• Smart Structures and Systems
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• v.8 no.5
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• pp.501-524
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• 2011

Recent studies have discovered that a conventional passive isolation system may suffer from an excessive isolator displacement when subjected to a near-fault earthquake that usually has a long-period velocity pulse waveform. Semi-active isolation using variable friction dampers (VFD), which requires a suitable control law, may provide a solution to this problem. To control the VFD in a semi-active isolation system more efficiently, this paper investigates experimentally the possible use of a control law whose control logic is similar to that of the anti-lock braking systems (ABS) widely used in the automobile industry. This ABS-type controller has the advantages of being simple and easily implemented, because it only requires the measurement of the isolation-layer velocity and does not require system modeling for gain design. Most importantly, it does not interfere with the isolation period, which usually decides the isolation efficiency. In order to verify its feasibility and effectiveness, the ABS-type controller was implemented on a variable-friction isolation system whose slip force is regulated by an embedded piezoelectric actuator, and a seismic simulation test was conducted for this isolation system. The experimental results demonstrate that, as compared to a passive isolation system with various levels of added damping, the semi-active isolation system using the ABS-type controller has the better overall performance when both the far-field and the near-fault earthquakes with different PGA levels are considered.

• Earthquakes and Structures
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• v.15 no.2
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• pp.133-144
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• 2018

To study the effectiveness of sliding isolation in a CRLSS (concrete rectangular liquid-storage structure) and develop a reasonable limiting-device method, dynamic responses of non-isolation, sliding isolation with spring limiting-devices and sliding isolation with steel bar limiting-devices are comparatively studied by shaking table test. The seismic response reduction advantage of sliding isolation for concrete liquid-storage structures is discussed, and the effect of the limiting-device type on system dynamic responses is analyzed. The results show that the dynamic responses of sliding isolation CRLSS with steel bar-limiting devices are significantly smaller than that of sliding isolation CRLSS with spring-limiting devices. The structure acceleration and liquid sloshing wave height are greatly influenced by spring-limiting devices. The acceleration of the structure in this case is close to or greater than that of a non-isolated structure. Liquid sloshing shows stronger nonlinear characteristics. On the other hand, sliding isolation with steel bar-limiting devices has a good control effect on the structural dynamic response and the liquid sloshing height simultaneously. Thus, a limiting device is an important factor affecting the seismic response reduction effect of sliding isolation. To take full advantage of sliding isolation in a concrete liquid-storage structure, a reasonable design of the limiting device is particularly important.

• Smart Structures and Systems
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• v.26 no.2
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• pp.195-211
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• 2020

Among anti-seismic technologies, base isolation is a very effective means of mitigating damage to structural and nonstructural components, such as equipment. However, most seismic isolation systems are designed for mitigating only horizontal seismic responses because the realization of a vertical isolation system (VIS) is difficult. The difficulty is primarily due to conflicting isolation stiffness demands in the static and dynamic states for a VIS, which requires sufficient rigidity to support the self-weight of the isolated object in the static state, but sufficient flexibility to lengthen the isolation period and uncouple the ground motion in the dynamic state. To overcome this problem, a semi-active VIS, called the piezoelectric inertia-type vertical isolation system (PIVIS), is proposed in this study. PIVIS is composed of a piezoelectric friction damper (PFD) and a leverage mechanism with a counterweight. The counterweight provides an uplifting force in the static state and an extra inertial force in the dynamic state; therefore, the effective vertical stiffness of PIVIS is higher in the static state and lower in the dynamic state. The PFD provides a controllable friction force for PIVIS to further prevent its excessive displacement. For experimental verification, a shaking table test was conducted on a prototype PIVIS controlled by a simple controller. The experimental results well agree with the theoretical results. To further investigate the isolation performance of PIVIS, the seismic responses of PIVIS were simulated numerically by considering 14 vertical ground motions with different characteristics. The responses of PIVIS were compared with those of a traditional VIS and a passive system (PIVIS without control). The numerical results demonstrate that compared with the traditional and passive systems, PIVIS can effectively suppress isolation displacement in all kinds of earthquake with various peak ground accelerations and frequency content while maintaining its isolation efficiency. The proposed system is particularly effective for near-fault earthquakes with long-period components, for which it prevents resonant-like motion.

• Journal of The Korea Institute of Healthcare Architecture
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• v.22 no.4
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• pp.79-86
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• 2016

Purpose: The purpose of this study is to identify the effect of Progressive Space Organization (ante-rooms) in Negative Pressured Isolation Unit(NPIU) such as National and Regional Isolation Units in Korea in order to build basic data for the evidence based design of Airborne Infection Isolation Units which should prepare and respond effectively to the public health crisis due to the hazardous airborne infectious disease. Methods: 1) Gas(SF6) test and analysis on the 23 Korean Isolation Units under operation. 2) Assessment of the isolation level of the space components by checking the Gas concentration. 3) Analysis of the Isolation Effectiveness according to Space Organizational levels. Results: 1) The higher segregation level is, the lower Gas(SF6) concentration is. 2) Too many segregations(anterooms) of Isolation Unit are not efficient for the prevention of infectious bacillus spread. For example, 4 level of segregation has similar segregation effect to the 3 level of segregation. Implications: Many anterooms in front of the isolated patient bedroom will guarantee the safe environment against the danger of hazardous airborne nosocomial infection. On the other hand, too many segregations is inefficient, expensive, inconvenient, narrow(unflexible) and so on. This study can be used as basic data for further development of design guidelines of isolation units.

• Journal of Korean Association for Spatial Structures
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• v.18 no.4
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• pp.81-88
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• 2018

Seismic isolation systems have typically been used in the form of base seams in mid-rise and low-rise buildings. In the case of high-rise buildings, it is difficult to apply the base isolation. In this study, the seismic response was analyzed by changing the installation position of the seismic isolation device in 3D high - rise model. To do this, we used 30-story and 40-story 3D buildings as example structures. Historic earthquakes such as Mexico (1985), Northridge (1994) and Rome Frieta (1989) were applied as earthquake loads. The installation position of the isolation device was changed from floor to floor to floor. The maximum deformation of the seismic isolation system was analyzed and the maximum interlaminar strain and maximum absolute acceleration were analyzed by comparing the LB model with seismic isolation device and the Fixed model, which is the base model without seismic isolation device. If an isolation device is installed on the lower layer, it is most effective in response reduction, but since the structure may become unstable, it is effective to apply it to an effective high-level part. Therefore, engineers must consider both structural efficiency and safety when designing a mid-level isolation system for high-rise buildings.

• Smart Structures and Systems
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• v.18 no.2
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• pp.293-315
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• 2016

Seismic isolation is often used in protecting mission-critical structures including hospitals, data centers, telecommunication buildings, etc. Such structures typically house vibration-sensitive equipment which has to provide continued service but may fail in case sustained accelerations during earthquakes exceed threshold limit values. Thus, peak floor acceleration is one of the two main parameters that control the design of such structures while the other one is peak base displacement since the overall safety of the structure depends on the safety of the isolation system. And in case peak base displacement exceeds the design base displacement during an earthquake, rupture and/or buckling of isolators as well as bumping against stops around the seismic gap may occur. Therefore, obtaining accurate peak floor accelerations and peak base displacement is vital. However, although nominal design values for isolation system and superstructure parameters are calculated in order to meet target peak design base displacement and peak floor accelerations, their actual values may potentially deviate from these nominal design values. In this study, the sensitivity of the seismic performance of structures equipped with linear and nonlinear seismic isolation systems to the aforementioned potential deviations is assessed in the context of a benchmark shear building under different earthquake records with near-fault and far-fault characteristics. The results put forth the degree of sensitivity of peak top floor acceleration and peak base displacement to superstructure parameters including mass, stiffness, and damping and isolation system parameters including stiffness, damping, yield strength, yield displacement, and post-yield to pre-yield stiffness ratio.

• Journal of Korean Association for Spatial Structures
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• v.19 no.2
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• pp.109-116
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• 2019

In this study, the seismic response is investigated by using a relatively low-rise building under torsion-prone conditions and three seismic loads with change of the location of the seismic isolation system. LRB (Lead Rubber Bearing) was used for the seismic isolator applied to the analytical model. Fixed model without seismic isolation system was set as a basic model and LB models using seismic isolation system were compared. The maximum story drift ratio and the maximum torsional angle were evaluated by using the position of the seismic layer as a variable. It was confirmed that the isolation device is effective for torsional control of planar irregular structures. Also, it was shown that the applicability of the mid-story seismic isolation system. Numerical analyses results presented that an isolator installed in the lower layer provided good control performance for the maximum story drift ratio and the maximum torsional angle simultaneously.

• Nuclear Engineering and Technology
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• v.50 no.8
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• pp.1387-1401
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• 2018

An aircraft impact (AI) on a nuclear power plant (NPP) is considered to be a beyond-design-basis event that draws considerable attention in the nuclear field. As some NPPs have already adopted the seismic isolation technology, and there are relevant standards to guide the application of this technology in future NPPs, a new challenge is that nuclear power engineers have to determine a reasonable method for performing AI analysis of base-isolated NPPs. Hence, dynamic influences of the seismic isolation on the vibration and structural damage characteristics of the base-isolated CPR1000 containment are studied under various aircraft loads. Unlike the seismic case, the impact energy of AI is directly impacting on the superstructure. Under the coupled influence of the seismic isolation and the various AI load, the flexible isolation layer weakens the constraint function of the foundation on the superstructure, the results show that the seismic isolation bearings will produce a large horizontal deformation if the AI load is large enough, the acceleration response at the base-mat will also be significantly affected by the different horizontal stiffness of the isolation bearing. These concerns require consideration during the design of the seismic isolation system.

• Journal of the Korean Society of Safety
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• v.37 no.3
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• pp.45-51
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• 2022

This paper focuses on a recently proposed asymmetric base-isolation coupling control system (ABiCS) for the vibration control of adjacent twin buildings. The ABiCS consists of inter-story diagonal dampers, a connecting damper between the two buildings, and a seismic isolation device at the base floor of one building. To investigate the control characteristics of ABiCS, a parametric study was performed by numerically simulating the 20-story twin buildings. In the parametric study, the control capacities of the inter-story diagonal dampers, connecting damper, and seismic isolation device were considered as varying parameters. The parametric study results indicate that the connecting damper between the two buildings reduces the responses of both buildings only at optimal or near-optimal capacity. In addition, adjusting the stiffness of the base isolation is found to be the most effective method for improving seismic performance and achieving cost-effectiveness. Accordingly, we presented a scenario-based performance improvement approach in which reducing the stiffness of the base isolation device could be an effective technique to improve the seismic performance of both buildings. However, note that checking the maximum allowable displacement of the base isolation device is essential.

• Structural Engineering and Mechanics
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• v.88 no.3
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• pp.263-271
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• 2023

Base isolation is a widely used technique for the seismic control of structures as it reduces the structural seismic demand. However, displacement of the isolation layer is not economically feasible in congested urban areas. To resolve the issue, an innovative system is proposed here to isolate both horizontally at the base and vertically in the upper portion of the structure. A simplified linear three degree-of-freedom (3DOF) model of the system that considers the mass and stiffness ratios of the substructure has been introduced and analyzed in MATLAB by spectrum analysis. The 3DOF model results revealed that, when the period of the soft substructure reaches 2.5 times that of the stiff substructure, the isolation and the lower substructure responses decrease by 65% and 51%, respectively. Time-history analysis of a MDOF system at three frequency ratios under a wide range of ground motions indicated that, at the expense of accepting a certain large drift by the soft substructure in the upper portion of the structure, base isolation displacement can be decreased by 10%.