Timber Framers Guild Forums Tools Timber Engineering Adjusting Woodhandbook Mech. Properties

How do you adjust the Wood Handbook mechanical properties to acceptable design values? I am planning on building a mixed species frame and the NDS does not have vaules for several species I would like to consider using. Any advice on how to proceed would be greatly appreciated.

several logical approaches some of which are

group your wood species by similar if not nearly identical numbers and see how you can get the contrasts you are looking for in the design.
If some of your species are significantly "weaker" in the force moment you are considering than you can T&E the numbers in less critical locations like braces.
Design a "model" frame using the midline numbers from your predominant species labeling the drawing with the caculated load properties.
then by inspection and selection from your list you can replace a stick with the desired color/texture contrast knowing that the properties of the chosen one will fit in the range required from your "model" calculations.
kinda like playing 3D tictactoe using specimen numbers within ranges to pass the engineering specs.
the only caution is to "normalize" the moisture content of the real wood so the drying rates are not at conflict with each other. endgrain sealer big time.
have fun

The NDS values are derived basically by taking the lower 5th percentile of the breaking strengths of each species and then dividing that by 2.8 (this of course, depends on the strength characteristic being tested, but is true for deriving bending strength allowable numbers). I could explain the 2.8 in more detail if you like, but that is the number that is used. I believe many of the numbers reported in the Wood Design Handbook are average values so they would need to be reduced by more then the result of dividing by 2.8.