Twisted and Checked Timber Beams

[bigmig]

Can someone point me in the right direction in terms of finding a codified reference that out lines
limits for twisted and checked timber (and log if possible) beams and columns?

Thanks in advance.

 

[TehMightyEngineer]

The criteria I've used for checks in timber has been the grading agency criteria with a healthy dose of engineering judgement; I've found no codified tolerance other than that so far.

For twisting tolerance, other than grading agency standards, I don't know of any. Typically any significant twist in wood is cause for rejection by the contractor and/or owner.

Is this new or existing construction?

Ian Riley, PE, SE
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[dhengr]

Bigmig:
That isn’t really bldg. code stuff. Rather, it will more likely be found in the various grading rules, and their justifications for their various down-grading and up-grading determinations, due to different wood conditions and characteristics. Normal twist (whatever that is) in a log is probably not too detrimental. While too much twist in a large timber or in framing lumber starts to cause problems with joinery, section properties, stress flow, etc. Some checking in large timbers and logs is fairly common and generally not too detrimental as long as it is fairly straight, with the grain (not crossing the grain), and not all the way through the member. It generally doesn’t affect the stress flow much, as long as it is oriented properly. The one big exception is high horiz. shear demand in the region of the checking. These determinations are fairly subjective as are the grading rules, because of the nature of the material being considered. These also lead to the fairly high factors of safety on the allowable stresses and loads for wood construction. The fact is that the grading of logs actually gives some credit for the fact that a good straight log does not disrupt the grain structure in that same way that a sawn timber or piece of lumber might.