The MOTION module reads the transfer functions generated in previous steps and performs an efficient frequency domain interpolation using a complex domain scheme.

The interpolated transfer functions are then, used to compute the SSI response motions at a set of nodes selected by the user.

The baseline correction option is used to compute acceleration, velocity, or displacement response spectra at different location points and degrees of freedom (this produces a significantly more approximate solution for relative displacements in a structure than using the RELDISP module), the nodal point motions including acceleration, velocity and displacements if desired.

Output file provides at each time step, the accumulated time, the absolute acceleration, absolute velocity and absolute displacement values.

The computed acceleration histories and response spectra can be optionally saved.

In addition to the output file that could be often very large size (if time histories are saved), MOTION produces specific text files for post-processing. These text files contain nodal SSI responses for the three translation Degrees Of Freedom respectively, the computed TF (TFU), interpolated TF (TFI), acceleration time histories (ACC) and the in-structure response spectra (RS) for selected damping values.

If the MOTION post-processing restart option is used, then additional text files for post-processing are generated. These frame text files contain the SSI response values computed for all active nodal DOF at each frequency step or time step. These frame files are used by the ACS SASSI PREP module to create structural bubble plots, TF vector plots, contour plots, or deformed shape animations.

In addition to the ACC frames, MOTION also generates files that contain the maximum acceleration or Zero Period Acceleration frame.

MOTION can generate also compressed binary databases for the computed SSI response acceleration histories.

MOTION may also combine the X, Y and Z input direction nodal acceleration histories from the three directional binary databases.

The MOTION module can be also used to generate response spectra for external acceleration histories provided by the user.