initial loading in time history

huangyhg

initial loading in time history
hi all,
i would like to know what kind of approach i should take to define an initial loading/condition in time-history analyse(ritz vector used). generaly the ground acceleration at principal axes is been applied(in various examples and tutorials), depending on which direction you want to find the solution. as far as i understand ritz vector calculates the resulting eigenvalues and eigenvectors with taking into account these initial loading.  
so, may i include the dead and live loads as initial loading to make much more precise(with being on safe side)calculation, because in my understanding these loads as wells as accelerations are contributing to the eigenvalues and eigenvectors.