For each joint of a structural model, displacement may either be unknown and solved for, or known and input. Known joint displacement is either zero or non-zero. Zero displacement is specified for fixed DOF at restraint support locations. Non-zero joint displacement is specified for such a condition as given support settlement, or application of displacement time history to specific supports, which is described in the Displacement time-history record article.
When joint displacement is known for a given DOF (whether zero or non-zero), a restraint must be assigned along that DOF. A non-zero displacement value may then be assigned using the Assign > Joint Loads > Displacements menu.
Numerical solution proceeds by solving the matrix equation K u = F
where
K represents the stiffness matrix;
u represents joint displacements; and
F represents joint forces.
CSI
Software transfers non-zero joint displacements to the right side of this equation such that equivalent applied loads represent their effect. Unknown displacements on the left side are then solved.
