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NODAL COORDINATES AND NODAL MASSES
Once the dimensions of the problem is defined, it recommended that the user define the coordinates of the nodes, the mass associated with each node and DOF and the boundary conditions at the nodes.
The nodal coordinates are defined using the node command. The number of parameters associated with this command are referenced to the model command. Nodal masses can be defined at the same time as the coordinates. In the two-dimensional problem considered here, only the x and y coordinates of each node need to be defined, and three mass parameters (two translation and one rotation of the plane) need to be defined:
node 1 0. 0.; # column base is located at the origin of the plane
node 2 0. $Lcol -mass $Mnode 0. 0.; # the column end has one translational mass in the x direction, only
the nodal mass can also be defined using the mass command:
mass 2 $Mnode 0. 0.; # this command supersedes any previous mass definition at this node.
BOUNDARY CONDITIONS
The boundary conditions are defined using the fix command. The tag 0 represents an unconstrained (free) degree of freedom, the tag 1 represents a constrained (fixed) DOF. For the structure under consideration, the column base is completely fixed (1-1-1) and the end is free (0-0-0). Three DOF's need to be defined here, the two translations and the rotation in the x-y plane:
fix 1 1 1 1; # fixed base
fix 2 0 0 0; # free end
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