SMC (Strong Motion CD) is a format used by the U.S. Geological Survey National Strong-Motion Project. SMC-files for existing earthquakes can be downloaded or purchased from several websites.
A format description can be found at: http://escweb.wr.usgs.gov/nsmp-data/smcfmt.html
Note that the unit of length in the SMC files is [cm], so accelerations are given in [cm/s2]. This has consequences for the value of the prescribed displacements.
Since the unit for SMC-files is specified as [cm/s2], it is possible to do a conversion from the SMC file’s acceleration values in [cm/s2] to the PLAXIS project units. In PLAXIS 2D AE and PLAXIS 3D, the import of SMC files is aware of the units used in the project. When using e.g. [m] as project length unit, the SMC-files will be converted from [cm/s2] to [m/s2].
Since PLAXIS 2D AE and in PLAXIS 3D the value for the prescribed displacement can be kept as unity to directly use SMC files: 1 project length unit.
This includes PLAXIS 2D Classic, PLAXIS 2D 2012, 2D 2011 and earlier
E.g. when using the standard unit of length [m], it is necessary to use the input values of 0.01 [m] for prescribed displacements. Alternatively, when using a unit of length [ft] it is necessary to use input values of 0.0328 [ft] for prescribed displacements. In this way, the SMC file can directly be used for dynamic analysis of earthquakes.