The cast steel Yielding Brace System (YBS) is a new hysteretic damper that was developed at the University of Toronto to enhance the seismic performance of braced frames. In this system, a ductile, cast steel connector dissipates seismic energy through inelastic, flexural yielding of specially designed, triangular fingers. The cyclic, plastic bending of the yielding fingers replaces the tensile yielding and inelastic buckling of traditional ductile braces. This provides a symmetrical hysteresis with increased energy dissipation.
This paper first presents the development stages of the new cast steel YBS system with an overview of the cast steel material characterization tests and prototype component tests. Results are then presented from a test pro- gram in which two prototype YBS-brace assemblies were tested in a full-scale braced frame that simulates the in-situ boundary conditions that would be present in a steel-braced frame that employed the YBS as its primary lateral force-resisting system.
The prototypes were designed for the second floor of a six-story sample structure. The prototypes were subjected to displacement protocols that consisted of large, inelastic, quasi-static, and pseudo-dynamic cycles up to three times the design level brace elongation as calculated in the sample building design. The system exhibited a high initial stiffness, excellent ductility capacity with a very stable hysteretic response, and a desirable large deformation stiffening effect. As such, the YBS represents a viable new alternative to existing yielding brace systems.