The EQUAKE module generates earthquake acceleration time histories that are compatible with given seismic design ground response spectra. The EQUAKE module combines both frequency domain and time domain algorithms to generate the spectrum compatible accelerograms. The generated accelerograms are then used for site response analysis and SSI analysis through the SOIL, MOTION and STRESS modules.
The POINT module computes information required to form the frequency dependent flexibility matrix. Soil columns compatible with the structure mesh is defined in this module.
The SOIL module performs a nonlinear site response analysis under vertically propagating S waves using the Seed-Idriss iterative equivalent-linear model for the soil hysteretic behavior. The SOIL module is based on the SHAKE code methodology with some additional programming improvements done over years. The computed equivalent soil properties can be sequentially used in the SSI analysis.
The SITE module solves the site response problem. The control point and wave composition of the control motion are defined in this module.
The FORCE module forms the load force vector for external load cases apart from seismic load. Such external loads may correspond to impact forces, rotating machinery, crashing aircraft or simple unit forces to be used to determine the impedance of a flexible foundation.
The HOUSE module forms the element mass and stiffness matrices of all elements. This is the module where the structural model is input into ACS SASSI.
The ANALYS module computes the linearized SSI problem solution for the required frequency steps. It forms the soil flexibility matrix, computes the soil impedance matrix at interaction nodes, determines seismic load vector including the considered incoherency effects and then solves the equation system for each frequency step and obtains complex response transfer functions for each degree of freedom.
The MOTION module reads the transfer functions generated by the ANALYS module 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 desired nodes.
The STRESS module computes requested stress, strain, and force time histories and peak values in the structural elements.
Using SSI substructuring methods, the ACS SASSI software solution in complex frequency is restricted to linearized SSI analysis solutions. However, nonlinear SSI analysis including soil and structure hysteretic behavior can be performed using an iterative equivalent linearization algorithm. This is the module that allows nonlinear SSI response to be calculated in ACS SASSI.
The RELDISP module computes the relative displacements at different selected nodes.
The COMBIN module combines results computed for different frequencies from two ANALYS runs. This module is useful when after the solution was obtained it is found that some additional frequencies are needed to be included. ACS SASSI has your back!
ACS SASSI uses a number of modules to define the soil-structure interaction problem. Another series of modules are then used for the post-processing.