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RSL III 2D

RSL III 2D is the software for the evaluation of the Level III local seismic response by means of a finite element approach, in the time domain, in terms of total stresses.

Based on the seismic input, represented by one or more accelerograms applied to the bedrock, the wave propagation motion is evaluated for every node of the model, discretised by means of triangular finite elements.

Numerous theoretical studies and the observation of real cases have widely demonstrated that the local seismic response is strongly influenced by the topography and the stratigraphy of the site. In the most recent microzonation studies, numerical methods on two-dimensional models have frequently been used, in which the effects of the real geometry of the subsoil have been taken into account.

The evaluation of the two-dimensional local seismic response cannot disregard an accurate reconstruction of the geotechnical model of the subsoil. The acquisition of numerous parameters, including the geometry, the propagation velocity of the shear waves and the density of the soils involved, obtained through suitable geotechnical or geophysical investigations, is the first step for two-dimensional seismic microzonation studies, which constitute the input for the 2D modelling.

RSL III 2D is a calculation tool for the two-dimensional modelling of the local seismic response by means of a finite element approach, in the time domain. It makes it possible to remove the assumption of a perfectly rigid bedrock used in the one-dimensional model of wave propagation in a Kelvin-Voigt soil. The calculation code allows complex geometries and boundary conditions to be modelled, both of the substratum, of the topographic surface and internal to the deposit itself (cavities, inclusions). It performs a finite element analysis (FEM) by discretising the section through a mesh of triangular elements, according to a scheme of masses, springs and viscous dampers lumped at the nodes, solving the equations of motion written for each node in the time domain.

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

The final values provided by the Level III 2D analysis are the accelerograms and the related response spectra, the mean spectrum and the normalised mean spectrum, to be compared with the code spectrum, and various amplification factors for different period ranges.

RSL III 2D features a particularly intuitive user interface, which 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 discretisation of the geotechnical model, taking into account the interfaces or the holes present in the assigned geometry;

  • the determination of the seismic response in terms of accelerograms and acceleration response spectra for each node of the model;

  • the export of the spectra in .txt or .csv format, to allow their import into the Edifici in C.A. software and/or any structural software;

  • the normalisation of the spectra according to the NTC and the EUROCODES;

  • the determination of the seismic parameters and of the quantities needed to perform a complete characterisation of the seismic motion at the surface (PGA, PGV, amplification factors over different periods, Housner intensity).