• Title/Summary/Keyword: Numerical Analyses

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Numerical Evaluation of Geosynthetic Reinforced Column Supported Embankments (개량체 기둥지지 성토공법의 지오그리드 보강효과에 대한 수치해석)

  • Jung, Duhwoe;Jeong, Sidong
    • Journal of the Korean Geosynthetics Society
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    • v.20 no.2
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    • pp.13-22
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    • 2021
  • Pile or column supported embankments have been increasingly employed to construct highway or railway embankments over soft soils. Piles or columns of stiffer material installed in the soft ground can provide the necessary support by transferring the embankment load to a firm stratum using a soil arching. However, there has been reported to occur a relatively large differential settlement between the piles and the untreated soils. Geosynthetic reinforced pile or column supported embankment (GRPS) is often used to minimize the differential settlement. Two dimensional finite element anlyses have been performed on both the column supported embankments and the geogrid reinforced column supported embankments by using a PLAXIS 2D to evaluate the soil arching effect. Based on the results obtained from finite element analyses, the stress reduction ratio decreases as the area replacement ratio increases in the column supported embankments. For the geogrid reinforced column supported embankments, the geogrid reinforcemnt can reduce differential settlements effectively. In additon, the use of stiffer geogrid is appeared to be more effective in reducing the differential settlements.

Comparison of behavior of high-rise residential buildings with and without post-tensioned transfer plate system

  • Byeonguk Ahn;Fahimeh Yavartanoo;Jang-Keun Yoon;Su-Min Kang;Seungjun Kim;Thomas H.-K. Kang
    • Computers and Concrete
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    • v.31 no.4
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    • pp.337-348
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    • 2023
  • Shear wall is commonly used as a lateral force resisting system of concrete mid-rise and high-rise buildings, but it brings challenges in providing relatively large space throughout the building height. For this reason, the structure system where the upper structure with bearing, non-bearing and/or shear walls that sits on top of a transfer plate system supported by widely spaced columns at the lower stories is preferred in some regions, particularly in low to moderate seismic regions in Asia. A thick reinforced concrete (RC) plate has often been used as a transfer system, along with RC transfer girders; however, the RC plate becomes very thick for tall buildings. Applying the post-tensioning (PT) technique to RC plates can effectively reduce the thickness and reinforcement as an economical design method. Currently, a simplified model is used for numerical modeling of PT transfer plate, which does not consider the interaction of the plate and the upper structure. To observe the actual behavior of PT transfer plate under seismic loads, it is necessary to model whole parts of the structure and tendons to precisely include the interaction and the secondary effect of PT tendons in the results. This research evaluated the seismic behavior of shear wall-type residential buildings with PT transfer plates for the condition that PT tendons are included or excluded in the modeling. Three-dimensional finite element models were developed, which includes prestressing tendon elements, and response spectrum analyses were carried out to evaluate seismic forces. Two buildings with flat-shape and L-shape plans were considered, and design forces of shear walls and transfer columns for a system with and without PT tendons were compared. The results showed that, in some cases, excluding PT tendons from the model leads to an unrealistic estimation of the demands for shear walls sit on transfer plate and transfer columns due to excluding the secondary effect of PT tendons. Based on the results, generally, the secondary effect reduces shear force demand and axial-flexural demands of transfer columns but increases the shear force demand of shear walls. The results of this study suggested that, in addition to the effect of PT on the resistance of transfer plate, it is necessary to include PT tendons in the modeling to consider its effect on force demand.

Centrifuge Model Tests on Trafficability of Very Soft Ground Treated with Geotextile and Sand Mat (토목섬유와 모래로 처리된 초연약지반의 장비주행성에 대한 원심모형실험)

  • Jun, Sang-Hyun;Lee, Jong-Ho;Yoo, Nam-Jae
    • Journal of the Korean Geotechnical Society
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    • v.26 no.3
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    • pp.13-23
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    • 2010
  • In this study, centrifuge model tests with 50 g gravitational condition were performed to evaluate the bearing capacity of very soft ground, improved by spreading geotextile and sand on the surface of ground, for the heavy machinery to be able to access. For undrained shear strength of ground model, prepared with the clay sampled from the field, being in the range of 3.1~11.7 kPa, bearing capacity tests were performed with the model footing and the loading system built to simulate the heavy machinery on the ground model treated with geotextile and sand. Test results were compared with theoretically and numerically evaluated ones. Test results about load-settlement curves showed that the bearing capacity increases with the increase of the undrained shear strength of ground. Punching shear or local shear failure was also observed. For a relatively low undrained shear strength of ground, settlement behavior is found to be crucial to evaluating the trafficability of machinery whereas bearing capacity becomes a dominant factor with the increase of undrained shear strength of ground. The method for assessing the bearing capacity of the ground related to trafficability of machinery is presented by acquiring the regression relationship between the contact pressure of machinery and settlements using load-settlement curves with the change of the undrained shear strength. Furthermore, results of numerical analyses about load-settlement relation are in relatively good agreement with those of centrifuge model test.

A Comparison of Bearing Capacity Equations for a Single Pile Considering Negative Skin Friction (부주면마찰력을 고려한 단말뚝의 허용지지력 공식 분석)

  • Lee, Sung-June;Jeong, Sang-Seom;Ko, Jun-Young
    • Journal of the Korean Geotechnical Society
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    • v.26 no.8
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    • pp.27-37
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    • 2010
  • Downdrag force develops when a pile is driven through a soil layer which will settle more than a pile. There is no obvious criterion for application of the current pile design method considering the negative skin friction. Therefore, in this study, numerical analyses were performed to investigate the behavior of a single pile subjected to negative skin friction and their results were used to determine the applicability of the current design method. Including three different sites in Song-do area and two different cases with friction pile and end bearing pile conditions, total six cases were considered. The load-settlement relationships and the neutral points were estimated for different end bearing conditions and the allowable bearing capacity of piles with negative skin friction was investigated through parametric studies. Based on the results showed that the negative skin friction made a major influence on the settlement of a pile and its stress. However the allowable bearing capacity may not be influenced by the negative skin friction. Compared with the allowable bearing capacity obtained from the ultimate bearing capacity with the safety factor of 3, the current design method with the safety factor of 3 underestimated the allowable bearing capacities regardless of the end bearing conditions. On the other hand, the current design method with the safety factor of 2 yielded reasonable results depending on the end bearing conditions.

Load-Settlement Characteristics of Concrete Top-Base Foundation on Soft Ground (연악지반에 시공된 팽이말뚝기초(Top-Base)의 하중-침하량 분석)

  • Kim, Jae-Young;Jeong, Sang-Seom;Kim, Soo-Kwan
    • Journal of the Korean Geotechnical Society
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    • v.26 no.1
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    • pp.35-43
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    • 2010
  • The behavior of the Top-Base foundation was investigated by carrying out 3D finite element method. Special attention is given to the settlement behavior of concrete Top-Base foundation due to the consolidation settlement of the embedding depth and the effect of footing dimensions which are not included in the practical design. To obtain the detailed informations, a series of numerical analyses were performed for different pile configurations. It is shown that as the number of piles in a group increases, the calculated settlement also increases. However, for the $7\times7$ group, there is no further increase in settlement. Based on this study, it is found that the total settlement of Top-Base foundation is highly influenced by the consolidation settlement and footing configurations. It is also found that the current design method overestimates the settlement, and thus, needs to be modified and supplemented.

Seismic performance assessment of single pipe piles using three-dimensional finite element modeling considering different parameters

  • Duaa Al-Jeznawi;Jitendra Khatti;Musab Aied Qissab Al-Janabi;Kamaldeep Singh Grover;Ismacahyadi Bagus Mohamed Jais;Bushra S Albusoda;Norazlan Khalid
    • Earthquakes and Structures
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    • v.24 no.6
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    • pp.455-475
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    • 2023
  • The present study investigates the non-linear soil-pile interaction using three-dimensional (3D) non-linear finite element models. The numerical models were validated by using the results of extensive pile load and shaking table tests. The pile performance in liquefiable and non-liquefiable soil has been studied by analyzing the liquefaction ratio, pile lateral displacement (LD), pile bending moment (BM), and frictional resistance (FR) results. The pile models have been developed for the different ground conditions. The study reveals that the results obtained during the pile load test and shaking cycles have good agreement with the predicted pile and soil response. The soil density, peak ground acceleration (PGA), slenderness ratio (L/D), and soil condition (i.e., dry and saturated) are considered during modeling. Four ground motions are used for the non-linear time history analyses. Consequently, design charts are proposed depended on the analysis results to be used for design practice. Eleven models have been used to validate the capability of these charts to capture the soil-pile response under different seismic intensities. The results of the present study demonstrate that L/D ratio slightly affects the lateral displacement when compared with other parameters. Also, it has been observed that the increasing in PGA and decreasing L/D decreases the excess pore water pressure ratio; i.e., increasing PGA from 0.1 g to 0.82 g of loose sand model, decrease the liquefaction ratio by about 50%, and increasing L/D from 15 to 75 of the similar models (under Kobe earthquake), increase this ratio by about 30%. This study reveals that the lateral displacement increases nonlinearly under both dry and saturated conditions as the PGA increases. Similarly, it is observed that the BM increases under both dry and saturated states as the L/D ratio increases. Regarding the acceleration histories, the pile BM was reduced by reducing the acceleration intensity. Hence, the pile BM decreased to about 31% when the applied ground motion switched from Kobe (PGA=0.82 g) to Ali Algharbi (PGA=0.10 g). This study reveals that the soil conditions affect the relationship pattern between the FR and the PGA. Also, this research could be helpful in understanding the threat of earthquakes in different ground characteristics.

Lifetime Reliability Based Life-Cycle Cost-Effective Optimum Design of Steel Bridges (생애 신뢰성에 기초한 강교의 LCC최적설계)

  • Lee, Kwang Min;Cho, Hyo Nam;Cha, CheolJun;Kim, Seong Hun
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.26 no.1A
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    • pp.75-89
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    • 2006
  • This paper presents a practical and realistic Life-Cycle Cost (LCC) optimum design methodology of steel bridges considering time effect of bridge reliability under environmental stressors such as corrosion and heavy truck traffics. The LCC functions considered in the LCC optimization consist of initial cost, expected life-cycle maintenance cost and expected life-cycle rehabilitation costs including repair/replacement costs, loss of contents or fatality and injury losses, road user costs, and indirect socio-economic losses. For the assessment of the life-cycle rehabilitation costs, the annual probability of failure which depends upon the prior and updated load and resistance histories should be accounted for. For the purpose, Nowak live load model and a modified corrosion propagation model considering corrosion initiation, corrosion rate, and repainting effect are adopted in this study. The proposed methodology is applied to the LCC optimum design problem of an actual steel box girder bridge with 3 continuous spans (40 m+50 m+40 m=130 m), and various sensitivity analyses of types of steel, local corrosion environments, average daily traffic volume, and discount rates are performed to investigate the effects of various design parameters and conditions on the LCC-effectiveness. From the numerical investigation, it has been observed that local corrosion environments and the number of truck traffics significantly influence the LCC-effective optimum design of steel bridges, and thus realized that these conditions should be considered as crucial parameters for the optimum LCC-effective design.

Estimation of Tensile Strain Effect Factor of Layer Interface Considering Lateral Loads of Moving Vehicle (주행차량의 수평하중을 고려한 층 경계면의 인장변형률 영향계수 개발)

  • Seo, Joo Won;Choi, Jun Seong;Kim, Soo Il
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.26 no.6D
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    • pp.951-960
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    • 2006
  • Structural pavement analysis considering lateral loads of moving vehicle was carried out in order to simulate passing vehicle loads under various interface conditions. To verify of existing multi-layer elastic analysis of layer interface effect parameters, this study compared outputs by using ABAQUS, a three dimensional finite element program and KENLAYER, multi-layer elastic analysis as vertical load was applied to the surface of asphalt pavements. Pavement performance depending on interface conditions was quantitatively evaluated and fundamental study of layer interface effect parameters was performed in this study. As results of the study, if only vertical loads of moving vehicle is applied, subdivision of either fully bonded or fully unbonded is enough to indicate interface effect parameters. On the other hand, when lateral loads are applied with vertical loads, pavement behavior and performance are greatly changed with respect to layer interface conditions. The thinner thickness of the asphalt layer is and the smaller elastic moduli of the asphalt layer is, the more pavement behavior is influenced by interface conditions. In addition, regression analysis equation analytically computing tensile strain which was considered thicknesses and elastic moduli of the asphalt layer and layer interface effect parameters at the bottom of the asphalt layer was presented using database from numerical analyses on national pavement model sections.

Opto-Mechanical Detailed Design of the G-CLEF Flexure Control Camera

  • Jae Sok Oh;Chan Park;Kang-Min Kim;Heeyoung Oh;UeeJeong Jeong;Moo-Young Chun;Young Sam Yu;Sungho Lee;Jeong-Gyun Jang;Bi-Ho Jang;Sung-Joon Park;Jihun Kim;Yunjong Kim;Andrew Szentgyorgyi;Stuart McMuldroch;William Podgorski;Ian Evans;Mark Mueller;Alan Uomoto;Jeffrey Crane;Tyson Hare
    • Journal of The Korean Astronomical Society
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    • v.56 no.2
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    • pp.169-185
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    • 2023
  • The GMT-Consortium Large Earth Finder (G-CLEF) is the first instrument for the Giant Magellan Telescope (GMT). G-CLEF is a fiber feed, optical band echelle spectrograph that is capable of extremely precise radial velocity measurement. G-CLEF Flexure Control Camera (FCC) is included as a part in G-CLEF Front End Assembly (GCFEA), which monitors the field images focused on a fiber mirror to control the flexure and the focus errors within GCFEA. FCC consists of an optical bench on which five optical components are installed. The order of the optical train is: a collimator, neutral density filters, a focus analyzer, a reimager and a detector (Andor iKon-L 936 CCD camera). The collimator consists of a triplet lens and receives the beam reflected by a fiber mirror. The neutral density filters make it possible a broad range star brightness as a target or a guide. The focus analyzer is used to measure a focus offset. The reimager focuses the beam from the collimator onto the CCD detector focal plane. The detector module includes a linear translator and a field de-rotator. We performed thermoelastic stress analysis for lenses and their mounts to confirm the physical safety of the lens materials. We also conducted the global structure analysis for various gravitational orientations to verify the image stability requirement during the operation of the telescope and the instrument. In this article, we present the opto-mechanical detailed design of G-CLEF FCC and describe the consequence of the numerical finite element analyses for the design.

A Study on Colour Properties for Colour Recognition in Digital Media Environments (디지털 미디어 환경에서 색상을 인지하는 색채 속성 연구)

  • Ji-Young Hong
    • The Journal of the Institute of Internet, Broadcasting and Communication
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    • v.24 no.3
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    • pp.9-14
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    • 2024
  • Hue, value, and chroma are the fundamental colour components used in colour property research to identify colour in the digital media environment. In the Munsell colour system, which is based on the characteristics of visual perception, the basic properties are classified into hue, value, and chroma. The methods for recording these three properties can be divided into the colour appearance system and the colour mixing system: in the former, they are documented based on a colour chart that focuses on visual perception, and in the latter, accurate numerical records are kept without concern for discolouration. Colour terminology is crucial for conveying and expressing colours, and colours can be classified and defined according to the combination of hue, value, and chroma. With the development of various media, it has become possible to represent a range of colours previously unachievable, necessitating basic research into the characteristics of colour perception by further subdividing digital-oriented colour studies. In this study, we conducted psychophysical experiments to identify and analyse the categories of value and chroma needed to recognise each colour among the ten representative colours of the Munsell colour system, based on visual perception on a display. This study analyses the results of these experiments, defines their significance as foundational research data on colour perception characteristics, and suggests directions for future research.