Bolted Connection Between Two Flat Plates [CLAMP]

[simon2452]

Hello,

Me and a colleague have been discussing a load case and cant find anything in machinery's ,Shigley's etc to verify who might be right.

Basically if the bolt is preloaded to 80,000lbs, is that force shared between the two flat plates ?

For Example i may want to do a bending calc on the flat plate between the supports however not sure if this force is shared through the bolt and on the other plate

thanks
simon

 

[rb1957]

"is that force shared between the two flat plates ?" ...

no!
the threaded rod has two nuts on it (loading the two plates). both nuts are loading their plates with the preload ... one is the load, the other is the reaction ...

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

 

[desertfox]

Hi

Both plates see the 80000lbf preload, imagine if one plate was infinitely thick and the other plate as shown in your diagram, if you tighten the nut at the thin end to 80000lbf then the infinitely thick end will still see 80000lbf otherwise equilibrium cannot be met.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[rb1957]

btw "FLATE" is a typo ...

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

 

[simon2452]

Okay thanks a lot guys !!!

 

[racookpe1978]

The total load on each plate is 3x the 80,000 lbf preload. There are 3x bolts, and 4x supports (braces) behind the supports. The bolt will pull the 3x "holes" towards their mate while spreading the force between the "U" shapes supports under the plate. So the middle of each plate will sag towards the centerline of the clamp, supported on three sides - probably with a fillet weld all around, right?

The clamping force will increase some if the pipe and clamp heat up significantly (expand), but the 3x bolts remain relatively cool. If the bolts also heat up, and if the bolts are the same material as the clamp and ring and pipe, then there will be little extra force.

 

[simon2452]

Racookpe, exactly with a fillet weld.

I seem to be getting a rather high amount of stress induced when doing bending calcs in the middle of where each bolt is placed. Its not the end of the world, however a small pain

I'm getting more then enough clamping force with bolt pretension as low as 30,000 lbf so i will aim to be safe rather than sorry

Thanks guys,

Great forum

 

[Tmoose]

Hi simon2452 -

You found high stress "in the middle of where each bolt is placed."

Is that In the shared flat plate, under each bolt? Assuming point load, would you expect something else?

 

[simon2452]

Tmoose,

Yes i used point load for basic calculation [ will do some FEA with washer in place]

Cheers
Simon

 

[rb1957]

if you model the bolt as a point load, then the analytical moment that occurs at that point is not real ('cause a point load is not real).

the interaction between the head and the plate and preload is very complicated, but a simple analysis would be to distribute the preload over the annulus of contact between the head and the plate as a uniform pressure and then look into the plate. If the bolt is good for the 80 kips, preferably with a healthy margin to account for thermal and other effects, then there's no need to look any closer.

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

 

[simon2452]

Thanks Rb that is a good plan of action