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Calculate the response to seismic loading, via the spectral modal approach, based on the accumulation of modal responses, under the assumption of elastic linear behavior. (Spectral response = response from the accumulations)

The seismic load consists of two parts:

• the static deformation movement of the structure under the effect of the displacements imposed on the supports (training), represented by the seismic differential displacements DDS;

• the deformation movement relative to the static (inertial) deformation, represented by oscillator response spectrum SRO.

The analysis is either mono-support (single excitation of all the supports by the same SRO), or multi-support (excitations differentiated according to the supports). In the multi-support case, the excitations are either all correlated with each other, or relating to (uncorrelated) groups of correlated supports.

the spectral modal approach allows an estimation of the probable mean maximum values in absolute value of the quantities of interest, resulting from the quadratic sum of the response to DDS and of the inertial response.

The spectral modal method is strictly limited to the evaluation of quantities that depend linearly on displacements: deformations, stresses (excluding equivalent quantities), generalized forces, nodal forces, support reactions.

Produces a multipurpose concept.