Response spectrum analysis

Response spectrum analysis is one of the methods of dynamics in the field of FEM. Its primary objective is to determine the reaction of a structure exposed to a known, non-permanent excitation spectrum. The excitation spectrum is the description of a load as a function of frequency. The results are maximum displacements, strains and stresses. The analysis provides a conservative estimate of the structural load. It does not contain information on the sequence and frequency with which this maximum structural response will occur. In addition to the reaction, the participation factors of the individual natural oscillations are also calculated.

The response spectrum analysis takes place in the frequency domain and is based on the results of a modal analysis. Therefore, non-linear effects such as changes in the contact state or plastic material behavior cannot be taken into account.

Depending on the type of excitation, a distinction is made in response spectrum analysis between single point and multiple point excitation. In the normal case of a single point excitation, the same spectrum is applied to all excitation points, whereas in the case of a multiple point excitation, different spectra attack at different points of the structure.

Computation time / model size

The execution of a response spectrum analysis is connected with a small additional numerical effort to the upstream modal analysis. The limitations of modal analysis therefore essentially apply with regard to model size and calculation time.

Relevance

Due to the conservative character of the results and the comparatively low effort for modeling and solving the equation system, response spectrum analysis has an important position in the field of FEM simulation. This method is used in particular for verifying the stability of plants and buildings due to earthquakes, wind loads and waves.