Clamping Force on cylindrical object 1

[MrNut]

Hello, I have some questions regarding clamping force.

I have a two-piece cylindrical clamp which is to be clamped around a cylindrical part. It is a clamp installed on a product during transportation, where lashings go between the clamp and trailer.
The coefficient of friction and surface area between clamp and cylinder is known.

How would I go about finding the necessary clamping force to ensure the clamp does not slide down the cylinder, nor rotates around its own axis? There is to be a tension force applied in the two brackets.

I applied the forces which I believe will have an affect on the clamping force, but I believe the tension force will make the clamping force non-uniformly distributed across the cylinder.

From what I have found so far, the hoop stress may be relevant. I also looked at Roark's Formulas For Stress And Strain, it had a chapter (9.3) about circular rings and arches, this may also be relevant.

This is completely new to me, and I struggle to find good literature about the topic, so any help is greatly appreciated!

 

[mfgenggear]

OP
link may be useful

Quick and Dirty Bolt Sizing Calculation.xls

https://www.youtube.com/watch?v=x5G5xPAt5To The following values are required as inputs to the calculation: 1) BOLT GRADE - Enter the two num...

www.excelcalcs.com

 

[mfgenggear]

here is very informative hopefully not deleted

 

[Stress_Eng]

Just as a side note, be mindful of the fact that due to the two bend radii (for following pipe curvature and at the sharp elbow bend at the flange to strap intersection), the true condition is a 'curved beam'. With low r/t ratios, such as at the elbow bend, the stress at the inner radius will have an elastic concentration factor (stress increase). I suggest having a look at Roark; from memory I believe there is a section and calculation table on the subject. If it does need to be considered, you'll probably be able to factor this into you standard prismatic beam bending calculation at the elbow.

 

[mfgenggear]

Just as a side note, be mindful of the fact that due to the two bend radii (for following pipe curvature and at the sharp elbow bend at the flange to strap intersection), the true condition is a 'curved beam'. With low r/t ratios, such as at the elbow bend, the stress at the inner radius will have an elastic concentration factor (stress increase). I suggest having a look at Roark; from memory I believe there is a section and calculation table on the subject. You'll probably be able to factor this into you calculations, bending at the elbow.

stress
that is why I suggested wrought milled clamps. while you are the expert , I have only my experience. from actual design parts.
after watching the above video I now have better under standing why some of my designs worked well.
coefficient of friction, preloads, the moment from shear loads, clamped force.

the above OP design have moment that could possibly cause the preload to loosen.
then have shear or tear out, or even shear failure of the bolts.
your thoughts
also ps the video touches upon the % elongation and how to measure more precisely.
best regards

 

[dgeesaman]

The diagram with the green arrows assume a purely radial load.

I would treat that clamp as a 'bearing' load applied across the opposite sides of the tube. Bearing loads are not radial in direction and will more accurately represent the bending across the section of the tube. Stiffening the clamp won't change the stress distribution much but it will help support the pipe a bit.

 

[mfgenggear]

Would it depend if it free standing on a floor or if it was hanging by two pivot points only.
Should it not require two clamps to prevent the bottom from rotation. Torque from directional force.

 

[dvd]

This thing looks like a piping riser clamp. Can you weld shear lugs onto the cylinder? You could key the shear lugs into the clamp band and react the vertical load and lock position, also.

 

[MrNut]

Thanks, will definetly keep this in mind!

 

[Stress_Eng]

If the design isn’t yet finalised, you may want to consider a clamp hinged on one side (pivot pin). Attached is a go at determining the band clamp bending and contact distribution for such a design. In the case of trying to reduce the bending over the bolted flange length, I can only suggest thickening it in some way, maybe by attaching a plate?

Edit- Just a thought, could you have a hinged joint on one side and, instead of a bolted flange arrangement on the other, could you have some retained but free rotating circular bar arrangement on the other (circular bars in blocks welded to the ends of the band clamps), with one threaded and the other with a clearance hole? This way, the bolt will line-up the circular bars while torquing. I think I’ve seen this type of bolted joint before. The idea is to try and introduce a short moment arm, from the bolt to the band clamp.