• KSCE Journal of Civil and Environmental Engineering Research
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• 제43권5호
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• pp.567-576
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• 2023

In general, RC beam members are designed as flexural members, considering only the bending load. However, in actual buildings, axial and bending load are simultaneously applied due to the continuity between members. As a result, the bending strength of the RC beam member increases, but the displacement decreases, and cracks are mainly concentrated in the center of the beam. Therefore, in this study, the bending performance of both normal and strengthened RC beam using carbon fiber sheets subjected to combined axial and bending load was experimentally evaluated. The carbon fiber sheets were wrapped around the middle of the specimens, and axial and bending load were applied simultaneously to the beams. The magnitude of the axial force and the effects of carbon fiber sheet reinforcement on the deformed shape, bending strength, deflection, and ductility of the RC beams were analyzed. The results show that as the applied axial force increased, the maximum bending strength increased, but the ductility decreased 64%. The bending strength of the strengthened beams increased up to 27%, the maximum deflection decreased around 8% and the ductility increased by up to 43%.

• Journal of the Korean Geotechnical Society
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• 제22권7호
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• pp.65-72
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• 2006

This study is about the estimation of the mechanical properties of cement grout material using a magnetic field treated water instead of tap water. The water that passed through a magnetic system is called MFTW. Similar research indicates that 5% of cement dosage can be saved by decreasing bleeding of concrete and improving resistance to freezing. The reason why MFTW can improve characteristics of concrete can be explained by molecular structure of water. Magnetic force makes water clusters into single molecule or small ones. Hence, the activity of water is improved by the magnetic force. While hydration of cement particles is on progress, the MFTW can penetrate the core region of cement particles more easily. Therefore, the hydration can be carried out more efficiently and the compression strength of concrete is highly improved. The sample of the sodium silicate cement grout's homogel using the MFTW results in highly compressive strength increases in compressive strength approximately from 20% to 50%.

• Journal of the Korean Geotechnical Society
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• 제24권8호
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• pp.81-88
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• 2008

In this study, to determine the priority of the effect factors and the preferences of commonly used reinforcing methods for the cut-slope, the reasonable analysis using AHP technique was performed. Analytic Hierarchy Process (AHP) technique is the most widely used method out of all existing decision making methods. On choosing the methods, the most important factor is analyzed to be the stability and durability. Stability, durability and environmental compatibility took up over 50% of the total contributing factors. Cut-slope reinforced method preference with increasing stability method confirmed that concrete retaining wall, reinforced-soil wall and cutting method showed the highest preference rate. Also, in practical field conditions, the cutting method out of four methods was chosen to be the most effective method. This reflected that the methods that are equally superior in all aspects of evaluation factors are more important than the methods with superiority in highly prioritized evaluation factors.

• Journal of Korean Tunnelling and Underground Space Association
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• 제11권2호
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• pp.141-150
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• 2009

When constructing a subsea tunnel in discontinuous rock mass, fluid flow in joints has a great influence on the behavior of the tunnel so that hydro-mechanical coupled analysis should be performed for the stability estimation. In practice, relaxed rock load is generally used for the design of tunnel concrete lining. In a continuum analysis, a method based on the distribution of local safety factor around a tunnel was proposed for the estimation of a potential relaxed zone. However, in the case of discontinuous rock mass in which joints are developed, the whole stability of tunnels depends on the behavior of the joints. In this study, therefore, a method is proposed for the estimation of a potential relaxed zone occurred by the excavation of a tunnel in discontinuous rock mass. The suggested method is validated by sensitivity analysis and the comparison with the results of continuum analysis.

• Journal of Korean Tunnelling and Underground Space Association
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• 제12권6호
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• pp.451-461
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• 2010

Utilization of the fiber reinforced polymer (FRP) material has been enlarged as a substitution material to the general construction materials having certain long-term problems such as corrosion, etc. However, it could be difficult to apply the FRP material, which has a linear shape generally, to an arch-shaped tunnel structure. Therefore, an attempt has been made in this study to develop a device to form a designed cross section of FRP material by pulling out with a curvature. A sample of the circled FRP product was successfully produced and then the sample has been tested to identify its physical characteristics. Then, intensive feasibility studies on the circled FRP panel to be used for a tunnel lining structure have been carried out by numerical analyses. As a result, it appears that the new circled FRP-concrete composite panel has a high capability to be used for a tunnel lining material without any structural problem.

• Proceedings of the Korea Water Resources Association Conference
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• 한국수자원학회 2022년도 학술발표회
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• pp.250-250
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• 2022

호안은 유수로부터 제방과 하안을 보호하는 구조물로 태풍 또는 집중호우로 인한 홍수로부터의 안정성이 확보되어야 한다. 일반적으로 호안공법은 강성호안과 연성호안으로 구분되는데 호안재료로써의 기준과 설치 및 유지상태 기준에 따라 다르게 해석되고 있는 것이 현실이다. 최근에는 호안공법의 재료의 연결성에 따라 강성호안과 연성호안을 구분짓는다고 언급되기도 한다. 본 연구에서는 친환경 석재를 사용하고 재료와 기반재의 체결을 통해 연결성을 확보하고 굴요성을 갖게 하는 연성호안공법에 대해 실규모 실험을 계획하였다. 수리 안정성 검토를 위한 실규모 실험은 안동 하천실험센터에서 수행하였다. 실험에 사용된 수로는 8°의 경사를 갖는 급경사수로에서 수행하였으며, 수로의 제원은 폭 3m, 길이 30m 의 직사각형 형태의 직선수로로 이루어져 있다. 시험체는 실규모로 제작되며 실험수로 내 2m × 10m 의 제원을 갖는 공간에 제작된 호안공을 크레인을 이용하여 실험수로에 설치하였다. 수리 안정성 실험은 실험대상유량을 단계별로 나누어 점차적으로 증가시키고, 시험체의 이탈, 파괴 등의 큰 변화가 발생(미국 재료시험학회 연결형 콘크리트 블록 시험방법, ASTM D 7277)하였을 경우 실험을 종료하도록 계획하였다. 수리량 측정항목은 유속, 수위 등이 있으며, 호안공 의 물리적 변화는 3D스캐너를 이용하여 설치 전·후 변위를 검토하였다. 총 3회에 걸쳐 실험을 수행하였으며 실험조건에 따라 일부 시험체에서 돌출 또는 침하현상이 발생하기도 하였으나 호안의 손상이나 이탈, 연성기반재의 찢어짐 등 안정정을 저해하는 호안공 시험체의 변화는 발생하지 않는 것으로 확인되었다. 실험결과 실험수로에서 발생가능한 최대유량인 4.6cms 조건에서 본 호안공법은 약 337.7N/m² 의 소류력을 확보하는 것으로 확인되었다.

• Journal of the Korea institute for structural maintenance and inspection
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• 제28권1호
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• pp.90-97
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• 2024

In this study, we employed Highly Ductile Cement Composite (HDCC) to evaluate the flexural performance of a RC slab that simulates the laminating structure of a seashell. To evaluate flexural performance, we produced conventional RC slab specimens, HDCC slab specimens, and HDCC-M slab specimens which biomimics a seashell's layered structure by inserting PE mesh inside the slab made of HDCC. A series of 4-point bending tests were conducted. Experimental results shows the flexural strength of the HDCC-M slab specimen was 1.7 times and 1.2 times higher than that of the RC and HDCC slab specimens, respectively. Furthermore, the ductility was evaluated using the ratio of yield deflection to maximum deflection, and it was confirmed that the HDCC slab test specimen exhibited the best ductility. This is most likely due to the fact that the inserted PE mesh separates the layers and increases ductility, while the HDCC passing through the mesh prevents the loss of load carrying capacity due to layer separation.

• Journal of the Korea institute for structural maintenance and inspection
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• 제12권5호
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• pp.109-115
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• 2008

As structures are getting super-rise and large-sized, introducing the construction methods such as prefabrication of bar-meshes and complex method are being actively discussed to pursue the high quality of reinforced concrete, the simplification of field works, and the reduction of duration, as well as the study on how to connect reinforcing rods, which occurs while applying the same methods, is in progress Also, the pressure welded joint is a kind of method that heats the ends of reinforced bars locally and joint them, and after the pressure welding, the vulnerable part in the reinforced bar occur. Thus, in the construction field, the throughout quality control is necessary because of the delayed duration and the lowered construct ability. In this study, of the traditional lap splice method and the mechanical splice one, the screw coupler, we tried to look into through experiments the prefabrication method of bar-meshes, a typical joint method usually used for the joint parts for PSC structures applying the reinforced bar with its big diameter, and a newly-developed up-set coupler method. And we also examined the characteristic of tensile.

• Journal of the Computational Structural Engineering Institute of Korea
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• 제21권4호
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• pp.325-334
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• 2008

The standard prestressed concrete I-girder bridge (PSC I-girder bridge) is one of the most prevalent types for small and medium bridges in Korea. When determining the member forces in a section to assess the safety of girder in this type of bridge, the general practice is to use the simplified practical equations or the live load distribution factors proposed in design standards rather than the precise analysis through the finite element method or so. Meanwhile, the live load distribution factors currently used in Korean design practice are just a reflection of overseas research results or design standards without alterations. Therefore, it is necessary to develop an equation of the live load distribution factors fit for the design conditions of Korea, considering the standardized section of standard PSC I-girder bridges and the design strength of concrete. In this study, to develop an equation of the live load distribution factors, a parametric analysis and sensitivity analysis were carried out on the parameters such as width of bridge, span length, girder spacing, width of traffic lane, etc. As a result, the major variables to determine the size of distribution factors were girder spacing, overhang length and span length in case of external girders. For internal adjacent girders, the determinant factors were girder spacing, overhang length, span length and width of bridge. For internal girders, the factors were girder spacing, width of bridge and span length. Then, an equation of live load distribution factors was developed through the multiple linear regression analysis on the results of parametric analysis. When the actual practice engineers design a bridge with the equation of live load distribution factors developed here, they will determine the design of member forces ensuring the appropriate safety rate more easily. Moreover, in the preliminary design, this model is expected to save much time for the repetitive design to improve the structural efficiency of PSC I-girder bridges.

• Journal of Korean Tunnelling and Underground Space Association
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• 제20권6호
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• pp.1125-1146
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• 2018

Segment lining applied to the TBM tunnel is mainly made of concrete, and it requires sufficient structural capacity to resist loads received during the construction and also after the completion. When segment lining is design to the Limit State Design, both Ultimate Limit State (ULS) and Service Limit State (SLS) should be met for the possible load cases that covers both permanent and temporary load cases - such as load applied by TBM. When design segment lining, it is important to check structural capacity at the joints as both temporary and permanent loads are always transferred through the segment joints, and sometimes the load applied to the joint is high enough to damage the segment - so called bursting failure. According to the various design guides from UK (PAS 8810, 2016), compression stress at the joint surface can generate bursting failure of the segment. This is normally from the TBM's jacking force applied at the circumferential joint, and the lining's hoop thrust generated from the permanent loads applied at the radial joint. Therefore, precast concrete segment lining's joints shall be designed to have sufficient structural capacity to resist bursting stresses generated by the TBM's jacking force and by the hoop thrust. In this study, bursting stress at the segment joints are calculated, and the joint's structural capacity was assessed using Leonhardt (1964) and FEM analysis for three different design cases. For those three analysis cases, hoop thrust at the radial joint was calculated with the application of the most widely used limit state design codes Eurocode and AASHTO LRFD (2017). For the circumferential joints bursting design, an assumed TBM jack force was used with considering of the construction tolerance of the segments and the eccentricity of the jack's position. The analysis results show reinforcement is needed as joint bursting stresses exceeds the allowable tensile strength of concrete. This highlights that joint bursting check shall be considered as a mandatory design item in the limit state design of the segment lining.