CLASSI

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CLASSI (Continuum linear analysis of soil structure interaction analysis) uses a combination of finite element and boundary element analysis techniques.  By modelling the soil using boundary elements and the structure using finite elements, CLASSI achieves an efficient representation of the SSI problem.  Furthermore, the time history for the input motion is reduced using a fast fourier transform and the whole problem solved in the frequency domain to couple together the components of the sub-structured analysis.  The result is a fast and efficient analysis of multiple detailed 3D structures for their SSI response resulting in time history results.  This results in a level of approximation not dissimilar from a finite element model, but with far greater computational efficiency due to the method employed.

            The solution for soil is carried out using various Green's function solution procedures (integral equation methods) for arbitrary surface or embedded foundations in a horizontally layered elastic or viscoelastic halfspace.  The integral equation procedures used approximate the stress distribution over the interface by a number of uniform stress patches.   The following is a list of capabilities and limitations for the program

            • The foundation medium can be defined as an elastic or viscoelastic, uniform or horizontally layered continuum halfspace.  Damping within the foundation medium is defined using constant hysteresis damping ratios for each of the soil layers.

            • The structural foundation is assumed to be rigid and bonded to the soil.

            • Multiple structural foundations can be analysed.

            • The wave environment can be defined using either vertical or inclined P, SV, and SH body waves with R and L surface waves, all within a three dimensional seismic incidence wave environment.

            • The program is linear and does not include an automatic iteration procedure.  Therefore the strain dependency of soil properties has to be considered using an succession of equivalent linear analyses.

CLASSI uses several steps to achieve this goal:

GLAY

The soil is represented as infinite horizontal layers (this limits the solution to surface mounted foundations), which are represented using Green’s functions to compare motions at one point with motions at radii from that point.

CLAN

The foundations are represented on the surface of the soil by defining a number of patches of uniform stress.

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