## 7 Discussion
### The Invariant Multi-Mode Vectors Pushover Analysis
It is suitable for preliminary design and design review but limited to elastic behavior and higher-mode consideration. * The upper-bound pushover analysis method, integrating aspects of the capacity spectrum method, energy balance, and modified modal pushover analysis, uniquely considers higher-mode effects in the nonlinear seismic evaluation of planar building frames, using a single load vector combining the first and a factored second mode shape. This method excels in predicting seismic demands in high-rise buildings, where higher-mode effects are significant, and offers a simplified procedure that yields more accurate nonlinear response estimates, applicable to both new and existing medium high-rise buildings. However, it tends to underestimate nonlinear responses at lower levels while overestimating them at higher levels in medium high-rise structures. Its accuracy may falter, particularly in irregular structures, and it is unsuitable for torsional flexible plan-asymmetric irregular structures. Additionally, the method overlooks variations in inertial load patterns and dynamic responses due to degrading strength and stiffness and does not account for other energy dissipation sources such as duration effects, viscous damping, and kinetic energy. * The modified and extended upper-bound (MUB) pushover analysis method emerges as an advanced and versatile approach to estimating seismic demands for tall buildings. It seamlessly combines the advantages of the UB pushover method (higher-mode consideration) and the conventional pushover method (accurate lower-level demands) to provide a more balanced and accurate assessment. Its adaptability to various building configurations, including symmetric and unsymmetrical plans, makes it a valuable tool for a broad spectrum of structures. However, it is important to be mindful of its simplifying assumptions and ensure adequate data availability for a comprehensive analysis. * The improved upper-bound (IUB) pushover analysis refines the lateral load pattern, resulting in more accurate predictions of roof displacements, story drift ratios, and plastic hinge rotations for tall buildings. It is more complex to implement than conventional pushover analysis but provides more reliable results. Its effectiveness and potential for improving seismic behavior prediction have been demonstrated through testing on various steel buildings. * The extension of the improved upper-bound pushover analysis procedure (EIUB) extends the capabilities of conventional IUB to accurately predict the seismic response of irregular structures with setbacks. It incorporates a third mode of vibration to account for the irregularity characteristic, resulting in improved predictions of roof displacements, story drift ratios, and plastic hinge rotations for irregular buildings. However, its complexity and data requirements make it more suitable for advanced engineering analyses. * The extended N2 method stands out as a refined version of the conventional N2 method, leveraging its strengths to enhance the accuracy of seismic demand estimation. Its unique feature lies in the integration of results from both basic pushover analysis and standard elastic modal analysis, providing a more reliable assessment of seismic demand distribution throughout the structure. This approach particularly excels in predicting seismic demand at the upper part of the building and at flexible edges, where the conventional N2 method may fall short. However, its complexity and data requirements make it more suitable for advanced engineering analyses compared to the conventional N2 method. * Spectrum-based pushover analysis (SPA) utilizes response spectra to estimate seismic demand in tall buildings. It offers a balance between simplicity and accuracy, making it suitable for preliminary design and design review purposes. SPA's key features include response spectra integration, simplified pushover analysis, and the generation of an envelope of results.