The analysis procedure should be selected in Table 12.6-1.

The four basic procedures provided in Table 12.6-1 are the equivalent lateral force (ELF, Section 12.8), the modal response spectrum (MRSanalysis, Section 12.9.1), the linear response history (LRH, Section 12.9.2), and the nonlinear response history (NRH, Section 16.1) analysis procedures.
The use of the ELF procedure is limited to buildings with the listed structural irregularities because the procedure is based on an assumption of a gradually varying distribution of mass and stiffness along the height and negligible torsional response.