• Journal of Korean Society of Steel Construction
• /
• v.29 no.6
• /
• pp.487-495
• /
• 2017

Recently rapid-transit railway systems have been constructed in many developing countries due to its advantages in congestions and environmental problems. Railway bridges show many different aspects compared to road bridges and passenger comfort and traffic safety are one of them. In particular, deflection and acceleration due to repeated vibration characteristics have a structural weakness that can cause undesirable response. Especially steel railway bridges have been known to have weaknesses due to its relatively light weights compared to concrete bridges. The purpose of this study is to analyze the dynamic response of steel box girder bridges due to passing trains then propose the appropriate method to mitigate the level of vibration in terms of accelerations. Three steel railway bridges are tested and the numerical model to analyze the dynamic response of the bridge by passing train are developed. For the verification of the model, the natural frequency extracted using the acceleration data measured in the bridge is compared with the natural frequency of the numerical model. To mitigate the acceleration level of the bridge, parametric studies are performed to find the effectiveness of the method. Based on the analysis, the appropriate method is proposed for decreasing the acceleration of the bridge for passenger comfort and traffic safety.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.28 no.6D
• /
• pp.895-904
• /
• 2008

CWR (Continuous Welded Rail) may be broken when a temperature drop below the neutral temperature changes in axial force, causing tensile fracture and rail gap, in winter. Rail-breaks may lead to the damage of the rail and wheel by dynamic load, and the reduction of running safety if not detected before the passage of a train. In this study, the track and train coupled model with open gap for dynamic interaction analysis, is proposed. Linear track and train systems is coupled by the nonlinear Herzian contact spring and the complete system matrices of total track-train system is constructed. And the interaction phenomenon considering open gap, was defined by assigning the irregularity functions between the two sides of a gap. Time history analysis, which have an iteration scheme such as $Newmark-{\beta}$ method based on Modified Newton-Raphson methods, was performed to solve the nonlinear equation. Finally, numerical studies are performed to assess the effect of various parameters of system, apply to various speeds, open gap size and the support stiffness of rail.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.25 no.4
• /
• pp.305-330
• /
• 2023

Unlike NATM tunnels, Shield TBM tunnels have split linings. Therefore, the stress distribution of the lining is different even if the lining is under the same load. Representative methods for analyzing the stress generated in lining in Shield TBM tunnels include Non-joint Mode that does not consider connections and a 2-ring beam-spring model that considers ring-to-ring joints and segment connections. This study is an analysis method by Break-joint Mode. However, we do not consider the structural role of segment lining connections. The effectiveness of the modeling is verified by analyzing behavioral characteristics against vibration loads by modeling with segment connection interfaces to which vertical stiffness and shear stiffness, which are friction components, are applied. Unlike the Non-joint mode, where the greatest stress occurs on the crown for static loads such as earth pressure, the stress distribution caused by contact between segment lining and friction stiffness produced the smallest stress in the crown key segment where segment connections were concentrated. The stress distribution was clearly distinguished based on segment connections. The results of static analysis by earth pressure, etc., produced up to seven times the stress generated in Non-joint mode compared to the stress generated by Break-joint Mode. This result is consistent with the stress distribution pattern of the 2-ring beam-spring model. However, as for the stress value for the train vibration load, the stress of Break-joint Mode was greater than that of Non-joint mode. This is a different result from the static mechanics concept that a segment ring consisting of a combination of short members is integrated in the circumferential direction, resulting in a smaller stress than Non-joint mode with a relatively longer member length.

• Journal of the Korean Society for Railway
• /
• v.18 no.3
• /
• pp.241-251
• /
• 2015

Compared with ballasted track (BT), ballasted asphalt track (BAT) has been increasingly adopted in many countries due to its more greatly reduced reinforced roadbed thickness and smaller cumulative plastic deformation, and its advantages in terms of maintenance. In this respect, the authors' previous research includes analysis of BAT sections that show performance similar to that of BT sections of the present specifications; reliability verification of the analysis results through real-sized static and dynamic train-load tests were performed. Based on previous research, this paper estimates the track lifetime using the strain of the lower roadbed according to reinforced roadbed thickness; using probabilistic LCC analysis, this paper presents a BAT section that satisfies the design lifetime and that has performance similar to or higher than that of BT.

• Journal of Korean Society of Steel Construction
• /
• v.20 no.4
• /
• pp.455-467
• /
• 2008

The dynamic vehicle running tests were performed to analyze dynamic behavioral characteristics such as displacement, strain history loop and vibration acceleration in arch bridges. Also, the validity of the modeling was verified by comparing the results of the tests and those of the structural analysis modeling. With the resonance revision of verified modeling, when the ratio of excited frequencies to natural frequencies exceeds ${1{\pm}0.04}$, the stability of the bridge is obtained. Also, in the event of resonance by speed parameter, the second mode shape is dominant to the dynamic behaviors of arch bridges. It is found that manipulating the parameters involving arch ribs can increase the second mode natural frequency. It makes critical velocity greater than operational velocities to guarantee the stability of arch bridges.

• Journal of the Korean Society for Railway
• /
• v.18 no.3
• /
• pp.252-260
• /
• 2015

Ballasted track on an asphalt roadbed can be beneficial for its various effects such as (i) decreasing of roadbed thickness by dispersing train load; (ii) prevention of both strength reduction and weakening in roadbed system by preventing rainwater penetration; and (iii) reducing maintenance cost by preventing roadbed mud-pumping and frostbite. With these beneficial effects, ballasted track on asphalt roadbed has been widely used in Europe and Japan, and relevant research for applying such ballasted track on asphalt roadbed systems in Korea is ongoing. In this study, full-scale static and dynamic train load tests were performed to compare the performance of ballasted track on asphalt roadbed and ballasted track. The optimum thickness levels of asphalt and reinforced roadbeds, corresponding to the design criteria for reinforced roadbed of high-speed railway, was estimated using the FEM program ABAQUS. Test results show that the earth pressure on reinforced roadbed of ballasted track on the asphalt roadbed was relatively low compared with that of simple ballasted track. The elastic and plastic displacements of simple ballasted track on the asphalt roadbed were also lower than those of ballasted track. These test results may indicate that the use of ballasted track on asphalt roadbed is an advantageous system in view of long-term maintenance.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.28 no.3D
• /
• pp.399-405
• /
• 2008

Development of the paved track is required as a low-maintenance of conventional line. The paved tracks are one of the types of the ballast reinforced tracks those are manufactured by adopting the prepacked concrete technique. The main elements of this tracks are large sleeper, low elastic pad, fastener, cement mortar, geotextile and recycled ballast. Low elastic pad is the most effective element of such tracks on the basis of stress-displacement characteristics, dynamic response and fatigue characteristics. The stiffness of the pad determine the stiffness of the track. Consequently, it is more important in case of concrete track structure such as paved track because application of low elastic pad seriously effect the durability and stability of the track. The main objective of this study is to confirm the reduction of train load, which transfer to roadbed through various pad effects. To achieve this task static, numerical analysis and real scale repeated loading test was performed while load reduction effect of low elastic pad was analyzed by using displacement, stress and strain ratio characteristics of the paved track.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.33 no.2
• /
• pp.121-128
• /
• 2020

The purpose of this study is to investigate the distribution patterns of displacement and acceleration fields in a nonlinear soil ground based on the interaction of high-speed train, wheel, rail, and ground. For this purpose, a high-speed train in motion was modeled as the actual wheel, and the vertical contact of wheel and rail and the lateral contact, caused by meandering motion, were simulated; this simulation was based on the moving mass analysis. The soil ground part was given the nonlinear behavior of the upper ground part by using the modified the Drucker-Prager model, and the changes in displacement and acceleration were compared with the behavior of the elastic and inelastic grounds. Using this analysis, the displacement and acceleration ranges close to the actual ground behavior were addressed. Additionally, the von-Mises stress and equivalent plastic strain at the ground were examined. Further, the equivalent plastic and total volumetric strains at each failure surface were examined. The variation in stresses, such as vertical stress, transverse pressure, and longitudinal restraint pressure of wheel-rail contact, with the time history was investigated using moving mass. In the case of nonlinear ground model, the displacement difference obtained based on the train travel is not large when compared to that of the elastic ground model, while the acceleration is caused to generate a large decrease.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.8 no.6 s.40
• /
• pp.1-11
• /
• 2004

In the previous study(1), the finite element method was used for the vertical vibration analysis of suspension bridge considering the effects of the shear deformation and the rotary inertia under moving load. This study firstly performs the eigenvalue analysis for the free vertical vibration of suspension bridge using FEM analysis. Next the equations of motion considering interaction between suspension bridge and vehicles/train are derived using mode superposition method. And dynamic analysis was performed using the Newmark $\beta$ Method. Finally through the numerical examples, the dynamic responses of bridges by this study are investigated.

• Journal of Korean Society of Steel Construction
• /
• v.19 no.4
• /
• pp.345-355
• /
• 2007

During winter, the CWR (continuous welded rail) may be broken when a temperature drop below the neutral level changes the axial force, causing tensile fracture and creating a rail gap. The passage of a train on a rail with an open gap may lead to very costly derailments. In this paper, the use of a track-and-train-coupled model whose rail has an open gap is proposed for dynamic interaction analysis. Linear track and train systems were coupled in this study by a nonlinear Herzian contact spring, and the complete system matrices of the total track-train system were constructed. Moreover, the interaction phenomenon considering the presence of an open gap in the rail was toughly defined by assigning the irregularity functions between the two sides of the gap. Time history analysis, which has an iteration scheme such as the Newmark-$\beta$ method (based on the Modified Newton-Raphson methods), was conducted to solve the nonlinear equation. .Finally, numerical studies were conducted to assess the effect of the various parameters of the system when applied to various speeds, open-gap sizes, and support stiffnesses of the rail.