MTR/SASSI Program Capabilities


2D and 3D Analysis of Soil-Structure Systems

  • Structure is represented by standard finite elements.
  • Excavated soil block is modeled using plane-strain and solid finite elements.
  • Fluid medium may be modeled with 2D or 3D acoustic finite elements.
  • Nonlinear components may be modeled using linearized properties.
  • Foundation piles are modeled using new Pile elements.
  • Piping system can be modeled using new Pipe element

Soil Model

  • Soil media is modeled with horizontally layered system over uniform halfspace.
  • Irregular soil zones are modeled using finite elements as part of the structure.
  • Primary nonlinearities in the free field are modeled using equivalent linear method.
  • Secondary soil nonlinearities in the SSI model may be accounted for by iterating on near-field soil properties using equivalent linear method.
  • Effect of ground water is accounted for by assigning appropriate Poisson’s ratio.

Types of Analysis

  • Site response due to body waves and surface waves
  • Forced vibration response of machine foundations
  • Ambient vibration response of vibration-sensitive facilities
  • Seismic response of nuclear facilities
  • Soil-structure-fluid interaction analysis
  • Structure-soil-structure interaction analysis
  • Seismic response of structures subject to incoherent ground motions
  • Random vibration analysis
  • Seismic racking response of tunnels and underground structures
  • Dynamic soil pressure analysis
  • Stress analysis of pipelines subject to spatially variable ground motions
  • Seismic response of structures on large pile group foundations
  • Seismic response of gravity-based offshore structures
  • Seismic response of structures founded on improved soils


  • Free format input data facilitates data entry, minimizes errors, and streamlines interfacing with other codes.
  • Data block input format provides flexibility for organizing and moving blocks of data in the input file and between different modules.
  • Flexible node, element and property labeling facilitates model development and allows structural models to be imported “as is” from other codes.
  • Structure and excavated soil models can be developed separately and glued together with different node and element numbering.
  • Free style commenting makes labeling and identifying data easy.
  • Built-in arithmetic operators enable easy and error-free units conversion for data entry.
  • Extensive internal program error checking minimizes user errors and saves time.
  • Extensive data generation capability facilitates input data preparation.
  • Input data for program modules can be provided in a single file in the new versions.


  • Detailed printout for checking results and documentation.
  • Time and date stamp for QA and production run documentation.
  • Automatic plot file generation from runs facilitates importing results for spreadsheets and other production environments for tabulation and plotting of results.

Sample Results

  • Transfer functions
  • Maximum values and time histories of acceleration, velocity, and displacement responses
  • Acceleration response spectra
  • Interstory forces and moments
  • Maximum values and time histories of base forces (normal & shear) and moments (overturning & twisting)
  • Maximum values and time histories of stresses, forces, and moments
  • Maximum values and time histories of dynamic soil reaction forces on below-grade sidewalls
  • Mean values and spectral density output from random vibration analysis