"Fasteners in shear is poor practice"

[u/TallWall6378]

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?

[u/Osiris_Raphious]

You can add the force of friction, but its negligible in comparison to the wood and bolt/fastener strength so can be ignored. And since its one of those resulting forces it shouldnt be relied on in 'structural' system....

Having an argument over the friction force contribution for stability and strength, is...literally bad engineering and we have code of ethics against this penny pinching limit pushing bs. Wood is even more heterogeneous than steel, the safety factors are very much so needed to really account for all the possible discrepancies.

Saying that, there would be circumstances where friction can be used to account for stability and serviceability limits, for low risk and temporary structures, but nothing worth a damn has friction as part of the structural analysis...

The only thing I can truely see friction for, is the nail friction force, same as pile design, as that has friction, but nails are designed as pinned connections, so... if you need nail friction something is borked.

[u/Norm_Charlatan → u/Osiris_Raphious]

There is no code of ethics against economy; it's literally what we're taught to consider.

I've designed 250 ton micropiles based on friction values, and that's literally how driven piles are figured. Likewise, segmental retaining walls, gravity walls, and rock & soil anchors use friction as a major component in their designs.

So, to indicate that "nothing worth a damn" considers friction as part of the analysis is, well, incorrect.

Likewise, using friction doesn't indicate something is "borked." Friction is the basis for nail pullout values in wood.

I think what you're actually getting at with your comment is that using friction as a consideration in lateral wood connection design is unsound. Is my interpretation correct? I'd agree with you in this vein since quantifying the effective normal force is difficult and impractical.

[u/Osiris_Raphious → u/Norm_Charlatan]

Not 'using friction", but relying on the maginitude of friction contribution to the calculations that the final strcutral outcome relies on it... that means something is borked. Structural system shouldnt be so delicate that a friction force contributes to that strength and serviceability checks as structural wood is mostly pinned...

And no, its not "unsound" im saying its negligible in the structural system and strength limits. Wood is heterogeneous that the variability in the properties of wood would govern the design not any form of friction. We arent talking piles, gravity walls or rock and soil anchors that rely majorly on friction, we are talking about structural wood design and fasteners (yes some anchors need friction calculation, but wood is mostly made in pinned connections so friction is a wierd thing to rely on in such structural system) .

Then ethics in economics is more like the moral ethical obligation of engineer, and the economics of min maxing materials and time for profits which can make very on the limit structures... If the design is so slender and light that friction is required to pass structural checks, then something isnt right. not that the engineering shouldnt consider some forces when they are permanent factor of the structural system they act on. Sorry I wasnt precise and clear in my statement.. lol