• Earthquakes and Structures
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• 제18권1호
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• pp.83-96
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• 2020

The main structural elements of historical masonry arch bridges are arches, spandrel walls, piers and foundations. The most vulnerable structural elements of masonry arch bridges under transverse seismic loads, particularly in the case of out-of-plane actions, are spandrel wall. The vulnerability of spandrel walls under transverse loads increases with the increasing of their length and height. This paper computationally investigates the out-of-plane nonlinear seismic response of spandrel walls of long-span and high masonry stone arch bridges. The Malabadi Bridge with a main arch span of 40.86m and rise of 23.45m built in 1147 in Diyarbakır, Turkey, is selected as an example. The Concrete Damage Plasticity (CDP) material model adjusted to masonry structures, and cohesive interface interaction between the infill and the spandrel walls and the arch are considered in the 3D finite element model of the selected bridge. Firstly, mode shapes with and without cohesive interfaces are evaluated, and then out-of-plane seismic failure responses of the spandrel walls with and without the cohesive interfaces are determined and compared with respect to the displacements, strains and stresses.

• Journal of Power Electronics
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• 제18권1호
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• pp.45-55
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• 2018

It is usually difficult for dual-active-bridge (DAB) dc-dc converters to operate efficiently at light loads. This paper presents an in-depth analysis of a DAB with triple-phase-shift (TPS) control under the light load condition to overcome this problem. A kind of operating mode which is suitable for light load operation is analyzed in this paper. First, an analysis of the zero-voltage-switching (ZVS) constraints for the DAB converter has been carried out and a reasonable dead-band setting method has been proposed. Secondly, the basic operating characteristics of the converter are analyzed. Third, under the condition of satisfying the ZVS constraints, both the reactive power and the root mean square (RMS) value of the current are simultaneously minimized and a particle swarm optimization (PSO) algorithm is employed to analyze and solve this optimization problem. Lastly, both simulations and experiments are carried out to verify the effectiveness of the proposed method. The experimental results show that the converter can effectively achieve ZVS and improved efficiency.

• Steel and Composite Structures
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• 제38권3호
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• pp.319-336
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• 2021

To achieve a rational detail of the girder-abutment joints in composite integral bridges, and validate the performance of the joints with perfobond connectors, this paper proposes two innovative types of I-shaped steel girder-concrete abutment joints with perfobond connectors intended for the most of bearing capacity and the convenience of concrete pouring. The major difference between the two joints is the presence of the top flange inside the abutments. Two scaled models were investigated with tests and finite element method, and the damage mechanism was revealed. Results show that the joints meet design requirements no matter the top flange exists or not. Compared to the joint without top flange, the initial stiffness of the one with top flange is higher by 7%, and the strength is higher by 50%. The moment decreases linearly in both types of the joints. At design loads, perfobond connectors take about 70% and 50% of the external moment with and without top flange respectively, while at ultimate loads, perfobond connectors take 53% and 26% of the external moment respectively. The ultimate strengths of the reduced sections are suggested to be taken as the bending strengths of the joints.

• 전력전자학회논문지
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• 제27권5호
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• pp.391-396
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• 2022

In this study, a new voltage-balancing dual-active bridge converter that integrates a DAB converter with a voltage balancer is proposed for a bipolar DC distribution system. The proposed converter is configured to connect two loads to the transformer secondary center tap of the DAB converter, and no additional components are added. The proposed converter has the same operation as the conventional DAB converter, and it makes both output voltages similar. Moreover, the imbalanced current offset between the two loads is bypassed only on the secondary side of the transformer. Consequently, the proposed converter integrates a voltage balancer without any additional components, and no additional loss occurs in the corresponding components. Thus, high efficiency and high power density can be achieved. The feasibility of the proposed converter is verified using 3 kW prototypes under 380 V input and 190/190 V output conditions.

• Structural Engineering and Mechanics
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• 제82권1호
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• pp.31-40
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• 2022

In structural engineering, the material properties of the structures such as elastic modulus, shear modulus, density, and size may not be deterministic and may vary at different locations. The dynamic response analysis of such structures may need to consider these properties as stochastic. This paper introduces a stochastic finite element method (SFEM) approach to analyze moving loads problems. Firstly, Karhunen-Loéve expansion (KLE) is applied for expressing the stochastic field of material properties. Then the mathematical expression of the random field is substituted into the finite element model to formulate the corresponding random matrix. Finally, the statistical moment of the dynamic response is calculated by the point estimation method (PEM). The accuracy and efficiency of the dynamic response obtained from the KLE-PEM are demonstrated by the example of a moving load passing through a simply supported Euler-Bernoulli beam, in which the material properties (including elastic modulus and density) are considered as random fields. The results from the KLE-PEM are compared with those from the Monte Carlo simulation. The results demonstrate that the proposed method of KLE-PEM has high accuracy and efficiency. By using the proposed SFEM, the random vertical deflection of a high-speed railway (HSR) bridge is analyzed by considering the random fields of material properties under the moving load of a train.

• 대한토목학회논문집
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• 제28권6A호
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• pp.799-808
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• 2008

국내 교통 현실을 반영한 중(重)차량에 대한 하중 분석은 케이블 교량의 유지관리시 잔존수명 예측을 위한 피로하중모델 개발이나 교량의 설계시 해석에 필요한 활하중 모델 개발시 반드시 필요하다. 이에 본 연구에서는 강합성 사장교 상부구조 하면에 설치된 변형률 센서에서 측정한 신호를 이용하여 교량을 주행하고 있는 중차량의 하중정보를 얻기 위하여, 인공신경망 및 영향선을 이용한 차량하중분석시스템을 개발하였다. 인공신경망의 학습과 테스트를 위한 데이터 확보에 있어서 이론적인 수치 시뮬레이션을 통하지 않고, 실제 교량을 주행하는 임의 차량에 대해 직접 측정한 데이터를 이용하였다. 또한, 학습된 신경망의정확도를 검증하기 위하여 3종류의 시험재하차량을 반복 주행시켜 구한 값과 계량소에서 측정한 정적 값을 비교하였다. 교량의국부거동을 고려하기 위하여 가로보를 이용하였고, 인공신경망을 이용한 방법과 영향선을 이용한 방법의 분석결과를 비교한 결과, 인공신경망이론을 적용한 분석방법이 하중 판별의 정확도에 있어서는 영향선 분석방법보다 높은 정확도를 얻을 수 있었다.

• 한국철도학회논문집
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• 제2권3호
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• pp.36-45
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• 1999

The basic idea of cable-stayed girder bridges is the utilization of high strength cables to provide intermediate supports for the bridge girder so that the girder can span a much longer distance. In the cable-stayed bridge, the cables exhibit nonlinear behavior because of the change in sag, due to the dead weight of the cable, which occurs with changing tension in the cable resulting from the movement of the end points of the cable as the bridge is loaded. Techniques required for the static analysis of cable-stayed bridges has been developed by many researchers. However, little work has been done on the dynamic analysis of such structures. To investigate the characteristics of the dynamic response of long-span cable-stayed bridges due to various dynamic loadings likes moving traffic loads. two different 3-D cable-stayed bridge models are considered in this study. Two models are exactly the same in structural configurations but different in finite element discretization. Modal analysis is conducted using the deformed dead-load tangent stiffness matrix. A new concept was presented by using divided a cable into several elements in order to study the effect of the cable vibration (both in-plane and swinging) on the overall bridge dynamics. The result of this study demonstrates the importance of cable vibration on the overall bridge dynamics.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2007년도 추계학술대회 논문집
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• pp.395-400
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• 2007

LRT(Light Railway Train), which is a intermediate system of train and bus, is arose for the solution of subway construction cost and the transportation capacity of bus. LRT was introduced in 1980's. About 30 local governments are plan to introduce LRT or constructing LRT, at present. AGT(Automated Guide-way Transit) system, which is a kind of LRT, is operated without driver. Rubber wheeled AGT system can reduce the noise and vibration compare to steel wheeled AGT, so it is estimated as ideal transportation system for urban area. And live loads at bridge are classified as the static load of vehicle and the dynamic wheel contact load which is occurred from the interaction of bridge and vehicle vibration, and the surface roughness. In the case of AGT system, the dynamic increment factor of bridge is greater than the normal train bridge and roadway bridge, because, the weight of AGT vehicle is more light that the train of truck. The exact method for dynamic increment factor is experiment. But this method is needed much money and time, moreover, this method cannot be adopted in design. Therefore, a simulation program for the interaction of AGT bridge, vehicle and surface roughness was developed, in this study. And the program was verified by experiment. As a result, the accuracy of the simulation program can be verified.

• Steel and Composite Structures
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• 제26권5호
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• pp.583-594
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• 2018

Although a lot of experimental and analytical investigations have been carried out for steel bridge piers made of SS400 and SM490, the formulas available for SS400 and SM490 are not suitable for evaluating ultimate load and deformation capacities of steel bridge piers made of high strength steel (HSS) SM570. The effect of various parameters is investigated in this paper, including plate width-to-thickness ratio, column slenderness ratio and axial compression force ratio, on the ultimate load and deformation capacities of steel bridge box piers made of SM570 steel subjected to cyclic loading. The elasto-plastic behavior of the steel bridge piers under cyclic loads is simulated through plastic large deformation finite element analysis, in which a modified two-surface model (M2SM) including cyclic hardening is employed to trace the material nonlinearity. An extensive parametric study is conducted to study the influences of structural parameters on the ultimate load and deformation capacities. Based on these analytical investigations, new formulas for predicting ultimate load and deformation capacities of steel bridge piers made of SM570 are proposed. This study extends the ultimate load and deformation capacities evaluation of steel bridge piers from SS400, SM490 steels to SM570 steel, and provides some useful suggestions.

• Structural Engineering and Mechanics
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• 제88권4호
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• pp.379-387
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• 2023

Wind and earthquake loads may cause strong vibrations in large-span cable-stayed bridges, leading to the inability of the bridge to operate normally. An improved Pounding Tuned Mass Damper (PTMD) system was designed to improve the safety of the large-span cable-stayed bridge. The vibration control effect of the improved PTMD system on the large-span cablestayed bridge under the combined action of earthquake-wind-traffic was studied. Furthermore, the impact of different parameters on the vibration suppression performance of the improved PTMD system was analyzed. The numerical results indicate that the PTMD system is very effective in suppressing the displacements of the bridge caused by both the traffic-wind coupling and traffic-earthquake coupling. Moreover, the number, mass ratio, pounding stiffness, and gap values have a significant influence on the vibration suppression performance of the improved PTMD system. When the number of PTMD is increased from 3 to 9, the vibration reduction ratio of the vertical displacement is increased from 25.39% to 48.05%. As the mass ratio changes from 0.5% to 2%, the vibration reduction ratio increases significantly from 22.23% to 53.30%.