Reshaping structural hysteresis response with semi-active viscous damping

Abstract

Semi-active control devices offer significant promise for their ability to add supplemental damping and reduce seismic structural responses in an easily controllable manner, and can be used to modify or reshape overall structural hysteretic response. This study uses a spectral analysis of semi-active viscous dampers to compare the impact of three methods of re-shaping structural hysteretic dynamics that resist: motion in all 4 quadrants (1–4), motion away from equilibrium (1–3) and motion towards equilibrium (2–4). Performance is assessed by evaluating reduction factors (RFs) from an uncontrolled structure for maximum displacement (Sd) total base-shear (Fb), and maximum acceleration (Sa) which assess performance in mitigating response damage, a risk of foundation damage and contents damage respectively. Spectra are created using 20 design level earthquakes from the medium suite of the SAC project with equal probability of occurrence and structural periods of T = 0.1–0.5 s. The RF spectra results are presented as median (50th) and 5th, 25th, 75th, and 95th percentile RF to define the distribution and change in risk across the 20 events. Statistical summaries of the results indicate that a 2–4 control method reduces the median value of Sd, Fb and Sa by approximately 10–40%, over all periods up to 5.0 s. These results are consistent over the 5–95th percentile range of all responses for a given period. The other control laws (1–3, 1–4) reduce Sd as much or more, but at a cost of increased base-shear (Fb) in comparison to the uncontrolled state. Overall, the reduction in terms of both displacement and base-shear demand is only available with the semi-active 2–4 control method. Finally, analytical expressions for the median displacement reduction factor are presented and compared to current Eurocode standards for comparison. These results indicate the robustness of simple semi-active viscous dampers could be better managed to mitigate response to the structure, foundation and risk.