| Applies To | |||
| Product(s): | RAM Elements | ||
| Version(s): | 11.00.00.00 or later | ||
| Environment: | N/A | ||
| Area: | Design | ||
| Subarea: | N/A | ||
| Original Author: | Bentley Technical Support Group | ||
RAM Elements - Local versus Principal Axis in Unsymmetrical Shapes
It's important to note that members in RAM Elements have two axis; a Local Axis (1, 2, 3), and Principal Axis (1', 2', 3').
Each frame member and shell of a structure has its own local coordinate system that is referred to as its local axes (represented by number 1, 2, and 3). Some data and results are presented in this coordinate system; these include local loads, bending moments, axial forces, etc. Also, local axes are useful for defining the orientation of the elements in space.
The principal axes are cartesian axes. Section properties such as moment of inertia and section modulus are related to the principal axis.
In most cases, local and principal axes of the element coincide. However, for certain shapes the local axis is different from the principal axes, such as with Z, and L profiles as well as WT profiles when the flange is larger (longer and/or thicker) than the stem (web).
The Analysis results in the View>Member Forces Dialog reports the results relative to the principal axes (hence the 2' and 3').
This sometimes causes confusion in unsymmetrical shapes.