Dear Neziric

if displacements be known in all nodes, the traction should be unknown in each node.

best regards

Panji 

Well, I know displacement in one node, but I need to calculate displacements in all nodes by solving simple matrix equation: [Keff] {D}n+1 = {Reff}n+1

I have matrix K, M and C. Matrix [Keff] could be obtained by

[Keff]=4/dt2 [M]+2/dt [C] + [K]

where dt is time step.

{Reff}n+1={Rext}n+1 + [M]((4/dt2) {D}n + (4/dt) {D'}n + {D''}n) + [C] ((2/dt) {D}n + {D'}n)

where Rext is external load vector, D' - velocity vector, D'' acceleration vector.

Displacement of one node is known. I should calculate displacements for other nodes during some time (i.e. 20 sec.). Only problem here is how to add known displacement in vector with unknowns which should be calculated.

Boundary condition is either the displacement or reaction known at particular nodes

Reaction is known in some nodes and it is displacement dependant.