| Applies To | |||
| Product(s): | AutoPIPE, | ||
| Version(s): | all | ||
| Area: | Modeling | ||
| Original Author: | Bentley Technical Support Group |
Dec 2014, AutoPIPE V8i 09.06.01.10
Problem:
How to model buried piping going thru a pipe sleeve for wall penetrations, under roadways / railways, etc..?
Solution:
Pipeline buried with no pipe casing or sleeve -
Simply model the pipe routing and apply soil properties as needed. Refer to the "PIPE-SOIL Interaction: Transition Example" in the AutoPIPE's online help for techniques of apply vertical soil and horizontal soil properties.
Pipeline buried with casing or sleeve-
A carrier pipe will be pass though a steel casing / sleeve of length as determined by the design documentation.
1. Model the carrier pipe routing as needed.
Casing: Ensure that node points are added on the carrier pipe at the locations where the spider supports (illustrated below) are positioned to properly space the pipe within the casing.
Sleeve: Again, add node points on the carrier pipe where supports inside of the casing are to be placed.
2. Model the Pipe casing / sleeve as a new segment relative to the carrier pipe.
Easy approach - select a section of the carrier pipe that will be enclosed within the casing or sleeve. Utilize the copy and paste commands to generate a new segment (note AutoPIPE does not like components that have identical coordinates; thus, ensure that the new piping is pasted with a slight offset (for example, Dy = 0.1") to create a new segment). Lastly, assign the appropriate PipeID along with the casing pipe properties to the new segment and extend its length as necessary.
3. Model Supports between carrier pipe and casing
Spider supports
Select node point on the carrier pipe where the spider supports are to be placed, insert a support (V-stop, Guide, incline), specify the corresponding casing pipe node point for the support's "Connected To:" field. Thus supporting the carrier pipe from the casing pipe.
Pipe Seal or Link-Seal (hydrostatic sealing system of rubber applies secure, consistent pressure around pipes)
AutoPIPE modeling approach for a Link-Seal:
Step #1: Assumptions, Non-Linear analysis, Pipe slides in Link-Seal but does not come into contact with the hole
Support #1 - Guide (restrains vertical & lateral pipe movement against Link-Seal)
Stiffness = Link-Seal stiffness after being installed (suggest contacting manufacture for valid values)
Gaps = 0.00 in all directions
Friction = Pipe material on rubber
Step #2: In your opinion does a Link-Seal have a certain breakaway force before axial movement?
If No, go to Step #3
If Yes, insert axial Incline support
Ultimate force gap = enabled
Breakaway force = calculate and insert value
Assuming that after breakaway, axial pipe movement is modeled on support #1 above, therefore remaining dialog stiffness and phase settings remain 0.00.
Step #3: Analyze the model and Review the Support sub-report
Question:
Does the pipe vertical or lateral displacement exceed the gap distance between the pipe and the hole where the Link-Seal was installed.
If No, modeling approach complete, stop here.
If Yes, continue to step #4.
Step #4: Insert 2nd support that restrains vertical & lateral pipe movement against hole
Support #2 - Guide
Stiffness = Rigid (assuming the hole to be rigid, otherwise enter a stiffness for the material the hole is bored in).
Gaps = Enter distance between pipe and hole in all directions
Friction = 0.00
Note, if the inner pipe was to come into contact with the hole the piping is passing through, the Link-Seal has completely failed and the rubber is no longer present. At this point support friction will no longer be pipe material on rubber, but pipe material on hole material (typically Steel on Steel or Steel on Concrete). AutoPIPE cannot modify the friction setting from the first support or account for a change in friction during the analysis. Therefore, only option is for the user to understand the limitation of this modeling approach. Yes, the real loads will be different but this is a good approximation. Feel free to change the settings of this modeling approach to meet your opinion / requirements.
4. Model the end connections of the casing to the carrier pipe
Rubber boot / Seal-Wrap - not really considered a support, nor does it provide any form of resistance to pipe movement. AutoPIPE modeling approach would be to ignore this component at this location.
Casing welded to Carrier pipe - select the casing end point insert a rigid beam or connected anchor to the corresponding carrier pipe node point. Length of rigid beam will be the same as the offset from Step #2 above (ex dy = 0.1").
5. Insert Soil properties / anchors as needed along the carrier pipe and casing / sleeve piping.
Note,
a. No soil properties should be placed on piping that is running inside of the casing / sleeve pipe.
b. If casing sleeve pass thru a concrete block / wall. pending on the thickness of concrete add one or more anchors to correctly account for the stiffness along the casing / sleeve.
Traffic Load:
AutoPIPE V8i 09.06.xx.xx and higher has the ability to calculate soil overburden stresses for a horizontal buried pipe line crossing a roadway / railway track taking in to account the live load from the traffic.
See Also
Model Soil Properties with Soil Calculator