...
2- Define nonlinear static load case Lcase2, Lcase3 etc. with loads applied that correspond to same used as in the mass source. Make sure to select the correct mass source while in nonlinear static case i,e, MsSrc2, MsSrc3...for nonlinear static load cases Lcase2, Lcase 3 etc. While in the nonlinear static cases, under Other Parameters select Pdelta from the Geometric Nonlinearity Option to account for updated Pdetla stiffness in the subsequent modal cases as defined in step 3 below.
3- Define > modal cases and add new case, say ModalCase2, ModalCase3 etc. and make sure to choose radio button "use nonlinear case..." and select Lcase2, Lcase3... respectively.
...
- Fahjan, Y., Tuzun, C., Kubin, J. (2006). An Alternative Procedure for Accidental Eccentricity in Dynamic Modal Analyses of Buildings. First European Conference on Earthquake Engineering and Seismology, 1166.
...