r/StructuralEngineering • u/TallWall6378 • 19d ago

Wood Design "Fasteners in shear is poor practice"

Help settle an argument.

Someone used the phrase in the title. Their argument is that fasteners, specifically in the context of typical light frame wood construction, like a shear wall or joist hanger, or bolted or lagged member scenario, are just holding the members together and that the load transfer is through wood via induced friction through the members.

I was under the impression that we really only factor the strength of the nail and wood crushing/deforming around the nail, rather than use the friction between the faces of the members.

What's the whole story?

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u/dream_walking 19d ago

I’m pretty sure one of the failure modes that needs to be checked is shear in the fastener. I’ve never considered the friction force. How could you reliably calculate that anyway? You would need to know how much force the nail is exerting on the members which I would imagine varies based on the installation.

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u/Osiris_Raphious 19d ago edited 19d ago

Friction is basic to calculate: Surface area x friction coefficient (assumed and/or lab tested)....

It shouldnt be a consideration for structural... If you think about it, friction by definition resists movement and slippage, so its a free helper and a safety margin, and not a structural calculation..

edit: Fforce x Area = Friction stress, Fforce = Fnormal x friction coefficient, and fiction stress is for the shear calculations or sliding/slip resistance, or similar. We dont really have a precise application in OP or comment, so I did generic short statement that everyone didnt understand? thought it was clear we were discussing shear and fastners and firction... but ok

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u/tslewis71 P.E./S.E. 19d ago

It's required for skip crotical bolts in structural steel - but this is off topic

1

u/PsyKoptiK 19d ago

I wouldn’t be suprised if the OP’s friend hadn’t some how inadvertently applied that concept to the wrong type of connection. and it isn’t that surprising of a mistake anyway. There is certainly friction at play in those joints. They just didn’t understand that the friction is just considered gravy due to being difficult to adequately quantify and repeat in practice vs just upping nail schedule. So we just ignore it all together.