Seismic Design and Behavior of Self-Centering Braced Frame with Controlled Rocking and Energy Dissipating Fuses

This research aims to develop a self-centering controlled rocking structural system for earthquake resistant buildings that provides significantly improved performance through reduction in structural damage, repair costs, and downtime of buildings subjected to severe earthquakes. The controlled rocking system primarily consists of a post-tensioned steel braced frame that is designed to rock upon its foundation during an earthquake, elastic post-tensioning strands to provide overturning resistance and self-centering action, and replaceable structural fuses to dissipate earthquake energy. The system can minimize earthquake-induced damage and facilitate quick and economical post-earthquake repairs through its self-centering capability and concentration of inelastic deformation in the replaceable fuses.

Steel shear plates with butterfly-shaped links are employed as structural fuses, and their ductile performance was verified by quasi-static cyclic tests. A two-thirds scale shaking table test of a three-story rocking system was conducted at the E-Defense facility in Japan. Test results demonstrated that the system responds predictably to earthquake excitation with column uplifting and frame rigid-body rotation. Under input motions scaled to the level of the Maximum Considered Earthquake, the resulting roof drift ratio stayed below the implied building code limit of 3%, and the braced frame completely self-centered without any damage. Effectiveness of key design details and behavior of the major structural components are examined, and a numerical model is validated through comparison with the test results.

Analytical case studies are conducted and a general design procedure is proposed, which is compatible with current building code approaches. Simple methods are formulated to predict the earthquake-induced rocking frame drifts and member force demands. The proposed methods are validated through nonlinear dynamic analyses of various case buildings subjected to a set of 22 earthquake ground motions.