Coordinate systems

Few types of coordinate systems are used in programs Fin 2D and Fin 3D:

Global coordinate system

The global coordinate system is the fundamental coordinate system and and has axes X,Y,Z. It is used for the input of the structure geometry. This system is a right-hand Cartesian coordinate system. The main attribute is, that the Z-axis is oriented in the upward direction. It means, that the gravity loads act against the global axis Z.

The global coordinate system consists of axes Y,Z in the software Fin 2D.

Local coordinate systems

Any member has local coordinate system. It is necessary for the definition of cross-section orientation, for load input and for display of internal forces along the member length. Local coordinate system uses axes 1,2,3. Following rules are used for local coordinate systems:

The axis 1 is identical to the centre line of the member, beginning is in the start joint of the member, positive direction is given by the end joint of the member.
The axis 3 lies in the vertical plane (parallel to global axis Z). Orientation is identical to the orientation of axis Z (upward direction). Only exception are the members parallel with the global axis Z (vertical members). In these cases, local axis 3 is parallel to the global axis Y.

Cross-sectional coordinate systems

The cross-sectional coordinate system is used for the definition of cross-section geometry. It has axes y,z and for rotation angle 0° the axis y is equal to the axis 2 and the axis z is equal to the local axis 3. This local coordinate system is used for rotation of cross-section or for calculation of internal forces along members with rotated cross-sections.