This book presents the select proceedings of the Twelfth International Conference on Behaviour of Steel Structures in Seismic Areas (STESSA 2026), serving as the only world reference specifically devoted to the seismic performance of structural steel and its applications. The volume compiles the latest global research on the behaviour, design, assessment, testing, and application of steel structures under earthquake loading, with papers critically analyzing current structural performance and proposing advanced methodologies to enhance ductility and resilience. Key themes covered include the inelastic performance of structural materials, components, and connections, alongside sophisticated analysis and design methods like Performance-Based Design (PBD), Nonlinear Modelling, and Plastic Analysis. Furthermore, the book details innovative seismic mitigation systems such as Seismic-Resilient Systems, Self-Centering and Rocking Systems, and the use of Energy Dissipation Devices, in addition to contributions on vulnerabilityassessment, retrofitting by steel technologies, and the latest developments in Codes and Design Standards verified through Structural Testing and Hybrid Simulation.

Dr. Federico M. Mazzolani is an Emeritus Professor of Structural Engineering at the Department of Structures for Engineering and Architecture of the University of Naples "Federico II". His extensive academic career is complemented by numerous international distinctions, including being named Doctor Honoris Causa by the Technical University of Bucharest (1995) and by the Politehnica University of Timisoara (1996). He is also an elected member of prestigious bodies, such as the Royal Academy of Engineers of Spain (since 2000) and the Academy of Engineers of Czech Republic (since 2004).

Dr. Dipti Ranjan Sahoo is currently a Professor in the Department of Civil Engineering and the Dean (Infrastructure) at the Indian Institute of Technology Delhi. He holds the distinctions of FNAE, FICE, FIE(I), FISET, FCDRI, MACI, and MEERI. Dr. Sahoo obtained his B.Eng. in Civil Engineering from Indira Gandhi Institute of Technology Sarang, Utkal University (2001). He then completed his M.Tech. (2003) and Ph.D. (2008) in Civil Engineering, both from the Indian Institute of Technology Kanpur, specializing in Structural Engineering. His major areas of expertise and research interests include the seismic design and analysis of concrete, steel, and composite structures.

Prof. Raffaele Landolfo is a Full Professor of Structural Engineering at the Department of Structures for Engineering and Architecture, University of Naples Federico II, Italy, where he has served since 2003. He obtained both his degree in Civil Engineering (1987) and his Ph.D. in Structural Engineering (1992) from the same institution. Over the course of his career, Prof. Landolfo has become internationally recognized for his contributions to steel structures, seismic engineering, cold-formed steel systems, sustainability of constructions, and the assessment and retrofit of existing buildings. Prof. Landolfo is deeply engaged in international standardization and research coordination.

Professor Vincenzo Piluso is a Full Professor of Structural Analysis and Design at the Department of Civil Engineering of Salerno University, a position he has held since 2001. He currently serves in a key administrative role as the Director of the Department of Civil Engineering at the university. His academic career at Salerno began when he won a competition for a position as a tenured university researcher in 1991. Prof. Piluso completed his graduate studies by obtaining his PhD in Structural Engineering in 1992, and he was promoted to Associate Professor in 1998 before achieving the rank of Full Professor in 2001. His extensive research activity is internationally recognized and focused primarily on advanced topics in structural engineering, particularly seismic-resistant steel structures and the behavior of steel framed systems

Dr. P. C. Ashwin Kumar is currently an Assistant Professor in the Department of Earthquake Engineering at the Indian Institute of Technology Roorkee, a position he has held since January 2018. He possesses a strong academic background in structural engineering, having obtained his B. Tech. in Civil Engineering from Govt. Engineering College Thrissur (2002-2006). He earned his M. Tech. in Structural Engineering from the Indian Institute of Technology Madras (2008-2010), where his project focused on Distribution Factors for Beam-Slab Bridge Decks. Dr. Kumar completed his Ph. D. in Structural Engineering from the Indian Institute of Technology Delhi in 2017. His doctoral research focused on the Local and Global Performance Assessment and Seismic Design of Special Concentrically Braced Frames (SCBFs).