Large-Scale Cyclic and Hybrid Simulation Testing and Development of a Controlled-Rocking Steel Building System with Replaceable Fuses

Abstract

Current U.S. building codes and earthquake engineering practice utilize inelasticity in the seismic force resisting system to dissipate seismic energy and protect against collapse. Inelasticity in conventional structures can lead to structural damage distributed throughout the building and permanent drifts after the earthquake motion ceases which can make the structure difficult if not financially unreasonable to repair. A controlled rocking system has been developed that virtually eliminates residual drifts and concentrates the majority of structural damage in replaceable fuse elements. Portions of the development related to but not contained in this report include fuse testing, fuse analysis, large-scale shake table testing, development of a displacement based design procedure, and collapse modeling. The controlled rocking system is investigated and developed through analytical, computational, and experimental means. A large-scale experimental program was conducted including quasi-static cyclic and hybrid simulation tests. Nine specimens were tested representing three-story frames at approximately half scale. These experiments validated the performance of the system, demonstrated system response when subjected to simulated ground motions, allowed the investigation of detailing and construction methods, provided information on frame member forces, and provided data to confirm and calibrate computational models. Computational models were developed based on the experimental behavior and two computational studies were conducted. A single degree-of-freedom study consisting of over 25,000 analyses was performed to investigate system proportioning including defining the amount of restoring force that is necessary to provide reliable self-centering in the presence of ambient building resistance. A multi-degree-of-freedom study consisting of approximately 1500 analyses was performed to investigate the application of the controlled rocking system in different configurations. This study was also used to investigate the probabilities of reaching limit states for earthquake events with varying recurrence period. The experimental and computational studies described in this report demonstrate that the controlled rocking system for steel-framed buildings can satisfy the performance goals of virtually eliminating residual drift and concentrating structural damage in replaceable fuses even during large earthquakes. The results of all phases of this work were synthesized into design recommendations which summarize the practical application of this system to building structures.published or submitted for publicatio