This section illustrates methods for incorporating spring hanger design into CAESAR II models.
For detailed information about using the software to define hangers, see Hangers in the Boundary Conditions section of the CAESAR II User's Guide. For more information on how CAESAR II selects hangers, see Hanger Sizing Algorithm in the Technical Discussions section of the CAESAR II User's Guide.
Hanger Design Basics
Select Model > Hanger Design Control Data from the Classic Piping Input dialog box to enter values that affect hanger design throughout the model. The hanger control options, with default values, are shown below. Complete descriptions of each item can be found in the CAESAR II User's Guide.
To set the default value displayed in the Hanger Table box, specify the Default Spring Hanger Table setting in Configuration Editor > Database Definitions.
Double-click Hanger on the Classic Piping Input dialog box to define the spring hanger data for a particular node.
Whenever CAESAR II detects a proposed spring hanger location supporting zero load, the software displays a warning and does not select a hanger for this location. You can remove this proposed hanger location from the model to eliminate the warning.
Hanger Design Recommendations
There are instances where the stiffness of the adjacent piping and the hanger location restraints in the restrained weight case interact unfavorably. This can produce an unwanted distribution of loads. Often, reducing the stiffness used to compute the hanger loads in the restrained weight run eliminates these load distribution problems. The default for this stiffness is 1.0E12. Values on the order of 50,000 or 75,000 have been used successfully to somewhat relax the system and redistribute these piping loads. You can define the value the software uses for calculating hanger restrained weight loads in the Hanger Default Restraint Stiffness configuration setting in Tools > Configure/Setup > Computational Control. .
The operating case for hanger travel (free thermal case) can be analyzed either with no spring stiffness at the hanger locations, or with the stiffness of the selected springs inserted at those locations. In the second case, the software selects the springs through an iterative process.
You can specify the manner in which the software handles spring hangers in the Include Spring Hanger Stiffness in Hanger OPE Travel Cases configuration setting in Tools > Configure/Setup > Computational Control. Inserting the actual hanger stiffness into the Operating Case for Hanger Travel may give a more accurate result, but may also introduce convergence problems. Therefore, in the latter case, it is very important that you adjust the hanger load in the cold case (in the physical system) to match the reported hanger cold load.