Bolt Threads in the Shear Plane of a Tapped Bolted Joint 1

[struclearner]

The threads of a bolt in a bolted joint with a nut can and can’t not be fall in a shear plane. This might not be an issue in a slip resistant joint where the friction between mating surfaces takes the external load.
In a tapped bolted joint with internal threads in the lower member of the joint, is this possible that threads might not fall in a shear plane, as the external threads engage with internal threads right at the shear plane, unless there is a chamfer at the hole edge.

Thanks for your comments and insight.

 

[hydtools]

The bolt threads, capscrew threads could be in the shear plane. If that would be a concern, I would counterbore the threaded hole with clearance for the bolt shank so the threads would not be in the shear plane. This would require a longer bolt.

Ted

 

[IFRs]

The bolt would behave differently if one or both of the surfaces were countersunk. The idealized simple shear plane would now be a more complicated joint with bending on one side, shear on the other.

 

[dvd]

Why isn't this post in the structural forum? AISC and RCSC have plenty to say on this sort of topic.

 

[struclearner]

Hello dvd,

AISC does not focus more on Civil structures, mechanical structure are subjected to more severe loads and fluctuation of these loads as compared to civil structures.
Please enhance my knowledge, if I don't have the full information about AISC.

 

[dvd]

struclearner -

I misread your intent, based on your name and structural affiliation. I will correct myself, and state that AISC and RCSC don't really say a lot about these topics,

https://www.aisc.org/globalassets/modern-steel/steel-interchange/2011/122011_dec11_si.pdf

. I think that your desire to place threads at non-shear-plane location will be difficult, if using standard hardware, because of bottoming of the thread length of the fastener and/or runout engagement with the tapped hole.

 

[struclearner]

Hello dvd,
Thanks a lot for your help.
Usually, the structural engineering is taken as civil engineering structures, but mechanical structure engineering is the branch, dealing with the design of mechanical components subjected to loading and the validation of these components under these loading which are mostly dynamic and fluctuating loads for the intent life of the design.

 

[hydtools]

Tap the threads deep enough and bore to fit the unthreaded shank deep enough to prevent bottoming the bolt or running into the thread runout. Put the full dimension unthreaded shank in the shear plane.

Ted

 

[dvd]

It seems like there are a few ways to attack this problem - most all of these would involve a conversation with your machinist for practical advice - dowels, shoulder screws that don't bottom out on the shoulder, undercut shank sections.

 

[mfgenggear]

I agree DVD if standard bolts are not at the correct lengths the specials will need fabricated.

 

[RRiver]

I'm a bit lost about why you say both external and internal thread shear won't be an issue? The shear load on the bolt is equal to the shear load on the joint. The only way to remove a shear load on the bolt is to remove the shear load on the joint.

The 4 stresses on the bolt:

Preload stress
Tensile stress
Shear stress-internal and external
Bending stress

Another shear consideration is the friction coefficient of the jointed surfaces.

Bolted joint analysis calculator:

https://mechanicalc.com/calculators/bolted-joint-analysis/