capacity, design values for a whole log

huangyhg

capacity, design values for a whole log
i have an application with whole logs being used, basically the only milling done is having the bark removed.  i was wondering just how strong a log is when compared to sawn lumber.  you would think that leaving the cell structure of a log alone would be stronger than the individual pieces of that log.  what would you use for design values . . . we were thinking df-l #2 would be conservative, but just wondering how high we could take that.  we have designed to the nds values for round columns, which says to make the section an equivalent square post, and so i was wondering what a fair value for the compressive stress would be.
check out our whitepaper library.
consider reviewing the rough draft 鈥?icc standard on log construction at:
the icc standars on log construction give tpi grading standards which are often used for unsawn timber.  tpi has seems to have stricter standards than wwpa.  you will notice that a tpi no. 2 df is has approximately the same bending allowable as a wwpa no. 1 df.
i engineer a lot of log homes and pole barn type structures.  i usually use the full section properties of the round log rather than using a square equivalent.  it isn't hard to figure the section properties of the round log.  if you aren't having the logs graded and aren't sure what you have as far as quality, then use a conservative value such as wwpa no. 2 df.  if you have the logs graded then you know what you have and can then use the proper allowable based on the grading system whether it is tpi, wwpa or another system.  from my experience most grading systems other than tpi don't grade the raw logs.  
del2000 - you may find several of these (free) .pdf documents and powerpoint presentations about "wood pole strength concerns", "wood equivalent poles", etc. to be of use. here is the link to them at the north american wood pole council