.. _R4.05.03: **r4.05.03** Seismic response by spectral method ==================================================== **Summary:** The study of the response of a structure under the effect of imposed movements of the seismic type, with a single imposed movement (mono-support) or multiple (multi-support) is possible in transitory analysis (time history). Please refer to note [:external:ref:`R4.05.01 `]. For design studies, one can only be interested in an estimate of the maximum efforts induced by the stresses, in order to evaluate the safety margin with building regulations, without resorting to a transitory analysis. The spectral method is based on the notion of the oscillator spectrum of an earthquake accelerogram. The method for developing this response spectrum available in operator CALC_FONCTION [:ref:`U4.32.04 `] is detailed. It is shown how this oscillator spectrum can be used to evaluate an increase in the relative displacement response of a simple oscillator. This approach is justified if we do not want to know the history of movements and efforts, by limiting ourselves to the analysis of inertial effects. The spectral method uses general notions of the modal recombination method [:external:ref:`R5.06.01 `]. The various combination rules that can be used to obtain a realistic but conservative increase in the maximum response of the structure are described. These methods are available in operator COMB_SISM_MODAL [:ref:`U4.84.01 `]. .. toctree:: :hidden: self .. toctree:: :maxdepth: 2 :numbered: Notion_de_spectre_d_oscillateur R_ponse_sismique_par_recombinaison_modale R_ponse_sismique_par_m_thode_spectrale R_gles_de_combinaison_des_r_ponses_modales Bibliographie Description_des_versions_du_document