Checks According EN 1998-1 (EC 8)

Response Spectrum Method for the Earthquake Check

The Dynamics extension module conducts the earthquake check according to EN 1998-1 for any 2D and 3D beam, shell or solid structures according to the response spectrum method.

The norm provides the soil acceleration and the calculation coefficients depending on the earthquake zone, the foundation, the damping and the ductility of the structure.

For the check the reactions of the structure corresponding to the resonant frequencies are calculated and superposed according to the response spectrum method.

The resulting internal forces are available for further superposition with the static actions and subsequent design.


Evaluating the effective modal masses
Evaluating the effective modal masses

For every eigenmode the respective response spectrum is analyzed and the deformations, internal forces, etc. are saved.

In order to evaluate the modes of vibration to be considered, the applied masses are contrasted with the effective modal masses.

Soil Acceleration

The soil acceleration is applied according to the earthquake zone. When doing so, the direction can be applied for individual components and superposed at a later time (for instance: ± 1.0 Edx ± 0.3 Edy). If necessary, the frame of reference can be rotated into the local building axes.

Coefficients According to EN 1998-1

The selected subsoil conditions determine the parameters for the horizontal and vertical response spectra. These are then analyzed and superposed under consideration of the structural properties. The program selects the required static superposition (SRSS or CQC) in accordance with the standard. The user can optionally override this selection.

Depending on the period of oscillation, the relating spectral acceleration can be taken directly from the response spectrum (for instance, for determining the foundation shear).

To allow for further analysis (for instance, calculation according to the second-order theory), the static pseudo loads associated with the modal components can be saved.