As we know that the analysis of the multi-story building is consists of very complex loading calculations and time-consuming. So for approximate and quick analysis, the Subsitute method is used for analysis.
This method is used only for vertical loading conditions. The moments in the beam are assumed that are influenced by the loading on that floor alone.
In this method, we are dividing the whole multi-story building frame into a smaller frame, which is called an equivalent frame or substitute frame. These subframes are analyzing by the Moment Distribution Method.