The seismic impact at a site is strongly influenced by the local soil- and subsoil conditions. Resonance effects, which lead to an amplification in the response spectrum, are not captured by generalised code spectra. In order to account for site effects and for an accurate specification of the seismic loads, we conduct soil dynamic analyses. Therefore, the soil layers are modelled with their dynamic properties. Based on an input seismic motion at engineering bedrock – given by a code spectrum or out of a site specific seismic hazard study – the motion and response spectra at the free-field level or at any other level at depth (e.g. foundation level) is calculated.
The interaction between the soil and the building construction influences the transmission of the seismic waves from the free-field to the foundation of the building and modifies the response spectrum. The direct application of the free-field motion at the building foundation is not always conservative. For the calculation of floor response spectra combined models with soil layers and building structure are used. Besides the application in the nuclear industry, accounting for soil-structure-interaction leads to a more optimised and more efficient design also for other constructions. For instance, for the design of wind turbines soil-structure-interaction has a considerable influence on the calculated results and has to be taken into account under certain circumstances.