• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.6
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• pp.177-184
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• 2021

In recent years, large-scale earthquake activity has occurred in Korea, and thus public interest in earthquakes is increasing. Accordingly, the importance of seismic performance management of structures is emerging. In particular, the collapse of a bridge, one of main road facilities, directly leads to many casualties. Therefore, engineers need to evaluate the seismic fragility of the bridge and prepare for the earthquake event. The service life of these bridges has been over 30 years, which requires a study on the aging effect on bridges. In this study, seismic analysis of the target RC slab bridge was performed considering the aging effects of each component of the bridge. Components of the bridge included pier and bearing, which dominate the seismic response of the bridge. The seismic performance of the bridge was evaluated using nonlinear static and dynamic analyses. In addition, the limit state and dynamic response of each component were used to evaluate the seismic fragility according to the aging of each component.

• Journal of Korean Society of Steel Construction
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• v.23 no.2
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• pp.147-158
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• 2011

The purpose of this research was to analyze the connections of the seismic-performance values for domestic-performance-based designs. Basic research on the performance design method has been increasing of late, along with performance-based organization investigations. These investigations concern the performance level state of steel structure buildings. According to the performance limit state, seismic-performance values should be presented as appropriate steel structure engineering amounts. The first step, based on the full-scale steel structure experiments, involves researching on the making of a basic document. The moment-rotation angle relationship results of the experiment on the moment-frame connection were used to assort the functional and undamaged limits, which were assumed to be less than the yield moment. Moreover, the repairable and safety limits, which were assumed to exist between the yield and maximum moments, were assorted by investigating the accumulated plastic deformation ratio.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.49 no.7
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• pp.363-369
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• 2000

To flexibly evaluate performance and reliability of an electric power system in the aspect of the real-time system which is intrinsically characterized by stringent timing constraints fails catastrophically if its control input is not updated by its digital controller computer within a certain time limit called the hard deadline, we propose fuzzy-random variables and build a discrete event model embedded with fuzzy-random variables. Also, we adapt fuzzy-variables to a path-space approach, which derives the upper and lower bounds of reliability by using a semi-Markov model that explicitly contains the deadline information. Consequently, we propose certain formulas of state automata properly transformed by fuzzy-random variables, and present numerical examples applying the formulas as well.

• Earthquakes and Structures
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• v.9 no.6
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• pp.1291-1311
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• 2015

This study investigates the seismic energy dissipation capacity of a hybrid passive damper composed of a friction and a hysteretic slit damper. The capacity of the hybrid device required to satisfy a given target performance of a reinforced concrete moment resisting frame designed with reduced design base shear is determined based on the ASCE/SEI 7-10 process, and the seismic performances of the structures designed without and with the hybrid dampers are verified by nonlinear dynamic analyses. Fragility analysis is carried out to investigate the probability of a specified limit state to be reached. The analysis results show that in the structure with hybrid dampers the residual displacements are generally reduced and the dissipated inelastic energy is mostly concentrated on the dampers. At the Moderate to Extensive damage states the fragility turned out to be smallest in the structure with the hybrid dampers.

• Journal of Advanced Marine Engineering and Technology
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• v.15 no.2
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• pp.73-83
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• 1991

A tracking controller which can improve the performance of nonlinear electrohydraulic position control systems is designed and implemented. The method is based on augmenting the system with both compensated integrator and additional integrator, obtaining the feedback control law which stabilizes the linear part of the original nonlinear system, and then readjusting the feedback gains using the describing function method to eliminate the limit cycle in the steady-state. The proposed control law is implemented using OP amplifiers and electronic components, and step and ramp response tests are carried out in the electrohydraulic servomechanism EHS-160. The results show the improvement in both transient and steady-state responses.

• Earthquakes and Structures
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• v.4 no.5
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• pp.527-555
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• 2013

This paper proposes probabilistic models for estimating the seismic demands on reinforced concrete (RC) bridges with base isolation. The models consider the shear and deformation demands on the bridge columns and the deformation demand on the isolation devices. An experimental design is used to generate a population of bridges based on the AASHTO LRFD Bridge Design Specifications (AASHTO 2007) and the Caltrans' Seismic Design Criteria (Caltrans 1999). Ground motion records are used for time history analysis of each bridge to develop probabilistic models that are practical and are able to account for the uncertainties and biases in the current, common deterministic model. As application of the developed probabilistic models, a simple method is provided to determine the fragility of bridges. This work facilitates the reliability-based design for this type of bridges and contributes to the transition from limit state design to performance-based design.

• Proceedings of the KIPE Conference
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• 1998.07a
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• pp.63-69
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• 1998

A new current controlled PWM technique with NPC structure is proposed in this paper. A current controlled PWM technique with neutral-point-clamped pulse-width modulation inverter composed of main switching devices which operates as switch for PWM and auxiliary switching devices to clamp the output terminal potential to the neutral point potential is described. The proposed current controller has a first and second current band. The switching pattern will be made by the first current band. According to the second current band, the output state of the switching pattern is changed into positive and negative state. This inverter output contains less harmonic content and lower switching frequency than that of conventional current controlled PWM technique at the same current limit. Two inverters are compared analytically and the performance is investigated by the computer simulation.

• Computers and Concrete
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• v.20 no.5
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• pp.573-582
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• 2017

Chloride-induced cover cracking will aggravate the performance deterioration for RC structures under the chlorideladen environment, which may endanger the safety of structures and occupants. Traditional design method cannot ensure that a definite performance is satisfied. To overcome the defects, a study on the performance-based design method was carried out in this paper. Firstly, the limit state functions were established for the corrosion initiation and cover cracking. Thereafter, the uncertainty analysis was performed to study the effects of random factors on the time-dependent performances. Partial factor formulae were deduced through the first-order reliability method for performance verification. Finally, an illustrative example was presented and the sensitivity of cover depth to other parameters was carried out. It is found that the uncertainties of the random variables have great effects on the required cover depth. It is demonstrated that the performance-based design method can ensure that the target performance can be satisfied and support to formulate a rational maintenance and repair strategy for RC structures under the chloride environment.

• Journal of Communications and Networks
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• v.8 no.1
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• pp.70-84
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• 2006

We propose a new distributed QoS routing scheme called pre-computation based selective probing (PCSP). The PCSP scheme is designed to provide an exact solution to the constrained optimization problem with moderate overhead, considering the practical environment where the state information available for the routing decision is not exact. It does not limit the number of probe messages, instead, employs a qualitative (or conditional) selective probing approach. It considers both the cost and QoS metrics of the least-cost and the best-QoS paths to calculate the end-to-end cost of the found feasible paths and find QoS-satisfying least-cost paths. It defines strict probing condition that excludes not only the non-feasible paths but also the non-optimal paths. It additionally pre-computes the QoS variation taking into account the impreciseness of the state information and applies two modified QoS-satisfying conditions to the selection rules. This strict probing condition and carefully designed probing approaches enable to strictly limit the set of neighbor nodes involved in the probing process, thereby reducing the message overhead without sacrificing the optimal properties. However, the PCSP scheme may suffer from high message overhead due to its conservative search process in the worst case. In order to bound such message overhead, we extend the PCSP algorithm by applying additional quantitative heuristics. Computer simulations reveal that the PCSP scheme reduces message overhead and possesses ideal success ratio with guaranteed optimal search. In addition, the quantitative extensions of the PCSP scheme turn out to bound the worst-case message overhead with slight performance degradation.

• The Journal of Asian Finance, Economics and Business
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• v.6 no.3
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• pp.131-140
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• 2019

The study aims to examine the impact of productivity in addition to the policy of increasing the foreign investors' ownership rate on the performance of businesses which were listed on Vietnam's stock exchange market from 2010 to 2017. With the database of 3.961 observations, the study employs a statistical method - multiple regression to estimate the relationship between labor productivity, foreign ownership as well as other firm-level characteristics and firm performance. Research findings show that increasing labor productivity and increasing foreign ownership rates help increase firm performance. In addition, except for financial leverage, variables such as liquidity and firm size have positive effects on firm performance measured by Tobin's Q. These findings have theoretical contributions and practical implications for managers, investors and government in Vietnam. Managers should pay attention to improving labor productivity through employing incentive mechanisms, building a good working environment, investing in technology, etc. in order to enhance the firm performance. Investors could utilize the labor productivity and foreign ownership indicators to select stocks of good companies for investment. For Vietnamese government, relaxing the limit of foreign ownership and accelerating the divesting of State capital in State-owned enterprises could help increase the investment scale of foreign investors and resulting in positive effects on the firm performance.