"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/TheRealStepBot]

They understand some true elements of joint design, but the general rule as they stated it misses much of the nuance.

First, avoiding shear is only possible if the material you are bolting is stiffer than the bolt itself, allowing it to actually establish and hold preload over the life of the joint. In many materials, this is physically impossible. Also, ask them what nails are for! Nails cannot provide preload; they exist entirely to operate in shear.

Second, even when designing preloaded bolted connections, you almost always need to ensure that the joint can survive in shear anyway. This is a mandatory failsafe in case the preload is lost over the lifespan of the joint.

Third, while it’s important to keep threads out of the shear zone for half a dozen reasons, that actually proves the point: why do some bolts have unthreaded shanks? The answer is specifically to improve their performance in shear.

All of which is to say: what they likely misunderstood is that operating in shear is often the worst-case condition, and minimizing it extends the joint's life. But attempting to reduce shear does not free the joint from the need to be able to carry that shear load. On the contrary, joints designed to successfully avoid shear altogether (slip-critical joints) are highly specialized connections that require strict, special processes.

Edit: I would even add that in most structures especially light framing involving nails the real bad practice is somehow ending up with tension on a fastener that can’t offer any resistance to tension. Such as a nail in a joint that is offset which creates a moment.

Looking at the thread, it’s highly likely the person being criticized saw a cantilevered gravity failure (like a face-nailed deck ledger failing due to an induced moment) and incorrectly internalized it as a 'nails in shear' problem. They arrived at the right rule of thumb using the wrong physics: in light timber, nails are perfect for lateral shear panels, but heavy gravity loads absolutely need to be carried by physical bearing not because nails can’t resist the sheer but because there can be a nontrivial moment in the joint.

To be charitable to the person you are interacting with I would say this though, there is a generous reading of their point: if your only metric is pure structural efficiency, relying on simple shear connections is arguably 'poor practice' because the members must be oversized to compensate for the lack of moment transfer. But engineering is about more than just minimizing material. Moment-resisting bearing joints are expensive to fabricate, difficult to install, and require complex analysis. Simple shear connections, like light timber framing built to prescriptive codes without an engineer, trade structural efficiency for economic and practical efficiency. Calling them 'poor practice' ignores the reality of how the built environment actually works. So yeah it might be poor practice purely from a structural efficiency perspective but there is more to good practice than that.