The Effect of the Earthquake on a Structure Depends Not Only on the Peak Value of Ground Acceleration, But Also on the Size and Shape of the Building, the Arrangement of Structural Elements, And The Presence of Mass and Stiffness Irregularities. Basic Modes In Irregular Structures Are Often Isolated And May Not Affect the Response of Other Areas of the Structure In any Significant Way. Straight-Line Fit To Semi Logarithmic Graphs Between Key Frequency F1 Rigid Frequency Independent of Damping Are Used To Derive the Empirical Expressions For Rigid Response Coefficient. As the Study's Findings Demonstrate, The Fundamental Mode Approach For Regular Structures 90 Modal Mass Criteria For the Number of Modes To Be Included For Dynamic Analysis of Irregular Structures Are Insufficient. Shear Forces Are Underestimated at the Top and Bottom Levels In Numerical Instances When the Current Criterion Is Used. Elastic Seismic Analysis of Irregular Structures Can Be Simplified By the Residual Mode's Ability To Simulate Dampened Periodic Response. A Tool Mathcad Is Used For Developing Different Mathematical Models For Dynamic Analysis and To Calculate Section Capacity of Rc and Steel Sections As Per Is Codes. Further Software Staad.Pro and Etabs Is Used For Modelling and Dynamic Analysis of Real-Life Structures. the Output of Both the Models Is Used to Verify and Validate Output and Correctness of Each Other