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Jang S.Y.,Korea Railway Research Institute | Jang B.S.,Korea Water Resources Corporation | Oh B.H.,International Association of Fracture Mechanics for Concrete and Concrete Structures IA FraMCoS
ACI Materials Journal | Year: 2010

Expansion of a steel bar due to corrosion causes tensile stresses in concrete around the reinforcing bar and may induce cracking through the concrete cover. The purpose of the present study is to explore realistic mechanical properties of the corrosion layer, including the pressure-free corrosion strain and the stiffness of the corrosion layer. The corrosion products that penetrate into the pores and cracks around a steel bar have been considered in the calculation of expansive pressure due to steel corrosion. A realistic relationship between the expansive pressure and the average strain of the corrosion product layer has been derived and the representative stiffness of the corrosion layer was also determined. A concept of free-expansion (pressure-free) strain of the corrosion product layer was newly introduced to describe the relationship between the expansive pressure and the corrosion layer strain. The comparisons were made between the theory and test data on the surface strains of the concrete cover according to the corrosion amount for various concrete strengths and cover thicknesses. The proposed theory reasonably agrees with experimental data and may be a good base for the realistic durability analysis/design of concrete structures. © 2010, American Concrete Institute. All rights reserved.

Lee J.-H.,Ajou University | Kim Y.-G.,Korea Railway Research Institute | Paik J.-S.,Korea Railway Research Institute | Park T.-W.,Ajou University
Journal of Mechanical Science and Technology | Year: 2012

The global trend in the railway industry is the effort to increase the maximum speed and stability of a train. For an electric railway vehicle to meet this driving performance, stable electric power should be supplied by a catenary system. Various factors affect the current collection performance, most important of which is the dynamic characteristics of a pantograph. In this paper, the sensitivity analysis and design optimization of a pantograph for a high-speed train were conducted using a finite element method. The dynamic catenarypantograph interaction was analyzed by using the commercial finite element analysis software, SAMCEF. The pantograph was modeled as a three degrees of freedom mass-spring-damper system, and the pre-sag of the contact and messenger wire due to gravity was implemented. The span data of a high-speed line was applied in the analysis model. And the dynamic characteristics of the pantograph model were obtained by a performance test. The reliability of the simulation model was verified by comparing the analysis contact force results with the test data. By simulation, the mean contact force and its standard deviation etc. were evaluated, and then sensitivity of the pantograph was analyzed. Based on the sensitivity analysis results, the specification of the pantograph was optimized. In the optimization process, response surface analysis and differential evolutionary algorithm were applied to define the regressive function and to determine the optimum values for stable current collection performance. Finally, the improvement of the current collection performance was verified by comparing the optimum specification results with the original specification. © 2012 The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.

Rhee I.,Korea Railway Research Institute | Choi E.,Hongik University | Roh Y.-S.,Seoul National University of Science and Technology
KSCE Journal of Civil Engineering | Year: 2012

Approximately 35% of Korean railroad bridges are classified as steel plate girder bridges. Their connections in the vicinity of stiffeners and other secondary members toward the main girder can be progressively deteriorated owing to stress concentrations, residual stress, welding defects, and harsh environmental conditions. Most bridges of this type were built in the early 1900s, hence, they suffer from aging and progressive degradation of connection zones, and they require extensive maintenance. In accordance with these efforts, the objective of this study is to address the detailed analysis of thin steel plates with bolt connections in order to simulate a method for detecting damage due to loosening in mechanically fastened zones of steel plate girders. For simplicity, we confine this study to previous laboratory-scale experiments for bolt connection problems using PZT (Lead-Zirconate-Titanate) sensors, and we carry out a comparative study with the aid of stress wave transmission using the finite element method, signal processing using wavelets, and piezoelectricity. We carried out fundamental modal analysis and transient dynamic analysis with 3D piezoelectric elements as a sensor/actuator in an open circuit. The material deviation effect of the piezoelectric patch manufacturing process, poling directional properties, geometrical modeling of bolts (bolt pressure), waveform sensitivity, and phase/group velocity characteristics of generated Lamb waves are discussed in conjunction with time-frequency-scale domain analysis. © 2012 Korean Society of Civil Engineers and Springer-Verlag Berlin Heidelberg.

Jeon K.W.,Hanbat National University | Shin K.B.,Hanbat National University | Kim J.S.,Korea Railway Research Institute
Transactions of the Korean Society of Mechanical Engineers, A | Year: 2011

We describe the evaluation of the fatigue life and strength of a lightweight railway bogie frame made of glass fiber/epoxy 4-harness satin-woven composites. To obtain the S-N curve for the evaluation of the fatigue characteristics of the composite bogie frame, we performed a tension-compression fatigue test for composite specimens with different stacking sequences of the warp direction, fill direction, and 0°/90° direction. We used a stress ratio (R) of -1, a frequency of 5 Hz, and an endurance limit of 10 . The fatigue strength of the composite bogie frame was evaluated by a Goodman diagram according to JIS E 4207. The results show that the fatigue life and strength of the lightweight composite bogie satisfy the requirements of JIS E 4207. Given its weight, its performance was better than that of a conventional metal bogie frame based on an SM490A steel material. © 2011 The Korean Society of Mechanical Engineers.

Song K.Y.,Chung - Ang University | Yoon H.J.,Korea Railway Research Institute
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

We newly propose and experimentally demonstrate high-sensitivity optical time-domain reflectometry based on Brillouin dynamic grating in polarization maintaining fiber. Distributed measurements with strain sensitivity as high as ∼ 1 MHz/με is demonstrated in a 110 m fiber under test with 0.8 m spatial resolution. The operation principle with the condition for proper measurement of the grating spectrum and the advantageous features such as low operating power, high signal to noise ratio, and simple data-acquisition process are explained in comparison with ordinary Brillouin optical time-domain reflectometry, which is verified by the experimental results. © 2012 SPIE.

Song K.Y.,Chung - Ang University | Yoon H.J.,Korea Railway Research Institute
Optics Letters | Year: 2010

We propose and experimentally demonstrate a high-resolution distributed measurement of the Brillouin gain spectrum in a polarization-maintaining fiber (PMF) using Brillouin dynamic grating. In our approach, acoustic waves which contain the information of the local Brillouin frequency are generated by a long pump pulse in one polarization along the PMF and are read out by a short probe pulse with an orthogonal polarization at a different optical frequency from the pump. In experiments, a distributed strain measurement with a 10 cm spatial resolution is demonstrated in a 105 m PMF. © 2009 Optical Society of America.

Pil Jung S.,Korea Automotive Technology Institute | Guk Kim Y.,Korea Railway Research Institute | Sung Paik J.,Korea Railway Research Institute | Won Park T.,Ajou University
Journal of Computational and Nonlinear Dynamics | Year: 2012

This paper presents a model of the catenary and pantograph and an analysis of their dynamic interaction, using the finite element method. An analytical procedure to calculate the length of droppers is introduced. The calculated dropper length is applied to the catenary model and the static deformation due to gravity is simulated. The presag result of the contact wire is validated by comparison with the design specification. The wave propagation speed of the catenary model is acquired by applying the impact force to the contact wire. The result, regarding the wave propagation speed, agrees well with the reference speed as defined by the UIC code. On the contrary, the pantograph model is unified with the finite element catenary model, and the dynamic interaction of the catenary-pantograph is simulated. An optimization technique to find the material properties of the pantograph model is proposed. Based on the following performance test data, the optimum values of the material properties are found by using the response surface analysis method. The reliability of the pantograph-catenary model is verified by comparing the contact force results obtained from the simulation and test. When the pantograph drives at 305 km/h, 370 km/h, and 430 km/h, the contact force variation and the possibility of loss of contact are discussed. © 2012 American Society of Mechanical Engineers.

Choi H.-Y.,Korea Railway Research Institute | Lee D.-H.,Korea Railway Research Institute | Lee J.,Yonsei University
Wear | Year: 2013

Damage to wheels and rails due to wear and fatigue affects the safety and maintenance of railway vehicles. The present study optimizes profile of the wheel flange for reducing flange wear and surface fatigue on a curved track. The railway dynamic analysis program VAMPIRE is employed to calculate different loading conditions, contact pressure, wear and fatigue on the running surface of the wheel. The multi-objective optimization of minimizing both flange wear and surface fatigue is handled by a fast non-dominated sorting genetic algorithm, NSGA-II. Optimized designs yield better performance and reduced wear and fatigue compared to an initial wheel profile. © 2013 Elsevier B.V.

Song K.Y.,Chung - Ang University | Yoon H.J.,Korea Railway Research Institute
Optics Letters | Year: 2010

We experimentally demonstrate that the reflection spectrum of a Brillouin dynamic grating in a polarizationmaintaining fiber can be much narrower than the intrinsic linewidth of the stimulated Brillouin scattering, matching well with the theory of a fiber Bragg grating in terms of the linewidth and the reflectivity. A 3 dB bandwidth as narrow as 10.5 MHz is observed with the Brillouin dynamic grating generated in a 9 m uniform fiber. © 2010 Optical Societv of America.

Lee Y.-H.,Korea Railway Research Institute
ICCAS 2010 - International Conference on Control, Automation and Systems | Year: 2010

The train control system (TCS) plays the core role to secure the safety and punctuality for railway train operation. There are various systems applied to urban transit lines which are developed differently and independently from other countries. The national standard specifications and guidelines have been established and maintained for the TCS in Korea. As the requirements of the high-efficient and economic operation of the urban transit system is getting higher, the unmanned operation of the train is moving to the limelight. Lots of systems supporting unmanned operation are being applied to the new lines such as Yongin, Busan (3rd line), Incheon (2nd line) and so on. The standard of the TCS for urban transit supports the system for unmanned operation as requirements. The function model of TCS has been established on the basis of the standard specification to analyze the requirements and behavior of the TCS. The model is also to support the test and evaluation of the system to be operated with the unmanned through the standard. ©ICROS.

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