Pipe Stress Analysis Coordinate Systems - CAESAR II - Help

CAESAR II Users Guide

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CAESAR II
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CAESAR II Version
13

As noted previously, most pipe stress analysis computer programs use the 3D beam element. This element can be described as an infinitely thin stick, spanning between two nodes. Each of these nodes has six degrees of freedom three translations and three rotations. Piping systems models are constructed by defining a series of elements, connected by nodes. These pipe elements are typically defined as vectors, in terms of delta dimensions referenced to a global coordinate system.

For most pipe stress applications, there are two dominant global coordinate systems to choose from, either Y-axis or Z-axis up.

The global coordinate system is fixed, and all nodal coordinates and element delta dimensions are referenced to this global coordinate system. In the example that follows, the pipe element spanning from node 10 to node 20 is defined with a DX (delta X) dimension of 5 ft. Node 20 also has a global X coordinate 5 ft. greater that the global X coordinate of node 10. Similarly, the other two elements align with the global Y and global Z axes.

In CAESAR II, you can choose between the two global coordinate systems. The default global coordinate system puts the global Y-axis vertical. You can use two different methods to change the global coordinate system to global vertical Z-axis.

The first method modifies the configuration file in the current data directory. This can be accomplished by selecting Home > Setup > Configuration Editor on the main window ribbon. In the Configuration Editor, select Geometry Directives and select True for New Job Z-axis Vertical.

This configuration affects all new jobs created in this data directory. Existing jobs with the Y-axis vertical are not affected by this configuration change.

The second method switches coordinate systems from within the input for the specific job at hand. This can be accomplished from the Special Execution Parameters dialog box of Classic Piping Input.

Select Z Axis Vertical to change the orientation of the global coordinate system axis, with corresponding updates to the element delta dimensions. The relative positions and lengths of the elements are not affected by the vertical axis change.