Local Axes - Important Information
- Darrell Foster
Local axes for joints/points (aka "nodes") are often different from pipe and frame local axes, which can be different from the local axes of some pipe support types, which can be different from "link" support local axes.
The easiest way to find the local axes of a particular object type is to use the 'Set display options' icon 
to view local axes of selected object types.
The local axes color convention for joints, piping and frame elements, pipe supports, links, etc. is as follows:
local 1 axis: red
local 2 axis: green
local 3 axis: blue
In the example below, we graphically display local axes for piping and also for a vertical stop. For piping and frames, the red arrow (local 1) always points along the positive longitudinal direction. For horizontal piping local 2 direction points upward (+Z).. Vertical stop pipe supports always act in the vertical (global Z) direction. In the example below with inclined piping, vertical stop local axes are different from piping local axes.
Unlike vertical stop and hanger pipe supports, guides, anchors, distributed supports, snubbers, and line stops are automatically aligned with piping local axis to which they are assigned.
Joint/point local axes always align with global axes unless the user has assigned a rotation to the joint local axis. Therefore, when generating a joint displacement output table, U1, U2, U3 corresponds to displacements in the global X, Y, and Z directions respectively if joint local axes were not rotated.
Pipe and frame forces & moments are only reported in local directions. Support reactions and joint displacements can be reported in local or global directions. Pipe and frame concentrated joint loads, imposed displacements, distributed load and strain load assignments (cold spring) all require, or have options to assign in local directions. Pipe and frame thermal gradient (bowing) load assignments require local directions. The ability to assign load and report reactions in local axes is a time saving option, especially when there is skewed piping in the model.