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RE: Sewer Aerial Crossing

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Thanks for the responses; feel free to add should one wish.
A few other items to clarify.
It is a stream crossing.
The total length is 60' +/-.  Each individual span length will be 20', equal to the lay length of the pipe.
The pipe is continuously supported by a concrete "beam" or cradle or straddle.  The cradle spans between abutments and bents.  The cradle is a flat rectangle with a semicircle cut from the top to hold the pipe.  The pipe will be strapped to the cradle using stainless steel brackets at each pipe segment end. 
I'd still like to hear what type of stainless steel one would recommend.
Straight pipe with a slight vertical grade.
Any thoughts on the differential vertical movement due to soil heave?
Thanks, again.
-----Original Message-----
From: Speck, Todd M [mailto:tmspeck(--nospam--at)]
Sent: Wednesday, August 28, 2002 8:16 AM
To: SEAInt (E-mail)
Subject: Sewer Aerial Crossing
Importance: High

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.