For each joint of a structural model, displacement may either be unknown and solved for, or it may be known and input. Known joint displacement is either zero or nonzero. Zero displacement is specified for fixed DOF at restraint support locations. Nonzero 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 nonzero), a restraint must be assigned along that DOF. A nonzero 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

• F represents joint forces

CSI Software transfers nonzero 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.

See Also

• Ground motion at specific supports – Manual multi-support excitation