Coordinate System

Coordinate System#

The local coordinate system of a structural member is a dextrorotary Cartesian system with the following orientation of axes:

  • The local x-axis is always the longitudinal axis of the element, defined from the beginning node (A) to the end node (B). The origin of the system is positioned at the beginning node of the member.

  • The local y-axis and z-axis lie in the plane of the member’s cross-section and are arranged according to dextrorotary rotation. By default:

    • The y-axis represents the axis of the greater moment of inertia of the member.

    • The z-axis represents the axis of the lesser moment of inertia of the member.

Element local axes.

Sectional Analysis#

For sectional analysis, the local y-axis and z-axis are critical for understanding the orientation of the member’s cross-section. Below is an illustration of the cross-section with the local y-axis and z-axis:

Cross-section of a member with local y and z axes