EXPERIMENTAL EVALUATION OF THE ULTRA-LOW CYCLE FATIGUE LIFE OF CAST STEEL YIELDING FUSES

Several cast steel hysteretic yielding dampers have been proposed for seismic applications in recent years. This is primarily due to the advantages offered by steel casting technology such as freedom of geometry, reduction of stress concentration, elimination of weld defects, strict heat treatments and fabrication quality control processes. Most recently, cast steel replaceable yielding links were proposed for use in eccentrically braced frames (EBFs), which not only improve the performance of EBFs, but also simplify their design process, construction, and post-earthquake repairs. This paper provides an overview of an experimental program focused on evaluating the remaining ultra-low cycle fatigue (ULCF) life of cast steel yielding components, after having sustained maximum credible event (MCE) level earthquakes. A brief background on cast steel yielding links and cast steel yielding connectors is first provided, and their mechanics are presented. The experimental program consists of large-scale component-and system-level reversed cyclic tests, and large-scale hybrid simulations. Selected test results on cast steel yielding links and cast steel yielding connectors from the experimental program are presented, with attention to their ULCF life. Overall, the results demonstrate significant ductility capacity and ULCF life for cast steel yielding components. Even though the cast steel yielding fuses had sustained deformation histories associated with three back-to-back MCE-level earthquakes, they were able to sustain the qualification loading protocols.