Reshaping structural hysteresis response with semi-active viscous damping

Abstract

emi-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. © 2016, Springer Science+Business Media Dordrecht

Earthquake Protection of Existing Structures with Limited Seismic Joint: Base Isolation with Supplemental Damping versus Rotational Inertia

“…Additionally, the class of socalled semi-active devices, having variable effective stiffness and/or variable effective damping, provides supplemental damping while keeping the overall base shear limited. In this context, resettable stiffness devices using electrorheological and magnetorheological materials have been increasingly developed [65][66][67] and studied in large-scale experimental validations in an attempt to optimize damping and minimize response by effectively reshaping and customizing the hysteretic loops (see, e.g., [68][69][70][71]). e nonlinearity of these models, including valve size, mass flow rate, and friction, has been investigated in experiments and numerical models [72].…”

Seismic Behavior of a Self-Centering System with 2–4 Viscous Damper

“…Spectral analysis shows typical viscous dampers increase the base shear of long period linear structures, typically greater than 2.7 sec [Hazaveh et al, 2016b]. However, adding a 2-4 viscous damper decreases base shear and displacement for all periods [Hazaveh et al, 2015, Hazaveh et al, 2016b, Mulligan et al, 2009, Rodgers et al, 2007. The 2-4 device also has the potential benefit that it does not provide added forces during uplift, which can help to limit the total compression force applied to the toe of the wall during uplift, potentially reducing toe crushing during uplift of reinforced concrete rocking walls, while damping the return motion and re-seating of the wall.…”

“…Thus, on the basis of a traditional performance-based seismic design and retrofit philosophy, designers are challenged by the difficult tradeoff between costs and acceptable damage (or targeted performance). To address these issues, Hazaveh et al [Hazaveh et al, 2016a, Hazaveh et al, 2016b, Hazaveh et al, 2015 introduced and examined two types of viscous dampers. Based on semi-active resettable stiffness devices [Mulligan et al, 2009, Rodgers et al, 2007 a 1-3 viscous damper provides resisting forces only in the first and third quadrants of the force-displacement plot.…”

Damping reduction factors and code‐based design equation for structures using semi‐active viscous dampers

“…Hazaveh et al evaluated the concept of semi‐active viscous dampers and examined three types of device control laws (a 1–4, 1–3 and 2–4) to sculpt hysteretic behavior. Three control laws control the opening and closing time of orifices of the proposed semi‐active device to achieve three different hysteresis loops.…”

“…Therefore, the only difference between these passive devices and semi‐active viscous dampers is the ability to modify the orifice, and hence dynamically change the damping behavior within a response cycle. Hazaveh et al clarified the effect of three types of semi‐active viscous damper that could add a nominal 15% supplemental damping to the structure but did not consider the effect of different damping of the semi‐active viscous device.…”