• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.4
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• pp.65-75
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• 1993

Presented is a method for nonstationary response analysis of an offshore guyed tower subjected to strong earthquake motions under moderate random waves and current loadings. By taking the time varying envelope function and the auto-correlation function of the ground acceleration in terms of complex exponential functions, an analytical procedure is developed for computing time varying variances of the tower response. The stationary responses due to small random waves are obtained by using frequency domain method, and the results are combined with the nonstationary results due to earthquakes. Finally, the expected maximum responses are estimated. Through the example analyses, the nonstationary method developed in this study is verified, and the contributions of the earthquake, wave and current loadings to the total maximum response are investigated.

• Journal of the Earthquake Engineering Society of Korea
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• v.6 no.3
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• pp.31-40
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• 2002

The purpose of this study is to investigate the seismic behavior of RC bridge piers and to provide the data for developing improved seismic design criteria. The accuracy and objectivity of the assessment process may be enhanced by the use of sophisticated nonlinear finite element analysis program. A computer program, named RCAHEST(reinforced concrete analysis in higher evaluation system technology), for the analysis of reinforced concrete structures was used. Material nonlinearity is taken into account by comprising tensile, compressive and shear models of cracked concrete and a model of reinforcing steel. The smeared crack approach is incorporated. n boundary plane at which each member with different thickness is connected, local discontinuity in deformation due to the abrupt change in their stiffness can be taken into account by introducing interface element. The effect of number of load reversals with the same displacement amplitude has been also taken into account to model the reinforcing steel and concrete. In the companion paper, the proposed numerical method for seismic damage evaluation of RC bridge piers is verified by comparison with the reliable experimental results.

• Journal of Korean Society of Steel Construction
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• v.28 no.4
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• pp.293-301
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• 2016

Stability of cylindrical liquid storage tanks under seismic excitation could prevent catastrophic disaster of human life and economic loss. Domestic provisions on allowable compressive stress in tank walls to prohibit buckling failure are either incomplete or inconsistent, so foreign specifications such as API 650, BS EN 1998-4:2006 or New Zealand Standards are employed in stability design. In this study, response spectrum analyses are performed for plant tanks having different ratios of height to diameter or diameter to thickness to calculate hydrodynamic pressure on tank walls. Then nonlinear buckling analyses are conducted to estimate magnitude of buckling stress. By comparing analysis results with those from foreign design specifications, appropriate domestic design provisions are suggested.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.3
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• pp.58-65
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• 2016

Various passive energy dissipation systems have been proposed and widely applied to real building structures under seismic load due to their high energy-dissipation potential and low cost for installation and maintenance. This paper presents nonlinear dynamic analysis results of the effectiveness of exterior-installed Kagome damping system(EKDS) in passively reducing seismic response. Kagome damping system proposed by previous studies has isotropic and bi-linear hysteretic characteristics and the installation configuration is newly presented in this study. The 15 and 20 story RC framed apartment buildings are used for verifying the effectiveness of the EKDS. The stiffness ratio of the damper supporting column to the original building, the number of the dampers, and the installed stories were considered as design parameters. Numerical results demonstrated that the EKDS were very effective in reducing both the two horizontal directional seismic responses by just using smaller number of exterior-installed damping system when compared to the traditional one-directional inter-story installed damping systems.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.9
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• pp.67-75
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• 2006

A fully nonlinear model accounting for swirling effect has been applied in analyzing the dynamic response for a classical swirl injector. The current work applied highly accurate Boundary Element Methods (BEMs) in assessing its static and dynamic characteristics. On the basis of moving surface treatment method and surface instability study, which are obtained from the previous static characteristics analysis in pressure-swirl injectors, this work was expanded for analyzing the dynamics of a classical swirl injector. The dynamic response through injector components for disturbed inflow condition was investigated. The modified code was validated from comparison with the theoretical result for a typical swirl injector. Clearly the simulated result shows the interesting characteristics of swirl injectors to provide either amplification or damping of the input disturbance through each component. These results give promise in applying the current model to nonlinear dynamic characteristics of swirl injectors.

• Journal of the Korean Society for Railway
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• v.18 no.4
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• pp.363-373
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• 2015

The purpose of this study is to develop a nonlinear algorithm for the dynamic interaction analysis of KTX trains and bridge girders with consideration of separation and flange contact phenomena between wheel and rail. For this, three interaction models between wheel-rail are implemented and compared through numerical examples. That is, the spring model and the non-jump model are briefly explained, and a nonlinear contact model is then proposed to accurately simulate interaction forces of the train-bridge system. Dynamic interaction analysis of a simply supported girder and trains is performed and the analyzed results are presented and compared for the proposed contact model and the other model types. Particularly, flange contact phenomena in the nonlinear contact model are demonstrated under a specific condition.

• Journal of the Earthquake Engineering Society of Korea
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• v.1 no.4
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• pp.21-28
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• 1997

The aseismic capacity of a traditional three-bay-straw-roof wooden house for soft soil site condition is quantitatively estimated. One 1/4 scale model was tested for the Imperial Valley Earthquake up to failure. The natural frequency of the wooden house measured in elastic range is 1.66 Hz and 1.76 Hz in the longitudinal and transversal direction, respectively. Damping ratio of the house measured in elastic range is 7%. The peak horizontal acceleration response of the house was reduced compared with input motion due to the nonlinear inelastic characteristics of the wooden frame. The horizontal displacement response was significantly increased as the level of input motion was increased. The model was collapsed at 0.25g due to the low frequency contents of the input motion. The results of nonlinear seismic analysis were compared with the test results.

• Journal of IKEEE
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• v.26 no.4
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• pp.577-583
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• 2022

Verilog-HDL-based modeling can be performed to confirm the fast operation characteristics after setting the design parameters of each block considering the stability of the system by performing linear phase-domain modeling on the phase-locked loop. This paper proposed Verilog-HDL modeling including DCO noise and DTC nonlinear characteristic. After completing the modeling, the time-domain transient simulation can be performed to check the feasibility and the functionality of the proposed PLL system, then the phase noise result from the system design based on the functional model can be verified comparing with the ideal phase noise graph. As a result of the comparison of simulation time (6 us), the Verilog-HDL-based modeling method (1.43 second) showed 484 times faster than the analog transistor level design (692 second) implemented by TSMC 0.18-㎛.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.36 no.2
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• pp.105-112
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• 2023

In this study, structural analyses were conducted to analyze the performance of a bridge to which friction pendulum systems (FPSs) were applied using different friction models. A Coulomb friction model and a rate dependent friction model were constructed using the friction coefficient of a PVDF/MgO friction material to analyze the effect of different friction analysis models. The Coulomb friction model uses a single friction coefficient regardless of friction velocity, while the rate dependent friction model can reflect the change in the friction coefficient with friction velocity. Nonlinear time history and seismic fragility analyses were conducted to confirm responses of the bridge. The seismic responses of a deck and a column were used to evaluate the performance of the base isolated bridge, and a friction model that can effectively evaluate the performance of isolated bridges was analyzed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.1A
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• pp.155-162
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• 2006

This study presents the seismic risk assesment for an extradosed bridge with seismic isolators of lead rubber bearings(LRB). First, the seismic vulnerability of a structure and then the seismic hazard of the site are evaluated using earthquake data set and seismic hazard map in Korea, and then the seismic risk of the structure is assessed. The nonlinear seismic analyses are carried out to consider plastic hinges of bridge columns and nonlinear characteristics of soil foundation. The ductility demand is adopted to describe the nonlinear behavior of a column, and the moment-curvature curve of a column is assumed to be bilinear hysterestic. The fragility curves are represented as a log-normal distribution function for column damage, movement of superstructure, and cable yielding. And seismic hazard is estimated using the available seismic hazard maps. The results show that the effectiveness of the seismic isolators for the columns is more noticeable than those for cables and girders, in seismic isolated extradosed bridges under earthquakes.