Effect of damper failure on the seismic loss assessment of retrofitted steel moment-resisting frames

Abstract Metallic yielding damper is widely utilized to improve the seismic resilience of steel moment-resisting frames. It is a kind of displacement-depended damper and may fail when the ultimate displacement is reached under strong earthquakes. Nevertheless, little research has considered the damper failure behavior in seismic loss assessment of damper-retrofitted steel frames. In this paper, three representative buildings, including a 3-story, 9-story and 20-story steel frame, are retrofitted by a high efficient bending-yield metallic damper. The damper is designed based on the stiffness and displacement demands, and able to keep normal working under maximum considered earthquakes. Numerical models of the retrofitted steel frames with and without considering damper failure are then built, and cyclic behavior of the damper element is validated through the experimental results. Subsequently, nonlinear dynamic analysis is performed to evaluate effectiveness of the design procedure, and incremental dynamic analysis (IDA) is conducted to discuss the effect of damper failure on structural seismic fragility. Combing with the obtained seismic fragility curves, the effect of damper failure on the seismic losses of steel moment-resisting frames are quantitatively assessed using a story-based loss estimation methodology. The results show that the employed damper can effectively mitigate dynamic responses of low-, mid- and high-rise frames; the effect of damper failure on IDA curves is significant at relatively large seismic intensity, especially for the high-rise frame; ignoring the damper failure would lead to significant underestimation of collapse and demolition probability; the models without considering damper failure present higher expected total losses, and the damper failure has few effects on the expected annual losses.