Comments, Questions, and Answers on AutoPIPE help example: Hinged Expansion Joint:
Q1. In step #6, how does one know what direction in the model the expansion joint will be hinged?
Answer:
On this step the user was asked to insert 2 flexible joints with the following criteria.
The Hinged joint is suppose to restrict movement to only bending in the Global X-axis direction. How does assigning Flexible Joint Y bending Stiffness accomplish this modeling?
Simple, first users should understand exactly what does each of these flexible joint direction truly represent:
> Axial stiffness
> Y-shear stiffness
> Z-shear stiffness
> Torsional stiffness
> Y-bending stiffness
> Z-bending stiffness
With the flexible joint dialog open select Help button, look down towards the bottom of the help page and select the hyperlink for "Flexible Joint Dialog Explained". This will explain each of these fields and with an image of the type of movement allowed. In this case, bending looks like this (imaged below).
As indicated in the modeling approach, this flexible joint bending will be about the local Y-axis direction.
Now you may be asking, how does one know which direction is the local Y-axis direction compare to the global Y-axis direction. Again, simple, turn on "Local Axis" command.
This clearly indicates the local axis direction around the entire model. Thus bending about the Flexible joint Y-axis would allow bending in the Global X -axis direction.
Question:
How to model a simple horizontal hinged expansion joint?
Answer:
As indicated above, knowing the segment direction to be able to identify the local axis direction is the secrete. In this case the pipe is moving in the +ve X-axis direction.
Insert Flexible Joint:
As mentioned in AutoPIPE Help, Hinged Joint tutorial:
a. Enter a length:
b. Select Joint Type:
c. Enable options as needed:
d. Specify a very small Y-bending stiffness and all other stiffnesses = Rigid
e. Enter Weight
f. Enter Pressure thrust area
Example: (all values are fictitious)
Done.
This joint will not flex in the Local Z-axis (also Global Z-axis in this example) or extend in the local X-axis (also the Global X-axis in this example) due to pressure thrust. The joint also has rigid settings for both local Y-axis and Z-axis shear axis direction (also Global Y-axis and Global Z-axis respectively). However because the the local Y-axis bending (also the Global Y-axis in this case) has a very small value the joint can bend in that axis direction.
Continue modeling the rest of the piping system.
Test the joint
In this example, add a concentrated moment in the global Z-axis and global Y-axis.
Animate the load case to see the movement due to U1 load case:
Notice the case is flexing in the Global Y bending direction
Animate the load case to see the movement due to U1 load case:
Notice the case is not flexing in the Global Z bending direction
Question:
How to specify a hinged joint to flex up and down instead of left and right as shown above?
Answer:
Correct, specify all values to be rigid except Z-bending value, which would be very small.
Thus bending would now be about global Z axis,or Up and Down