1D Member Axes

Member axes for linear members are defined in a similar manner to the axes of beam elements by two nodes locating the ends of the member. The x axis of the element is along the axis of the element (taking account of any offsets) from the first topology item to the second. For curved members the basic axis system of linear members holds.

The definition of the member y and z axes then depends on the member's orientation, verticality, orientation node and orientation angle. The member is considered vertical in GSA if the element is within the “vertical element tolerance”.

Non-vertical members

If an orientation node is not specified, the member z axis of a non-vertical member defaults to lying in the vertical plane through the member and is directed in the positive sense of the global Z direction. The member y axis is orthogonal to the member z and x axes. The member y and z axes may be rotated out of this default position by the orientation angle.

Vertical members

If an orientation node is not specified, the member y axis of a vertical member defaults to being parallel to and is directed in the positive sense of the global Y axis. The member z axis is orthogonal to the member x and y axes. The member y and z axes may be rotated out of this default position by the orientation angle.

Orientation Node and Angle

If an orientation node is specified, the member xy plane is defined by the member x axis and a vector from the first topology position to the orientation node, such that the node has a positive y coordinate. The member z axis is orthogonal to the member x and y axes. Specifying an orientation node overrides the “vertical member” and “non-vertical member” definitions described above. The member y and z axes may be rotated out of this default position by the orientation angle.

With an orientation angle the member y and z axes are rotated from their default positions about the member x axis by the orientation angle in the direction following the right hand screw rule. This occurs regardless of whether or not the member is vertical and of whether or not an orientation node is specified.