• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.22 no.4
• /
• pp.396-402
• /
• 2021

A cross section in RC flexural members must be designed to satisfy flexural strength and ductility requirements simultaneously. In design provisions, ductile behavior is ensured by a sufficient reinforcement ratio or depth of the neutral axis. If the reinforcement ratio is less than the balanced reinforcement ratio, ductile behavior is secured, and this value is theoretically the maximum reinforcement ratio. But for a cross section with less steel, brittle failure can occur regardless of ductile behavior because of unqualifying a cracking moment. Recently, designs with a minimum steel ratio have been increasing along with the use of high-strength material, so in design provisions, a minimum amount of reinforcement is suggested. In the KCI(2012) standard, a minimum amount of reinforcement was suggested in terms of strength of steel and concrete. But in the revised KCI(2017) standard, a minimum amount of reinforcement was suggested by a relationship between the design flexural strength and cracking moment indirectly. This code can reflect the effect of cover thickness, but a material model must be defined. Therefore, the minimum amount of reinforcement in KCI(2012) and KCI(2017) was examined, and a rational review method was studied by parametric analysis.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.19 no.11
• /
• pp.750-757
• /
• 2018

The mechanically stabilized earth wall abutment is an earth structure using a mechanically stabilized earth wall and it uses in-extensional steel reinforcements having excellent friction performance. In order to analyze the pullout behavior of in-extensional steel reinforcements usually applied on the mechanically stabilized earth wall abutment, effects of stiffness and particle-size distributions of backfills and also horizontal spacings were considered in this study. As a result of parametric analyses, the highest pulling force acted on the uppermost reinforcement, and the stiffness and the particle-size distributions of the backfill significantly affected the pulling resistance of the reinforced soils. The internal friction angle of backfills should be at least 25 degrees, the coefficient uniformity factor should be at least 4, and the horizontal spacing of the uppermost steel reinforcement should be less than 25cm. Therefore, in order to secure the pullout resistance of the reinforced soil, it is necessary a properly spacing of reinforcement and more strict quality control for the backfill.

• Tunnel and Underground Space
• /
• v.29 no.3
• /
• pp.197-213
• /
• 2019

We simulated the fault reactivation experiment conducted at 'Main Fault' intersecting the low permeability clay formations of Mont Terri Underground Research Laboratory in Switzerland using TOUGH-FLAC simulator. The fluid flow along a fault was modelled with solid elements and governed by Darcy's law with the cubic law in TOUGH2, whereas the mechanical behavior of a single fault was represented by creating interface elements between two separating rock blocks in FLAC3D. We formulate the hydro-mechanical coupling relation of hydraulic aperture to consider the elastic fracture opening and failure-induced dilation for reproducing the abrupt changes in injection flow rate and monitoring pressure at fracture opening pressure. A parametric study was conducted to examine the effects of in-situ stress condition and fault deformation and strength parameters and to find the optimal parameter set to reproduce the field observations. In the best matching simulation, the fracture opening pressure and variations of injection flow rate and monitoring pressure showed good agreement with field experiment results, which suggests the capability of the numerical model to reasonably capture the fracture opening and propagation process. The model overestimated the fault displacement in shear direction and the range of reactivated zone, which was attributed to the progressive shear failures along the fault at high injection pressure. In the field experiment results, however, fracture tensile opening seems the dominant mechanism affecting the hydraulic aperture increase.

• Journal of the Korean GEO-environmental Society
• /
• v.19 no.12
• /
• pp.25-32
• /
• 2018

This paper investigates the effect of rock discontinuities on a shear stress wave that is induced by earthquake or blasting and provides the result of numerical parametric studies. The numerical tests of different conditions of rock and discontinuity have been carried out after confirming that the numerical approach is valid throughout a verification analysis from which the test results were compared with a theoretical solution. In-situ stress condition was considered as a rock condition and internal friction angle and cohesive value, which are the shear strength parameters, were considered as discontinuities condition. The joint inclination angle was also taken into account as a parameter. With the various conditions of different parameters, the test results showed that a shear stress wave propagating through a mass is highly influenced by the shear strength of discontinuities and the condition of joint inclination angle as well as in-situ stress. The study results indicate that when earthquake or blasting-induced dynamic loading propagates through a jointed rock mass or a stratified soil ground the effect of in-situ stress and discontinuities including a stratum boundary should be taken into account when evaluating the dynamic effect on nearby facilities and structures.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.20 no.6
• /
• pp.1105-1123
• /
• 2018

The main risk factors of tunnel excavation through urban areas are ground settlement and surface sink which caused by ground conditions, excavation method, groundwater condition, excavation length, support method, etc. In the process of ground settlement assessment, the numerical analysis should be conducted considering the displacement and stress due to tunnel excavation. Therefore a technique that can simplify such process and easily evaluate the influence of tunnel excavation is needed. This study focused on the tunnelling-induced ground settlement which is main consideration of underground safety impact assessment. The parametric numerical analyses were performed considering such parameters as ground conditions, tunnel depth, and lateral distance from tunnel center line, etc. A simplified ground settlement evaluation chart was suggested by analyzing tendency of ground subsidence, lateral influence area and character by depth. The applicability of the suggested settlement evaluation chart was verified by comparative numerical analysis of settlement characteristics.

• The Korean Journal of Applied Statistics
• /
• v.32 no.4
• /
• pp.543-559
• /
• 2019

Data often include missing values due to various reasons. If the missing data mechanism is not MCAR, analysis based on fully observed cases may an estimation cause bias and decrease the precision of the estimate since partially observed cases are excluded. Especially when data include many variables, missing values cause more serious problems. Many imputation techniques are suggested to overcome this difficulty. However, imputation methods using parametric models may not fit well with real data which do not satisfy model assumptions. In this study, we review imputation methods using nonlinear models such as kernel, resampling, and spline methods which are robust on model assumptions. In addition, we suggest utilizing imputation classes to improve imputation accuracy or adding random errors to correctly estimate the variance of the estimates in nonlinear imputation models. Performances of imputation methods using nonlinear models are compared under various simulated data settings. Simulation results indicate that the performances of imputation methods are different as data settings change. However, imputation based on the kernel regression or the penalized spline performs better in most situations. Utilizing imputation classes or adding random errors improves the performance of imputation methods using nonlinear models.

• Journal of Korea Water Resources Association
• /
• v.52 no.5
• /
• pp.337-347
• /
• 2019

This study proposes the framework to select the representative general circulation model (GCM) for climate change projection. The grid-based results of GCMs were transformed to all considered meteorological stations using inverse distance weighted (IDW) method and its results were compared to the observed precipitation. Six quantile mapping methods and random forest method were used to correct the bias between GCM's and the observation data. Thus, the empirical quantile which belongs to non-parameteric transformation method was selected as a best bias correction method by comparing the measures of performance indicators. Then, one of the multi-criteria decision techniques, TOPSIS (Technique for Order of Preference by Ideal Solution), was used to find the representative GCM using the performances of four GCMs after the bias correction using empirical quantile method. As a result, GISS-E2-R was the best and followed by MIROC5, CSIRO-Mk3-6-0, and CCSM4. Because these results are limited several GCMs, different results will be expected if more GCM data considered.

• Journal of the Korean Geotechnical Society
• /
• v.35 no.7
• /
• pp.29-39
• /
• 2019

Load distributive compression anchors distribute the compressive stress in the grout and increase the pull-out capacity of the anchor by using multiple anchor bodies. In this anchor type, the spacing between the anchor bodies has a large influence on the stress in the grout. However, there are few researches about the spacing and there are no design standards. Therefore, the effect of the anchor body spacing on the grout stress was analyzed by performing finite element analyses. First, the applicability of the numerical modeling was verified by comparing with field test results of a compression anchor. Then, the parametric study was performed varying soil type, anchor body spacing, and load magnitude. The analysis results showed that the maximum compressive stress in the grout increased at the narrower spacing and the tensile stress developed at the wider spacing. Therefore, the optimum spacing was defined as the spacing, which prevents the superposition of compressive stresses and minimize the tensile stress. Finally, the optimum spacing was proposed according to the soil type and the load magnitude.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.47 no.5
• /
• pp.364-370
• /
• 2019

In this paper, an individual blade control (IBC) methodology is applied to find the best input scenario for vibratory hub loads reduction of XH-59A co-axial rotorcraft in high speed flight. A comprehensive aeromechanics analysis code CAMRAD II is employed to analyze the aircraft. A parametric study is conducted for optimum IBC inputs leading to the maximum vibration reduction. Numerical results demonstrate that up to 50% reduction in the hub vibration index is obtained for an IBC input at 3/rev frequency with the amplitude and phase angle of 0.5 deg. and 300 deg., respectively. The upper rotor exhibits as much as 6% more vibration reduction as compared to that of the lower rotor due to a clean inflow characteristic of the rotor. It is found that further vibration reduction gain is reached for IBC inputs with advancing-side only control. The hub vibration becomes reduced by up to 17% in reference to that with full rotor disk control. It is noted that the additional gain is obtained with significantly less power input with the advancing-side only control.

• Journal of the Society of Disaster Information
• /
• v.17 no.3
• /
• pp.454-464
• /
• 2021

Purpose: There is a need to construct an evacuation passageway for the 2-Arch tunnel, which has been constructed and is in operation. Therefore, it aims to analyze tunnel and center wall behaviour and stability due to excavation of the center wall. Method: We describe the theoretical background of 2-Arch tunnel and evacuation passageway, and focused on analyzing the behaviour of tunnel and wall using 3-dimensional finite element analysis. Parametric analysis according to rock rating was performed with various ground conditions, and the displacement and stress of the center wall were intensively analyzed. Result: With the center wall excavation, the largest amount of settlement was shown in the center of the opening, and the stress was greatest during the first excavation. In addition, it was shown that stress concentration occurred at the top of both openings, and stability reviews considering the concept of allowable stress showed that it exceeded the allowable stress. Conclusion: Although the displacement of the tunnel has secured stability within the allowable standard, the generated stress is found to exceed the allowable standard, so it is necessary to prevent sudden stress release by applying appropriate reinforcement methods during construction.