Applies To
Product(s):	AutoPIPE
Version(s):	ALL;
Area:	Report
Date Logged & Current Version	Dec 2024 24.00.01.152

Problem:

What causes a breakaway to happen in AutoPIPE when the entered value is less than the reported force?

Example: 

In this example model, a section of weightless pipe and contents is restrained by two supports in the X-axis, a minimal anchor stiffness in X-axis direction, and an additional force and moment load was applied. What causes this section of pipe to move when the reported loads (ex, 750 Lbs) on each support are below the breakaway load (ex. 1000 Lbs)?

 

Model Details: 

B00: anchor with 0.1 Flexible stiffness in the X-axis direction.

 

B00, Add Force = 1500 lbs in the +ve X-axis.

B01 and B02, incline support with the following configuration:

Solution:

In the above example, the 1500 Lbs load is applied at B00, the only restraining forces present are those from the anchor at B00 and the support at B01. Recall the anchor was configured with an almost negligible restraining stiffness and thus will ultimately be disregarded throughout this explanation. The pipe does not encounter any further restraining force until the support at B01 fails or a breakaway event takes place. At that moment of breakaway, the full load will be transmitted to the next support or anchor. (in this example, support at B02), and the same event repeats itself.

AutoPIPE will report that the load was uniformly distributed among the relevant supports. It is important to note that the applied 1500 Lbs force remains constant across each support it encounters. Another words, it is like a zipper effect. There can be 10 supports on the pipe, each with a 1000 Lbs breakaway, and each support will experience the full 1500 lb load one support at a time. Each support will experience breakaway and movement as indicated below:

Another abstract example, imagine eating a slice of pizza, where both the front teeth and back teeth come into contact with the pizza equally to hold it the slice in place. Now start to pull the pizza slice away from your mouth, does the back of your teeth experience any pull or just the front teeth? Answer: just the front teeth feel the pull. There is no support provided by the back teeth until the front give way.  :)

These examples serve to illustrate how AutoPIPE manages breakaway. However, in practical applications involving complex models, comprehending the results may not be as straightforward. To aid in understanding breakaway did occur at a particular node point, suggest the following process:

1. Insert one or more Reference points looking in both directions of a node point where breakaway support was located. Configure the allowable with the Breakaway limit (ex. 1000 Lbs). 

2. For a given combination (ex. GRP1T1), report all of the individual load cases that make up the combination (ex. report loads for Gr, P1, and T1). 

3. Next, replace a single breakaway support with a rigid support, 

3. Analyze and generate a report containing the following sub reports: Support, Reference Point, and Forces and Moments

4. Review these sub reports one at a time to understand how the rigid support may face a pipe force that would exceed the breakaway of 1000 Lbs. 

Support Report, under GR load case, the support would experience a force greater than the Breakaway setting

Reference Report indicates a load greater than the breakaway setting if it had been set.

Forces and Moments report also indicates a load in the pipe that would cause breakaway to occur if it was applied.

In summary, this situation may initially appear to be impossible, and the results may seem to be wrong. One might question how the a support could exhibit movement with a force that is below the designated breakaway load. Nevertheless, upon deeper review, it becomes evident that the support does indeed attain the defined breakaway load, leading to movement and reporting of forces redistributed across the affected supports.