Spectral Density Multi-Field Energy Theory in Structural Dynamics: Methods and Applications introduces a powerful analytical framework for advancing structural dynamics and disaster prevention. Traditional time-domain and frequency-domain methods often struggle with evaluating complex dynamic behaviors, especially under multi-dimensional excitations and evolving multi-hazard scenarios. This book presents a novel spectral density multi-field energy theory that addresses these challenges through an energy-based lens. It covers the theoretical derivation in depth and explores applications such as damage identification in large-span spatial structures, catastrophe modeling, macro strain energy methods, and energy flow analysis. Real-world case studies demonstrate its effectiveness in structural health monitoring, disaster chain analysis, and dynamic response evaluation under intricate excitation conditions. This book provides researchers, engineers, and postgraduate students in civil, mechanical, and aerospace engineering with a clear and practical framework for tackling complex dynamic structural problems, combining advanced spectral energy methods with real-world engineering examples.