Vertical Line Objects. For vertical line objects the local axes have the following default orientation:
- Local axis 1 is along the line object. The positive local 1 axis is in the same direction as the positive global Z-axis, upward.
- Local axis 2 is perpendicular to the line object. The projection of the positive local 2 axis onto the global X-axis is in the same direction as the positive global X-axis.
- Local axis 3 is perpendicular to the line object. The direction of the positive local 3 axis is determined from applying the right-hand rule using the directions of the 1 and 2 axes described in the preceding bullets.
Horizontal Line Objects. For horizontal line objects (parallel to the global X-Y plane), the local axes have the following default orientation:
- Local axis 1 is along the line object. The projection of the positive local 1 axis onto the global X-axis is in the same direction as the positive global X-axis. If the line object is parallel to the global Y-axis such that there is no projection onto the global X-axis, the positive direction of the local 1 axis is the same as the direction of the positive global Y-axis.
- Local axis 2 is perpendicular to the line object. The positive local 2 axis points in the same direction as the global Z-axis, upward.
- Local axis 3 is perpendicular to the line object and is horizontal. The direction of the positive local 3 axis is determined from applying the right-hand rule using the directions of the 1 and 2 axes described in the preceding bullets.
Other (neither vertical nor horizontal) Line Objects. For line objects that are not vertical and are not horizontal, the local axes have the following default orientation:
- Local axis 1 is along the line object. The positive local 1 axis has an upward sense. The projection of the positive local 1 axis onto the global Z-axis is in the same direction as the positive global Z-axis, upward.
- Local axis 2 is perpendicular to the line object. The local 1-2 plane is vertical. The positive local 2 axis has an upward sense. The projection of the positive local 2 axis onto the global Z-axis is in the same direction as the positive global Z-axis, upward.
- Local axis 3 is perpendicular to the line object and is horizontal. The direction of the positive local 3 axis is determined from applying the right-hand rule using the directions of the 1 and 2 axes described in the preceding bullets.
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I am structural Engineer working in a reputable firm in Los Angeles
Thanks a lot. I´m just starting in the design of structures and this was very very helpful.
So, for a wall element the is parallel to the global x-axis, M22 is the out of plane moment. But when your wall is perpendicular to the global x axis, M22 is the in-plane wall moment??
M22 is based on local axis therefore it doesnt matter where is your global axis, M22 will always be out of plane moment.
Thanks.
Hi Zstructures. I used SAP2000, and now I have started to use ETABS. In SAP2000, I could rotate a frame local axis with reference to two joints, but in ETABS I don’t know how do it. Please I need your help. Thanks.