effect of (a circular) plate stiffness on bolt load distribution?

[JBlack68]

To all

I am looking for info on the effect of stiffness/flexibility on bolt load distribution for a ring-type of plate. Consider the following
A part like a flange (diameter D, thickness t) with N bolt on a PCD d so that d < D. A basic load balance at the CofG of the bolt group produces a (shear) force Fs and a Moment M. A simple calc would say the shear force per bolt = Fs / N. The tensile load in each bolt produced by M is calculated by any traditional method. So far so good

I now have a FE model with which I can extract the force on each bolt. The force Fs and moment M transmitted by the FEM appears to be correct (as expected) but the load distribution is nowhere near the simple hand calc.

Is this because of the flexibility of the plate? If so then how does one take this into account in a "simple" hand calc?

Thanks
Regards

 

[JoshPlumSE]

I'm not sure whether FEM or hand calc methods will be more accurate in this case. But, I suspect the difference is likely related to flexibility of the plate like you've suggested.

Where did you get the "simple" hand calc method for circular plates? Because there are multiple different methods you could use.

Have you read Dan Horn / TnxTower's Technical manual about the design of Monopole Bases? That's a really good reference for this subject.

 

[JStephen]

I would expect bolt loading to be highly dependent on the distribution of loads applied to the flange, which is usually not known, either, and one reason for using the normal approximations in bolt loading.

 

[JBlack68]

Thanks for the reply. Appreciated
What I meant about the simple calc. refered to a traditional way of checking a bolt group subjected to moments (one of them being a overturning moment)
Found the pdf of the suggestion reference

 

[rb1957]

how do you load the flange ? like do you use an RBE to take the load from a point or do you have a structure from the point to the blot flange ?

how is the FEM deflecting ? is the flange very flexible so the loading structure can pull away from the tension loads (off-loading the peak tension fasteners) ?

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

 

[JBlack68]

No RBE 2/3 used. The (key) structure is modelled and attached to 1 side of the bolts and the other side (of the bolt) being attached to the (base) plate/flange. Normally one would't modelled the base plate (and SPC the key structure) but for some reason a base plate has been considered and its throwing my basic check out-of-the-window.

Deflection a in line with one what expect and appears quite reasonable

One can describe the base plate/flange as very chunky but it is carrying a fair load.

As 1st pass I'll interested to know why the shear force/bolt is higher than the simple Fs/N.

 

[JBlack68]

I reckon the higher shear force are due to the plate/flange bending. Did a test with very high E value and the shear force/bolt was as per the hand calc. What is this effect called. It it like the brazier effect? Is there a way of estimating the shear force by hand calc