• Earthquakes and Structures
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• v.16 no.4
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• pp.401-413
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• 2019

The concept of base isolation for equipment is well known. Its application in buildings and structures is rather challenging. Introduction of horizontal flexibility at the base helps in proper energy dissipation at the base level thus reducing the seismic demand of the super structure to be considered during design. The present study shows the results of a series of numerical simulation studies on seismic responses of secondary system (SS) housed in non-isolated and base-isolated primary structures (PS) including equipment-structure interactions. For this study the primary structure consists of two similar single bay three-store reinforced cement concrete (RCC) Frame building, one non-isolated with conventional foundation and another base isolated with Lead plug bearings (LPB) constructed at IIT Guwahati, while the secondary system is modeled as a steel frame. Time period of the base isolated building is higher than the fixed building. Due to the presence of isolator, Acceleration response is significantly reduced in both (X and Y) direction of Building. It have been found that when compared to fixed base building, the base isolated building gives better performance in high seismic prone areas.

• Earthquakes and Structures
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• v.25 no.6
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• pp.399-415
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• 2023

In this study, we investigate the use of a negative stiffness tuned inerter damper system to improve the performance of a base-isolated structure. The negative stiffness tuned inerter damper system consists of a tuned inerter damper connected in parallel with a negative stiffness element. To find the optimal parameters for the base-isolated structure with negative stiffness tuned inerter damper system, we develop an optimization method based on performance criteria. The objective of the optimization is to minimize the superstructure acceleration response ratio, while ensuring that the base displacement response ratio remains below a specified target value. We evaluate the proposed method by conducting numerical analyses on an eight-story building. The structure is modeled using both a simplified 3-degree-of-freedom system and a more detailed story-by-story shear-beam model. Lastly, a comparative analysis using time history analysis is performed to compare the performance of the base-isolated structure with negative stiffness tuned inerter damper system with that of the base-isolated structure and base-isolated structure with tuned inerter damper systems. The results obtained from the comparative analysis show that the negative stiffness tuned inerter damper system outperforms the tuned inerter damper system in reducing the dynamic seismic response of the base-isolated structure. Overall, this study demonstrates that the negative stiffness tuned inerter damper system can effectively enhance the performance of base-isolated structures, providing improved seismic response reduction compared to other systems.

• Structural Engineering and Mechanics
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• v.43 no.4
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• pp.527-543
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• 2012

This paper presents a response spectrum analysis procedure suitable for base isolated regular buildings subjected to near fault ground motions. This procedure is based on the fact that the isolation system may be treated separately since the superstructure behaves as a rigid body on well selected isolation systems. The base isolated building is decomposed into several single-degree of freedom systems, the first one having the total weight of the building is isolated while the remainder when superposed they replicate approximately the behavior of the superstructure. The response of the isolation system is governed by a response spectrum generated for a single isolated mass. The concept of the procedure and its application for the analysis of base isolated structures is illustrated with an example. The present analysis procedure is shown to be accurate enough for the preliminary design and overcomes the limits of applicability of the conventional linear response spectrum analysis.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.35 no.7
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• pp.165-170
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• 2019

The structural damage caused by earthquake to the upper structure of seismic base-isolated system can be suppressed effectively because it is designed to concentrate the input energy on the seismic isolation floor. Further, the response acceleration of seismic base-isolated system can be greatly reduced compared to the seismic structure because of the long period, which means that the design shear force of the seismic base-isolated system can be reduced appropriately. However, when the design shear force is determined to be reduced, the design stiffness will decrease, and the response acceleration will increase oppositely. Therefore, for finding the extent to which the design shear force of the upper structure can be reduced, this paper considered the seismic base-isolated structure as the analytical model and proposed the design shear force reduction factor of the base-isolated structure through the dynamic response analysis, while considering the decrement effect of response acceleration. The research result shows that the response acceleration of the isolated the upper structure can be reduced by 50%~70% of the seismic structure under the same design conditions, and the design shear force can be reduced by up to 40%. By increasing the design stiffness over to 1.8 times of the original design value, the design shear force can be reduced to the same extent as the response acceleration can be reduced compared to the seismic structure.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2001.09a
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• pp.331-338
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• 2001

Seismic performances of the base isolated model of Five Story Stone Pagoda were studied through shaking table tests. Friction pendulum system (FPS), Pure-friction system with laminated rubber bearing (LRB) and Ball with rubber bearing were selected fur the comparison of performances. Performances of specially designed isolation systems were tested dynamically using shaking table. The test results of isolated model are compared with those of fixed base model. Compared with fixed base model, the isolated model showed that it could withstand much higer intensity of earthquake motion. The Effective Peak Ground Acceleration (EPGA) value of isolated model when the top component tipped over was above twice of that value in case of fixed base model. According to the additional test results, the lower value of coefficient of friction than that of common frictional base isolation systems is more effective to protect the piled multi-block system of Pagoda against moderate intesity of ground motion.

• Earthquakes and Structures
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• v.5 no.4
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• pp.461-475
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• 2013

A new experimental system of base-isolated structures is proposed. There are two kinds of dampers usually used in the base-isolated buildings, one is a viscous-type damper and the other is an elastic-plastic hysteretic-type damper. The base-isolated structure with a viscous damper and that with an elastic-plastic hysteretic damper are compared in this paper. The viscous damper is modeled by a mini piston and the elastic-plastic hysteretic damper is modeled by a low yield-point steel. The capacity of both dampers is determined so that the dissipated energies are equivalent at a specified deformation. When the capacity of both dampers is determined according to this criterion, it is shown that the response of the base-isolated structure with the elastic-plastic hysteretic damper is larger than that with the viscous damper. This characteristic is demonstrated through the comparison of the bound of the aspect ratio. It is shown that the bound of aspect ratio for the base-isolated structure with the elastic-plastic hysteretic damper is generally smaller than that with the viscous damper. When the base-isolated structure is subjected to long-duration input, the mechanical property of the elastic-plastic hysteretic damper deteriorates and the response of the base-isolated structure including that damper becomes larger than that with the viscous damper. The effect of this change of material properties on the response of the base-isolated structure is also investigated.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11a
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• pp.247-251
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• 2001

Nowadays, base isolation systems such as lead-rubber bearing, elastomer bearing and sliding bearing have been installed to the various structures to prevent the disaster from seismic. The performance of base isolation system have been well proved by model-scale experiments and numerical analysis. However. the seismic response data measured at real large base-isolated structures is still insufficient. This paper presents a seismic monitoring system, acquiring real-time acceleration signals up to 32 channels, displaying time history and spectrum of the signals, storing the acquired data at a PC hard disk, and replaying the saved data. Moreover, the system can be operated without any limitation for monitoring period by automatic management of stored data file. The developed system has been installed at a real base-isolated building using lead-rubber bearings and we expect its seismic response data with ground motion signal can be well licquired in case of earthquake occurrence.

• Smart Structures and Systems
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• v.3 no.3
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• pp.385-403
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• 2007

The effectiveness of the newly developed smart passive control system employing a magnetorheological (MR) damper and an electromagnetic induction (EMI) part for seismic protection of base isolated structures is numerically investigated. An EMI part in the system consists of a permanent magnet and a coil, which changes the kinetic energy of the deformation of an MR damper into the electric energy (i.e. the induced current) according to the Faraday's law of electromagnetic induction. In the smart passive control system, the damping characteristics of an MR damper are varied with the current input generated from an EMI part. Hence, it does not need any control system consisting of sensors, a controller and an external power source. This makes the system much simpler as well as more economic. To verify the efficacy of the smart passive control system, a series of numerical simulations are carried out by considering the benchmark base isolated structure control problems. The numerical simulation results show that the smart passive control system has the comparable control performance to the conventional MR damper-based semiactive control system. Therefore, the smart passive control system could be considered as one of the promising control devices for seismic protection of seismically excited base isolated structures.

• Earthquakes and Structures
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• v.13 no.6
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• pp.561-572
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• 2017

Seismic base isolation has been accepted as one of the most popular design procedures to protect important structures against earthquakes. However, due to lack of information and experimental data the application of base isolation is quite limited to nuclear power plant (NPP) industry. Moreover, the effects of inelastic behavior of soil beneath base-isolated NPP have raised questions to the effectiveness of isolation device. This study applies the wavelet analysis to investigate the effects of soil-structure interaction (SSI) on the seismic response of a base-isolated NPP structure. To evaluate the SSI effects, the NPP structure is modelled as a lumped mass stick model and combined with a soil model using the concept of cone models. The lead rubber bearing (LRB) base isolator is used to adopt the base isolation system. The shear wave velocity of soil is varied to reflect the real rock site conditions of structure. The comparison between seismic performance of isolated structure and non-isolated structure has drawn. The results show that the wavelet analysis proves to be an efficient tool to evaluate the SSI effects on the seismic response of base-isolated structure and the seismic performance of base-isolated NPP is not sensitive to the effects in this case.

• Structural Engineering and Mechanics
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• v.51 no.2
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• pp.277-297
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• 2014

Since the isolation bearings undergo large displacements in base-isolated structures, impact with adjacent structures is inevitable. Therefore, in this investigation, the effect of impact on seismic response of isolated structures mounted on double concave friction pendulum (DCFP) bearings subjected to near field ground motions is considered. A non-linear viscoelastic model of collision is used to simulate structural pounding more accurately. 2-, 4- and 8-story base-isolated buildings adjacent to fixed-base structures are modeled and the coupled differential equations of motion related to these isolated systems are solved in the MATLAB environment using the SIMULINK toolbox. The variation of seismic responses such as base shear, displacement in the isolation system and superstructure (top floor) is computed to study the impact condition. Also, the effects of variation of system parameters: isolation period, superstructure period, size of seismic gap between two structures, radius of curvature of the sliding surface and friction coefficient of isolator are contemplated in this study. It is concluded that the normalized base shear, bearing and top floor displacement increase due to impact with adjacent structure. When the distance between two structures decreases, the base shear and displacement increase comparing to no impact condition. Besides, the increase in friction coefficient difference also causes the normalized base shear and displacement in isolation system and superstructure increase in comparison with bi-linear hysteretic behavior of base isolation system. Totally, the comparison of results indicates that the changes in values of friction coefficient have more significant effects on 2-story building than 4- and 8-story buildings.