Frequency analysis calculates the resonant frequencies and corresponding mode shapes only. Linear dynamic studies use the information to calculate the dynamic response of your structure to dynamic environments.
For nonlinear systems, use nonlinear dynamic studies to calculate the response in the time domain. Nonlinear dynamic studies solve the dynamic response problem as function of time and do not require the calculation of mode shapes and frequencies.
The effect of loads on frequencies and mode shapes is not considered when using linear dynamic studies, as their calculation is based on a stress-free model state.
It is recommended to define a Nonlinear Dynamic study instead to account for any possible stress-stiffening or stress-softening effects that can alter the modal characteristics of the model.
The effect of time-varying loads with frequencies less than 1/3 of the lowest resonant frequency of the model, can be approximated by static analysis in most cases.