An experimental study was carried out to evaluate the shear performance at the interface composed of structural laminates and concrete. The main variables are the number of CLT layers and the shape of the shear connector. The number of CLT layers consisted of 3 and 5 layers. A total of 6 test specimens for shear performance evaluation were prepared in the form of a shear connector, a direct screw type and a vertically embedded type. As a result of the experiment, similar behavior was shown in all specimens, regardless of the number of layers, including direct screw type (SC series) and vertically embedded type (VE series). The behavior at the joint surface was damaged due to the occurrence of initial shear cracks, expansion of shear groove cracks, and splaying at the interface after the maximum load.After the maximum load, the shear strength decreased gradually due to the effect of the shear connector. It can be seen that the shear strength of all specimens is determined by shear and compression stress failure of concrete at the interface of the notch joint.

Recently, the demand for atypical structures with functions and sculptural beauty is increasing in the construction industry. Existing mold-based structure production methods have many advantages, but building complex atypical structures represents limitations due to the cost and technical characteristics. Production methods using molding are suitable for mass production systems, but production cost, construction period, construction cost, and environmental pollution can occur in small quantity batch production. The recent trend in the construction industry calls for new construction methods of customized small quantity batch production methods that can produce various types of sophisticated structures. In addition to the economic effects of developing related technologies of 3D Concrete Printers (3DCP), it can enhance national image through the image of future technology, the international status of the construction civil engineering industry, self-reliance, and technology export. Until now, 3DCP technology has been carried out in producing and utilizing residential houses, structures, etc., on land or manufacturing on land and installing them underwater. The final purpose of this research project is to produce marine structures by directly printing various marine structures underwater with 3DCP equipment. Compared to current underwater structure construction techniques, constructing structures directly underwater using 3DCP equipment has the following advantages: 1) cost reduction effects: 2) reduction of construct time, 3) ease of manufacturing amorphous underwater structures, 4) disaster prevention effects. The core element technology of the 3DCP equipment is to extrude the transferred composite materials at a constant quantitative speed and control the printing flow of the materials smoothly while printing the output. In this study, the extruding module of the 3DCP equipment operates underwater while developing an extruding module that can control the printing flow of the material while extruding it at a constant quantitative speed and minimizing the external force that can occur during underwater printing. The research on the development of 3DCP equipment for printing concrete structures underwater and the preliminary experiment of printing concrete structures using high viscosity low-flow concrete composite materials is explained.

In seismic design, hollow section concrete columns offer advantages by reducing the weight and seismic mass compared to concrete section RC bridge columns. However, the flexure-shear behavior and spirals strain of hollow section concrete columns are not well-understood. Octagonal RC bridge columns of a small-scale model were tested under cyclic lateral load with constant axial load. The volumetric ratio of the transverse spiral hoop of all specimens is 0.00206. The test results showed that the structural performance of the hollow specimen, such as the initial crack pattern, initial stiffness, and diagonal crack pattern, was comparable to that of the solid specimen. However, the lateral strength and ultimate displacement of the hollow specimen noticeably decreased after the drift ratio of 3%. The columns showed flexure-shear failure at the final stage. Analytical and experimental investigations are presented in this study to understand a correlation confinement steel ratio with neutral axis and a correlation between the strain of spirals and the shear resistance capacity of steel in hollow and solid section concrete columns. Furthermore, shear strength components (Vc, Vs., Vp) and concrete stress were investigated.

바다숲 복원과 함께 굴 패각의 새로운 자원화를 위해 굴 패각을 피복시킨 콘크리트 기질을 부산광역시 기장군 일광면 동백리 연안에 설치하여 약 1년간(2020년 1월~11월) 해조류 피도 변화를 모니터링하였다. 1월 모니터링 결과, 대조구인 일반 콘크리트 기질에는 해조류가 출현하지 않았다. 이에 반해 굴 패각을 10 ~ 90 % 피복시킨 실험구에는 해조류가 약 10 ~ 80 %의 피도로 착생한 것을 확인하였다. 또한, 11월 실험구의 피도는 대조구 대비 최대 49 % 높게 나타났다. 이상의 결과로부터 콘크리트 기질의 인공어초에 굴 패각 피복을 통해 인공어초의 해조류 착생을 촉진할 수 있으며, 수산 부산물인 굴 패각의 새로운 자원화 방안을 제시하였다.

PURPOSES : The purpose of this study was to develop the evaluation methodologies for spraying amount and sprayed condition of curing compound based on IoT technology when concrete pavements are constructed. METHODS : To measure the spraying amount of curing compound, a turbine type flowmeter was selected and a number of laboratory experiments were performed to verify the applicability of the selected sensor. To evaluate the uniformity of the sprayed curing compound on the concrete pavement surface, image process technologies were examined using pictures taken from the actual construction sites and from the test specimens. RESULTS : By performing experiments using water and curing compound, the selected flowmeter was verified to properly be applied to measure the spraying amount of curing compound with an acceptable accuracy. By conducting image processing using pictures of the sprayed curing compound on the concrete pavement surface, it was found that the 8 color analysis method was the best to evaluate the uniformity of the sprayed curing compound. CONCLUSIONS : From this study, it was concluded that the spraying amount of curing compound could be accurately measured using a turbine type flowmeter and the uniformity of the sprayed curing compound on the concrete pavement surface could be properly evaluated using an image processing technology.

PURPOSES : This study suggests an estimated texture depth (ETD) equation for concrete pavements, applicable to highway pavement texture, and the measurement method of mean profile depth (MPD) in a longitudinal texture. METHODS : First, we proposed the most suitable ETD equation through the correlation between ETD data and the measured mean texture depth (MTD) data. Second, we suggested a novel MPD measurement method, by checking the error of the ETD data and measured MTD data by the measurement method. RESULTS : The ETD equation presented by Fisco and Plati was considered the most appropriate for the transverse texture. In addition, the correlation between ETD and the measured MTD was good in the longitudinal measurement method. The ETD equation of Fisco and Plati is suitable for longitudinal texture, and the MPD measurement method obtained good results when applied to transverse measurements. To verify the novel measurement method, we confirmed the correlation between the SR and MPD data using a novel method. The correlation for the novel measurement method is 0.7. CONCLUSIONS : Accordingly, the ETD equation presented in the existing literature has a good correlation between ETD data and the measured MTD data, but it did not reflect longitudinal texture data. Therefore, we assumed the ETD equation produced in this study, and suggested the transverse measurement method in the longitudinal texture.

철근콘크리트 구조물은 반영구적인 구조물로 여겨지고 있으나 해상 구조물 및 해상에 인접한 구조물은 부식에 대한 위험에 노출이 되어 있다. 내륙 구조물의 경우에도 제설제 사용으로 인한 콘크리트의 중성화, 콘크리트 균열 등의 다양한 부식 요인이 발생한다. 또한 건설공사 시 철근은 외부환경에 장시간 노출된 상태로 보관이 되어 부식되기 쉽다. 따라서 본 연구에서 는 철근콘크리트 보의 인장 주철근을 3%와 10%의 부식률로 부식을 시켜 휨 실험을 통해 부식률에 따른 철근콘크리트 보의 휨 거동을 나타내었다. 철근콘크리트 보와 콘크리트 공시체를 동시에 제작하여 재료실험을 수행하였으며, 전위차 부식촉진법을 활용하여 철근콘크리트 보의 부식을 촉진시켰다. 실험결과 부식으로 인해 철근콘크리트 보의 초기 강성이 증가하였으며, 10%의 부식률에서는 철근콘크리트 보의 전단파괴의 발생 및 누적에너지소산능력이 취약하게 나타났다.

PURPOSES : In this study, an ASR-reducing (alkali-silica reaction) cement was developed to prevent the blow-up of concrete pavements. To develop ASR-reducing cement, various amounts of ground granulated blast furnace slag (GGBFS), and fly ash (FA) were substituted with Portland cement, and the ASR reduction effect was verified through various experiments. METHODS : The physical properties of ASR-reducing cement, varying with the substitution amounts of GGBFS and FA, were verified through compressive strength tests. In addition, the ASR reduction effect was examined using accelerated mortar bar tests. Furthermore, the reasons for the ASR reduction were investigated using microstructural analysis techniques, such as XRD and TG/DTG. RESULTS : There was a difference in the compressive strength results according to the amount of GGBFS and FA substitution. In addition, the samples with GGBFS and FA exhibited relatively lower compressive strengths at 3 days, than OPC samples, but the compressive strength at 28 days was higher than that of the OPC samples. The samples with GGBFS and FA had higher compressive strength at 28 days than OPC samples, because the substituted GGBFS and FA induced pozzolanic reaction. Through XRD and TG/DTG analyses, various degrees of pozzolanic reaction occurring in the samples were examined, and a more active pozzolanic reaction occurred in the samples with FA than in the samples with GGBFS. Therefore, it appeared that the ASR reduction effect occurred because of the induced pozzolanic reaction. CONCLUSIONS : GGBFS and FA substituting Portland cement indicated an ASR reduction effect, which was owing to the pozzolanic reaction. In addition, FA indicated a greater ASR reduction effect than GGBFS, which suggested that FA induced a more active pozzolanic reaction than GGBFS.

본 연구는 재래 철근콘크리트공법의 거푸집 및 철근보강재를 FRP 판으로 대체한 개념이다. FRP판에 리브를 갖게 하여 FRP 판과 콘크리트 합성을 개선하고 거푸집의 강성증가를 유도하여 영구거푸집 및 철근보강재로 활용하는 방안이다. 본 연구는 전단경간비가 짧고 리브가 있는 FRP 판과 콘크리트 합성보의 휨/전단 파괴거동과 균열형태를 비교 분석하였다. 콘크리트의 경우 CDP 모델을 사용하였고, 외연적 비선형 유한요소해석 결과와 기존 실험결과를 정점 하중 및 균열형태에 대해 비교 분석하였다. 유효균열방향 개념을 사용하여 콘크리트 균열패턴을 시각적으로 표현하였다. 인장 등가소성변형률이 0 보다 큰 곳에서 균열이 시작된다고 가정하고, 균열평면에 수직인 벡터의 방향은 최대 주소성변형률의 방향과 평행한 것으로 가정하였다. 이 방향을 콘 크리트의 균열으로 생각하여 실험에서 확보한 균열형태와 비교 분석하였다. ABAQUS/Explicit 의 CDP 모델은 FRP 합성구조체의 비선형 거동 및 균열형태 모사가 가능한 것으로 판단된다. 초기강성의 불일치는 리브가 있는 FRP 판과 콘크리트 사이의 미세균열 및 접착력 등의 문제로 인해 발생한 것으로 사료되며 1차 정점 하중 및 균열형태를 적절히 추적할 수 있으므로 앞으로 다양 한 FRP 합성구조시스템의 거동 및 균열해석에 이용 가능할 것으로 판단되나 보다 다양한 파괴 매카니즘에 대한 지속적인 연구가 필요하다고 사료된다.

초고강도 섬유보강 콘크리트 데크플레이트는 높은 콘크리트 압축력과 섬유에 의한 휨인장력의 우력으로 동바리 지지없이 얇은 두께의 데크플레이트로 고정하중과 작업하중을 견딜 수 있는 강성을 가지고 있다. 본 연구는 슬래브 두께, 섬유의 종류와 혼입률, 철근 및 GFRP를 변수로 휨실험을 수행하였다. 40mm∼50mm 두께의 120MPa 초고강도 콘크리트에 강섬유를 체적 대비 1.5% 이상을 혼입한 데크플레이트로 슬래브의 자중과 작업하중을 부담할 수 있으며, 철근을 보강하면 내하력이 더욱 증진 되고 연성거동을 하는 데크플레이트 특성을 가지는 것을 검증하였다.

Existing old reinforced concrete buildings could be vulnerable to earthquakes because they were constructed without satisfying seismic design and detail requirements. In current seismic design standards, the target collapse probability for a given Maximum Considered Earthquake (MCE) ground-shaking hazard is defined as 10% for ordinary buildings. This study aims to estimate the collapse probabilities of a three-story, old, reinforced concrete building designed by only considering gravity loads. Four different seismic design categories (SDC), A, B, C, and D, are considered. This study reveals that the RC building located in the SDC A region satisfies the target collapse probability. However, buildings located in SDC B, C, and D regions do not meet the target collapse probability. Since the degree of exceedance of the target probability increases with an increase in the SDC level, it is imminent to retrofit non-ductile RC buildings similar to the model building. It can be confirmed that repair and reinforcement of old reinforced concrete buildings are required.

최근 국내 원자력발전소의 격납건물 벽체와 Containment Liner Plate(CLP) 사이에서 다양한 크기의 공극이 발견됨에 따라 원전 격납건물의 보수를 위해 내부 공극의 분포와 크기를 정밀하게 평가할 수 있는 진단기법의 개발이 요구되고 있다. 이에 따라 이 연구에서 는 격납건물 벽체에서의 탄성파 전파거동을 계산하는 2차원 유한요소해석 기법을 제시한다. 격납건물 벽체를 기반으로 해석영역을 구성하고 경계면에서의 반사파를 제거하기 위해 수치적 파동흡수 경계층인 perfectly matched layer를 도입하였다. Galerkin 기반 혼합 유한요소법을 이용해 2차원 유한영역에서 탄성파 파동방정식의 해를 구하여 충격하중에 대한 격납건물 벽체의 변위와 응력을 계산하였다. 제시한 수치적 기법을 이용하여 격납건물 콘크리트 벽체의 CLP 부착 유무와 공동의 위치 및 크기 변화에 따른 탄성파 전파거 동을 살펴보았다. 이 연구의 결과는 원전 격납건물 내부의 공동을 진단하는 탄성파 전체파형 역해석 기법 개발에 활용될 수 있다.

This study presents the estimation of crack depth by analyzing temperatures extracted from thermal images and environmental parameters such as air temperature, air humidity, illumination. The statistics of all acquired features and the correlation coefficient among thermal images and environmental parameters are presented. The concrete crack depths were predicted by four different machine learning models: Multi-Layer Perceptron (MLP), Random Forest (RF), Gradient Boosting (GB), and AdaBoost (AB). The machine learning algorithms are validated by the coefficient of determination, accuracy, and Mean Absolute Percentage Error (MAPE). The AB model had a great performance among the four models due to the non-linearity of features and weak learner aggregation with weights on misclassified data. The maximum depth 11 of the base estimator in the AB model is efficient with high performance with 97.6% of accuracy and 0.07% of MAPE. Feature importances, permutation importance, and partial dependence are analyzed in the AB model. The results show that the marginal effect of air humidity, crack depth, and crack temperature in order is higher than that of the others.

This paper aims to develop numerical models for seismically-deficient reinforced concrete columns retrofitted using a fiber-reinforced polymer jacketing system under blast loading scenarios. To accomplish the research goal, a coupling model reproducing blast loads was developed and implemented to the column model. The column model was validated with a past experimental study, and the blast responses were compared to the numerical responses produced by past researchers. The validated modeling method was implemented to the non-retrofitted and retrofitted column models to estimate the effectiveness of the retrofit system. Based on the numerical responses, the retrofit system can significantly reduce the peak dynamic responses under a given blast loading scenario.

This study develops finite element models for seismically-deficient reinforced concrete building frame retrofitted using fiber-reinforced polymer jacketing system and validates the finite element models with full-scale dynamic test for as-built and retrofitted conditions. The bond-slip effects measured from a past experimental study were modeled using one-dimensional slide line model, and the bond-slip models were implemented to the finite element models. The finite element model can predict story displacement and inter-story drift ratio with slight simulation variation compared to the measured responses from the full-scale dynamic tests.