Design rules, experimental evaluation, and fracture models for high-strength and stainless-steel hourglass shape energy dissipation devices

Steel yielding hysteretic devices provide a reliable way to increase the energy dissipation capacity of structures under seismic loading. Steel cylindrical pins with hourglass shape bending parts (called web hourglass shape pins - WHPs) have been recently used as the energy dissipation system of posttensioned connections for self-centering steel moment-resisting frames. This work evaluates the cyclic behavior of WHPs made of high-strength steel and two grades of stainless steel, i.e., austenitic grade 304 and duplex. Design rules for WHPs are established using principles of mechanics. Twenty-six tests using different cyclic loading protocols and different WHP geometries were conducted. The tests showed that the WHPs have stable hysteretic behavior and high fracture capacity. WHPs made of duplex stainless steel have the most favorable and predictable performance for seismic applications. Two micromechanics-based fracture models, i.e., the void growth model and the stress-modified critical strain model, were calibrated and their parameters are provided for high-strength steel and the two types of stainless steel. The ability of the cyclic void growth model to predict fracture in WHPs under cyclic loading is also evaluated.