Local seismic response 2D – RSL III 2D

Software for the evaluation of two-dimensional level III local seismic response.

Numerous theoretical studies and observation of real cases have amply demonstrated that the local seismic response is strongly influenced by surface and buried morphology. In more recent microzonation studies, numerical methods on two-dimensional models have been frequently employed to consider the effects of real subsurface geometry.

The assessment of the local 2D seismic response cannot be separated from an accurate reconstruction of the subsurface geological model through the use of surface geological information and geognostic and geophysical surveys. The acquisition of numerous parameters, including thicknesses, velocities, and densities of the investigated lithotypes, obtained through the use of geognostic and geophysical surveys is the first step for two-dimensional seismic microzonation studies, which are the input for 2D modeling.

RSL III 2D software is a computational tool that enables two-dimensional modeling of local seismic response using a finite-element, time-domain approach, which eliminates the completely rigid bedrock assumption used, in the one-dimensional model of wave propagation in a Kelvin-Voigt soil. The RSL IIII 2D computational code allows for modeling complex geometries and boundary conditions of both the substrate, the topographic surface, and internal to the deposit itself (cavities, inclusions). It performs finite element analysis (FEM) by discretizing the section using a mesh of triangular-shaped elements, according to a scheme of masses, springs and viscous dampers concentrated at nodes, solving in the time domain the equations of motion written for each node.

The seismic input, represented by one or more accelerograms (REXEL allows the search for combinations of natural accelerograms compatible with normative spectra), is applied to the bedrock, with linear elastic behaviour, and the response of the system at instant t is evaluated in the time domain as a function of the response at instant t -Δt by a sequence of equivalent linear analyses in which the stiffness and damping parameters are updated following an iterative procedure and according to a predetermined convergence criterion.

The final values provided by the Level III 2D analysis are the accelerograms and their response spectra, the mean and normalized mean spectra, to be compared with the normative spectrum, and various amplification factors for different period intervals.

RSL III 2D has a particularly intuitive user interface and allows:

• • the import of spectrum-compatible accelerograms;
  • the import of the two-dimensional geometric model from DXF;
  • the automatic generation of the mesh for the discretization of the geotechnical model taking into account the interfaces or holes present in the assigned geometry;
  • the determination of the seismic response in terms of accelerograms and acceleration response spectra at each model node;
  • the export of the spectra in .txt or .csv format to allow their import into the software Buildings in C.A. and/or any structural software;
  • the normalization of the spectra according to EUROCODES;
  • the determination of seismic parameters and quantities necessary to carry out a complete characterization of seismic motion at the surface (PGA, PGV, amplification factors over different periods, Housner intensity).