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Re: Sewer Aerial Crossing

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A couple of thoughts:
 
You say the pipe is continuously supported.  Is it being supported by a beam spanning between the columns or do you have just the pipe?  I think the latter is more common.  Whether the pipe is self-supporting or not will have an impact on the pipe material that can be used.
 
Since the pipe is withing the 100 year water elevation, has the effect of the pipe on the upstream stages and downstream discharges been evaluated?
 
You may want to consider putting neoprene (or some silmilar material) between the pipe and the concrete and also between the pipe and the straps.  It provides a dielectric break and helps allow for movement.
 
Any changes in the pipe geometry (bends, sweeps, etc.) will result in thrust.
 
The pipe may need to be painted a specific color according to the contents, in this case green for sewer.
 
Allow for rodent/pedestrian barriers as needed.
 
 
M. David Finley, P.E.
3810 South First Street - Suite 7
Lake City, FL  32025
386-752-6400
----- Original Message -----
Sent: Wednesday, August 28, 2002 9:15 AM
Subject: Sewer Aerial Crossing

I'm designing a sewer aerial crossing bridge.  The bridge will only support the sewer itself, no vehicular traffic.  It's a 16" ductile iron pipe continuously supported by a cast in place cradle/saddle spanning between single column bents/abutments.  The pipe/bridge at 100 yr occurrence will be completely submerged.  The overall span length is only 60'.  I don't believe expansion/contraction will be an issue.
 
1.  I'd appreciate any words of wisdom with respect to general design issues.  I also have a few specific questions.
 
2.  I'll be specifying stainless steel brackets and bolts to connect pipe to the cradle.  What type of stainless steel should I specify?
 
3.  The soil has a potential vertical rise of 2.5".  The abutment foundation will be drilled shafts socketed into hard limestone and will not move.  What is done to assure the pipe can handle the differential movement at the abutment?
 
4.  Sitting in a cradle with a semi-circle cut out to hold the pipe I can envision water being held in contact with the pipe indefinitely.  Is corrosion of the pipe a concern.
 
Thank you in advance for your comments.

Todd M. Speck, P.E.