This paper introduces a novel computational framework that integrates a three-dimensional (3D) nonlinear time history analysis (NLTHA) of buildings subjected to combined flood and earthquake events. Unlike traditional single-hazard analyses, this research explores the complex interactions between hydrodynamic forces from flooding and seismic loads. Using steel special moment-resisting frames (SMRFs) of varying heights in Los Angeles (USA), the response to 13 earthquake hazard levels and four flood inundation depths is evaluated. The framework incorporates computational fluid dynamics (CFD) for hydrodynamic modelling and finite element (FE) analysis for structural response assessment. Results highlight a significant increase inengineering demand parameters (EDPs), such as inter-story drift, floor accelerations, base shear, and ductility in multi-hazard scenarios. These findings underscore the need for a re-evaluation of building resilience in flood-prone areas.

With climate change intensifying risks of extreme precipitation and riverine flooding, reassessing building resilience under multi-hazard scenarios, particularly those involving earthquakes, has become increasingly important. This study proposes an integrated framework for three-dimensional (3D) nonlinear time history analysis (NLTHA) to evaluate structural performance under sequential earthquake and flood events. By coupling advanced Computational Fluid Dynamics (CFD) simulations with earthquake engineering methods, the framework captures the time-dependent interaction of seismic and hydrodynamic forces. This overcomes limitations of previous research that relied on oversimplified flood-earthquake interaction models. The analysis focuses on steel special moment-resisting frame (SMRF) buildings in Los Angeles, California. Thirteen seismic hazard levels and four flood inundation depths are analysed, producing detailed engineering demand parameters (EDPs) for both earthquake-only and combined hazard scenarios. Structural vulnerability is evaluated through ductility and plastic hinge rotation in columns and beams. Results show flooding significantly amplifies EDPs, especially in lower stories and front-facing elements, emphasising the need to revise design and assessment strategies for buildings in flood-prone areas. Furthermore, vortex shedding and asymmetric water flow patterns around corners and side columns increase localised hydrodynamic pressures. This integrated approach provides engineers with a comprehensive framework for analysing structures to withstand future climate-driven multi-hazard events.