Evaluating ultra low cycle fatigue based on ductile fracture model in double core BRBs

Abstract

While lots of efforts have been made to develop accurate numerical models for prediction of ultra-low cycle fatigue (ULCF), it still needs more studies. As it is crucial to exactly define the mechanical behavior of steel for entire range up to failure, this study first examines the required theories and presents a simple single-parameter model to predict the crack initiation. After selecting appropriate behavior models, to ensure the proper performance in numerical solution of the problem, the cyclic performance of steel coupons and two types of buckling restrained braces (BRBs) are validated comparing their local and global behaviors to experimental ones. The double core BRB consisting of two parallel steel cores is then introduced and its cyclic behavior is evaluated. Its advantages include easy connection to gusset plates, increased brace moment of inertia around the weak axis, high stability of connections under local buckling, and low impact of unpredictable defects. Finally, hysteresis curves, energy absorption rate, crack initiation and evolution, and cumulative ductility are discussed in this research.