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Re: Local Stresses at Pipe Supports

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you may try 

this may be helpfulto you

>>> Jim.Lutz(--nospam--at) 10/18/06 12:11 PM >>>
I have been asked to do a stress check on a proposed ductile iron
pipeline which will be suspended on roller type hangers on a highway
bridge.  The ductile iron pipe people recommend hanging the pipe with
single hanger behind each bell, where the section is thicker, in order
to avoid overstressing the pipe. My own preference, and the highway
department's standard mounting detail, supports each length of pipe
two hangers, one at each quarter point. It's easy to compute the
stresses in the pipe due to flexure and water pressure, however I am
struggling with local stresses in the vicinity of the hangers. There
readily available formulas for computing stress in a pipe at cradle
supports, but a roller is more like a knife support, particularly in
this case, where the designer wants to use oversized rollers to
facilitate installation, so there is no cradling effect at the roller.

In an attempt to evaluate the stresses, I estimated the contact area
between the pipe and roller using Roark's formulas for two crossing
cylinders, then used this area and the reaction load to estimate
with formulas in WRC-107 (Bijlaard's curves). The membrane stresses
looked reasonable, but the pipe wall bending stresses were way over
yield. I have seen plenty of ductile iron and steel pipe supported on
fairly narrow channels with no apparent problems and am wondering if I
am missing something here or should just ignore this issue. Does
out there have any suggestions regarding ways to evaluate local stress
in this situation. I have spent more time than I want to trying to
Google a reference with no real luck. 

I need to wrap this up. Contact me off list if you prefer.

Jim Lutz, P.E., S.E.
206 505 3400 Ext 126
206 505 3406 (Fax)

BHC Consultants, LLC
720 3rd Avenue, Suite 1200
Seattle, WA 98104-1820

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