This project will develop a new structural system that will protect buildings, their contents, and occupants during large earthquakes and will enable immediate post-earthquake occupancy. This earthquake-resilient structural system will be particularly valuable for essential facilities, such as hospitals, where damage to buildings and contents and occupant injuries must be prevented and where continuous occupancy performance is imperative. The new system will use practical structural components to economically protect a building from damaging displacements and accelerations. The project team will collaborate with Japanese researchers to study the new system with full-scale earthquake simulations using the 3D Full-Scale Earthquake Testing Facility (E-Defense) located in Miki, Japan, and operated by the National Research Institute for Earth Science and Disaster Resilience. This project will advance national health, prosperity, and welfare by preventing injuries and loss of human life and minimizing social and economic disruption of buildings due to large earthquakes. An online course on resilient seismic design will be developed and offered through the American Institute of Steel Construction night school program, which will be of interest to practicing engineers, researchers, and students across the country. This project contributes to NSF's role in the National Earthquake Hazards Reduction Program. The novel steel frame-spine lateral force-resisting system with force-limiting connections (FLC) that will be developed in this project will control multi-modal seismic response to protect a building and provide resilient structural and non-structural building performance. This frame-spine-FLC system will rely on a conventional, economical base system that resists a significant proportion of the lateral load. The system judiciously employs floor-level force-limiting deformable connections and an elastic spine to protect the base system. Integrated experiments and numerical simulations will provide comprehensive understanding of the new frame-spine-FLC system, including rich full-scale experimental data on building seismic performance with combined in-plane, out-of-plane, and torsional response under 3D excitation. The FLCs will be tested using the NHERI facility at Lehigh University. This project will be conducted in collaboration with an ongoing synergistic research program in Japan. The extensive dataset from this integrated U.S.-Japan research program will enable unique comparisons of structural and non-structural performance, including critical acceleration-sensitive hospital contents that directly affect the health and safety of patients. In addition, the dataset will enable the advancement of computational modeling for the assessment of building performance and the development of practical, accurate models for use in design that capture the complex 3D structural response that occurs during an earthquake.