Joint - Springs

Form:  Joint Springs, Coupled 6 x 6 Springs

Springs are flexible connections to ground and are always linear elastic. Assigning a spring to a joint is only meaningful if structural objects are connected to the joint. Otherwise, the spring will support air, so to speak; that is, it will not support anything.

Important Note: It is possible to assign negative spring stiffness to a joint as long as the total stiffness at the joint remains positive (or zero). If some negative spring stiffness is to be assigned to a joint, do it with great care. Negative spring stiffness at a joint during the analysis causes the structure to be unstable. CSiBridge will attempt to solve an unstable structure. If a linear analysis is being performed, CSiBridge will issue several warnings. If a nonlinear analysis is being performed, no warnings will be issued, although the solution may have trouble converging. CSiBridge does not check for negative spring stiffness before running the analysis.

Tip: If a nonlinear spring to ground is needed, use a one-joint (grounded) link object. If springs are needed to connect between two points in the structure, use a two-joint (connecting) link object. Linear or nonlinear properties can be assigned to the link in either case.

Use the Advanced > Assign > Joints > Springs command to open the Joint Springs form and assign to selected joints springs that are oriented in the global axes directions. Both translational and rotational springs can be assigned to a joint.

  1. Select the joint(s) to be applied springs.

  2. Click the Advanced > Assign > Joints > Springs command to display the Joint Springs form.

The above figure illustrates the 6x6 symmetric matrix of spring stiffness coefficients. When coupling is present, all 21 terms in the upper triangle of the matrix are specified. The other 15 terms are known by symmetry. For springs that do not couple the degrees of freedom, only the 6 diagonal terms are needed since the off-diagonal terms are all zero. The diagonal terms are specified for the spring stiffnesses when the Advanced button is not used.

 

See Also

Display - Show  Miscellaneous Assigns - Joints