Tohoku University · Engineering
Professor Kohju Ikago's research lab specializes in seismic protection of civil structures, with a primary focus on innovative vibration control systems for low-frequency buildings. The lab develops advanced passive and semi-active control devices such as the tuned viscous mass damper (TVMD), which leverages mechanical components like ball-screw mechanisms and inerters to enhance energy dissipation. A key research direction involves optimizing damping systems—particularly rate-independent linear damping (RILD)—to effectively mitigate excessive displacements during strong earthquakes. The lab also emphasizes practical design methodologies for multi-degree-of-freedom structures, integrating dynamic analysis with numerical optimization.
Figures are computed from collected data and may differ slightly.
SUMMARY In this study, we propose a new seismic control device, tuned viscous mass damper (TVMD), for building systems. We give a detailed description of an apparent mass amplifier using a ball‐screw mechanism, which is one of the most important components for realizing the new device. We also derive a closed‐form solution of an optimum seismic control design for a single‐degree‐of‐freedom structure subjected to harmonic excitation. The performance of the new device is compared with those of the
A new seismic control device using a ball screw mechanism as an apparent mass amplifier has been developed, which is referred to as the tuned viscous mass damper (TVMD). This device enables effective seismic control using a tuned mass. For a multiple-degree-of-freedom (MDOF) seismic control system incorporated with the TVMD, a design method based on numerical optimization has been previously presented by the authors. However, simpler design methods that are suitable for a practical design have n
This study examines the performance of rate-independent linear damping incorporated into a low-frequency structure subjected to strong ground motion. Linear viscous damping and rate-independent linear damping are known to yield similar response displacements and velocities during earthquakes. If the central response frequency is close to the fundamental frequency of the structure, the two linear damping elements yield almost identical damping forces. However, if the two frequencies differ signif
Abstract Rate‐independent linear damping (RILD), which is also known as structural damping or hysteretic damping, refers to a type of damping having a constant imaginary part in its complex stiffness that generates damping forces independent of the excitation frequency. In contrast, linear viscous damping (LVD) is another type of damping with a frequency‐proportional imaginary part in its complex stiffness, resulting in damping forces proportional to frequency. RILD demonstrates similar performa
Abstract Connecting a flexible supporting element to an inerter arranged in parallel with a viscous element yields a tuned‐mass damper‐like system, designated as a tuned viscous mass damper (TVMD). The advantage of a TVMD is that it exploits the flexibility of the supporting member, which is usually considered to compromise the energy‐dissipating performance, and the inerter and soft spring form a supplemental oscillator to enhance the damping performance with resonance to the primary structure.
The past two decades have witnessed the adverse effects of low-frequency components of severe earthquakes in low-frequency structures. The development of displacement control technologies for the seismic protection of low-frequency structures has been identified as a growing challenge in earthquake engineering. Related studies have suggested that rate-independent linear damping (RILD) could be a viable option for reducing excessive displacements in low-frequency structures. However, previous stu
In the 2011 Great East Japan Earthquake, low-frequency components of ground motion brought long-duration shaking to high-rise buildings in mega-cities far from the epicenter, resulting in damage to their interior and exterior walls, and unsafe conditions for the building occupants. Rate-independent linear damping (RILD) has been suggested as a viable option for simultaneously reducing the excessive displacement and floor response acceleration of a low-frequency structure. While the majority of p
The first two decades of the 21st century witnessed adverse effects induced by low-frequency components of severe earthquakes in low-frequency structures. In the 2011 Great East Japan Earthquake, it was reported that many high-rise buildings suffered long-duration vibration with excessive displacements, resulting in damaged interior and exterior walls. Thus, the development of displacement control technologies for the seismic protection of low-frequency structures has been identified as a growin
Damage to nonstructural components or excessive displacements in low-frequency structures caused by recent major earthquakes, such as the 2011 Great East Japan Earthquake, highlighted the need to protect these structures against earthquake-induced damage. Rate-independent linear damping (RILD) has been found to be a viable option for reducing the excessive displacement of low-frequency structures because its control force is larger in the low-frequency region than that of conventional damping el
When rate-independent linear damping (RILD) is incorporated into a base-isolated structure, it achieves a similar response displacement reduction effect with significantly lower floor response acceleration compared with linear viscous damping (LVD) with the same loss factor. To address the undesirable stiffness added to an isolation layer when we adopt a mechanical device comprising a few branches of a spring–dashpot link to realize RILD, this study proposes canceling the undesirable isolator st
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