• Journal of Korean Society of Coastal and Ocean Engineers
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• v.31 no.3
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• pp.180-198
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• 2019

In recent years, countries like Europe and Japan have been involved in many researches on the Low-Crested Structure (LCS) which is the method to protect beach erosion and it is regarded as an alternative to the submerged breakwaters, and compiled its results and released the design manual. In the past, studies on LCS have focused on two-dimensional wave transmission and calculating required weight of armor units, and these were mainly examined and discussed based on experiments. In this study, three-dimensional numerical analysis is performed on permeable LCS. The open-source CFD code olaFlow based on the Navier-Stokes momentum equations is applied to the numerical analysis, which is a strongly nonlinear analysis method that enables breaking and turbulence analysis. As a result, the distribution characteristics of the LCS such as water level, water flow, and turbulent kinetic energy were examined and discussed, then they were carefully compared and examined in the case of submerged breakwaters. The study results indicate that there is a difference between the flow patterns of longshore current near the shoreline, the spatial distribution of longshore and on-offshore directions of mean turbulent kinetic energy in case of submerged breakwaters and LCS. It is predicted that the difference in these results leads to the difference in sand movement.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.39 no.6
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• pp.751-758
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• 2019

This study tested various assumptions that simplified the configuration of the numerical model for unsaturated zone's contaminant transport to simulate the pathway to exposed point. This study investigated the contaminant migration through in the pollutant exposure pathway of vadoze zone for risk assessment of the contaminated site. For the purpose, generic scenarios as well as contaminant-based scenarios were simulated using the numerical code for transport of the contaminant in the pathway. The finite-difference one-dimensional transport with adsorption and biodegradation were considered, and it also assumed that the initial concentration was also depleted over time. The results of the generic-scenario show that as the groundwater infiltration rate decreases, the longer the path from the source to the groundwater level, the lower the concentration at the point of inflow into the groundwater level. In particular, in the case of high biodegradation rate and rapid depletion of pollutant sources, statistically outliers were found in the simulated results and generic scenarios was good at prediction.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.4
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• pp.55-66
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• 1991

Presented is a study on the realistic determination of design loads and design criteria for bridge structures. The current bridge design code does not consider realistically the uncertainties inherent in loads and resistances and thus the level of safety varies greatly among the bridge spans. The resonable bridge design loads and design criteria which exhibit uniform reliability among various bridge spans are therefore derived in the present paper. The proposed design loads are determined from the analysis of numerous data obtained from actual traffic survey and the design criteria are based on the advanced concept of load and resistance factor format. The live load factors take into account resonably the effects of traffic volume increase. The proposed design loads and design criteria show uniform safety level for various bridge spans and reasonably consider the effects of traffic volume increase. The present study provides useful and valuable data for new version of our bridge design code.

• Tunnel and Underground Space
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• v.13 no.1
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• pp.64-75
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• 2003

This study presents a newly suggested test method of Mode II fracture toughness measurement called "Punch Through Shear Test" which was originally proposed by Backers and Stephansson in 2001. The purpose of this study is to check the validity of the suggested testing method by performing Mode II fracture toughness tests for Daejeon Granite. In addition, the optimal specimen geometry for the testing and the relation between Mode II fracture toughness and confining pressure were also investigated. Fractured surface was observed to be very smooth with lots of rock debris which came off fracture surface which obviously implies that the surface was sheared off. This confirms that Mode II fracturing actually occurred. In addition, numerical analyses including continuum analysis, particle flow code analysis and crack propagation simulations were performed. Results of these numerical analyses indicated that the cracks occurred in the specimen were predominantly in Mode II and these cracks led to failure of the test specimen. From this investigation, it can be concluded that the newly suggested "Punch Through Shear Test" method provides a reliable means of determining the Mode II fracture toughness. fracture toughness.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.9 no.2
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• pp.1-10
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• 1989

In this paper, dynamic response of a truss bridge due to constantly moving train loads is analysed. Dynamic response of the bridge is found by the mode superposition method with the solution of the eigenvalue problem by Householder transformation and QL algorithm. To prove the validity of the analysis procedure, the response due to a very slowly moving load is compared with the result from the static analysis program, and the dynamic response is also compared with the result from the direct integration method. Based upon this, the variation of dynamic amplification factors is investigated by changing the train types and speeds, and the result is compared with the code specified impact factor. From this study, it was known that the dynamic amplification factor is not quite different by train types in low speeds but in high speeds it is, and in the case of electric car and U. I. C. loads the factor could exceed the code specified impact factor depending upon the speed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.36 no.1
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• pp.1-11
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• 2016

The domestic and foreign seismic design codes have specified that time history covers design response spectrum when the response spectrum, which calculated from the time history, is smaller than the design response spectrum at five points or less. In order to verify the design codes, time history analysis for a pier was performed by using five artificial time histories conforming design code with various characteristics and its member forces were evaluated according to them. It was confirmed from analysis results that, regardless of the conformity to design code requirement, seismic design using the artificial time histories could not guarantee earthquake resistant design if the response spectrum from them is lower than design response spectrum at the similar period to the natural frequency of structure. Thus, the time history generating method to make its acceleration response spectrum to be greater than design response spectrum at all period was proposed by two modification function in this study. It was also verified whether time histories from the proposed method satisfy the seismic design codes or not.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.2
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• pp.21-29
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• 1993

In this paper, a probability-based reliability analysis was proposed based on a finite element method-based random vibration analysis and serviceability limit state of structures. The limit state model defined for the study is a serviceability limit state in terms of the more realistic crack failure that might cause the emission of radioactive materials. The SAP V-2 is used for a three-dimensional finite element analysis of concrete containment structure, and the reliability analysis is carried out by modifying HRAS reliability analysis program for this study. In this study, the load factors for the design of reinforced concrete cointainment structures in Korea are proposed by considering appropriate load combination criteria for design, and the results are compared with the present ASME code. The proposed load factors were proved to be in accordance with a set of code performance objective and showed consistency in the limit state probability.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.3A
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• pp.227-234
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• 2011

Recently, a high strength concrete of more than 40 MPa has been increasingly used in practice. However, use of the high strength concrete may influence on design parameters, particularly stress distribution. This is very true since the current everyday practice employs equivalent rectangular stress distribution that is derived from normal strength concrete. Subsequently, the stress distribution seems to be reevaluated and then a new distribution with new parameters needs to be suggested for the high strength concrete. For this purpose, linear and multiple regression analyses have been carried out in term of using experimental data for the high strength concrete of 40 to 80 MPa available in literatures. Accordingly, new parameters associated with the stress distribution have been proposed and employed for the design of flexural and compressive members. Comparative design examples indicate that designs with new parameters reduce section dimensions compared to those with the current code parameters for concrete strengths of 40 to 70 MPa. In particular, for compressive members, design with new parameters exhibit conservative compressive force compared to those with the current code parameters.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.6A
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• pp.369-378
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• 2012

In this study, direct-search based optimization methods are applied for blade shape optimization of wind turbines and the optimization performances of several methods including conventional genetic algorithm, micro genetic algorithm and pattern search method are compared to propose a more efficient method. For this purpose, the currently available version of HARP_Opt (Horizontal Axis Rotor Performance Optimizer) code is enhanced to rationally evaluate the annual energy production value according to control strategies and to optimize the blade shape using pattern search method as well as genetic algorithm. The enhanced HARP_Opt code is applied to obtain the optimal turbine blade shape for 1MW class wind turbines. The results from pattern search method are compared with the results from conventional genetic algorithm and also micro genetic algorithm and it is found that the pattern search method has a better performance in achieving higher annual energy production and consistent optimal shapes and the micro genetic algorithm is better for reducing the calculation time.

• Journal of the Korea Concrete Institute
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• v.29 no.2
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• pp.179-187
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• 2017

The design provisions for the maximum steel ratio in reinforced concrete flexural members is normally provided to ensure sufficient ductility and economy by steel yielding at member failure. In the Concrete Structural Design Code (2012), the maximum steel ratio is expressed in terms of a net strain in tensile steel, and leading to very high steel ratio in the case of using high strength materials. Thereby, this may result in difficulty to satisfy a required workability at concrete placing. On the contrary, in the Korean Highway Bridge Design Code (Limit State Design) the maximum steel ratio is given in terms of the maximum neutral axis depth ratio that is 0.4. From these results, a rational model for the maximum steel ratio is suggested so as to satisfy a ductility as well as a workability.