Spectral Analysis of Customized 2-4 Viscous Damping for Mitigating Seismic Response

Abstract eng:
Many current active and semi-active supplemental damping devices are highly complex, limiting robustness, and those that can generate larger response forces typically suffer from increased response lag time. Thus, an ideal device would offer high forces, low complexity, and fast response time. A 2-4 viscous damper device provides damping in the second and forth quadrants of the force-displacement plot, resisting only motion from a displacement peak back toward the zerodisplacement position. The 2-4 viscous dampers offers significant promise for their ability to mitigate not only displacement, but also the base shear. This paper provides design spectra analysis that quantifies the risk of exceedance of an uncontrolled structure for displacement and base shear response. Spectral analysis results are compared to the uncontrolled case and to a standard, passive viscous damping case for context. In particular, performance is assessed by evaluating reduction factors (RFs) compared to an uncontrolled structure for maximum displacement (S d) and total baseshear (Vb) indicative of structural and foundation demand respectively. RF spectra results are presented as median percentile RF to define the distribution and change in risk across the 60 events. Statistical summaries of the results indicate that the 2-4 viscous damper reduces the median value of Sd and Vb by ~10- 40%, over all periods up to 5.0 seconds. There is thus no risk of exceedance greater than 5% that any response will increase over the uncontrolled case. In contrast, a conventional linear viscous damper reduces Sd as much or more, but at a cost of increased V b in comparison to the uncontrolled state. These results show that the reduction in terms of both displacement and base-shear is only available with the use of the 2-4 viscous damper device. Damping reduction factors play an important role in most design procedures. In this study, a method to calculate the damping reduction factor of response for structures using the 2-4 viscous devices with different device damping coefficients is presented. The overall results indicate the robustness of potentially very simple and robust 2-4 viscous dampers to mitigate the risk of seismic damage to all the structure and foundation in a way that is economically suitable for either new designs or retrofit.

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