Resolving torsional moment into shear force over 4 bolts

[SuG89]

Hello,
Please refer to the attached sketch. A torsional moment is applied on the plate at the plus sign location. Two possible shear force distribution are shown - red and green lines. Is the red one correct?
I ask this because the green one would have a component in the slotted hole direction which is undesired.
Regards,
Su

 

[WARose]

The green one would be the correct idea (i.e. the resultant of forces in both orthogonal directions).

 

[JoshPlumSE]

Either one works for me. The Green arrows are better for standard holes as they better reflect the direction the bolts want to move. The Red arrows may be better for the slotted holes that you've got as it may be more difficult to develop shear force in the slotted direction.

 

[WARose]

That's a good point JP. It would be hard to say with 100% certainty how exactly the bolts would "engage". Theoretically, I suppose the "red" scenario could happen before the bolts slid to the end of their slots.....but even then, the rotation would result in a bearing that would give a reaction force that would not be perfectly vertical. It really depends on the geometry of the situation.

 

[JoshPlumSE]

Green arrows also work better for a fully tensioned connection where the friction force is probably not going to be overcome. But, if I'm looking at base plates, I often assume some relaxation of pre-tensioning over time.

 

[rb1957]

the slotted holes make this an interesting question. With normal holes the green arrows would be the preferred solution; with slotted holes maybe the red are reasonable, assuming no lateral stiffness ?

another day in paradise, or is paradise one day closer ?

 

[WARose]

Just to see what would happen.....I modeled the scenario in FEA software I have.....and there were reactions in each orthogonal direction at each bolt. The interesting thing however, was the bulk of it (90%) was resisted by a pair of shears.....one at each bolt (the 2 bolts closest to the CL of the torque). To me, there wasn't a whole lot of rhyme or reason as to why the reactions resolved the way they did.

Of course, this did not take into account slots.

 

[KootK]

Red arrows for me.

1) You know you've reliably got that path available.

2) I agree with OP's concern about a green arrow component parallel to the slots.

You've got more options if you're slip critical of course.



I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[SwinnyGG]

The red arrows define the position of the applied moment in one axis only... I'm trying to wrap my head around the implications of that (if any...)

 

[KootK]

The red arrows define the position of the applied moment in one axis only... I'm trying to wrap my head around the implications of that (if any...)

How so? I believe that torques and moments are location independent.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[SwinnyGG]

The red reaction vectors imply a a moment of fixed magnitude, positioned anywhere on the y axis, to infinity in both directions.

The green reaction vectors imply a moment of fixed magnitude located exactly at the center of the bolt circle, and nowhere else.

This post and the one before it are thinking (typing?) out loud, not a claim of any kind.

With regard to which set is best, When dealing with analysis of surface contacts I always attempt to use primary vectors that are normal to the shared contact plane, and then do whatever math beyond that to make that model function- it always seems conceptually easier to me.

So, for slots, that means red arrows. If the slots were replaced with holes, green arrows.

 

[dik]

The green one would present perpendicular from the centre of rotation and is more correct.

Dik

 

[Tomfh]

I'd assume red ones.

I assume red in standard holes too.