Dec 2014, AutoPIPE V8i 09.06.01.10
How to model horizontal buried piping going under roadways / railways?
Any piping under a Roadway or Railroad are highly regulated by the respective municipalities (i.e. DOT, CSX Railroad, etc..). These companies will have clear guidelines about any pipeline crossing depending on the depth of cover. Recommend that you refer to these type of design specifications as needed for your design.
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.
Typically a carrier pipe will be properly encased within a steel casing of length as determined by the design documentation. See the following procedure:
1. Model the carrier pipe routing as needed. Be sure to add node points on the carrier pipe where spider supports (supports that centers the carrier pipe inside of the casing) are placed inside of the casing over the length of the casing.
2. Insert the casing pipe by selecting the same section of the carrier pipe that matches the casing length, copy, and pasting this section in the exact same location with a slight offset (ex. Dy = 0.1") as a new segment. Finally apply the correct PipeID with casing pipe properties to the new segment.
3. Select the 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.
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 no component at this location.
Casing welded to Carrier pipe - select the casing end point insert a rigid beam 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").
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
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.
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.
Model Soil Properties with Soil Calculator