Development, Validation, and Modeling of the New Cast Steel Yielding Brace System

The cast steel Yielding Brace System (YBS) is a new device for enhanced seismic performance of concentrically braced frames that is characterized by its full, symmetric stable and repeatable hysteretic response and its large ductility capacity. The YBS system is comprised of two specially designed cast steel connectors that are welded to one end of each diagonal brace in a building's lateral force resisting system. The axial force in the brace is transferred to the lower beam-column joint through triangular-shaped flexural yielding fingers. In order to develop the YBS concept and successfully design and test a full-scale prototype several small scale tests were conducted on specimens similar to the yielding fingers of the YBS. The result of this test series was an experimentally validated low-cycle fatigue prediction model using the Coffin-Manson relationship and Minor's rule. This prediction model was used to design a full-scale YBS prototype with a nominal brace yield load of 250 kips (1110kN). The prototype was full-scale tested in a frame to simulate actual in-situ boundary conditions with a pseudo-dynamic test protocol derived from Appendix T of AISC 341. In addition, a non-linear cyclic model was developed to predicted the cyclic response of the YBS and enable the modeling of an entire building equipped with this device. This model was validated through comparison with the full-scale prototype tests.