A 'LINE' cable (linear elastic cable) is the conventional type of cable where the tension is proportional to its extension, and the constant of proportionality is termed the STIFFNESS. This type of cable can be attached between a structure and a fixed point or attached between two structures. As the extension may vary during the analysis, the structure(s) to which the cable is attached will experience a force of varying magnitude and direction. The magnitude of this force, which is equal to the cable tension is given by

Force = (Stiffness(6))(Cable Extension)

Note that when the cable is slack, the cable extension, as defined below, is negative and the cable tension is set to zero.

(A) For a cable attached between a structure and a fixed point:

The extension, at any stage of the analysis, is calculated by subtracting the unstretched length (7) from the distance between the position of the attachment node (3) and the position of the fixed node (5) as defined in Data Category 1 in the Fixed Reference Axis System (FRA).

The direction of this force is given by the vector going from the position of the attachment node (3) to that of the fixed node (5)

(B) For a cable attached to two structures:

The extension, at any stage of the analysis, is calculated by subtracting the unstretched length (7) from the distance between the position of the attachment node (3) on one structure and the position of the attachment node (5) on the other structure.

The direction of the force on a structure is given by the vector going from the position of the attachment node (3) on that structure, to the position of the attachment node (5) on the other structure. The forces on each structure will therefore always be equal and opposite. Note that the interchange of parameters (2) and (3) with (4) and (5) has no effect.