Design of Reinforced Concrete Pipe Saddle for 108" Diameter Steel Waterline Pipe

[oengineer]

I have designed foundations in the past for horizontal vessels and exchanges. Usually the horizontal vessel or exchanger has a metal saddle and then I just designed the pedestal as a small column with a rho value of 0.005.

I am trying to design/analyze a Reinforced Concrete Pipe Saddle for 108" Diameter Waterline Pipe. Here is a picture of the kind of pedestal I am talking about:

http://files.engineering.com/getfil...164817ccac4&file=strapon-scan03042005-650.pdf

. The only differences is that mine will not have anchor bolts embedded into the concrete.

Should I design it as a regular pedestal of somehow treat it like a beam? Is there a design guide avaiable, like PIP has for horizontal vessel foundations? Any suggestions/comments are appreciated.

 

[BAretired]

If R is the vertical reaction on each saddle, the radial pressure on the saddle will be R/bd where b is the length of bearing and d is the diameter of the pipe. The saddle must be designed to resist axial tension and moment caused by the horizontal component of the radial pressure.

BA

 

[oengineer]

@BAretired - Thank you for your input. To design the saddle to resist the axial tension and moment caused by the horizontal component of the radial pressure, should I treat the saddle as a pedestal? By this I mean I would design the saddle pedestal height to be from the top of the footing to the bottom of the pipe. Would this be the correct approach? Are you aware of any design example for this type of foundation?

 

[SlideRuleEra]

oengineer - See Chapter 7 of Steel Pipe: A Guide for Design and Installation, 4th Ed. You may be able to read the needed section in this online fair use preview.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[JStephen]

If you look in the original Zick paper for vessel saddle analysis, he was assuming a concrete saddle on a steel vessel. One of the forces generated on the saddle is the "splitting force", tending to spread the saddle apart. That force does not usually affect the design with a steel saddle, but is something that needs to be checked. See the Zick analysis in the original paper, or in the various pressure vessel handbooks.

You don't say who's designing the pipeline itself- but the saddle dimensions need to be considered in the design of the pipeline, either by you or the pipe designer.

 

[BAretired]

oengineer,

I don't have much experience in this type of structure, but I am wondering about using a contact angle of 180^o as shown in the photo you referenced. Note in SlideRuleEra's reference that a maximum of 120^o is recommended. Also, you say you won't have anchor bolts embedded in the concrete. Do you have a different method of attaching hold-downs or are you suggesting that hold-downs are not required? Will you be considering seismic forces and temperature effects? If so, these can be important considerations in the design of saddles.

BA

 

[LittleInch]

Hmmm, a 108" pipe (9 ft) is more commonly called a tunnel not a pipe.

I can't think of why you would or could want to have a hard edged concrete support for something so large and which will have a bending moment around the saddle. It is quite difficult to accurately obtain all the forces you have on the vertical sides of the support.

Come more details would be interesting to see.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[BAretired]

There should be some sort of compressible material between concrete and pipe to act as a cushion. That would help to relieve the "hard edges".

BA

 

[bridgebuster]

Here's a link to NYCDEP standard sewer drawings. The have details for cradles up to 96" diameter (120" for elliptical pipe). Could serve as a sanity check.

Link

This is a link to their water main standard drawings but the larges cradle is only 72"

Link

 

[BAretired]

If the pipe changes direction, there will be anchorage forces from the flow of water.

BA

 

[oengineer]

@BAretired - There are no anchor bolts. The pipe is running underground for at least a mile. It is only being supported by this foundation at a certain point because some additional weight is being added to it. Here is a drawing of the proposed design:

https://files.engineering.com/getfi...a-9822a3863842&file=74__75_mark-ups_(002).pdf

All of this is about 4 ft below grade.

@LittleInch - Here is more detail:

https://files.engineering.com/getfi...a-9822a3863842&file=74__75_mark-ups_(002).pdf

 

[oengineer]

@bridgebuster - Thank you for the details!

 

[oengineer]

I think if I break the pedestal into 3 parts and treat the ends of the pedestals protruding over the pipes as cantilever beams, that should be adequate for design.

 

[bridgebuster]

You're welcome