• Journal of the Korea Concrete Institute
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• v.23 no.2
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• pp.185-193
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• 2011

In the present study, a unified shear design method was developed to evaluate the shear strength of concrete beams with and without FRP shear reinforcement. The contributions of FRP and concrete on shear strength were defined separately. By comparing the current design method calculated results with the existing test results, it was found that Triantafillou model shows a reliable prediction of FRP effective strain and FRP shear strength contributions. The concrete shear strength contribution was defined by the strain-based shear strength model developed in the previous study. The shear strength of concrete compression zone was evaluated based on the material failure criteria of the concrete subjected to the compressive normal and shear stresses. The proposed strength model was verified by comparing its prediction results to prior test results. The comparisons showed that the proposed method accurately predicts the strengths of the test specimens for both FRP shear reinforced and unreinforced concrete beams.

• Journal of the Korea Concrete Institute
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• v.22 no.3
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• pp.313-324
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• 2010

There are many problems in application of FRP reinforcing bars as shear reinforcement, since bending of FRP bars is not a feasible process on construction site. Even though FRP bars can be manufactured in bent shape, they have lower strength at bent location. However, there are no serious problems to use FRP bars as flexural reinforcement. Plates or slabs like bridge decks, in general, do not need shear reinforcements. These types of members with FRP flexural reinforcement have lower shear strength than those with conventional steel flexural reinforcement. However, reliable process or equation for shear strength estimation of FRP reinforced concrete without shear reinforcement are not established, yet. In this study, predicted shear strength obtained from available design equations and assessment equations are compared with 211 experimental results. The results showed that among the current design codes, the Architectural Institute of Japan (AIJ) and the Institution of Structural Engineers (ISE) provided the best estimation. ACI 440.1R-06 provided conservative results with degree of dispersion similar to that of ISE. In addition, regression analysis on the collected experimental results was conducted to develop regression models. As a result, a new reliable shear strength equation was proposed.

• Journal of the Korea Concrete Institute
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• v.28 no.1
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• pp.33-40
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• 2016

The KCI-12 and ACI 318-14 design codes limit the maximum yield strength of shear reinforcement to prevent concrete compressive crushing before the yielding of shear reinforcement. The maximum yield strength of shear reinforcement is limited to 420 MPa in the ACI 318-14 design code, while limited to 500 MPa in the KCI-12 design code. A total of eight post-tensioning prestressed concrete beams with high strength shear reinforcement were tested to observe the shear behavior of PSC beams and the applicability of the high strength reinforcement was thus assessed. In the all PSC beam specimens that used stirrups greater than maximum yield strength of shear reinforcement required by the ACI 318-14 design code, the shear reinforcement reached their yield strains. The observed shear strength of tested eight PSC beams was greater than the calculated ones by the KCI-12 design codes. In addition, the diagonal crack width of all specimens at the service load was smaller than the crack width required by the ACI 224 committee. The experimental and analytical results indicate that the limitation on the yield strength of shear reinforcement in the ACI 318-14 design code is somewhat under-estimated and needs to be increased for high strength concrete. Also the application of high strength materials to PSC is available with respect to strength and serviceability.

• Journal of Korean Society of Steel Construction
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• v.22 no.6
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• pp.543-551
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• 2010

The end-reinforced composite-beam (eco-girder) system was developed that has characteristics of the existing composite beams such as reduced floor height and increased strength. With it, less use of steel is expected. In the eco-girder system, only both ends of the steel-frame beam, which are vulnerable to the ultimate moment, are reinforced with steel plates so that the steel frame beam design will be based on the moment at the beam center. This study used fiber element analysis, which is a simple representation and numerical integration of the principles of the detailed Finite Element Method(FEM), to predict the hysteretic behavior of reinforced composite beams under cyclic loading. The validity of the numerical method was verified by comparing the results of this study with those of previous studies. In addition, the hysteretic behavior of the eco-girder was compared with that of the existing composite beams.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.57-60
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• 2008

Compared with a steel-reinforced section with equal areas of longitudinal reinforcement, a cross section using FRP flexural reinforcement after cracking has a smaller depth to the neutral axis because of the lower axial stiffness. The compression region of the cross section is reduced, and the crack widths are wider. As a result, the shear resistance provided by both aggregate interlock and compressed concrete is smaller. Research on the shear capacity of flexural members without shear reinforcement has indicated that the concrete shear strength is influenced by the stiffness of the flexural reinforcement. In this research, experimental observations were made for the shear strength of FRP reinforced concrete beam and validity of existing predicting equations were examined. Test results showed that shear strength decreased as shear-span increased.

• Journal of Korean Society of Steel Construction
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• v.19 no.3
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• pp.259-270
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• 2007

This paper presents an analytical method of evaluating the flexural behavior of RC (reinforced concrete) beams strengthened with high-strengh bars. The former experimental results were used to compare with the analytical results. The experimental results also outline the advantages of externally strengtheng method with high-strenght bars. To evaluate the flexural behavior of RC beams strenghtend with unbonded high-strength bars, this paper proposes a method involving a simple strength-summation method. This method basically assumes that the total strength of RC beams strengthened with high-strength bars is equal to the sum of the strengths of the RC beams and the high-strength bars. This analytical method also includes the effects of compressive force due to the tension from high-strength bars. A comparison of the analytical and experimental results leads to the conclusion that the simple strength-summation mothod can simulate the flexural behavior of RC beams strengthened with high-strength bars with a good level of accuracy.

• Tunnel and Underground Space
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• v.20 no.4
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• pp.260-266
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• 2010

In this study, wish to analyze effect that affect on each tunnel (right and left tunnel) according as proceeding of leading tunnel (right tunnel), following tunnel (left tunnel) and pilot tunnel excavation through behavior of tunnel and surrounding base by model tests. And stress-transfer mechanism that occurs from in-situ loosing area and arching effect by difference of stiffness ratio and overburden heights were verified experimentally. The model tests were carried out by varying the stiffness of reinforced area and overburden height, measured deformation of tunnel and displacement of surrounding base. The model tests followed exactly the real 2-Arch tunnel construction stages.

• Bulletin of the Korean Space Science Society
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• 2010.04a
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• pp.35.3-35.3
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• 2010

항공용 지역위성항법 보강시스템(Ground Based Augmentation System, GBAS)은 지상에서 위성항법시스템에 대한 위치보정정보와 무결성 정보를 생성 및 제공하여 공항 주변 항공기의 정밀 이착륙을 돕는 지상기반의 시스템이다. 이 시스템은 기본적으로 위성항법신호를 사용하기 때문에 전리층 영향을 받게 되는데 특히 전리층 폭풍(Ionospheric storm)의 경우 공간적으로 급격한 위치오차 차이를 발생시키기 때문에 안정적인 항공기의 정밀이착륙을 위해서는 전리층 폭풍의 영향을 최소화 하는 것이 중요하다. 이를 위하여 현재 항공용 지역위성항법 보강시스템의 지상시스템(Ground Facility)과 항공기 탑재시스템에서의 전리층 폭풍에 대한 정확한 감시와 전리층 폭풍의 지배적 영향을 받는 위상항법신호를 제거하거나 보완하는 방식 등 전리층 폭풍의 영향을 최소화하기 위한 기법들이 계속해서 연구 중이다. 이 논문에서는 2001년과 2003년 미국에서 발생한 전리층 폭풍에 대한 위성항법데이터 분석 결과와 기존의 연구결과를 기반으로 전리층 폭풍에 대한 모델링과 지상시스템과 항공기 간의 공간적 상이현상(Spacial decorrelation)을 고려하여 전리층 폭풍이 항공기 이착륙에 미치는 영향에 대한 분석 결과를 제시한다. 전리층 폭풍에 대한 수학적 모델링을 하기 위해서는 전리층 폭풍의 물리적 특성에 대한 이해와 전리층 폭풍 발생 시 획득한 위성항법 데이터를 이용한 통계학적 분석이 선행되며 이러한 분석결과와 항공기 이착륙에 절차를 반영하여 항공기에 미치는 영향 분석을 위한 수학적 모델을 완성하였다. 완성된 모델을 국내 공항에서 실제 비행시험을 통하여 획득한 위성항법데이터에 적용하여 전리층 폭풍이 국내 공항에서 항공기 이착륙에 어떠한 영향을 미치는지를 분석하였다. 또한, 대표적 전리층 폭풍 감지기법 중 하나인 Code-Carrier Divergence Test 알고리즘을 적용한 결과도 함께 제시하였다. 이 논문의 결과는 항공용 지역위성항법 보강시스템에 대한 전리층 폭풍의 영향을 최소화하기 위한 기법 연구의 기반이 되며 시스템의 성능평가를 위한 다양한 시뮬레이션환경의 하나로서도 활용이 가능할 것이다.

• Conservation Science in Museum
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• v.21
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• pp.29-40
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• 2019

An experimental study was conducted to test the applicability of natural hydraulic lime (NHL) as a reinforcing agent for the supporting layers of mural paintings in ancient tombs.Drawing upon preceding studies on mural paintings inancient tombs, samples of reinforcing agents for various conditions were prepared using NHL products, and pseudo-samples of the supporting layers of mural paintings were also produced. The samples were cured for 7, 28, and 84 days in a high-humidity condition similar to that of the mural-tomb environment. Physical properties such as dimensional stability and compressive strength were measured for each curing period.The results indicated that the NHL samples had a rapid curing speed and a low contraction ratio and are therefore suitable as reinforcing agents, whereas they showed a poor match in terms of strength compared to the supporting layer,and also low whiteness. The dimensional stability and compressive strength testsrevealedthat an NHL product mixed with a pseudo-sample of a supporting layer provided desirable conditions for reinforcing agent. The findings suggested that different conditions for curing time and strength should be considered for each supporting layer prior to applying NHL as a reinforcing agent for damaged mural paintings in ancient tombs.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.3
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• pp.150-159
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• 2019

The bond analysis model equation was proposed through the regression analysis of the experimental values of bond behavior for each rebar. In order to verify the appropriateness of the bond analysis model equation, the bond behaviors calculated by the proposed bond analysis model, BPE model and CMR model were compared with experimental values. The proposed bond model showed the closest behavior to the experimental values when compared to other analysis models. The former models can not consider the different properties of GFRP rebar according to composed materials, mixing and manufacturing method and the latter has limitation to express the relationships between bond behavior because of derived formula by numerical analysis. This study proposed the analytical model different considering bond mechanism according to surface type. In order to verity the appropriateness of the bond analytical model, the bond behaviors calculated by the proposed bond analytical model, BPE model and CMR model were compared with experimental values. The proposed bond model showed the closest behavior to the experimental values when compared to other analysis models.