This book aims to comprehensively examine the fundamental nonlinear mechanisms determining the behavior of reinforced concrete structural systems under earthquakes and other repeated loads, particularly within the framework of concepts such as moment-curvature relationship, ductility capacity, and effective section rigidity. It emphasizes the necessity of nonlinear analysis methods for accurately representing the actual behavior of structural elements when traditional elastic analysis approaches are insufficient; in this context, a multi-scale evaluation approach extending from the section level to the system level is adopted.

In this study, the moment-curvature behavior of reinforced concrete sections is analyzed using theoretical and numerical methods, based on the stress-strain relationships of concrete and reinforcing steel; the effects of parameters such as reinforcement ratio, axial load level, concrete strength, and confinement effect on section behavior are systematically presented. The concept of curvature ductility is discussed in detail, and ductility definitions and performance criteria according to different design and evaluation approaches are examined comparatively.

Furthermore, the concept of effective section stiffness, which is critical in integrating nonlinear behavior into practical engineering calculations, is evaluated within the framework of models proposed in various international regulations and literature; the accuracy and applicability of these models in the analytical modeling of reinforced concrete elements are discussed. Approaches developed by TBDY (2018), Eurocode 8, and various researchers are compared, and implications for engineering applications are presented.

The book serves as a reference for both academic studies and engineering applications, aiming to provide a scientific foundation for performance-based evaluation, strengthening, and design of reinforced concrete structures. In this respect, it offers a comprehensive resource for researchers, graduate students, and practicing engineers interested in nonlinear analysis techniques.