AISC 360 contains specific requirements regarding the analysis of the lateral frames. Three methods are listed: The Effective Length Method, the First-Order Analysis Method, and the Direct Analysis Method. Generally any of the three approaches is acceptable, but if the ratio of the 2nd -order drift to 1st -order drift is greater than 1.5 (based on a model with nominal member properties), the Direct Analysis Method is required. Direct Analysis Method (2nd-order by amplified 1st-order elastic analysis) is implemented. The reader is referred to Chapter C and Appendix 7 in AISC 360 for further information.