grades and values be more appropriate than those in the NDS when designing pole rafters in a timber frame? What about those cruck creations of Mr. Sobon and others?

A company called Timber Products Inspection, Inc. (TPI) has created a document they call “Appendix D, Building Log Design Values.” They can be reached at the following locations:
Portland, OR 503/254-0204; Conyers, GA 770/922-8000

The design values they publish, and that their graders certify, are derived from ASTM Standards.

Regarding your question about the use of these values for pole rafters I would suggest that they would be ideal for this type and similar (such as purlins, valleys, hips) applications. The tables include values for unsawn and sawn log cross sections used as structural members (beams, etc.), as well as values for wall logs. An unsawn log is one with little or no wood removed. A purlin or rafter might be an example of this when only a small amount of wood is cut from one side of the log in order to provide a nailing surface for roof boards, or similar material attached to the top face of the purlin or rafter. Where these members are supported at their ends, or along their span, there may be additional notching required. This may then place these members from the unsawn category into the sawn category, with its lower allowable unit stresses.

Cruck buildings, like most buildings, need to be evaluated case by case. For example if a curved log is split in half to form the opposing pieces of the roof, then I would suggest that this is more like a timber and less like a log and I would use NDS values for timbers. If a curved log is matched up with another curved log to for the arch, then the TPI values may be of some use. As is often the case, individual judgment is what determines which values work best with a given design, the wood being used, and the joinery and shaping employed.

I hope this is helpful and if you have further questions the best way to reach me is typically phone, with email as a 2nd choice.

Tom Hahney
7928 Lynwood Dr.
Ferndale, WA 98248
360/354-5840 USA
designing_change@compuserve.com