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hdn32 (Structural) (OP)
9 Mar 10 16:20
Hello,

I need to connect two perpendicular pipe sections together using 2 pairs of u-bolts and a steel plate. I am concern about the capacity of this connection against sliding at the u-bolt and pipe interface. I founded several similar details, stand-off mounts in particular, shown in antenna supporting structure catalog of various manufaturers. But there is not anything about the connection capacity.

Does anyone know any reference on clamping capacity of u-bolt?

hdn.
Ron (Structural)
9 Mar 10 17:22
Nope.  Use a torque wrench on it.  Convert the torque to tension (yes, I know it isn't exact) but it will get you in the ballpark.
MintJulep (Mechanical)
9 Mar 10 17:38
The usual way is to determine how much force you need to resist first, then select a connection.

But it's a simple friction joint.  Clamping force and friction.

If it's an important connection, you should determine these things by test using your actual components.  Otherwise you can guess or use handbook values and torque-tension tables, which amount to about the same thing.

 
desertfox (Mechanical)
9 Mar 10 19:33
Hi hdn32

Here is some data on torque capacity for U bolts:-

http://lhrods.com/ubolttorque.htm

It would be best however if you analysed the max load you can put on the two pipes without crushing them and determine a torque for the U bolt based on that load.

an approximate formula for axial load = P = T/(0.2*d)

where P = axial load

      T = Torque on nut

      d = bolt size

      0.2 = friction factor for dry threads.

desertfox
unclesyd (Materials)
9 Mar 10 19:52
Your concerns are warranted big time.

You need clamps similar to these to clamp a pipe as U-bolts don't do a very good job.

http://www.jerman.com/pipeclamps.html
 
MikeHalloran (Mechanical)
9 Mar 10 20:36
In the antenna business, cheap seems to always win over strong, so you may find 'pipe' with extremely thin walls, and with a seam that may or may not actually be welded, and 'plate' that anyone working in any other trade would call 'sheet' or maybe 'foil'.

So the actual clamping capacity of the u-bolt may be irrelevant, because something else in the joint may bend or collapse.


 

Mike Halloran
Pembroke Pines, FL, USA

apsix (Structural)
9 Mar 10 20:37
Resistance against sliding will be greatly improved if you can also pin bolts straight thru each pipe and backing plate.
paddingtongreen (Structural)
10 Mar 10 7:57
I don't have experience with this, but I strongly suspect that if a bar clamp is used correctly, it deforms the pipe, within it's elastic limit, but enough to gain mechanical interlock as well as friction. To slide, the clamp must overcome friction, and, climb up the hill.

Michael.
Timing has a lot to do with the outcome of a rain dance.

paddingtongreen (Structural)
10 Mar 10 8:03
I forgot to say, I expect that the tightening would be by feel, you can feel the grip, when the deformation happens.  

Michael.
Timing has a lot to do with the outcome of a rain dance.

hdn32 (Structural) (OP)
10 Mar 10 8:38
Thanks everyone very much for responding to my question.

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