cross grain bending

[Robert216]

Does anyone know of a code reference that prohibits cross grain bending as a load transfer mechanism? I have read numerous articles that state things such as "wood is weak in cross grain bending" or "this would create cross grain bending". Is there no value for cross grain bending? I know that it is not desirable, but the loads I am working with are pretty small and I may be able to simplify the design. Any comments are appreciated.

Thanks,

Rob

 

[frv]

The problem is tension. Wood is terrible in tension perpendicular to grain. I can't remember if it's specifically prohibited, but you most likely won't find any literature on allowable values. Just don't do it.

 

[msquared48]

There was a code reference specifically prohibiting it in the UBC. If I can find it I will post it.

Mike McCann
MMC Engineering

 

[jberg]

Note sure about the UBC, but in the 2003 IBC, Chapter 1620.3.1 states:

"In wood diaphragms, the continuous ties shall be in addition to the diaphragm sheathing. Anchorage shall not be accomplished by use of toenails or nails subject to withdrawal, nor shall wood ledgers or framing be used in cross-grain bending or cross-grain tension."

Note this is the Earthquake loads section, so I have not found a reference in the IBC that covers non-seismic applications. Hopefully the UBC has additional guidance.

Joel Berg

 

[woodengineer]

Design values do exist. Contact AF&PA for guidance. Also the ANSI TPI addresses this issue regarding bolted hangers on bottom chords of trusses. Good luck.

woodengineer

 

[Lion06]

The NDS specifically prohibits it - sort of. They only mention it in the tension section, but they say that if "tension stress perpendicular to grain cannot be avoided, mechanical reinforcement sufficient to resist all such stresses shall be considered." Bending stress across the grain does cause tensile stress across the grain, so I have to think that this clause applies. It is 3.8.2 in the '05 NDS.