Answer:
Just as in the "Forced Vibrations" add-on module, the "Equivalent Loads" add-on module performs the multimodal response spectrum analysis.
Although the name may suggest otherwise, the simplified response spectrum method is not carried out here, as explained in EN 1998‑1, for example.
The equivalent loads are determined separately for each direction of excitation according to the following formula:
The differences between both add-on modules are described in FAQ 2062:
FAQ | Differences Between Add-on Modules "Forced Vibrations" and "Equivalent Loads"
