• Earthquakes and Structures
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• v.6 no.2
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• pp.163-179
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• 2014

Dynamic test with scaled model of a group of intake towers was performed to study the dynamic interaction between water and towers. The test model consists of intake tower or towers, massless foundation near the towers and part of water to simulate the dynamic interaction of tower-water-foundation system. Models with a single tower and 4 towers were tested to find the different influences of the water on the tower dynamic properties, seismic responses as well as dynamic water-tower interaction. It is found that the water has little influence on the resonant frequency in the direction perpendicular to flow due to the normal force transfer role of the water in the contraction joints between towers. By the same effect of the water, maximum accelerations in the same direction on 4 towers tend to close to each other as the water level increased from low to normal level. Moreover, the acceleration responses of the single tower model are larger than the group of towers model in both directions in general. Within 30m from the surface of water, hydrodynamic pressures were quite close for a single tower and group of towers model at two water levels. For points deeper than 30m, the pressures increased about 40 to 55% for the group of towers model than the single tower model at both water levels. In respect to the pressures at different towers, two mid towers experienced higher than two side towers, the deeper, the larger the difference. And the inside hydrodynamic pressures are more dependent on ground motions than the outside.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.3
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• pp.289-296
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• 2009

Natural frequency is a key parameter to determine the seismic and wind loading of tall flexible structures, and to assess the wind-induced vibration for serviceability check. In this study, natural frequencies and associated mode shapes were obtained from measured acceleration data and system identification technique. Subsequently, finite element(FE) models for a tall reinforced concrete buildings were built using a popular PC-based finite element analysis program and calibrated to match their natural frequencies and mode shapes to actual values. The calibration of the FE model included: 1) compensation of modulus of elasticity considering the mix design strength, 2) flexural stiffness of floor slabs, and 3) major non-structural components such as plain concrete walls. Natural frequencies and mode shapes from the final FE model showed best agreement with the measured values.

• Journal of the Earthquake Engineering Society of Korea
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• v.12 no.4
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• pp.55-61
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• 2008

One of the most recent base-isolation systems to improve the earthquake resistance of structures is the Friction Pendulum System(FPS). Simple in design but with versatile properties, the FPS has been used in some of the world s largest seismically isolated buildings, bridges and chemical tanks. FPS using PTFE(Polytetrafl-uoroethylene) based material has been developed to provide a simple and effective way for structures to achieve earthquake resistance. PTFE materials are soft, and are apt to become deformed easily after a few working cycles. In this study, magnetic force is used rather than the usual PTFE materials to improve the material shortcomings. A MF-FPS(Magnetic force-Friction Pendulum System) is proposed, and us shown to effectively protect structures against earthquakes. To demonstrate the advantages of this new system, the MF-FPS is compared with FPS as an attempt to prove its performance. A six-degree-of-freedom model is considered as a numerical example. The ground acceleration data of El Centro, Mexico and Gebze earthquakes are used as seismic excitations. The results showed that MF-FPS improved performance compared with FPS.

• Structural Engineering and Mechanics
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• v.9 no.3
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• pp.241-256
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• 2000

The major sources of energy dissipation in steel frames with partially restrained (PR) connections are evaluated. Available experimental results are used to verify the mathematical model used in this study. The verified model is then used to quantify the energy dissipation in PR connections due to hysteretic behavior, due to viscous damping and at plastic hinges if they are formed. Observations are made for two load conditions: a sinusoidal load applied at the top of the frame, and a sinusoidal ground acceleration applied at the base of the frame representing a seismic loading condition. This analytical study confirms the general behavior, observed during experimental investigations, that PR connections reduce the overall stiffness of frames, but add a major source of energy dissipation. As the connections become stiffer, the contribution of PR connections in dissipating energy becomes less significant. A connection with a T ratio (representing its stiffness) of at least 0.9 should not be considered as fully restrained as is commonly assumed, since the energy dissipation characteristics are different. The flexibility of PR connections alters the fundamental frequency of the frame. Depending on the situation, it may bring the frame closer to or further from the resonance condition. If the frame approaches the resonance condition, the effect of damping is expected to be very important. However, if the frame moves away from the resonance condition, the energy dissipation at the PR connections is expected to be significant with an increase in the deformation of the frame, particularly for low damping values. For low damping values, the dissipation of energy at plastic hinges is comparable to that due to viscous damping, and increases as the frame approaches failure. For the range of parameters considered in this study, the energy dissipations at the PR connections and at the plastic hinges are of the same order of magnitude. The study quantitatively confirms the general observations made in experimental investigations for steel frames with PR connections; however, proper consideration of the stiffness of PR connections and other dynamic properties is essential in predicting the dynamic behavior.

• Smart Structures and Systems
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• v.20 no.2
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• pp.151-162
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• 2017

In practical engineering, the friction damper is a widely used energy dissipation device because of its large deformation capacity, stable energy dissipation capability, and cost effectiveness. While based on conventional friction dampers, the double-sliding friction damper (DSFD) being proposed is different in that it features two sliding friction forces, i.e., small and large sliding friction forces, rather than a single-sliding friction force of ordinary friction dampers. The DSFD starts to deform when the force sustained exceeds the small-sliding friction force, and stops deforming when the deformation reaches a certain value. If the force sustained exceeds the large sliding friction force, it continues to deform. Such a double-sliding behavior is expected to endow structures equipped with the DSFD better performance in both small and large earthquakes. The configuration and working mechanism of the DSFD is described and analyzed. Quasi-static loading tests and finite element analyses were conducted to investigate its hysteretic behavior. Finally, time history analysis of the single-degree-of-freedom (SDOF) and multi-degree-of-freedom (MDOF) systems were performed to investigate the seismic performance of DSFD-equipped structures. For the purpose of comparison, tests on systems equipped with conventional friction dampers were also performed. The proposed DSFD can be realized perfectly, and the DSFD-equipped structures provide better performances than those equipped with conventional friction dampers in terms of interstory drift and floor acceleration. In particular, for the MDOF system, the DSFD helps the structural system to have a uniform distributed interstory drift.

• Journal of the Earthquake Engineering Society of Korea
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• v.9 no.1 s.41
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• pp.61-70
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• 2005

Shaking table tests are carried out on a single-degree-of-freedom mass that is equipped with a hybrid base isolation system. The isolator consists of a set of four specially-designed friction pendulum systems (FPS) and a magnetorheological (MR) damper. The structure and its hybrid isolation system are subjected to various intensities of near- and far-fault earthquakes on a large shake table. The proposed fuzzy controller uses feedback from displacement or acceleration transducers attached to the structure to modulate resistance of the semi-active damper to motion. Results from several types of passive and semi-active control strategies are summarized and compared. The study shows that a combination of FPS isolators and an adjustable MR damper can effectively provide robust control of vibration for a large full-scale structure undergoing a wide variety of seismic loads.

• Journal of the Korean Geotechnical Society
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• v.36 no.4
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• pp.17-30
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• 2020

In this study, liquefaction evaluation was performed by applying liquefaction evaluation criteria commonly applied in Korea and recently revised evaluation criteria to five sites where liquefaction was observed or potential for liquefaction was high during the 2017 Pohang earthquake. The purpose of this study is to examine the validity of the revised domestic liquefaction evaluation criteria by comparing and reviewing the results of the theoretical liquefaction evaluation with the actual liquefaction occurrence at the sites. For the analysis of earthquakes for the evaluation of the liquefaction, the actual Pohang earthquake wave, as well as the waves that was conventionally used in Korea, was used. The magnitude of the peak ground acceleration of analysis earthquake varied from 0.097 g to 0.2713 g. From the analysis results, the validity of the liquefaction evaluation criteria presented in the 2016 Foundation Design Criteria, which has been commonly applied in Korea, was evaluated. From the evaluation results, the improvement of the existing criteria was suggested, and the suitability of revised items of liquefaction evaluation criteria presented in the Seismic Design General established in 2018 was confirmed.

• Journal of the Korean Geosynthetics Society
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• v.10 no.3
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• pp.53-62
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• 2011

This paper presents the characteristics behavior of dike structure and foundation ground through the shaking table model test. The vibration loadings of design earthquake acceleration of 0.154g was applied to this laboratory model test regarding on dike structure and foundation ground under the structure. The model was formulated with 1/100 design of representative cross section for evaluating the effectiveness of vibration. Based on the test results, we can analysis the behavior of lateral displacement and settlement characteristics of structure under the earthquake loading. The pore water pressure was also monitored in the upper, middle and lower layers of ground. Finally, the actual displacements and pore water pressure of the structure can be predicted by using the results of the laboratory shaking table test.

• Structural Engineering and Mechanics
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• v.75 no.1
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• pp.33-47
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• 2020

In this paper the dynamic behavior of an isolated building subjected to idealized near-fault pulses is investigated. The building is represented with a simple 2-DOF model. Both linear and non-linear behavior of the isolation system is considered. Using dimensional analysis, in conjunction with closed form mathematical idealized pulses, appropriate dimensionless parameters are defined and self-similar curves are plotted on dimensionless graphs, based on which various conclusions are reached. In the linear case, the role of viscous damping is examined in detail and the existence of an optimum value of damping along with its significant variation with the number of half-cycles is shown. In the nonlinear case, where the behavior of the building depends on the amplitude of the excitation, the benefits of dimensional analysis are evident since the influence of the dimensionless 𝚷-terms is easily examined. Special consideration is given to the normalized strength of the non-linear isolation system that appears to play a complex role which greatly affects the response of the 2-DOF. In the last part of the paper, a comparison of the responses to idealized pulses between a linear fixed-base SDOF and the respective isolated 2-DOF with both linear and non-linear damping is conducted and it is shown that, under certain values of the superstructure and isolation system characteristics, the use of an isolation system can amplify both the normalized acceleration and displacement of the superstructure.

• Structural Engineering and Mechanics
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• v.76 no.1
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• pp.83-99
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• 2020

Shear walls are structural members in buildings that are used extensively in reinforced concrete frame buildings, and almost exclusively in the UK, regardless of whether or not they are actually required. In recent years, the UK construction industry, led by the Concrete Centre, has questioned the need for such structural elements in low to mid-rise reinforced concrete frame buildings. In this context, a typical modern, 5-storey residential building is studied, and its existing shear walls are replaced with columns as used elsewhere in the building. The aim is to investigate the impact of several design variables, including concrete grade, column size, column shape and slab thickness, on the building's structural performance, considering two punching shear limits (V_Ed/V_Rd,c), lateral drift and accelerations, to evaluate its maximum possible height under wind actions without the inclusion of shear walls. To facilitate this study, a numerical model has been developed using the ETABS software. The results demonstrate that the building examined does not require shear walls in the design and has no lateral displacement or acceleration issues. In fact, with further analysis, it is shown that a similar building could be constructed up to 13 and 16 storeys high for 2 and 2.5 punching shear ratios (V_Ed/V_Rd,c), respectively, with adequate serviceability and strength, without the need for shear walls, albeit with thicker columns.