• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.2
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• pp.157-165
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• 2011

Base isolation system is widely used for reduction of dynamic responses of structures subjected to seismic load. Recently, research on a smart base isolation system that can effectively reduce dynamic responses of the isolated structure without accompanying increases in base drifts has been actively conducted. In this study, a smart base isolation system was applied to an arch structure subjected to seismic excitation and its control performance for reduction of seismic responses was evaluated. In order to make a smart base isolation system, 4kN MR dampers and low damping elastomeric bearings were used. Seismic response control performance of the proposed smart base isolation system was compared to that of the optimally designed lead-rubber bearing(LRB) isolation system. To this end, an artificial ground motion developed based on KBC2009 design response spectrum was used as a seismic excitation. Fuzzy control algorithm was used to control MR damper in the smart base isolation system and multi-objective genetic algorithm was employed to optimize the fuzzy controller. Based on numerical simulation results, it has been shown that the smart base isolation system can drastically reduce base drifts and seismic responses of the example arch structure in comparison with LRB isolation system.

• Earthquakes and Structures
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• v.3 no.6
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• pp.853-867
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• 2012

In this paper, a new type of passive energy dissipating system similar to added damping and stiffness (ADAS) and triangular added damping and stiffness (TADAS) is proposed and implemented in the analytical model of a building with hybrid structural system in the structure's base which we call it; Telescopic column. The behavior and performance of a high rise R.C. structure equipped with this system is investigated and compared with conventional base isolation systems such as rubber isolator bearings and friction pendulum bearings. For this purpose a series of ground acceleration records of the San Fernando, Long Beach and Imperial Valley earthquakes are used as the disturbing ground motions in a series of numerical simulations. The nonlinear numerical modeling which includes both material and geometric nonlinearities were carried out by using SAP2000 program. Results show suitable behavior of structures equipped with telescopic columns in controlling the upper stories drifts and accelerations.

• International Journal of High-Rise Buildings
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• v.3 no.1
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• pp.1-8
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• 2014

When seismic isolation system is applied to high aspect-ratio (height/wide-ratio) steel structures, there are several problems to be taken into consideration. One is lifting up tensile force on the isolation bearing by overturning moment caused by earthquake. Another is securing building stiffness to produce seismic isolation effects. Under these conditions, this paper reports the structural design of high-rise research building in the campus of Tokyo Institute of Technology. With the stepping-up system for the corner bearings, the narrow sides of single span framework are designed to concentrate the dead load as counter-weight for the tensile reaction under earthquake. Also we adopted concrete in-filled steel column and Mega-Bracing system covering four layers on north & south framework to secure the horizontal stiffness of the building.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1993.10a
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• pp.186-192
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• 1993

Proto-type seismic isolation rubber bearings are investigated through nonlinear hyperelasticity finite elements using the ANSYS general purpose structural analysis code. The purpose of the analysis was to determine the maximum horizontal strain range which can be obtained with a 250KN hydraulic actuator. A Mooney-Rivlin strain energy density function was used as a constitutive law for rubber. The results are compared with the test data available in the literature and found to in good agreement only in the higy strain range. The analysis results can be used with conservatism to predict the necessary force required to a specified displacement such as the purpose of this analysis. However, more precise constitutive model will be required to simulate the bearing behavior with accuracy in the mid-range strain.

• Structural Engineering and Mechanics
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• v.35 no.6
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• pp.759-772
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• 2010

Seismic isolation is a well-known method to mitigate the earthquake effects on structures by increasing their fundamental natural periods at the expense of larger displacements in the structural system. In this paper, the seismic response of isolated and fixed base vertical, cylindrical, liquid storage tanks is investigated using a Finite Element Model (FEM), taking into account fluid-structure interaction effects. Three vertical, cylindrical tanks with different ratios of height to radius (H/R = 2.6, 1.0 and 0.3) are numerically analyzed and the results of response-history analysis, including base shear, overturning moment and free surface displacement are reported for isolated and non-isolated tanks. Isolated tanks equipped by lead rubber bearings isolators and the bearing are modeled by using a non-linear spring in FEM model. It is observed that the seismic isolation of liquid storage tanks is quite effective and the response of isolated tanks is significantly influenced by the system parameters such as their fundamental frequencies and the aspect ratio of the tanks. However, the base isolation does not significantly affect the surface wave height and even it can causes adverse effects on the free surface sloshing motion.

• Earthquakes and Structures
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• v.15 no.3
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• pp.319-334
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• 2018

In this paper, an analytical study was carried out to propose an optimum base-isolated system for the design of steel structures equipped with lead rubber bearings (LRB). For this, 5 and 10-storey steel moment resisting frames (MRFs) were designed as Special Moment Frame (SMF). These two-dimensional and three-bay frames equipped with a set of isolation systems within a predefined range that minimizes the response of the base-isolated frames subjected to a series of earthquakes. In the design of LRB, two main parameters, namely, isolation period (T) and the ratio of strength to weight (Q/W) supported by isolators were considered as 2.25, 2.5, 2.75 and 3 s, 0.05, 0.10 and 0.15, respectively. The Force-deformation behavior of the isolators was modelled by the bi-linear behavior which could reflect the nonlinear characteristics of the lead-plug bearings. The base-isolated frames were modelled using a finite element program and those performances were evaluated in the light of the nonlinear time history analyses by six natural accelerograms compatible with seismic hazard levels of 2% probability of exceedance in 50 years. The performance of the isolated frames was assessed in terms of roof displacement, relative displacement, interstorey drift, absolute acceleration, base shear and hysteretic curve.

• Earthquakes and Structures
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• v.19 no.6
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• pp.427-444
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• 2020

The performance of an isolated horizontally curved continuous bridge with High Damping Rubber (HDR) Bearings has been investigated under seismic loading conditions. The effectiveness of response controls of the bridge by HDR bearings for various aspects viz. variation in ground motion characteristics, multi-directional effect, level of earthquake shaking, varying incidence angle, have been determined. Three recorded ground motions, representative of historical earthquakes along with near-field, far-field and forward directivity effects, have been considered in the study. The efficacy of the bearings with bidirectional effect considering interaction behavior of bearing and pier has also been investigated. Modeling and analysis of the bridge have been done by finite element approach. Sensitivity studies of the bridge response with respect to design parameters of the bearings for the considered ground motions have been performed. The importance of the nonlinearity of HDR bearings along with crucial design parameters has been identified. It has been observed that the HDR bearings performed well in different variations of ground motions, especially for controlling torsional moment. However, the deck displacement has been found to be increased significantly in case of Turkey ground motions, considering forward directivity effect, which needs to be paid more attention from designer point of view.

• Earthquakes and Structures
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• v.9 no.1
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• pp.195-219
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• 2015

A partial (hybrid) seismic isolation scheme for precast girder bridges in the form of a "buffer-gap-elastomeric bearings" system has been endorsed in the literature as an efficient seismic design system. However, no guides exist to detail an optimal gap size for different configurations. A numerical study is established herein for different scenarios according to Euro code seismic requirements in order to develop guidelines for the selection of optimal buffer-gap arrangements for various design cases. Various schemes are hence designed for ductile and limited ductility behavior of the bridge piers for different seismic demand levels. Seven real ground records are selected to perform incremental dynamic analysis of the bridges up to failure. Bridges with typical short and high piers are studied; and different values of initial gaps at piers are also investigated varying from a zero gap (i.e., fully locked) condition up to an initial gap at piers that is three quarters the gap left at abutments. Among the main conclusions is that the as-built initial gaps at piers (and especially large gap sizes that are ${\geq}1/2$ as-built gaps at abutments) do not practically reduce the seismic design demand and do not affect the reserve capacity of the bridge against failure for bridges featuring long piers, especially when these bridges are designed a priori for ductile behavior. To the contrary, the "buffer-gap-elastomeric bearings" system is more effective for the bridge schemes with short piers having a large difference between the stiffness of the bearings and that of their supporting (much stiffer) squat piers, particularly for designs with limited ductility. Such effectiveness is even amplified for the case of larger initial as-built gap sizes at piers.

• Journal of Korean Association for Spatial Structures
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• v.4 no.1 s.11
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• pp.49-59
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• 2004

A previous study evaluated the seismic response of typical multi-span simply supported (MSSS) and multi-span continuous (MSC) steel-girder bridges in the central and southeastern United States. The results showed that the bridges were vulnerable to damage resulting from impact between decks, and large ductility demands on nonductile columns. Furthermore, fixed and expansion bearings were likely to fail during strong ground motion. In this paper, several retrofit measures to improve the seismic performance of typical multi-span simply supported and multi-span continuous steel girder bridges are evaluated, including the use of elastomeric bearings, lead-rubber bearings, and restrainer cables. It is determined that iead-rubber bearings are the most effective retrofit measure for reducing the seismic vulnerability of typical bridges. While isolation provided by elastomeric bearings limits the forces into the columns, the added flexibility results in pounding between decks in the MSSS steel-girder bridge. Restrainer cables, which are becoming a common retrofit measure, are only moderately effective in reducing the seismic vulnerability of MSSS and MSC steel girder bridges.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.25-28
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• 2004

Many highway bridges in Korea need seismic retrofit because only one decade has passed since the seismic design criteria was introduced. In this experimental study, the effectiveness of base isolation bearings was discussed for the seismic retrofit of the highway bridges. Four real scale RC pier specimens were constructed for the test. These RC piers didn't have seismic details. Except for one RC pier for the pilot test, three types of bearings such as Pot bearing, Rubber bearing (RB), Lead-rubber bearing (LRB) were applied to the other RC piers respectively. The RC pier with Pot bearing means current state of the prototype bridge that is not retrofitted seismically. And two RC piers with RB or LRB mean assumed states of the prototype bridge that are retrofitted seismically. To simulate dynamic behavior of these RC piers under earthquake loads, Pseudo-dynamic test method was used.