Accurate prediction of structural response under seismic excitation is the cornerstone of Performance-Based Seismic Design (PBD). While Nonlinear Time History Analysis (NLTHA) is the most rigorous approach, the choice between modal-based and step-by-step integration methods remains a critical decision for structural engineers. This study presents a comprehensive comparative evaluation of Fast Nonlinear Analysis (FNA) and Direct Integration (DI) techniques using a G+15 story reinforced concrete (RC) 3D building modelled in ETABS. The structural model incorporates material nonlinearities through concentrated plastic hinges at beam-column junctions and accounts for P-Delta effects to simulate realistic high-rise behaviour. A suite of seven ground motion records, scaled to the target Design Basis Earthquake (DBE) and Maximum Considered Earthquake (MCE) levels, was employed for the NLTHA. The comparison focuses on key performance indicators, including peak roof displacements, inter-story drift ratios, base shear distributions, and energy dissipation patterns. Preliminary results indicate that FNA, leveraging a reduced modal space, significantly reduces computational time—by up to 70%—while maintaining high accuracy in predicting global displacement demands. However, Direct Integration demonstrates superior capability in capturing complex hysteretic damping and high-frequency effects during severe inelastic incursions at the MCE level. The findings provide practical guidance for engineers on the trade-off between computational efficiency and analytical precision, highlighting that FNA serves as a robust tool for iterative design stages, whereas Direct Integration remains the "gold standard" for final performance verification of high-rise structures with significant nonlinearities.
Singh et al. (Wed,) studied this question.