SSI Soil-Structure-Interaction

What is Soil-Structure-Interaction?

In case of vibration of the ground, i.e. during Earthquakes, earthworks or machine vibrations, Waves spread throughout the subsoil, interact with buildings and be reected and broken. This mutual inuence of soil and structure is called Soil Structural Interaction (SSI).

Where is the SSI needed?

  • Earthquake proofs of dams
  • Proofs of Nuclear Power Plant buildings, their components and pipe systems for earthquake
  • Propagation calculation of vibrations i.e. induced by impact pile-driving


Our tool - ACS Sassi

In the eld of soil-building interaction ACS Sassi is currently the leading software package from Ghiocel Predictive Technologies Inc.

1 Generation of spektra compatible Time-Histories

Given are earthquake loads for a location in the form of free-eld excitations. For the SSI calculation Time Histories are needed. These can be either generated articially or derived from real earthquake events.


2 SSI-computational Model

  • Model of building with the main internals and possibly sourrounding soil (HOUSE)
  • Soil-Model of the upper Layers and of the infinite halfspace (LAYER)


Modeling of the building and possibly the near field soil. The level of details in the FE model for the SSI calculation determines the computing time. Subsequent transfer of the calculation model and the boundary conditions from the SSI in ANSYS with the possibility of model renement and stress evaluation.

Soil-Layer Model

Soil parameters of each Soil layer down to the halfspace:

  • Layer thickness
  • specic weight
  • S-Wave speed
  • P-Wave speed
  • damping

Iteration of dyn. soil properties:

  • shear modulus
  • damping

3 SSI-Calculation

  • SV-Waves in X-Direction
  • SH-Waves in Y-Direction
  • P-Waves in Z-Direction
  • frequency dependent stiffness (Impedance)
  • mass- and stiffness matrix
  • SSI-Calculation

4 Postprocessing

  • Output of accelerations, displacements and stresses
  • calculation and processing of the In-Structure-Response-Spectra




Broadening of spectra

  • RSS-Superposition of the responses in each spatial direction due to the excitation in each single direction
  • Averaging of spectra for the excitation of various time histories
  • Capping of peaks
  • Broadening of Spectra
  • Enveloping the calculation results from different Soil models