• Journal of the Korean Society for Railway
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• v.20 no.5
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• pp.668-682
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• 2017

Alignments of railways recently constructed in Korea have been straightened due to the advent of high-speed rail, which means increasing the numbers of tunnels and bridges. Overbreak during tunnel construction may be unavoidable, and is very influential on overall stability. Over-excavation in tunneling is also one of the most important factors in construction costs. Overbreak problems around crown areas have decreased with improvements of excavation methods, but overbreak problems around bottom areas have not decreased because those areas are not very influential on tunnel stability compared with crown areas. The filling costs of 10 cm thickness of overbreak at the bottom of a tunnel are covered under construction costs by Korea Railway Authority regulations, but filling costs for more than the covered thickness are considered losses of construction cost. The filling material for overbreak bottoms of tunnels should be concrete, but concrete and mixed granular materials with fractured rock are also used for some sites. Tunnels in which granular materials with fractured rock are used may have a discontinuous section under the concrete slab track. The discontinuous section influences the propagation of waves generated from train operation. When the bottom of a tunnel is filled with only concrete material, the bottom of the tunnel can be considered as a continuous section, in which the waves generated from a train may propagate without reflection waves. However, a discontinuous section filled with mixed granular materials may reflect waves, which can cause resonance of vibration. The filled materials and vibration propagation characteristics are studied in this research. Tunnel bottom filling materials that have ratios of granular material to concrete of 5.0 %, 11.5 %, and 18.0 % are investigated. Samples were made and tested to determine their material properties. Static numerical analyses were performed using the FEM program under train operation load; test results were found to satisfy the stability requirements. However, dynamic analysis results show that some mixed ratios may generate resonance vibration from train operation at certain speeds.

• Structural Engineering and Mechanics
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• v.43 no.5
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• pp.607-621
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• 2012

The Expo Culture Centre is one of the permanent buildings at the World Expo 2010 in Shanghai, China. The main structure has an oval shape and consists of 36 radial cantilever steel trusses with different lengths and inner frames made of concrete-filled rectangular steel tube members. Tuned mass dampers are used to reduce the excessive vibrations of the sixth floor that are caused by human-induced resonance. A three-dimensional analytical model of the system is developed, and its main characteristics are established. A series of field tests are performed on the structure, and the test results show that the vertical vibration frequencies of most structural cantilevers are between 2.5 Hz and 3.5 Hz, which falls in the range of human-induced vibration. Twelve pairs of tuned mass dampers weighing 115 tons total were installed in the structure to suppress the vibration response of the system. These mass dampers were tuned to the vertical vibration frequency of the structure, which had the highest possibility of excitation. Test data obtained after the installation of the tuned mass dampers are used to evaluate their effectiveness for the reduction of the vibration acceleration. An analytical model of the structure is calibrated according to the measured dynamic characteristics. An analysis of the modified model is performed and the results show that when people walk normally, the structural vibration was low and the tuned mass dampers have no effect, but when people run at the structural vibration frequency, the tuned mass dampers can reduce the floor vibration acceleration by approximately 15%.

• Journal of the Korean Society for Railway
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• v.14 no.6
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• pp.526-534
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• 2011

In this study, proposed is the methodology to determine the upper limit for stiffness of rail pad for the ballasted and concrete track in high-speed railway in the viewpoint of running safety, considering the dynamic characteristics of train and track and the operation environment. For the track irregularity, one of the most important input parameters for traintrack interaction analysis, the reference vertical track irregularity PSDs(power spectral densities) for the ballasted and concrete track in a wide range of frequencies were proposed based on those presented in France and Germany and that obtained from the measured data at Kyeong-Bu 1st phase high-speed railway line. Using these reference PSD models, the input data for the vertical track irregularity data were regenerated by random generation process, and then, the wheel load reduction rates according to the stiffness of the rail pads have been calculated by the train-track interaction analysis technique. Finally, by comparing the wheel load reduction rates calculated with the derailment criteria prescribed in the Korean standards for railway vehicle safety criteria, the upper limits for the stiffness of rail pad have been proposed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.41 no.1
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• pp.21-28
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• 2021

The main purpose of this study is to assess the safety of the fixed anchorages subjected to the seismic motion for an operating facilities in the actual power plant. Thus, the experimental study was conducted to investigate the load response in the event of an actual seismic to the anchorages of a nonstructural components. Since there are economic and spatial constraints to study nonstructural components that actually have various forms, alternative test specimens of steel frames with mass were built and the shaking table test was carried out. In order to evaluate the dynamic characteristics and seismic performance, the natural frequency of the target structure was identified through the shaking table test and then the load response characteristics of the anchorage were evaluated by generating an artificial seismic effect like actual seismic. Finally, the structural stiffness was reinforced by fixing the steel frame to the test specimen using bolts, thereby reducing the load transmitted to the anchorage. It will be carried out on the reliability verification of the experiments and areas that have not been carried out due to the site conditions through the analytical approach in the future.

• Journal of the Korean Geotechnical Society
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• v.40 no.1
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• pp.5-14
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• 2024

PHC piles demonstrate superior resistance to compression and bending moments, and their factory-based production enhances quality assurance and management processes. Despite these advantages that have resulted in widespread use in civil engineering and construction projects, the design process frequently relies on empirical formulas or N-values to estimate the soil-pile friction, which is crucial for bearing capacity, and this reliance underscores a significant lack of experimental validation. In addition, environmental factors, e.g., the pH levels in groundwater and the effects of seawater, are commonly not considered. Thus, this study investigates the influence of vibrating machine foundations on PHC pile models in consideration of the effects of varying pH conditions. Concrete model piles were subjected to a one-month conditioning period in different pH environments (acidic, neutral, and alkaline) and under the influence of seawater. Subsequent repeated direct shear tests were performed on the pile-soil interface, and the disturbed state concept was employed to derive parameters that effectively quantify the dynamic behavior of this interface. The results revealed a descending order of shear stress in neutral, acidic, and alkaline conditions, with the pH-influenced samples exhibiting a more pronounced reduction in shear stress than those affected by seawater.

• Journal of the Korean Society for Railway
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• v.18 no.3
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• pp.175-185
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• 2015

Generally, in the train area, switch tracks have required high reliability because this system is directly associated with derailment. Especially, switch tracks of Maglev vehicles must be moved in terms of the whole geometric characteristics, in which the bogies are encased in the switch track. For this reason, switch track was constructed with steel lighter than concrete girders. But, the steel switch track was weak because of structural vibration as well as structural deformation. Therefore, it is important to predict the levitation stability when a vehicle passes over flexible switch track. The aims of this paper are to develop a coupled dynamic model to describe the relationship between a Maglev vehicle and switch track and to predict the levitation stability. In order to develop the coupled dynamic model, a three dimensional vehicle model was developed based on multibody dynamics; a switch model was made using the modal superposition method. And, the developed model was verified using comparison measured data.

• Tunnel and Underground Space
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• v.9 no.3
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• pp.185-193
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• 1999

This paper presents results of dynamic analysis for a bridge in intersection part of two tunnels subjected to moving vehicle load. Since such a bridge system is very unusual due to the fact that it is located in tunnel, the dynamic characteristics of the structure can not be assumed as conventional one. The structure investigated in this study it a reinforced concrete bridge in the intersection part of Namsan Tunnel-1 and Tunnel-2 in Seoul. It is supported by temporary steel structure which shall be constructed during the period of replacing lining in Tunnel-2. Dynamic analysis was carried out for the system using a finite element model constructed by general purpose FE program SAP2000. For this purpose, the structure, lining of tunnels, and surrounding rock were represented by finite elements, while the rock region it truncated and on its outer boundary viscous dampers were placed to simulate radiation of elastic waves generated tunnels. Several types of vehicle with various driving velocities were considered in this analysis. The FE model including vehicle loadings was verified by comparing calculated peak particle velocity with the measured one. From the analysis, the impart factor for the bridge was estimated as 0.21, which indicates that the use of upper bound for the impact factor in design code is reasonable for this kind of bridge system.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.12
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• pp.120-127
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• 2016

This study examined the dynamic characteristics of the gate to identify the optimal gate installation direction according to the installation direction. A 1:31 scale model was constructed for a 47.5m prototype gate using acrylic. The scaled weights were tuned by adding lead weights. The first step was to measure the natural frequencies of the model gates, and compare them with finite-element analysis of the prototypes as a calibration. The scaled model was tested in a 1.6 m wide concrete flume for two orientations to determine the effects of the gate orientation on structural vibrations. Vertical vibrations were measured under a range of operational conditions, including a range of bottom opening heights and different upstream and downstream water levels. For large bottom opening heights in the normal direction, relatively large vibrations were induced by vortices shed at the plate bottom that would strike the horizontal truss member. This phenomenon was avoided in the reverse direction. For small bottom opening heights in the normal direction, these vibrations were caused by a suction force that developed at the gate bottom. The gate model in the reverse direction was preferred because of its low overall vibrational response under general gate opening and flow level combinations.

• Geomechanics and Engineering
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• v.12 no.4
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• pp.611-626
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• 2017

The research reported herein is concerned with the model testing of piles socketed in soft rock which was simulated by cement, plaster, sand, water and concrete hardening accelerator. Model tests on a single pile socketed in simulated soft rock under axial cyclic loading were conducted and the bearing capacity and accumulated deformation characteristics under different static, and cyclic loads were studied by using a device which combined oneself-designed test apparatus with a dynamic triaxial system. The accumulated deformation of the pile head, and the axial force, were measured by LVDT and strain gauges, respectively. Test results show that the static load ratio (SLR), cyclic load ratio (CLR), and the number of cycles affect the accumulated deformation, cyclic secant modulus of pile head, and ultimate bearing capacity. The accumulated deformation increases with increasing numbers of cycles, however, its rate of growth decreases and is asymptotic to zero. The cyclic secant modulus of pile head increases and then decreases with the growth in the number of cycles, and finally remains stable after 50 cycles. The ultimate bearing capacity of the pile is increased by about 30% because of the cyclic loading thereon, and the axial force is changed due to the applied cyclic shear stress. According to the test results, the development of accumulated settlement is analysed. Finally, an empirical formula for accumulated settlement, considering the effects of the number of cycles, the static load ratio, the cyclic load ratio and the uniaxial compressive strength, is proposed which can be used for feasibility studies or preliminary design of pile foundations on soft rock subjected to cyclic loading.

• Journal of Korean Association for Spatial Structures
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• v.24 no.3
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• pp.43-51
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• 2024

Dynamic responses of nuclear power plant structure subjected to earthquake loads should be carefully investigated for safety. Because nuclear power plant structure are usually constructed by material of reinforced concrete, the aging deterioration of R.C. have no small effect on structural behavior of nuclear power plant structure. Therefore, aging deterioration of R.C. nuclear power plant structure should be considered for exact prediction of seismic responses of the structure. In this study, a machine learning model for seismic response prediction of nuclear power plant structure was developed by considering aging deterioration. The OPR-1000 was selected as an example structure for numerical simulation. The OPR-1000 was originally designated as the Korean Standard Nuclear Power Plant (KSNP), and was re-designated as the OPR-1000 in 2005 for foreign sales. 500 artificial ground motions were generated based on site characteristics of Korea. Elastic modulus, damping ratio, poisson's ratio and density were selected to consider material property variation due to aging deterioration. Six machine learning algorithms such as, Decision Tree (DT), Random Forest (RF), Support Vector Machine (SVM), K-Nearest Neighbor (KNN), Artificial Neural Networks (ANN), eXtreme Gradient Boosting (XGBoost), were used t o construct seispic response prediction model. 13 intensity measures and 4 material properties were used input parameters of the training database. Performance evaluation was performed using metrics like root mean square error, mean square error, mean absolute error, and coefficient of determination. The optimization of hyperparameters was achieved through k-fold cross-validation and grid search techniques. The analysis results show that neural networks present good prediction performance considering aging deterioration.