• Computers and Concrete
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• 제24권3호
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• pp.271-282
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• 2019

Concrete undergoes a series of thermo-based physio-chemical changes once exposed to elevated temperatures. Such changes adversely alter the composition of concrete and oftentimes lead to fire-induced explosive spalling. Spalling is a multidimensional, complex and most of all sophisticated phenomenon with the potential to cause significant damage to fire-exposed concrete structures. Despite past and recent research efforts, we continue to be short of a systematic methodology that is able of accurately assessing the tendency of concrete to spall under fire conditions. In order to bridge this knowledge gap, this study explores integrating novel artificial intelligence (AI) techniques; namely, artificial neural network (ANN), adaptive neuro-fuzzy inference system (ANFIS) and genetic algorithm (GA), together with traditional statistical analysis (multilinear regression (MLR)), to arrive at state-of-the-art procedures to predict occurrence of fire-induced spalling. Through a comprehensive datadriven examination of actual fire tests, this study demonstrates that AI techniques provide attractive tools capable of predicting fire-induced spalling phenomenon with high precision.

• 한국공간구조학회논문집
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• 제18권4호
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• pp.61-68
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• 2018

Tensile load tests were conducted on High-Shear Ring Anchors (HRAs) after shear load had been applied to the HRAs, which had been developed to reduce the number of the anchors. Test variables include the embedment length of the rod and the width of the specimens and a total of 12 specimens were tested. Test results show that the HRAs pulled out due to bond failure or steel failure occurred in case that the HRAs were installed to the members with 300mm or greater width and the embedment length of 160mm (the actual embedment of rod is 140mm) or deeper. Except 4 HRAs showing steel failure of rod, the minimum and average of test-to-prediction by ACI 318-14 ratios are 1.18 and 1.79, respectively. The tensile strength of HRAs, after shear load was applied to the HRAs, can be safely evaluated by the minimum among the concrete breakout strength and bond strength with the actual embedment length of the rod.

• KCI Concrete Journal
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• 제14권1호
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• pp.51-60
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• 2002

Strengthening of existing concrete structures is a major concern in recent years as the number of degraded structures increases. The purpose of this paper is to investigate the static and fatigue behavior of reinforced concrete (RC) beams strengthened with steel plates. To this end, a comprehensive test program has been set up and many series of strengthened beams have been tested. The major test variables include the plate thickness, adhesive thickness, and the shear-span to depth ratio. The test results indicate that the separation of plates is the dominant failure mechanism even for the full-span-length strengthened beams with steel plate. The theoretical ultimate load capacities for strengthened beams based on the full composite action of concrete beam and steel plate are found to be larger than the actual measured load capacities. The strengthened beams exhibit more dominant shear cracking as the shear-span to depth ratio decreases. The ultimate capacity of strengthened beams increases slightly with the increase of adhesive thickness, which may be caused by the late initiation of plate separation in the beams with thicker adhesive. A realistic concept of ductility for plate-strengthened beams is proposed in this study. It is seen that the strengthened beams show relatively low ductility compared with unstrengthened beams. The present study indicates that the strengthened beams exhibit much higher fatigue resistance than the unstrengthened beams. The increase of deflections of strengthened beams according to the number of load cycles is much smaller than that of unstrengthened beams. The present study provides very useful results for the realistic application of plate-strengthening method in reinforced concrete structures.

• International Journal of Concrete Structures and Materials
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• 제6권4호
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• pp.247-250
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• 2012

Composites are somewhat more difficult to model than an isotropic material such as iron or steel due to the fact that each layer may have different orthotropic material properties. In finite element literature the asphalt mixes are represented by using rectangular meshes, not the actual picture of their cross-sections. Asphalt aggregate size and distribution in the asphalt concrete sample, aggregate shape, and fractured surface effects are ignored. In this research, the actual image of the sample including all these effects were directly considered in the finite element. The samples, were cut into cross-sections and were scanned. The image-processing toolbox of Labview was utilized in obtaining the rectangular gray images of the scanned images. In the rectangular sample the aggregates were white and the asphalt binders were black. The grayscale images were converted by LABVIEW into the format required by ANSYS as an input file, with the same dimensions. The nodes at the bottom of the model were constrained in both x and y directions. Left and right edges were symmetry and top was free. Certain amount of pressure was applied along the top surface to simulate the tire pressure.

• Computers and Concrete
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• 제14권2호
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• pp.163-174
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• 2014

Damping as a material property plays an important role in decreasing dynamic response of structures. However, very little is known about the evaluation and application of the actual damping of Fiber Reinforced Polymer Confined Reinforced Concrete (FRP-C RC) material which is widely adopted in civil engineering at present. This paper first proposes a stress-dependent damping model for FRP-C RC material using a validated Finite Element Model (FEM), then based on this damping-stress relation, an iterative scheme is developed for the computations of the non-linear damping and dynamic response of FRP-C RC columns at any given harmonic exciting frequency. Numerical results show that at resonance, a considerable increase of the loss factor of the FRP-C RC columns effectively reduces the dynamic response of the columns, and the columns with lower concrete strength, FRP volume ratio and axial compression ratio or higher longitudinal reinforcement ratio have stronger damping values, and can relatively reduce the resonant response.

• Structural Engineering and Mechanics
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• 제45권5호
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• pp.703-722
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• 2013

In this paper a study about concrete arch bridges built by lattice cantilevers is presented. Lattice cantilevers are partial structures composed of deck, arch, piers and provisional steel diagonals, organized as reticular cantilever girders, in order to build arch bridges without the use of centrings, supports or temporary towers. Characteristics of this construction methodology with its variants are explained together with their implications in the erection sequence. Partial elastic scheme method is implemented in order to find initial forces of temporary cables and a forward analysis is carried out to follow the actual sequence of construction, by extending a procedure already applied to concrete cable-stayed bridges and to arches built by the classical suspended cantilever method. A numerical application on a case-study of a concrete arch bridge is performed together with a comparison between different methodologies followed for its construction sequence. Differences between erection by lattice cantilevers and cable-stayed cantilevers, are discussed. Results can be useful for designers in conceptual design of concrete arch bridges.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(II)
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• pp.229-232
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• 2005

Protective surface coating for concrete is available for applying to concrete structures for protecting chloride attack. However, the useful data obtained from real marine environment for surface coating materials is not sufficient yet in Korea and thus the engineers face many difficulties to apply the coating method in durability design. Surface-coated concrete specimens were fabricated and installed around the piers of Seohae grand bridge to observe long-term performance in actual marine environment. In this study, the results of durability of surface coatings for 3 years were reported.

• 한국철도학회논문집
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• 제12권6호
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• pp.944-952
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• 2009

이 논문은 철근콘크리트 구조물의 균열폭 계산을 위한 해석적 모델을 제안한 것이다. 철근과 콘크리트 경계면에서 발생하는 실제와 유사한 형태의 부착응력-슬립 특성을 수치적으로 전개하기 위해서 수치해석을 통하여 균열안정화단계에서의 철근과 콘크리트 경계면에서 발생하는 슬립이 선형 분포함을 확인하고, CEB-FIP Model Code 1990과 Eurocode 2에서 제시하고 있는 부착응력-슬립 관계에 적용하였다. 이와 같은 방법을 통하여 균열과 균열 사이에서 철근의 매입길이 방향으로 발생하는 철근과 콘크리트의 변형률 차이가 균열면으로 누적되는 양을 계산할 수 있는 평형방정식을 유도하고, 이로부터 두 재료의 축방향 변형량의 차이로부터 균열폭을 계산할 수 있는 모델을 제안하였다. 이렇게 정식화된 새로운 균열폭 모델을 기존 문헌에 발표된 여러 연구자들의 실험 자료에 적용하여 그 정확성을 검증한 결과, 제안식에 의한 예측값은 현재 사용되고 있는 여러 설계기준의 균열폭 규정으로 계산한 결과에 비하여 실험값을 비교적 정확하게 예측하는 것으로 나타났다.

• 디자인융복합연구
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• 제16권1호
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• pp.97-109
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• 2017

현대에 들어서 건축물의 외관 디자인에 대한 관심이 커짐에 따라 기존의 획일화된 건축물이 아닌 다양한 미관의 건축물에 대한 니즈가 증가하고 있다. 그러나 아직까지 미관창출을 위한 국내의 폼 라이너 재료 및 디자인은 한정되어 있는 실정이다. 따라서 본 연구는 3D프린터를 활용하여 기존의 값비싼 몰드 제작과정을 생략하고 디지털 데이터를 이용하여 입체구조의 제품을 다양한 소재를 사용하여 경제적으로 제작, 콘크리트의 열화방지 수단을 겸비하고 구조물의 수명을 연장시켜 생애주기비용을 절감하는 효과를 기대할 수 있다. 본 연구는 3D 프린터를 활용하여 콘크리트 구조물의 위치, 주변 환경, 용도에 적합한 폼 라이너의 미관 및 입체조형 디자인을 다양하게 개발하는 것을 목적으로 한다. 본 연구에서는 3D 프린트를 활용한 실물 출력 실험을 통해 3D프린터를 활용한 콘크리트 폼 라이너가 실제 적용이 가능하다는 가능성을 확인하였으며, 콘크리트 구조물의 용도, 지역특성, 주변 환경, 사용자 등을 고려하여 입체적이며 예술적인 조형미관을 위한 폼 라이너 디자인을 제안하였다.

• 한국공간구조학회논문집
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• 제21권3호
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• pp.77-84
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• 2021

In this study, In order to apply the U-flanged truss hybrid beam to the actual construction site, the structural design of the basic module of the middle and low-rise neighborhood living facilities was performed according to the Korea Design Standard, and the construction cost and construction period were compared with the traditional reinforced concrete structure system. As a result of analyzing the construction cost for the basic module, if the U-flanged truss hybrid beam and D-Deck slab system are used, the construction cost can be reduced by 86% compared to the traditional reinforced concrete structure system. In addition, as a result of analyzing the construction period for a floor area of 1,000m², using the U-flanged truss hybrid beam and D-Deck slab system can save 2.0days in construction period compared to the traditional reinforced concrete structure system. Therefore, the U-flange truss hybrid beam can secure sufficient economic feasibility compared to the existing reinforced concrete method in terms of cost reduction and shortening of construction period.