Forty years have passed since the first modern seismic isolation building was built in Japan. Seismic isolation, considered new structures has also become one-third of the history of earthquake-resistant design in Japan. For some people living today, seismic isolation is a technology that has existed since birth and for some people of my age, it is a technology that has witnessed its development and changes since its early days. In this paper, we look back on the history of seismic isolation in Japan, examine its role, consider the current issues and expect its development.

The widespread use of seismic isolation technology has led to diverse design requirements, including reducing seismic response not only in horizontal directions but also in vertical ones. To mitigate residual risk and improve evaluation, enhancing seismic isolation systems' safety margins and developing advanced analytical models and structural integrity assessment methods is crucial. Confronting Japan's growing human resource shortage, this paper explores the implementation of AI and optimization techniques to address diverse design requirements and refine evaluation methods, contributing to a resilient and sustainable society. The author explores the potential of AI-driven inspection method for quality assurance of isolation or vibration control devices.

This paper evaluated the tensile stress and tensile deformation on the seismic isolation members of the 10-story baseisolated building in collision to the retaining wall. As the results, the maximum tensile stress was about 1.9 N/mm² and the tensile deformation was about 17 mm. When the tensile stress reduction mechanism with low stiffness spring was used, the stress could be reduced by about 2/3, and the lifting displacement was about 22 mm. With the mechanism to bending yield of steel was used, the stress could be controlled within 1.0 N/mm², and the lifting displacement was smaller than the other case.

Re-shear tests have been conducted on the ruptured full-scale lead rubber bearings (LRBs) with a diameter of 1600 mm to confirm residual performance of LRBs. The ruptured specimens and the unruptured ones have been observed on the completely same hysteresis loops of restoring force up to strain of 100%, and the mechanical features of them are approximately similar to one another until shear strain 200%. Moreover, buckling phenomenon, i.e. the sudden vertical subduction, are not observed even after the contact surfaces of the ruptured specimens start to slide. These results suggest that horizontal and vertical resistance performance remains in ruptured bearings to some extent.

Sinusoidal loading test is used to evaluate the performance of devices for seismic isolation and supplemental damper. If a sine wave is input as it is, the velocity and acceleration will be large at the start and end of the loading, resulting in an impact and / or a delay in the loading. Desirable test results may not be obtained. An additional part of input waveform (tapered portion) is often applied to mitigate the above effects; however, that increase the cumulative deformation in the test. From the viewpoint of influence on the specimen and restrictions on the accumulated deformation of the machine, it needs to minimize the cumulative deformation increment due to the tapered portions as much as possible. We investigated the increase in acceleration and cumulative deformation due to the additional tapered portion and proposed a rational setting method. The method is based on constant-acceleration excitation, and the displacement and velocity can be continuous at the connection point. It is shown that this method can reduce the cumulative displacement increment to about 28% compared to the conventional method using a cosine-square type filter.

The difference between the vibration control performance assumed in the structural design and the actual performance is not always minor. In order to predict the seismic response of buildings against future earthquakes more accurately, it is desirable to reduce this difference. In this paper, a dynamic mechanical model identification is performed on a shaking table test for a full-scale five-story steel-frame building with oil dampers, and the accuracy of the response prediction is discussed. As a result, the identified values of the damper characteristics differ from one excitation level to another, and it is not easy to mention in terms of evaluating the damping member's characteristics. However, the applicability is suggested when estimating responses at the floor level. In particular, a significant difference from the initial model (before identification) is confirmed for the maximum story drift, demonstrating that the proposed identification process improves response estimation accuracy.

This paper proposes a cylindrical spring consisting of an inner cylindrical shell, an intermediate cylindrical shell and an outer cylindrical shell as a vertical seismic isolation spring. The inner and outer cylindrical shells are made of steel and are slidably fitted at both ends to form a cylindrical variable volume space. The intermediate cylindrical shell is mainly made of rubber and is stored without any gaps in the cylindrical variable volume space. The basic configuration of the cylindrical spring, the axial strain characteristic equation of the cylindrical spring, a compression volume test of a rubber material, a trial design of a vertical reaction force 15 MN type cylindrical spring, and a compression test of a vertical reaction force 150 kN type prototype are described. The reaction force-deflection curve of the prototype based on the axial strain characteristic equation corresponded well with the reaction force-deflection hysteresis curve obtained in the compression test.

The impact of large earthquakes on super high-rise buildings and seismically isolated buildings are concerned. A response displacement at the isolation layer may exceed the assumed clearance and is difficult to reduce increasing the number of dampers if the long-period pulse observed in the 2016 Kumamoto earthquake were to strike an isolated building. We have developed a fail-safe system for the isolation layer that consists of stoppers and molded rubber shock absorbers. This paper describes the characteristics of molded rubber shock absorber, the results of performance tests of fail-safe system and effect of fail-safe system obtained by response analysis.

The seismic isolation devices with damping performance deteriorates their damping performance when they are repeatedly deformed by long-period earthquake motions. Therefore, there are concerns that the superstructure collide with the retaining wall at the seismic isolation layer may or damage the seismic isolation devices in the event of a huge earthquake that exceeds the design assumption. Increasing the damping of seismic isolation devices is an effective way to cope with huge earthquakes, but excessive damping leads to an increase in acceleration of the superstructure, resulting in a reduces seismic isolation performance. To address this problem, we developed a fail-safe braking device that acts only in the event of a huge earthquake and prevents excessive displacement of the superstructure. Moreover, the effectiveness of the device was confirmed by seismic response analysis.

Authors suggest a magnetically levitated foundation, insulated from the ground by magnets and supported by the displacement control material, for reducing the seismic response of small buildings. In this paper, we used metal components to improve the levitation force and damping characteristics. The static loading test indicated that a steel plate on the magnets increased the levitation force. The electromagnetic field analysis showed that a copper plate between the magnets acted as an eddy-current damper and can be represented by the Maxwell material. In addition, the seismic response of the magnetically levitated foundation was discussed based on the shaking table test and the structural analysis.

Properties of building response and base-isolation devices are evaluated by periodic vibration experiments and earthquake/microtremor observations over nine years from the completion of the building using permanent equipment for vibration experiments and response observations of a base-isolated building. The building is capable of free vibration experiments with an initial displacement of 140 mm using jacks installed in the seismic isolation layer, and forced vibration experiments using moving mass structure installed on the roof. Parameter estimation was conducted considering viscous and friction damping of devices. Direct observation of damping force of oil-dampers show complex characteristics and its variation and variability. Results will lead to evaluate the performance change of seismic isolated buildings after large earthquakes and long-term operation.

It has been pointed out that seismically isolated buildings (SIBs) have low redundancy, which causes damage to develop rapidly when the response of the superstructure reaches a certain limit, and the importance of safety margin evaluation and assurance is increasing with the recent increase in earthquake ground motion levels. In this paper, the safety margin of SIBs is probabilistically evaluated by incremental dynamic analysis. The poor redundancy of the SIBs' superstructure is also considered the relationship between the D_s value and the ductility factor, and a formulation is attempted. Using this relationship, a simplified evaluation of the safety margin of SIBs is performed and compared with the probabilistic evaluation. Furthermore, based on the comparison with seismic resistant structures, we present a new concept of safety margin evaluation for SIBs and propose a design Method to secure the safety margin.

The number of dampers in isolation layer is determined based on required number for earthquakes or winds. In recent years, the target wind load have increased because the scale of building become taller and larger and the amount of damper required against winds is increasing. However, too many dampers in place to cope with large wind load, the isolation layer will not sufficiently during earthquakes. We develop a wind resistance lock mechanism that can lock the isolation layer displacement during winds in assumed range. The lock mechanism makes it possible to determine the number of dampers in isolation layer based on optimal value for earthquakes.

The experience of recent massive earthquakes and the damage they have caused have prompted conceptual studies for realizing resilient cities in order to achieve a higher level of safety. While levitation systems have been developed for horizontal seismic isolation that can provide high performance, improvements are needed for vertical seismic isolation. Although many performance verification tests have been conducted in the development of vertical seismic isolation systems, few studies have quantitatively demonstrated the required performance. This paper analyzes the seismic response of levitation base isolation systems based on the characteristics of observed vertical seismic motions, clarifies the required performance of vertical base isolation, quantitatively shows the effects of weight eccentricity and tower ratio on the response, and proposes a threshold value where the response increase is negligible. It also clarifies the tendency for the rocking response to become smaller with horizontal long periodization.

Many of ground motions observed in recent years not only have large acceleration amplitudes, but also often include long-period and pulse-like components. Although isolated buildings have high seismic performance against various ground motions, the responses to pulse-like ground motions can be large. The pulse-like ground motions are characterized by making the isolated buildings large deformation in one direction, and it is important to grasp a predominant response direction for design. In this paper, we study an effect of response reduction when buffer materials are installed in the predominant response direction of the pulse-like ground motions. Additionally, we propose a comprehensive response evaluation method for multiple observed ground motions in order to obtain effective design parameters of the buffer materials for multiple pulse-like ground motions.

The application of semi-active control is expected to reduce the response displacement of the isolation layer effectively without increasing the floor response acceleration of the superstructure. For this study, the real-time hybrid simulation (RTHS) of a semi-active base-isolation system installed with a magnetorheological fluid damper (MR damper) is conducted to verify the effectiveness of semi-active control, and the response reduction effects using semi-active control systems are evaluated by the damping factor based on the ARX model. The results of RTHS indicated that semi-active control exhibited high acceleration reduction effects, and the damping factor based on the ARX model enabled the evaluation of differences in control effects among several control algorithms.

Sliding base (SB) structures are attracting attention as one of the means of improving the seismic performance of detached houses, which is a seismic isolation technology that can be introduced relatively low cost. In the seismic safety evaluation of SB structures, it is necessary to design the friction coefficient of the sliding surface appropriately. It has been pointed out that the friction coefficient depends on the increase and decrease of surface pressure due to rocking of the building and the variation of sliding speed. However, the effect of these dependencies on response of the building is unclear. In this study, we conducted simulation analyses with and without each dependency, targeting the shaking table test of a full-scale two-story wooden building applied to the SB structure. Based on these analyses, the effects of each dependence on the response of the sliding foundation are discussed.

In recent years, earthquakes have frequently occurred in Japan, and the occurrence of events such as the Nankai Trough earthquake and near-field earthquakes is predicted. Traditional seismic isolation systems are effective in reducing damage to buildings, but they are insufficient to prevent infrastructure shutdowns, such as urban gas and elevators, which typically occur at seismic intensities of 4 or lower. To reduce the impact of strong earthquakes to a seismic intensity of 4 or less on a seismic isolation device, we are currently considering a passive 3D seismic isolation system. This system uses fluid levitation for horizontal isolation and a parallel link mechanism with hydraulic cylinders for vertical isolation. In this report, based on prior knowledge of horizontal isolation, we developed a mock-up to determine the required performance of vertical isolation, aiming to reduce vertical acceleration by one-third. Excitations were conducted using random waves and observed seismic waves. The results showed that the vertical isolation behaved as a friction-type mechanism, without resonance, and successfully reduced acceleration by one-fourth. It was confirmed that by combining this with the fluid levitation-type horizontal isolation system, it is possible to reduce the impact of strong earthquakes to a seismic intensity of 4 or less.

One of the technologies to suppress seismic responses in super high-rise or mid-to-high-rise buildings with a high aspect ratio is building mass dampers (BMDs). BMDs have a connecting layer with low horizontal stiffness located at a relatively high position of the building, where the upper part of the building acts as a tuned mass damper (TMD). BMDs that utilize a part of the building as a mass damper have an increased mass ratio. We verify the seismic response reduction effect of the BMD vibration control structure through numerical analysis and shaking table test using a six-story test model.