This document summarizes research on seismic response analysis of structures with mass irregularities at different floor levels. It discusses techniques for seismic analysis, focusing on time history analysis to evaluate nonlinear structural response under representative earthquake loads. The document reviews studies on analyzing reinforced concrete (RC) buildings with mass irregularities at different floors using time history analysis in ETABS software. It also provides background on irregular structure types according to building codes and discusses objectives of accurately modeling flexible diaphragms while maintaining seismic behavior of framed buildings.