• Journal of the Earthquake Engineering Society of Korea
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• v.19 no.4
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• pp.161-171
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• 2015

A series of tests was conducted for full-scale single-pylon asymmetric cable-stayed bridges using a system of multiple shaking tables. The 2-span bridge length was 28 m, and the pylon height was 10.2 m. 4 different base conditions were considered: the fixed condition, RB (rubber bearings), LRB (lead rubber bearings), and HDRB (high damping rubber bearings). Based on investigation of the seismic response, the accelerations and displacements in the axial direction of the isolated bridge were increased compared to non-isolated case. However, the strain of the pylon was decreased, because the major mode of the structure was changed to translation for the axial direction due to the dynamic mass. The response of the cable bridge could differ from the desired response according to the locations and characteristics of the seismic isolator. Therefore, caution is required in the design and prediction in regard to the location and behavior of the seismic isolator.

• Journal of the Earthquake Engineering Society of Korea
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• v.26 no.2
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• pp.95-103
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• 2022

In order to evaluate the earthquake safety of equipment in structures, it is essential to analyze the In-Structure Response Spectrum (ISRS). The ISRS has a peak value at the frequency corresponding to the structural vibration mode, but the frequency and amplitude at the peak can vary because of many uncertain parameters. There are several seismic design criteria for ISRS peak-broadening for fixed base structures. However, there are no suggested criteria for constructing the design ISRS of seismically isolated structures. The ISRS of isolated structures may change due to the major uncertainty parameter of the isolator, which is the shear stiffness of the isolator and the several uncertainty parameters caused by the nonlinear behavior of isolators. This study evaluated the effects on the ISRS due to the initial stiffness of the bi-linear curve of isolators and the variation of effective stiffness by the input ground motion intensity and intense motion duration. Analyzing a simplified structural model for isolated base structure confirmed that the ISRS at the frequency of structural mode was amplified and shifted. It was found that the uncertainty of the initial stiffness of isolators significantly affects the shape of ISRS. The variation caused by the intensity and duration of input ground motions was also evaluated. These results suggested several considerations for generating ISRS for seismically isolated structures.

• Earthquakes and Structures
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• v.1 no.3
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• pp.231-252
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• 2010

Previous research on pounding between seismically isolated buildings during earthquakes has been focused on impacts at the bases of structures and the effect of simultaneous interactions at the bases and at the superstructures has not been studied in details. In this paper, the seismic responses of adjacent buildings supported on different or similar base systems considering impacts between bases and superstructures are numerically investigated. The study is carried out in three parts for the two types of adjacent buildings: (i) both structures have fixed bases; (ii) one structure has fixed base and the other is seismically isolated and (iii) both structures have base isolation systems. The results of the study indicate that the pounding-involved responses of the buildings depend mainly on the type of structural base systems and on the structural parameters of both buildings. For the base-isolated building, the variation of the peak accelerations and displacements of the storeys have been found to be relatively low. On the other hand, significant differences have been observed for the fixed base building. The results of the parametric study conducted for different values of the gap size between colliding structures show the reduction in the peak base displacements as the gap distance decreases.

• Earthquakes and Structures
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• v.10 no.6
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• pp.1451-1465
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• 2016

The effectiveness of base isolation (BI) systems for mitigation of seismic vibration of bridges have been extensively studied in the past. It is well established in those studies that the performance of BI system is largely dependent on the characteristics of isolator yield strength. For optimum design of such systems, normally a standard nonlinear optimization problem is formulated to minimize the maximum response of the structure, referred as Stochastic Structural Optimization (SSO). The SSO of BI system is usually performed with reference to a problem of unconstrained optimization without imposing any restriction on the maximum isolator displacement. In this regard it is important to note that the isolator displacement should not be arbitrarily large to fulfil the serviceability requirements and to avoid the possibility of pounding to the adjacent units. The present study is intended to incorporate the effect of excessive isolator displacement in optimizing BI system to control seismic vibration effect of bridges. In doing so, the necessary stochastic response of the isolated bridge needs to be optimized is obtained in the framework of statistical linearization of the related nonlinear random vibration problem. A simply supported bridge is taken up to elucidate the effect of constraint condition on optimum design and overall performance of the isolated bridge compared to that of obtained by the conventional unconstrained optimization approach.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1998.10a
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• pp.144-153
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• 1998

Base isolation is an innovative design strategy that provides a practical alternative for the seismic design of structures. Base isolators, mainly employed to isolate large structures subjected to earthquake ground excitations and to rehabilitate structures damaged by past earthquakes, deflect and absorb the seismic energy horizontally transmitted to the structures. This study demonstrates that the base isolation system may offer effective performance for bridges during severe seismic events through shaking table tests. Two base isolation system using laminated rubber bearings with and without hydraulic dampers are tested. The test results strongly show that the laminated rubber bearings cause the natural period of the bridge structure increased considerably, which results in the deck acceleration and the shear forces on the piers reduced significantly. The results also demonstrate that the hydraulic dampers enhance the system's capacity in dissipating energy to reduce the relative displacement between the bridge deck and the pier.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2002.09a
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• pp.98-105
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• 2002

The effects of the base-isolation system and elastic soil foundation on the behavior of a liquid storage tank are studied. To evaluate the seismic response of liquid storage tank accurately, the coupled dynamic system considering base isolation and soil interaction problem is formulated in time domain. Results show that the base isolation system reduces effectively the radial displacements, base shears, overturning moments, axial resultant stresses and the hydrodynamic pressure by providing flexibility and energy dissipation capability. Base Isolation may, however, increase the relative liquid sloshing amplitude due to the effect of liquid-structure interaction and cause excessive large relative displacements between structure and foundation. In addition to base-isolator, the dynamic behavior of liquid storage tank is related to the flexibility of base foundation, so the analysis of soil-structure interaction s achieved.

• Earthquakes and Structures
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• v.27 no.1
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• pp.57-67
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• 2024

To assess the seismic performance of Plate-Shell Integrated Concrete Liquid-Storage Structure (PSICLSS), a scaled test model was constructed. This model incorporated a hybrid isolation system, which combined shape memory alloy (SMA), lead-cored rubber isolation bearing (LRB) and sliding isolation bearing (SB). By conducting shaking table test, the dynamic responses of both non-isolated and hybrid-isolated PSICLSS were analyzed. The results show that the hybrid isolation system can effectively reduce the acceleration and displacement responses of the structure. However, it also results in an increase in local hydrodynamic pressure and liquid sloshing height. Under extreme earthquake action, the displacement of isolation layer is small. When vertical ground motion is taken into account, the shock absorption rate of horizontal acceleration decreases. The peak hydrodynamic pressure increases significantly, and the peak hydrodynamic pressure position also changes. The maximum displacement of isolation layer increases, the residual displacement decreases.

• Earthquakes and Structures
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• v.5 no.5
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• pp.499-526
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• 2013

Seismic isolation is an effective method for the protection of buildings and their contents during strong earthquakes. This research work aims to assess the appropriateness of the linear and nonlinear models that can be used in the analysis of typical low-rise base isolated steel buildings, taking into account the inherent nonlinearities of the isolation system as well as the potential nonlinearities of the superstructure in case of strong ground motions. The accuracy of the linearization of the isolator properties according to Eurocode 8 is evaluated comparatively with the corresponding response that can be obtained through the nonlinear hysteretic Bouc-Wen constitutive model. The suitability of the linearized model in the determination of the size of the required seismic gap is assessed, under various earthquake intensities, considering relevant methods that are provided by building codes. Furthermore, the validity of the common assumption of elastic behavior for the superstructure is explored and the alteration of the structural response due to the inelastic deformations of the superstructure as a consequence of potential collision to the restraining moat wall is studied. The usage of a nonlinear model for the isolation system is found to be necessary in order to achieve a sufficiently accurate assessment of the structural response and a reliable estimation of the required width of the provided seismic gap. Moreover, the simulations reveal that the superstructure's inelasticity should be taken into account, especially if the response of the structure under high magnitude earthquakes is investigated. The consideration of the inelasticity of the superstructure is also recommended in studies of structural collision of seismically isolated structures to the surrounding moat wall, since it affects the response.

• Journal of Korean Society of Steel Construction
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• v.9 no.4 s.33
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• pp.625-635
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• 1997

The base isolation technique and its benefits in reducing the transmitted earthquake energy into a structure have gained increasing recognition during the last two decades. Unfortunately, the current available design procedures, especially for base-isolated bridges, seem inadequate and too restrictive. As a result, practical design procedure still relies upon a series of deterministic time history analyses. In this study, the evaluation of the possibility of the normal mode method to predict the nonlinear seismic responses of base isolated bridges has been performed. The applicability has been examined through the numerical approach with isolator's elastic or plastic states of the base isolated bridges. Numerical results show that the 1st. mode period and the various responses are varied with the state but are conversed. And, the result show that the normal mode method is applicable to predict the seismic responses and to design the babe isolated bridge. Various analysis method to bridges with bilinearized hysteresis isolator and various pier heights are evalulated.

• Earthquakes and Structures
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• v.14 no.5
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• pp.425-436
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• 2018

The design of seismically isolated structures considering the stochastic nature of excitations, base isolators' design parameters, and superstructure properties requires robust reliability analysis methods to calculate the failure probability of the entire system. Here, by applying artificial neural networks, we proposed a robust technique to accelerate the estimation of failure probability of equipped isolated structures. A three-story isolated building with susceptible facilities is considered as the analytical model to evaluate our technique. First, we employed a sensitivity analysis method to identify the critical sources of uncertainty. Next, we calculated the probability of failure for a particular set of random variables, performing Monte Carlo simulations based on the dynamic nonlinear time-history analysis. Finally, using a set of designed neural networks as a surrogate model for the structural analysis, we assessed once again the probability of the failure. Comparing the obtained results demonstrates that the surrogate model can attain precise estimations of the probability of failure. Moreover, our proposed approach significantly increases the computational efficiency corresponding to the dynamic time-history analysis of the structure.