Substructuring reduces computer time and allows solution of very large problems with limited computer resources. Nonlinear analyses and analyses of structures containing repeated geometrical patterns are typical candidates for substructuring. In a nonlinear analysis, you can substructure the linear portion of the model so that the element matrices for that portion need not be recalculated at every equilibrium iteration. In a structure with repeated patterns (such as the four legs of a table), you can generate one superelement to represent the pattern and simply make copies of it at different locations, thereby saving a significant amount of computer time. Since superelement generation can be computationally expensive, the main superelement files (.sub and .seld) are forward compatible so that they can be generated in one version and used in a more recent one.

You can also use substructuring on models with large rotations. For these models, the program assumes each substructure to rotate about its mass center. In 3D cases, the substructures contain three rigid body rotations and three translational motions. With a large rotation model, you do not constrain the substructure until the use pass because each substructure is treated as a single finite element that should allow rigid body motions.

An example is an analysis that is too large for the computer in terms of model size or disk space requirements. In such a situation, you can analyze the model in pieces, where each piece is a superelement small enough to fit on the computer.