For any joint in a model, the displacements are either unknown or known. Unknown displacements must be calculated from the analysis. Known displacements are either zero (representing fixed support condition for a given degree of freedom) or nonzero. Nonzero known displacement may represent known settlement of support, known displacement time history applied to a joint, etc. To "tell" the program the displacement for a given degree of freedom is known, you must assign restraint for the given degree of freedom. In addition, if the known displacement is not zero, you must assign the displacement value using "Assign > Joint Loads > Displacements" menu command.
Essentially, when the program solves the matrix equation for the structure (K u = f), the unknown displacements are kept on the left side of the equation, while the known nonzero displacements are transferred to the right side of the equation and applied as loads.
K ... stiffness matrix
u ... joint displacements
f ... joint forces
Related Incidents:
- Unknown macro: {incident}