Hi Geoff
If you are talking poly pipe at 20 Deg C you shouldnt have any problems if the SDR is 41 or less and the installation temperature is 20C or more. This is within standard limits as given by James Hardie Pipelines. For your question, consider the following approximation ignoring local effects:
To work out the stresses, draw the installation. You will have nine
supports for the pipe spaced at 11.25 degrees. The intermediate seven
supports will be inside the bend radius and the two at the ends will be
outside the the radius pushing inwards.
For fibre stress in the pipe you may remember from school: M/I = sigma/y =
E/R
This gives sigma = Ey/R where sigma is fibre stress, E is Youngs Modulus, y
is the pipe radius, and R is the bend radius. This is an approximation as
the standard formula assumes the deflection curve is circular.
For the reaction forces I think we will have to assume that the bending
moment is constant between the seven middle supports, and rises from zero to
a maximum from the first to the second support and the same at the other
end. We know M = sigma*I/y from above and we know the distance between the
supports so we can calculate the end reactions. I havent thought about the
reactions at the seven intermediate supports yet, but it seems unlikely that
their outward reaction would exceed the inward reaction of the end supports.
I would probably use vectors, but there is bound to be an easier way.
Chris can probably provide a more precise answer.
However as you know if you leave the bent pipe in the sun for a while the stresses will drop drastically due to plastic deformation. I have "preformed" large sweeps this way using a Tirfor and the sun. Its just the reverse to unrolling a coil of poly in the sun to straighten it out.
Sorry I didnt get to Sydney to catch up with you; the bastards in Melbourne made me work both weekends.
Cheers
Steve McKenzie
-----Original Message-----
From: Geoff Stone DD&D Australia [mailto:blenrayaust@yahoo.co.uk]
Sent: Friday, March 07, 2003 4:24 PM
To: paul bowers
Subject: [PipingDesign] Bending Thermoplastic Pipe
Question.
A client wants to bend a DN 225 plastic pipe in a 10 m radius. How do I find
the stresses in the pipe wall arising from the bending process? What would
be
the loads at supports spaced every 2000mm?
Geoff Stone
Your use of Yahoo! Groups is subject to <a href="http://docs.yahoo.com/info/terms/">http://docs.yahoo.com/info/terms/</a> Received on Fri Mar 07 04:47:00 2003
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