Upheaval Buckling Introduction
In this tutorial, we will review how AutoPIPE’s upheaval buckling calculator can be used to prevent upheaval
buckling on buried piping both onshore and offshore. AutoPIPE can use both the initial overbend geometry and
the compressive axial force due to loading to produce a recommended soil depth. Users are then expected to
update to the new soil depth to prevent upheaval buckling propagation.
The purpose of this analysis to provide the designer (or engineer) tools to determine a soil depth sufficient in
preventing upheaval buckling. Upheaval buckling can occur to any pipe where the inherent stiffness and weight
of the pipe is insufficient to restrain the compressive axial forces due to thermal loading, or pressure extension.
AutoPIPE considers other load cases as well, such as occasional loads, in the event that the designer is required
to prevent upheaval buckling for all conditions.
NOTE: AutoPIPE utilizes the K. Peters methodology of upheaval buckling. This method allows the
program to provide a recommended soil depth, instead of a simple pass or fail.
See Peters, K. About Upheaval and Lateral Buckling of Embedded Pipelines. Dusseldorf, Germany: 3R
International 2006. Paper.
Sample Workflow – Setting Up the Model
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New Inputs in AutoPIPE CONNECT Edition v12.1
AutoPIPE v12.1 introduces a new upheaval buckling button in the Edit Soil Properties dialog. This button opens
the Upheaval Buckling dialog, which provides settings and configuration for upheaval buckling analysis of the
associated soil identifier. Note that each soil identifier may have upheaval buckling analysis enabled or disabled
independent of the other soil identifiers in the model. The following inputs are available:
•
Consider Upheaval Buckling – When checked, AutoPIPE will perform upheaval buckling analysis on all
physical nodes (i.e. non-soil nodes) using the associated soil identifier. Additionally, this will enable
printing data for these nodes in the upheaval buckling output report. Soil nodes (e.g. +1, +2) are not
considered for upheaval buckling as the nature of a soil point on a straight pipe would yield no upheaval
buckling and no recommended soil depth would be provided.
•
Use K. Peters Compression Force Calculations – When checked, AutoPIPE will prefer the use of a noniterative thermal and pressure axial force values over more accurate AutoPIPE axial forces due to
thermal and pressure loading. Checking this option produces more conservative results and is a good
starting point to determine approximately how much soil depth is required.
The Upheaval Buckling Output Report
The upheaval buckling output report is a useful tool to help determine what the recommended soil depth is to
prevent upheaval buckling propagation. This report contains all the necessary information to assess the
possibility and resolution to upheaval buckling. Each node that is printed under this report must meet the
following criteria:
1. The node has applied soil that is configured to consider upheaval buckling, AND
2. The node has a preceding and following physical node, to calculate initial overbend 𝜑, AND
3. That initial overbend 𝜑 is greater than zero
If these three are true, AutoPIPE will print the results for all selected load combinations, including the buckling
length, length factor and the requirements of K. Peters method. Review the program help for more in depth
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discussion on what each column represents physically. In this tutorial, we are focused on the required soil depth
column.
The next feature is the Recommended Depth column. This column represents the solution to the upheaval
buckling algorithm for all physical points. Each value is printed for each load case and serves as a guide to
increase the soil depth, so no upheaval buckling occurs. Should the current soil depth prove to be insufficient,
two asterisks will appear next to the recommended depth, representing a failure to meet a balanced solution.
Additionally, two notes may appear when certain conditions are met – these notes serve to help the user
determine why no values have been printed. The notes are as follows:
1. Note 1 represents that selected calculation method cannot produce a required soil depth. The required
soil restraint, however, is still printed for reference.
2. Note 2 represents that the soil stiffness for the analysis set of the selected load combination is set to
‘none’ and no soil restraint or allowed angle of deflection is valid.
Both notes are added to the bottom of the upheaval buckling output report when necessary.
Example
Open the UpheavalBucklingTutorial_Initial.APC file in the Example folder (File > Open > Archive).
This profile represents a series of initial overbends during the installation process. The entire pipe is buried with
12 inches of soil. The 10”STD pipe has a thermal load of 140ºF during operation, and will cause an expansion
throughout the pipeline, causing a high vertical buckling deflection at A05. Run the analysis and generate the
displacement report.
D I S P L A C E M E N T S
Point
name
-----A05 N
Load
combination
-----------------------Thermal 1{1}
TRANSLATIONS (in )
X
Y
Z
------ ------ -----0.049
1.843 -0.066
ROTATIONS (deg )
X
Y
Z
------ ------ -----0.082
0.081
0.192
A05 F
Thermal 1{1}
0.050
0.072
1.848
-0.071
0.036
-0.070
Notice that the vertical deflection is 1.843 inches, highlighted in red. Access the Upheaval Buckling dialog
through the Upheaval Buckling button, located in the Edit Soil Properties dialog. Enable the Consider Upheaval
Buckling checkbox. Also, check the Use K. Peters Compression Force Calculations checkbox.
Accept all dialogs and re-run the analysis.
Generate the Upheaval Buckling report.
U P H E A V A L
B U C K L I N G
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Point
name
------
Axial
Buckling --Slope Deflection--- ---------- Soil Resistance ---------Load
force
length
Length Actual Allowed Length Actual Required Depth
combination
(lbf
) (in
) factor (deg ) (deg ) factor (lb/ft ) (lb/ft ) (in ) Ratio
----------------------- -------- -------- ------ ------ ------- ------ -------- -------- ------ -----
*** Segment A begin ***
A05 N Soil Depth to Centerline = 12.00 inch
Thermal 1{1}
157632 1089.74
A05 F
Soil Depth to Centerline = 12.00 inch
Thermal 1{1}
157632 1089.74
0.670
19.08
1.36
0.072
61.28
8006.83 137.17 130.7**
0.670
19.08
1.36
0.072
61.28
8006.83 137.17 130.7**
The depth column displays a recommended soil depth of 137.17 inches. Return to the Upheaval Buckling dialog
and uncheck the Use K. Peters Compression Force Calculations checkbox and apply the recommended depth of
137.17 inches to the Edit Soil Properties dialog. Be sure to click the Generate button to update the soil spring
stiffness values.
Re-run the analysis again and generate the upheaval buckling output report.
U P H E A V A L
Point
name
------
Axial
Buckling --Slope Deflection--- ---------- Soil Resistance ---------Load
force
length
Length Actual Allowed Length Actual Required Depth
combination
(lbf
) (in
) factor (deg ) (deg ) factor (lb/ft ) (lb/ft ) (in ) Ratio
----------------------- -------- -------- ------ ------ ------- ------ -------- -------- ------ -----
*** Segment A begin ***
A05 N Soil Depth to Centerline = 137.17 inch
Thermal 1{1}
105378 1332.81
A05 F
B U C K L I N G
Soil Depth to Centerline = 137.17 inch
Thermal 1{1}
105378 1332.81
0.059
19.08
28.56
0.088
8007.10
3584.35 91.775
0.45
0.059
19.08
28.56
0.088
8007.10
3584.35 91.775
0.45
Using the AutoPIPE compressive axial calculations, the upheaval buckling analysis results is recommending a
lower soil depth than is proposed by the design, as denoted by the values marked in red (recommended depth)
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and green (current depth). The designer can now elect to maintain the current depth or reduce the depth to
meet the recommended depth. If the latter is preferred, the following results are provided.
U P H E A V A L
Point
name
------
Axial
Buckling --Slope Deflection--- ---------- Soil Resistance ---------Load
force
length
Length Actual Allowed Length Actual Required Depth
combination
(lbf
) (in
) factor (deg ) (deg ) factor (lb/ft ) (lb/ft ) (in ) Ratio
----------------------- -------- -------- ------ ------ ------- ------ -------- -------- ------ -----
*** Segment A begin ***
A05 N Soil Depth to Centerline =
Thermal 1{1}
A05 F
B U C K L I N G
Soil Depth to Centerline =
Thermal 1{1}
91.78 inch
89100 1449.46
0.081
19.08
22.58
0.096
3584.31
2564.86 77.634
0.72
91.78 inch
89100 1449.46
0.081
19.08
22.58
0.096
3584.31
2564.86 77.634
0.72
Why has the recommended depth decreased again? This is due to the nature of the Peters method of calculating
the recommended depth, which is dependent on the compressive axial force. Since we are using the AutoPIPE
axial force results of the adjacent physical nodes, increasing the soil spring stiffnesses will increase the axial
force values as well. This process can continue until the soil depth to centerline nearly matches the
recommended depth. Remember that the requirements of this analysis are that the Soil Depth to Centerline is
greater than the Recommended Depth. Reducing the amount of soil to match the recommended depth is
merely a cost-saving measure. Reducing now to 70 inches:
U P H E A V A L
Point
name
------
Axial
Buckling --Slope Deflection--- ---------- Soil Resistance ---------Load
force
length
Length Actual Allowed Length Actual Required Depth
combination
(lbf
) (in
) factor (deg ) (deg ) factor (lb/ft ) (lb/ft ) (in ) Ratio
----------------------- -------- -------- ------ ------ ------- ------ -------- -------- ------ -----
*** Segment A begin ***
A05 N Soil Depth to Centerline =
Thermal 1{1}
A05 F
B U C K L I N G
Soil Depth to Centerline =
Thermal 1{1}
70.00 inch
78440 1544.82
0.100
19.08
19.54
0.102
2085.22
1989.48 68.374
0.95
70.00 inch
78440 1544.82
0.100
19.08
19.54
0.102
2085.22
1989.48 68.374
0.95
Notice that our soil depth now not only meets the requirements of the K. Peters solution to prevent upheaval
buckling propagation for this specific vertex, but it also does not require an exaggerated amount of soil.
Additionally, the vertical soil deformation has been reduced from 1.84 inches to 0.73 inches. Since A05 has the
most dramatic peak, it is expected that once this peak is resolved, all other vertices in the model should be
resolved, which is what we can see in the rest of the upheaval buckling report. Since all physical points under
this soil identifier have a soil depth greater than the recommended soil depth, upheaval buckling analysis is
complete.
Key Points
The following are key points in this tutorial:
•
The upheaval buckling analysis aids the designer in specifying a specific soil depth that will prevent
upheaval buckling for each buried physical node.
•
Should a pipe exceed this limit during operation, the program will provide a recommended soil depth to
prevent upheaval.
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•
Due to the iterative nature of the algorithm when the Use K. Peters Compression Force Calculations
option is unchecked, the initial recommended depth may not be the final recommended depth. Ensure
that no soil heights are exceeding the recommended soil depth before completing the analysis.
•
Changing the soil depth in the Edit Soil Properties dialog to exceed the recommended soil depth will aid
in preventing upheaval buckling propagation.
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