• Journal of the Korean Society for Railway
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• v.14 no.6
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• pp.535-544
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• 2011

The rail surface defects can cause the high impact load on the track and lead to the progress of the rail fatigue damage and the rail break. In case of the rail break, there is a great deal of risk for derailment, and thus the maintenance criteria for the rail surface defects are of great importance. In this study, using the dynamic train-track interaction analysis program, the impact wheel loads and rail bending stresses according to the depths of the surface defects have been calculated with the input data of the rail surface irregularities measured at 43 spots with surface defects in the ballasted track of high-speed railway. Considering the irregularity of track geometry, the allowable limits of wheel load and rail bending stress have been set, and the maintenance criteria for the rail surface defects was suggested by analyzing the relationship of the maximum values of wheel load and rail bending stress versus depth and width of rail surface defect. The analysis results suggest that the allowable depth of the surface defect is determined approximately 0.2mm from the limit of the impact wheel load.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.12
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• pp.5931-5937
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• 2011

The effects of coupling beam, which is generally used in high-rise building structure system as shear wall-coupling beam, on the lateral drift of high-rise buildings are studied in this paper. Six different analytical models, which are combination of two inputs, such as concrete strength and wall thickness, are selected and analyzed on lateral drifts with different stiffness of coupling beams. MIDAS GEN was used for analysis. Calculated lateral drifts were compared with allowable limits(H/400~H/500) proposed by standard CEN EC 3/1, in order to analyze the control evaluation of coupling beams. Calculated x-direction displacements were 68~87 percent of allowable limit(H/500). With increase of wall thickness(100mm) and concrete strength(5Mpa), eight to ten percent and four percent of x and y-direction displacement were decreased individually. About three percent of lateral displacement was increased with 20 percent decrease of coupling beam stiffness and additional 20 percent decrease resulted in additional five to eight percent increase.

• Journal of the Korean Society of Safety
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• v.35 no.5
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• pp.39-48
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• 2020

This study proposes a fast estimation method of dynamic reliability indices or failure probability for SDOF structure subjected to earthquake excitations. The proposed estimation method attempts to derive coefficient function for correcting dynamic effects from static reliability analysis in order to estimate the dynamic reliability analysis results. For this purpose, a total of 60 cases of structures with various characteristics of natural frequency and damping ratio under various allowable limits were taken into account, and various types of approximation coefficient functions were considered as potential candidate models for dynamic effect correction. Each reliability index was computed by directly performing static and dynamic reliability analyses for the given 60 cases, and nonlinear curve fittings for potential candidate models were performed from the computed reliability index data. Then, the optimal estimation model was determined by evaluating the accuracy of the dynamic reliability analysis results estimated from each candidate model. Additional static and dynamic reliability analyses were performed for new models with different characteristics of natural frequency, damping ratio and allowable limit. From these results, the accuracy and numerical efficiency of the optimal estimation model were compared with the dynamic reliability analysis results. As a result, it was confirmed that the proposed model can be a very efficient tool of the dynamic reliability estimation for seismically excited SDOF structure since it can provide very fast and accurate reliability analysis results.

• Earthquakes and Structures
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• v.5 no.1
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• pp.83-109
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• 2013

A simple damper optimization method is proposed to find optimal damper allocation for shear buildings under both target added damping ratio and interstorey drift ratio (IDR). The damping coefficients of added dampers are considered as design variables. The cost, which is defined as the sum of damping coefficient of added dampers, is minimized under a target added damping ratio and the upper and the lower constraint of the design variables. In the first stage of proposed algorithm, Simulated Annealing, Nelder Mead and Differential Evolution numerical algorithms are used to solve the proposed optimization problem. The candidate optimal design obtained in the first stage is tested in terms of the IDRs using linear time history analyses for a design earthquake in the second stage. If all IDRs are below the allowable level, iteration of the algorithm is stopped; otherwise, the iteration continues increasing the target damping ratio. By this way, a structural response IDR is also taken into consideration using a snap-back test. In this study, the effects of the selection of upper limit for added dampers, the storey mass distribution and the storey stiffness distribution are all investigated in terms of damper distributions, cost function, added damping ratio and IDRs for 6-storey shear building models. The results of the proposed method are compared with two existing methods in the literature. Optimal designs are also compared with uniform designs according to both IDRs and added damping ratios. The numerical results show that the proposed damper optimization method is easy to apply and is efficient to find optimal damper distribution for a target damping ratio and allowable IDR value.

• Journal of the Korean GEO-environmental Society
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• v.20 no.6
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• pp.5-13
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• 2019

The international trend in soil nailed wall design has been evolved from the allowable stress design to limit state design and it is still currently ongoing. The design guidelines in Korea and Hong Kong still adopts the allowable stress design philosophy while those in others mostly do the limit state design. In this study, four soil nail design methods presented in the major design guidelines (U.S. FHWA GEC 7 (2015), Clouterre in France (1991), Soil nailing - best practice guidance in U.K. (CIRIA, 2005), Geoguide 7 in Hong Kong (2008) and Design standard for slope reinforcement work in Korea (KDS 11 70 15 f: 2016)) are described and analyzed in brief. The factor of safety and CDR (Capacity-to-Demand Ratio) which is used to measure the degree of conservatism of a design guide are obtained for the two cases. One is the design example presented in CIRIA (2005) and the other is in-situ loading test performed on the top of backfill of the soil nail wall to investigate the conservatism of design guidelines. It is revealed that the design method in overall stability of soil nail walls in domestic design method (CDR=0.78) is the most conservative and those by Clouterre (CDR=0.99, 1.09), Geoguide 7 (CDR=1.13, 0.97), U.S. FHWA (CDR=1.09, 1.07) and CIRIA (CDR=1.40, 1.16) in order from the second most conservative to the least conservative for the design example presented in CIRIA. For the in-situ loading test performed on the top of backfill of the soil nail wall, the order of conservatism is identical except that the places of Geoguide 7 (CDR=0.66, 0.72) and FHWA (CDR=0.73, 0.72) are changed. However, the results obtained among U.S. FHWA (2015) and Clouterre (1991) and Geoguide 7 (2008) are not so different.

• Journal of radiological science and technology
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• v.25 no.2
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• pp.47-55
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• 2002

We came to the following conclusion as the results of experiment on the image quality of mammography and the average glandular dose using 4 apparatuses at 3 hospitals in Seoul. 1. Whereas the measurement of half value layer showed no differences among the apparatuses, the measurement by an attenuation curve method showed some differences by 5.9%. There were 9.1% differences in the measurement by aluminum conversion method. 2. The basic density of an automatic exposure control unit must be D = 1.40, but there was no automatic exposure unit adjusted precisely at any hospitals. The unit at the B hospital exceeded the allowable limit by ${\pm}0.15$. 3. In the photographing using an automatic exposure control unit and the management of an automatic film processor using a sensitometer, most automatic film processors were well kept. But in some cases the mean value of a fluctuation coefficient exceeded the allowable limit. There is a need for more cautious management. 4. The image quality of breast phantom photography was affected by the screen/film system among the hospitals. 5. The average glandular dose at a breast of 4.2 cm thickness depended on the tube voltage, In the case of Mo/Mo, it was measured $0.26{\sim}1.39\;mGy$ less than ACR standard 3.0 mGy.

• Journal of the Korean GEO-environmental Society
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• v.12 no.3
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• pp.5-12
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• 2011

In this paper, after studying structural performance for the representative corrugated steel plate used in Korea, we proposed the optimum shape for section of corrugated steel plate considering a width of steel plates that can be produced currently in the factory. Using AISI(1986) in examination for the performance of the corrugated steel plate, we determined the mechanical limit of the optimum sections considering shear force and bending moment of corrugated steel plate and also determined the geometric limit of them considering formability, shapes and ratio between width of steel plate before forming and that after forming. As a result of examination for performance of steel plate applying algorithm for searching optimal sections algorithm developed in this study to the existing representative corrugated steel plate, allowable force and moment of inertia indicated the maximum values at bending radius 76mm and internal bending angle $50^{\circ}$. And as an application result of the optimum design system that used SS490 with 1,550mm of width and 4,700mm of length considering current production situation in Korea, we developed the new section with more than 2 times of structural performance comparing with existing corrugated steel plate.

• Geomechanics and Engineering
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• v.35 no.1
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• pp.29-39
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• 2023

As the intensity of urban underground space development increases, more and more tunnels are planned and constructed, and sometimes it is inevitable to encounter situations where tunnels have to underpass the river embankments. Most previous studies involved tunnels passing river embankments perpendicularly or with large intersection angle. In this study, a project case where two EPB shield tunnels with 8.82 m diameter run parallelly underneath a river embankment was reported. The parallel length is 380 m and tunnel were mainly buried in the moderate / slightly weathered clastic rock layer. The field monitoring result was presented and discussed. Three-dimensional back-analysis were then carried out to gain a better understanding the interaction mechanisms between shield tunnel and embankment and further to predict the ultimate settlement of embankment due to twin-tunnel excavation. Parametrical studies considering effect of tunnel face pressure, tail grouting pressure and volume loss were also conducted. The measured embankment settlement after the single tunnel excavation was 4.53 mm ~ 7.43 mm. Neither new crack on the pavement or cavity under the roadbed was observed. It is found that the more degree of weathering of the rock around the tunnel, the greater the embankment settlement and wider the settlement trough. Besides, the latter tunnel excavation might cause larger deformation than the former tunnel excavation if the mobilized plastic zone overlapped. With given geometry and stratigraphic condition in this study, the safety or serviceability of the river embankment would hardly be affected since the ultimate settlement of the embankment after the twin-tunnel excavation is within the allowable limit. Reasonable tunnel face pressure and tail grouting pressure can to some extent suppress the settlement of the embankment. The recommended tunnel face pressure and tail grouting pressure are 300 kPa and 550 kPa in this study, respectively. However, the volume loss plays the crucial role in the tunnel-embankment interaction. Controlling and compensating the tunneling induced volume loss is the most effective measure for river embankment protection. Additionally, reinforcing the embankment with cement mixing pile in advance is an alternative option in case the predicted settlement exceeds allowable limit.

• Journal of the Korean GEO-environmental Society
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• v.15 no.2
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• pp.5-15
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• 2014

Target reliability index in the limit state design indicated the safety margin and it is important to determine the partial factor. To determine the target reliability index which is needed in the limit state design, the six design and construction case histories of gravel compaction piles (GCP) were investigated. The limit state functions were defined by bulging failure for the major failure mode of GCP. The reliability analysis were performed using the first order reliability method (FORM) and the reliability index was calculated for each ultimate bearing capacity formulation. The reliability index of GCP tended to be penportional to the safety factor of allowable stress design and average value was ${\beta}$=2.30. Reliability level that was assessed by reliability analysis and target reliability index for existing structure foundations were compared and analyzed. As a result, The GCP was required a relatively low level of safety compared with deep and shallow foundations and the currd t reliability level were similar to the target reliability in the reinforced earth retaining-wall and soil-nailing. Therefore the target reliability index of GCP suggested as ${\beta}_T$=2.33 by various literatures together with the computed reliability level in this study.

• Journal of the Korean Geotechnical Society
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• v.28 no.7
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• pp.55-65
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• 2012

Total reduction factor that is used when calculating allowable tensile strength of geogrids is made by multiplying the installation damage reduction factor ($RF_{ID}$), chemical degradation reduction factor ($RF_D$), and creep reduction factor ($RF_{CR}$) etc. In case of a model estimating allowable tensile strength considering reduction factor over the short-term tensile strength of geogrids, it has a limit of not considering interaction force between reduction factors. Junction strength comes to be reduced by installation damages or chemical degradation in the same way as tensile strength. Single junction test method cannot properly test damaged samples and shows large deviations as it does not consider scale effect. Besides, regarding calculating shear strength, no reasonable study on reduction factors was conducted yet. Therefore, in this study, reduction factors that may affect the long-term performance of geogrids were revaluated considering various conditions and accurate long-term allowable tensile strength was calculated considering interrelation between reduction factors. Creep results after installation damage and chemical resistance test showed lower value than calculated value according to GRI GG-4. After the installation damage test and the chemical resistance test, the reduction factor of junction strength was less than that of tensile strength. Shear strength before and after installation damage showed no change or increase.