Seismic Response of Hybrid Ductile-Rocking Buckling Restrained Braced Frames With Cast Steel Supplemental Energy Dissipation Elements

Abstract eng:
This paper presents numerical results on the seismic response of the design of a hybrid ductile-rocking (HDR) seismic force-resisting system. The HDR system consists of a code-designed buckling-restrained braced (BRB) frame with specially designed column-foundation connections that permit limited base rocking. The intent of the system is to economically improve the performance of BRB frames by reducing large concentrations of drift and damage at a few stories and reducing excessive residual deformations. The HDR system maintains the highly desirable limit on forces and accelerations that are typical of the response of BRB frames, in contrast to controlled rocking (CR) structures, where frame members are designed to remain elastic but can be overloaded by higher mode demands. This paper outlines the basic mechanics of the proposed HDR system and then presents an example design of a 6-storey BRB frame located in Los Angeles. The system is detailed with a column-foundation connection that includes a lockup device that ensures that the codified lateral resistance of the BRB frame can be achieved after the system locks up at a predetermined base rotation. Supplemental energy dissipation elements comprised of ductile cast steel yielding connectors are also included at the base of the structure to provide hysteretic damping to the rocking system. Results indicate that a significant reduction in drift concentrations, residual deformations, and cyclic damage can be achieved with the HDR system when compared to conventional BRB frames, while still controlling storey shear forces and accelerations as effectively as conventional BRB frames with a fixed base. This suggests that the HDR system offers an economical method for enhancing the performance of BRB frame structures.

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