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PERMAS-DRX Extended Dynamics

This module comprises additional methods for structural response analysis:

  • Spectral Response Analysis (or Earthquake Spectral Response Analysis),
  • Random Response Analysis.

Spectral Response Analysis

In case of a prescribed ground motion, like in earthquake analysis, the dynamic response behavior is determined by a special method, which results in maximum response values. There, the following requirements have to be fulfilled:

  • uni-directional and translational motion of the ground,
  • no other loads,
  • analysis can be performed in modal space,
  • only modal viscous damping.

After the specification of the direction of the ground motion the load is defined by a spectrum of the transient excitation (response spectrum). Then the analysis is performed as follows:

  • Calculation of all dynamic modes up to the highest interesting frequency.
  • Calculation of the maximum mode contributions.
  • Summation of the maximum contribution factors using one of 7 available summation rules (like CQC or 10% rule).
  • Output of peak values

Random Response Analysis

Frequently, vibrational loads are not predictable like for cars on a bumpy road, for a house under wind loads, or for a ship on rough sea.

Conveniently, such stochastic loads can be described by random processes. Correlations between such processes and their transformation into frequency domain are leading to the central concept of power spectral density.

One special phenomenon is white noise which describes a constant power spectral density over the full range of frequencies.

The loads are specified as power spectral densities and the results are derived as RMS quantities and power spectral densities as well.

This method is implemented as a modal method, i.e. an eigenvalue analysis is performed first followed by the response analysis in modal space and a subsequent back transformation into physical space where the results are made available for export and post-processing.