• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.45-46
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• 2010

Fatigue performance of a precast FRP-concrete composite deck with long span economically applicable to a cable-stayed bridge was evaluated. From the experiment, it is verified that the precast FRP-concrete composite deck has sufficient fatigue performance.

• Magazine of the Korea Concrete Institute
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• v.22 no.1
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• pp.65-70
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• 2010

• Computational Structural Engineering
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• v.27 no.3
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• pp.49-54
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• 2014

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2005.05a
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• pp.47-50
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• 2005

In this paper, we investigate a filtering technique to reduce the adverse effect of long motor leads on H-bridge cascaded 7-level inverter fed ac motor drive. The switching surge voltage becomes the major cause to occur the insulation failure by serious voltage stress in the stator winding of high voltage induction motor. However, the effect of switching surge appears un seriousin high voltage induction motor than low voltage induction motor. Consequently, we demonstrated that the filter connected to the motor terminals greatly reduces the transient voltage stress and ringing, moreover we show lowers the dv/dt of the inverter switching pulse. The results of simulation show the suppression of dv/dt and the reduced peak voltage at the motor end of a long cable.

• Wind and Structures
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• v.10 no.1
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• pp.61-82
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• 2007

This paper presents a novel finite element (FE) model for analyzing coupled flutter of long-span bridges using the commercial FE package ANSYS. This model utilizes a specific user-defined element Matrix27 in ANSYS to model the aeroelastic forces acting on the bridge, wherein the stiffness and damping matrices are expressed in terms of the reduced wind velocity and flutter derivatives. Making use of this FE model, damped complex eigenvalue analysis is carried out to determine the complex eigenvalues, of which the real part is the logarithm decay rate and the imaginary part is the damped vibration frequency. The condition for onset of flutter instability becomes that, at a certain wind velocity, the structural system incorporating fictitious Matrix27 elements has a complex eigenvalue with zero or near-zero real part, with the imaginary part of this eigenvalue being the flutter frequency. Case studies are provided to validate the developed procedure as well as to demonstrate the flutter analysis of cable-supported bridges using ANSYS. The proposed method enables the bridge designers and engineering practitioners to analyze flutter instability by using the commercial FE package ANSYS.

• Structural Monitoring and Maintenance
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• v.5 no.1
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• pp.51-65
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• 2018

A number of sensing techniques have been implemented for detecting defects in civil infrastructures instead of onsite human inspections in structural health monitoring. However, the issue of faults in sensors has not received much attention. This issue may lead to incorrect interpretation of data and false alarms. To overcome these challenges, this article presents a deep learning-based method with a new architecture of Stateful Long Short Term Memory Neural Networks (S-LSTM NN) for detecting sensor fault without going into details of the fault features. As LSTMs are capable of learning data features automatically, and the proposed method works without an accurate mathematical model. The detection of four types of sensor faults are studied in this paper. Non-stationary acceleration responses of a three-span continuous bridge when under operational conditions are studied. A deep network model is applied to the measured bridge data with estimation to detect the sensor fault. Another set of sensor output data is used to supervise the network parameters and backpropagation algorithm to fine tune the parameters to establish a deep self-coding network model. The response residuals between the true value and the predicted value of the deep S-LSTM network was statistically analyzed to determine the fault threshold of sensor. Experimental study with a cable-stayed bridge further indicated that the proposed method is robust in the detection of the sensor fault.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2005.03a
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• pp.277-283
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• 2005

Inelastic model of Second Jindo Bridge is investigated to perform nonlinear dynamic analyses with various earthquake ground motions. The modal analysis is performed to obtain dynamic characteristics of the bridge and verify the model. It proves that the model has an appropriate dynamic characteristic and its natural frequency is relatively low. Four ground motions are chosen for time history dynamic analyses; El Centro, Kobe, Taft, and Mexico earthquake. Each ground motion multiplied by specified factors to investigate damages of the structure. The analyses prove that responses of the bridge depend on the duration time and the frequency characteristics of ground motion, not only peak acceleration. Static push-over analysis of steel pylon shows that the dynamic analysis over-estimates the seismic behavior of steel pylon definitely. Nonlinear spring hinge model is suggest to improve the shortage of the inelastic model could not deliberate local buckling damage. According to the time history analysis of nonlinear spring hinge model, it is proved that the inelastic beam element analysis overestimate the seismic capacity of steel pylon unquestionably with a large amount of errors.

• Journal of the Korea Concrete Institute
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• v.24 no.4
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• pp.453-463
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• 2012

Steel-concrete composite rigid-frame bridge is a type of integral bridge having advantages in bridge maintenance and structural efficiency from eliminating expansion joints and bridge supports, the main problems in bridge maintenance. The typical steel-concrete composite rigid-frame bridge has the girder-abutment connection where a part of its steel girder is embedded in abutment for integrity. However, the detail of typical girder-abutment connection is complex and increases the construction cost, especially when a part of steel girder is embedded. Recently, a new type of bridge was proposed to compensate for the disadvantages of complex details and cost increase. The compensation are expected to improve efficiency of construction by simplifying the construction detail of the girder-abutment connection. In this study, a static load test has been carried out to examine the behavior of the girder-abutment connection using real-scale specimens. The results of the test showed that the girder-abutment connection of proposed girder bridge has sufficient flexural capacity and rebars to control concrete crack should be placed on the top of abutment.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.6
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• pp.147-154
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• 2014

The cable damages of the bridge structures induce very important impact on the structural safety, which implies the close monitoring of the cable damage is required to secure sustained safety of the bridges. Most usual available maintenance techniques are based on the monitoring the change of the natural frequency of the structures by damages. However, existing method are based on vibration method to calculate lateral vibration and system identification can calculate the axial stiffness using sensitivity equation by trial error method. But the frequency study by the longitudinal movement need because of the sag effect in system identification. This study proposes a new method to investigate the damage magnitudes and status. The method improves the accuracies in the magnitudes and status of damages by adopting the natural frequency of longitudinal movement. The study results have been validated by comparing them with the approximate solution of FEM. Thus, the relationship of cable damage and frequency appear with relation that the severe damage has the little frequency. If we know the real frequency we can estimate the cable damage severity using this relationship. This method can be possible the efficient management of the cable damage.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.1
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• pp.117-126
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• 2008

In this paper, it is presented a digital image processing method and the program (Visual C++) to determine the shape of the suspension bridge. To investigate the precision of this method, a suspension bridge is divided into 5, 13 and 19 images, respectively, by using the 6.3M pixels digital camera with 300mm zoom lens. Obtained results of the Kwang-Ahn Grand Bridge by using this method are fairly close to the real precision surveyed data. The accuracy is more improved by increasing the number of divided images of the structure. The total cost, man power and time of field survey by this method presented in this study could be much more reduced and the developed program could be applied with little modification for other structures like cable-stayed bridges, if lens compensation algorithms and program access capabilities are improved.