• The Journal of the Convergence on Culture Technology
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• v.10 no.3
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• pp.845-849
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• 2024

Currently, rail surface defects are increasing due to the aging of urban railway rails, but in the detailed guidelines for track performance evaluation established by the country, rail surface damage is inspected with the naked eye of an engineer and with simple measuring tools. It is very important to discover defects in the rail surface through periodic track tours and visual inspection. However, evaluating the severity of defects on the rail surface based on the subjective judgment of the inspector has significant limitations in predicting damage inside the rail. In this study, the characteristics of cracks inside the rail due to rail surface damage were studied. In field measurements, rail surface damage was selected, old rail samples were collected in the acceleration and braking sections, and a scanning electron microscope (SEM) was used to evaluate the rail surface damage was used to analyze the crack characteristics. As a result of the analysis, the crack mechanism caused by the running train and the crack characteristics of the acceleration section where cracks occur at an angle rising toward the rail surface were experimentally proven.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.44 no.4
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• pp.503-512
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• 2024

In the seismic design standard, input waves for different levels of seismic performance are proposed in the form of design response spectra. At the time of establishing these standards, measured records of significant earthquakes that occurred domestically, such as the 2016 Gyeongju earthquake and the 2017 Pohang earthquake, were not included. Additionally, for the ground response analysis, shear wave velocities representing ground amplification characteristics were derived from the results of standard penetration tests (N-values) and applied in empirical formulas. This approach may not adequately capture sufficient information about the characteristics of domestic ground properties. Therefore, in this study, seismic records from the Gyeongju and Pohang earthquakes were modified to adjust the bedrock standard design response spectra. Ground response analyses were conducted using shear wave velocity profiles obtained from borehole tests in the Sejong City area. The shape of the response spectrum and ground amplification coefficient obtained from the ground response analysis were then compared with those from existing studies and seismic design standard.

• Journal of Internet Computing and Services
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• v.21 no.6
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• pp.23-31
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• 2020

This study was carried out to generate various images of railroad surfaces with random defects as training data to be better at the detection of defects. Defects on the surface of railroads are caused by various factors such as friction between track binding devices and adjacent tracks and can cause accidents such as broken rails, so railroad maintenance for defects is necessary. Therefore, various researches on defect detection and inspection using image processing or machine learning on railway surface images have been conducted to automate railroad inspection and to reduce railroad maintenance costs. In general, the performance of the image processing analysis method and machine learning technology is affected by the quantity and quality of data. For this reason, some researches require specific devices or vehicles to acquire images of the track surface at regular intervals to obtain a database of various railway surface images. On the contrary, in this study, in order to reduce and improve the operating cost of image acquisition, we constructed the 'Defective Railroad Surface Regeneration Model' by applying the methods presented in the related studies of the Generative Adversarial Network (GAN). Thus, we aimed to detect defects on railroad surface even without a dedicated database. This constructed model is designed to learn to generate the railroad surface combining the different railroad surface textures and the original surface, considering the ground truth of the railroad defects. The generated images of the railroad surface were used as training data in defect detection network, which is based on Fully Convolutional Network (FCN). To validate its performance, we clustered and divided the railroad data into three subsets, one subset as original railroad texture images and the remaining two subsets as another railroad surface texture images. In the first experiment, we used only original texture images for training sets in the defect detection model. And in the second experiment, we trained the generated images that were generated by combining the original images with a few railroad textures of the other images. Each defect detection model was evaluated in terms of 'intersection of union(IoU)' and F1-score measures with ground truths. As a result, the scores increased by about 10~15% when the generated images were used, compared to the case that only the original images were used. This proves that it is possible to detect defects by using the existing data and a few different texture images, even for the railroad surface images in which dedicated training database is not constructed.

• Korean Journal of Construction Engineering and Management
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• v.16 no.4
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• pp.12-20
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• 2015

Construction industry has played a pivotal role in the national economy, but the crisis situation of a construction industry has been worse due to the lack of recognition of the contribution of a construction industry. In particular, the transport sector is responsible for a critical function in the movement of humans and material resources, and has a profound impact on national competitiveness and the peoples' welfare, which requires quantitative analysis. In this study, economic contribution and impact of the transportation sector are measured based on the input-output model. Road and railway facilities account for 1.03% and 0.165% of the total industry respectively, and consist of a final demand and total output. Although value-added inducing effect is small, production inducing effect and backward linkage effect has been high. The results in this study will be used as the basic information for validity of investment and policy decisions.

• Journal of the Korea Concrete Institute
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• v.26 no.4
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• pp.507-515
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• 2014

Although the construction joints of a concrete structure are properly treated with some measures, leakage has frequently occurred. A series of tests on the bond characteristics between new and old concrete were carried out in this study, assuming that the leakage at the construction joints has certain relationship with the bond of concrete. To assess the bond characteristics under various conditions, a number of specimens were made that have an interface between new and old concrete and bond strength, flexural strength and splitting tensile strength were measured. Main test variables are type and amount of mineral admixtures, treatment method of the interface and type of waterstops. In addition, the effects of placing interval between the concrete and of the age of the strength tests were investigated. The test results showed a slightly increased bond strength when applying mineral admixtures, which can be attributed to the interface filled with the calcium silicate hydrate that is formed by pozzolanic reaction. On the other hand, the bond strength was higher when the interface was treated rough and dry, and the roughness of a waterstop affected the bond capacity of the waterstop. Also, an assessment is required that considers the type of strength test because the bond strength varied according to the test methods.

• Journal of the Korea Concrete Institute
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• v.28 no.5
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• pp.545-553
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• 2016

This paper presents experimental static test results of the precast concrete panels developed for short-span concrete bridge deck form. Different from LB-DECK, concrete rib attached to the bottom surface of concrete panel, and Top-bar is not used at the top surface of concrete panel. Number of concrete ribs and cross-section details of concrete rib are determined from the analytical results of parametric study considering the span length and the thickness of concrete bridge decks. Shear rebars are installed at the top surface of concrete panel for composite action between precast concrete panel and cast-in-place concrete. In order to evaluate the safety and the serviceability of the developed short-span concrete panel subjected to design load, static load test is conducted. Three test panels with span length of 1.6m are fabricated, and during the load test displacements, strains and cracks of test panels are measured and final failure modes are investigated. Serviceability of the test panels is evaluated based on the results of displacements, cracking load, and crack width at the design load level. Safety is also evaluated based on the comparison of the ultimate strength and the factored design load of test panels. Based on the test results, it is confirmed the short-span precast concrete panel satisfies the serviceability and safety regulated in design codes. In addition, the range of span length of concrete bridge decks for the short-span concrete panel is discussed.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.86-95
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• 2006

Brillouin backscatter is a type of reflection that occurs when light is shone into an optical fibre. Brillouin reflections are very sensitive to changes in the fibre arising from external effects, such as temperature, strain and pressure. We report here several case studies on the measurement of strain using Brillouin reflections. A mechanical bending test of an I beam, deployed with both fiber optic sensors and conventional strain gauge rosettes, was performed with the aim of evaluating: (1) the capability and technical limit of the DTSS technology for strain profile sensing; (2) the reliability of strain measurement using fiber optic sensor. The average values of strains obtained from both DTSS and strain gauges (corresponding to the deflection of I beam) showed a linear relationship and an excellent one-to-one match. A practical application of DTSS technology as an early warning system for land sliding or subsidence was examined through a field test at a hillside. Extremely strong, lightweight, rugged, survivable tight-buffered cables, designed for optimal strain transfer to the fibre, were used and clamped on the subsurface at a depth of about 50cm. It was proved that DTSS measurements could detect the exact position and the progress of strain changes induced by land sliding and subsidence. We also carried out the first ever distributed dynamic strain measurement (10Hz) on the Korean Train eXpress(KTX) railway track in Daejeon, Korea. The aim was to analyse the integrity of a section of track that had recently been repaired. The Sensornet DTSS was used to monitor this 85m section of track while a KTX train passed over. In the repaired section the strain increases to levels of 90 microstrain, whereas in the section of regular track the strain is in the region of 30-50 microstrain. The results were excellent since they demonstrate that the DTSS is able to measure small, dynamic changes in strain in rails during normal operating conditions. The current 10km range of the DTSS creates a potential to monitor the integrity of large lengths of track, and especially higher risk sections such as bridges, repaired track and areas at risk of subsidence.

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.3
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• pp.277-291
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• 2020

Shield TBM is a tunnelling method that has a wider range of applications in the poor ground condition compared to conventional tunnels (Drill and Blast). Currently, a 13.3 m large-diameter slurry shield TBM is preparing for construction to pass under the Han River. Shield TBM is divided into slurry and EPB shield TBM, and management items during construction are different depending on each characteristic. In this paper, the equipment type, origin, application case and trouble case were analyzed for slurry shield TBM, which is mainly constructed in soft ground. In addition, 2D and 3D model tests were conducted on the condition of soil depth for the possibility of slurry leakage into front of the equipment, with appropriate chamber pressure. Based on this paper, it proposed to provide basic and reference data for proper excavation surface pressure and chamber pressure during construction of slurry shield TBM under soft ground conditions, and proposed measures to minimize stability and environmental decline due to slurry ejection.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.11
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• pp.604-613
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• 2018

In recent years, numerous train derailment accidents caused by deterioration and high speed technology of railways have increased. Guardrails or barriers of railway bridges are installed to restrain and prevent the derailment of the train body level. On the other hand, it can result in a high casualties and secondary damage. Therefore, a Derailment Containment Provision (DCP) within the track at the wheel/bogie level was developed. DCP is designed for rapid installation because it reduces the impact load on the barrier and inertia force on the steep curve to minimize turnover, fall, and trespass on the other side track of the bridge. In this paper, DCP was analyzed using LS-Dyna with a parameter study as the impact loading location and interface contact condition. The contact conditions were analyzed using the Tiebreak contact simulating breakage of material properties and Perfect bond contact assuming fully attached. As a result, the Tiebreak contact behaved similarly with the actual behavior. In addition, the maximum displacement and flexural failure was generated on the interface and DCP center, respectively. The impact analysis was carried out in advance to confirm the DCP design due to the difficulties of performing the actual impact test, and it could change the DCP anchor design as the analysis results.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.4
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• pp.519-534
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• 2019

Mechanized tunneling methods, including shield TBM, have been increasingly used for tunnel construction because of their relatively low vibration and noise levels as well as low risk of rock-falling accidents. In the excavation using the shield TBM, it is important to design penetration rate appropriately. In present study, both subsurface investigation data and shield TBM excavation data, produced for and during ${\bigcirc}{\bigcirc}{\sim}{\bigcirc}{\bigcirc}$ high-speed railway construction, were analyzed and used to compare with shield TBM penetration rates calculated using existing penetrating rate prediction models proposed by several foreign researchers. The correlation between thrust force per disk cutter and uniaxial compressive strength was also examined and, based on the correlation analysis, a simple prediction model for penetration rate was derived. The prediction results using the existing prediction models showed approximately error rates of 50~500%, whereas the results from the simple model proposed from this study showed an error rate of 15% in average. It may be said, therefore, that the proposed model has higher applicability for shield TBM construction in similar ground conditions.