Cast Steel Yielding Brace System for Concentrically Braced Frames: Concept Development and Experimental Validations

The Yielding Brace System is a highly ductile bracing system in which seismic energy is dissipated by the yielding fingers of a specially engineered cast steel connector. When the brace is severely loaded in tension and compression, the fingers yield in flexure, thus providing a full, symmetric hysteresis. Second-order geometric effects result in an increase in postyield stiffness at large displacements. The mechanics of the system are first presented, including several first principle equations used to predict a connector’s response. These equations are then used to design a prototype connector. The geometry of this prototype is evaluated using nonlinear finite element analysis. Following this analysis, the results of full-scale axial component testing of the prototype are discussed. These results include tensile coupon tests from material taken directly from unyielded portions of the test specimens. The prototype design and testing program presented demonstrate that the Yielding Brace System is a ductile connector that can enhance the energy dissipation and displacement capacity of braced frames. Good agreement between predicted and experimental response showed that the mechanics of the connector were well understood and that the method used to design the prototype was effective in meeting the targeted performance.