철근콘크리트 구조물의 동결융해, 염해, 부식 등의 열화 현상으로 인해 구조물의 노후화가 발생되고 있다. 노후화로 인해 성능이 저하된 구조물의 성능 복원을 위해 FRP를 활용한 보수보강이 수행되고 있다. 본 논문에서는 동결융해 작용을 받은 철근콘크리트 보에 카본판재와 카본섬유로 휨 보강하여 동결융해 및 보강에 따른 철근콘크리트 보의 휨 성능을 비교 분석한 실 험적 연구 결과를 제시하였다. 이를 위해 철근콘크리트 보를 제작하여 300회의 동결융해를 수행한 후 카본판재와 카본섬유로 휨보강을 하여 성능 실험을 수행하였다. 실험 결과, 동결융해로 철근콘크리트보의 항복강도는 11% 감소하였으며, 동결융해를 입 지 않은 철근콘크리트보의 항복강도 보강성능은 20%, 동결융해를 입은 후 보강된 철근콘크리트 보의 보강성능은 19%으로 나타 났다. 에너지소산능력을 분석한 결과 본 연구에서 수행한 CFRP 보강이 동결융해로 열화된 철근콘크리트 보의 휨 보강에 유리 한 것으로 나타났다.

Reinforcement learning (RL) is widely applied to various engineering fields. Especially, RL has shown successful performance for control problems, such as vehicles, robotics, and active structural control system. However, little research on application of RL to optimal structural design has conducted to date. In this study, the possibility of application of RL to structural design of reinforced concrete (RC) beam was investigated. The example of RC beam structural design problem introduced in previous study was used for comparative study. Deep q-network (DQN) is a famous RL algorithm presenting good performance in the discrete action space and thus it was used in this study. The action of DQN agent is required to represent design variables of RC beam. However, the number of design variables of RC beam is too many to represent by the action of conventional DQN. To solve this problem, multi-agent DQN was used in this study. For more effective reinforcement learning process, DDQN (Double Q-Learning) that is an advanced version of a conventional DQN was employed. The multi-agent of DDQN was trained for optimal structural design of RC beam to satisfy American Concrete Institute (318) without any hand-labeled dataset. Five agents of DDQN provides actions for beam with, beam depth, main rebar size, number of main rebar, and shear stirrup size, respectively. Five agents of DDQN were trained for 10,000 episodes and the performance of the multi-agent of DDQN was evaluated with 100 test design cases. This study shows that the multi-agent DDQN algorithm can provide successfully structural design results of RC beam.

이 논문에서는 기존의 조인트 교량을 일체식 교대 교량으로 변경할 경우, 온도하중에 의한 상부구조의 인장에 따른 흉벽의 휨거동을 보강하기 위한 흉벽 FRP 보강공법을 제안하고, 설계 및 유한요소해석을 통해 보강 효과를 검토하였다. FRP 보 강재는 펄트루젼 공정으로 제작하며, 흉벽 전면부에 부착하여 일체식 교대 교량으로 변경할 때, 흉벽에 부족한 인장철근의 역할 을 대체하게 된다. 흉벽 FRP 보강공법의 설계는 ACI Committee 440을 참고하여 수행하였으며, 유한요소해석은 콘크리트, 철근 및 유리섬유와 비닐에스터로 제작한 FRP 보강재의 최대응력을 보강 방법에 따라 비교하였다. 유한요소해석 결과, FRP 보강재는 콘크리트에 발생하는 인장응력을 감소시키는 역할을 하며, 흉벽이 저항할 수 있는 휨모멘트를 증가시킬 수 있는 것으로 나타났 다.

In this paper, the mechanical properties of glass fiber reinforced plastic (GFRP) rebar, which has been applied as an concrete reinforcement, and produced carbon fiber reinforced plastic (CFRP) grid were compared to develop a concrete reinforcement material with excellent mechanical properties. In addition, the mechanical properties of CFRP prepared with each molding process were evaluated. Three molding processes were evaluated: prepreg oven bagging, reaction injection molding (RIM), and pultrusion. The tensile strength of the CFRP grid prepared through pultrusion was 2.85GPa, the elastic modulus was 169.81GPa, and the strain was 1.68%, which was 2.85 times better in tensile strength, and 2.83 times better in elastic modulus compared mechanical properties of GFRP rebar. The strain was confirmed to be equivalent to GFRP rebar.

North Korea continues to upgrade and display its long-range rocket launchers to emphasize its military strength. Recently Republic of Korea kicked off the development of anti-artillery interception system similar to Israel’s “Iron Dome”, designed to protect against North Korea’s arsenal of long-range rockets. The system may not work smoothly without the function assigning interceptors to incoming various-caliber artillery rockets. We view the assignment task as a dynamic weapon target assignment (DWTA) problem. DWTA is a multistage decision process in which decision in a stage affects decision processes and its results in the subsequent stages. We represent the DWTA problem as a Markov decision process (MDP). Distance from Seoul to North Korea’s multiple rocket launchers positioned near the border, limits the processing time of the model solver within only a few second. It is impossible to compute the exact optimal solution within the allowed time interval due to the curse of dimensionality inherently in MDP model of practical DWTA problem. We apply two reinforcement-based algorithms to get the approximate solution of the MDP model within the time limit. To check the quality of the approximate solution, we adopt Shoot-Shoot-Look(SSL) policy as a baseline. Simulation results showed that both algorithms provide better solution than the solution from the baseline strategy.

본 논문은 철근대체재로 Carbon fiber reinforced polymer(CFRP) 그리드가 사용된 콘크리트 부재의 휨성능을 평가하기 위한 실험적 연구결과를 보고한다. 실험에 사용된 CFRP grid의 탄성계수와 인장강도는 각각 240GPa, 3964MPa이다. CFRP 그리 드가 인장 보강재로 사용된 콘크리트 부재의 휨거동 평가를 위해 총 7개의 1방향 슬래브 콘크리트 실험체가 제작되었다. 실험 변수로 피복두께, CFRP 그리드의 보강 겹 수, CFRP 그리드의 겹침 여부가 고려되었다. 실험체의 휨거동 평가는 3점 휨실험을 통해 수행되었으며, 각 실험변수가 초기균열하중에 미치는 영향은 미미한 것으로 확인되었다. 실험체에 초기균열이 발생된 이후 응력 재분배에 의해 하중 증가 없이 CFRP grid의 변형률이 증가하는 현상이 관측되었다. CFRP 그리드 보강 겹 수가 1겹 증가 함에 따라 실험체의 극한하중은 약 8.5kN씩 선형적으로 증가하였다. 또한, 피복두께가 증가함에 따라 실험체의 극한하중 및 강 성이 감소하였으며, 그리드 겹침 여부가 실험체 극한하중에 미치는 영향은 미미하다는 것이 확인되었다. 추가적으로 실험결과와 ACI 440.1R-15를 통해 계산된 공칭 휨강도를 비교하였다. 그 결과 실험을 통해 확보된 극한강도는 ACI 440.1R-15 대비 13%∼ 24% 큰 것으로 나타났다. 따라서, ACI 440.1R-15는 CFRP grid로 보강된 콘크리트 보의 휨강도를 보수적으로 평가하고 있음이 확인되었다.

As cable TV, which has been leading the paid broadcasting market, has given the lead to IPTV, which has huge communication capital, its competitiveness is gradually weakening. This study examines the operation status of local cable TV and seeks ways to strengthen competitiveness for survival. To this end, we conducted data analysis such as related statistics, broadcasting industry survey reports, IPTV growth reports, CMB management indicators, paid broadcasting literature data, marketing reports, industry success stories, and marketing mix and SWOT analysis. As a result, four strategies for strengthening the survival competitiveness of local cable TV, namely joint purchase apartment marketing strategy, influencer marketing strategy, relationship marketing strategy, and digital marketing strategy were derived. Therefore, the results of this study can contribute to the improvement of the competitiveness of local cable TV, which has been with local residents through close content, and can be used as basic data for establishing marketing strategies for local cable TV in the future.

This study is conducted to verify the seismic reinforcement effects of internally inserted buckling-restrained braces supported laterally by buckling-restrained rings for the seismic reinforcement of existing reinforced concrete buildings with non-seismic details. First, to evaluate the performance of KDS, the hysteretic characteristics of buckling-restrained braces are verified, and it is discovered that they satisfy the conformance criteria of the displacement-dependent damping device. Three full-scale, two-story reinforced concrete framework specimens are prepared to verify the seismic reinforcement effects, and the proposed buckling-restrained braces are bolstered with single diagonal and V-shaped braces to be compared with non-reinforced specimens. By performing a comparison with non-reinforced specimens that present intensive shear cracks at the bottom of first-floor columns, it is revealed that the maximum load and energy dissipation of specimens reinforced with the proposed buckling restrained braces, in which the structural damage extends evenly throughout the system, are approximately 4 and 6.2 times higher, respectively, which proves the effectiveness of the proposed seismic reinforcement method.

Recently, machine learning is widely used to solve optimization problems in various engineering fields. In this study, machine learning is applied to development of a control algorithm for a smart control device for reduction of seismic responses. For this purpose, Deep Q-network (DQN) out of reinforcement learning algorithms was employed to develop control algorithm. A single degree of freedom (SDOF) structure with a smart tuned mass damper (TMD) was used as an example structure. A smart TMD system was composed of MR (magnetorheological) damper instead of passive damper. Reward design of reinforcement learning mainly affects the control performance of the smart TMD. Various hyperparameters were investigated to optimize the control performance of DQN-based control algorithm. Usually, decrease of the time step for numerical simulation is desirable to increase the accuracy of simulation results. However, the numerical simulation results presented that decrease of the time step for reward calculation might decrease the control performance of DQN-based control algorithm. Therefore, a proper time step for reward calculation should be selected in a DQN training process.

Rapid development of carbon nanotubes (CNTs) reinforced to polymer composites has been recently noticed in many aspects. In this work, the latest developments on fatigue and fracture enhancement of polymer composites with CNTs reinforcement with diverse methods are thoroughly compiled and systematically reviewed. The existing available researches clearly demonstrate that fatigue fracture resistance of polymer composites can be improved accordingly with the addition of CNTs. However, this work identifies an interesting research gap for the first time in this field. Based on the systematic reviewing approach, it is noticed that all previously performed experiments in this field were mostly focused upon studying one factor only at a time. In addition, it is also addressed that there were no previous studies reported a relationship or effect of one factor upon others during examining the fatigue fracture of carbon nanotubes. Moreover, there was no adequate discussion demonstrating the interaction of parameters or the influence of one parameter upon another when both were examined simultaneously. It is also realized that the scope of the conducted fatigue fracture studies of carbon nanotubes were mainly focused on microscale fatigue analysis but not the macroscale one, which can consider the effect of environment and service condition. In addition, the inadequacy of fatigue life predicting models via analytical and numerical methods for CNT-reinforced polymer composites have also been highlighted. Besides, barriers and challenges for future directions on the application of CNT-reinforced polymer composite materials are also discussed here in details.

본 연구에서는 기존 비내진설계 콘크리트 기둥의 내진성능 개선을 위해 기둥 면적의 80% 영역을 12K 능직 카본 섬 유(CFRP sheet)와 카본용 에폭시 수지를 사용하여 보강한 후 보강량에 따른 내진성능을 실험적으로 평가하였다. 실험을 위해 실 험실 단위에서의 준실대형 기둥을 제작하였으며, 유압 풀링잭을 이용하여 약 10%만큼의 일정한 축력을 가력한 다음 변위제어를 통해 최대 10%의 변위비만큼 각 변위 사이클당 2회씩 반복 재하하여 가력을 수행하였다. 실험 결과 2겹의 12K CFRP sheet 보 강의 경우 누적에너지소산이 6.6배 증가하였으며, 4겹의 경우 9.6배 증가하였다.

다가구주택 필로티기둥은 전이구조 형식으로 되어 있어 지진하중에 대하여 전단파괴가 발생하기 쉽다. 이에 따라 내 진설계기준은 강화되고 있지만 이전에 지어진 건축물의 경우 내진보강이 필요한 실정이다. 하지만 기존 습식 공법의 경우 시간 적, 경제적 부담이 크기 때문에 내진보강이 잘 이루어지지 않는다. 따라서 모서리앵글과 CN복합섬유패널을 활용하여 DIY 시공 이 가능한 전단보강공법을 제안하고자 하며 본 실험에서 CN복합섬유패널의 전단성능을 평가하고자 한다. 볼트 연단거리 및 앵 글의 재질을 변수로 설정하여 실험한 결과, 볼트 연단거리가 가까울수록 각형띠판 래티스기둥의 전단내력이 증진되는 것을 확 인하였으며 슬리브 볼트는 고장력 볼트에 비하여 현저히 내력이 저하되어 CN복합섬유패널을 평가하기가 어려웠다. 또한, 알루 미늄앵글은 강재앵글에 비하여 내력은 낮지만 연성능력이 좋은 것으로 평가되었고, 강재앵글은 상대적으로 강성이 크기 때문에 CN복합섬유패널에 주는 영향이 미미한 것을 확인하였다. 이를 실용화하기 위해서 구체적으로 앵글의 크기와 볼트 연단거리를 변수로 설정하여 실험을 수행해야 할 것으로 판단된다.