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Establish the seismic load (unit inertia forces) for a calculation of the relative motion response in relation to the movements of the supports. For a better theoretical understanding of this loading, refer to the document [R4.05.01].

The product concept can be directly used during a direct transitory analysis or by modal synthesis with DYNA_VIBRA [U4.53.03]. On the other hand, for a direct non-linear transient analysis with DYNA_NON_LINE [U4.53.01], it is necessary to transform this concept into a load using the AFFE_CHAR_MECA [U4.44.01] operator.

Produce a field with nodes of magnitude DEPL_R.