This study aims to refine the existing shear strength model for reinforced concrete(RC) beam–column connections by explicitly incorporating the bi-directional loading effect, which more accurately reflects the actual loading conditions of RC structures during earthquakes. A new database consisting of 21 RC beam–column connection specimens tested under simultaneous bi-directional loading was collected and analyzed to investigate the influence of key parameters on joint shear strength. The results revealed that the joint configuration and the presence of a slab are the primary factors governing the extent of bi-directional loading effect on joint shear strength. Based on these findings, a set of simple and practical modification factors was proposed to refine the existing joint shear strength model to account for bi-directional loading effect. The outcomes of this study provide a rational basis for incorporating bi-directional loading effect into the shear strength evaluation of RC beam–column connections

AI-driven automation for structural design has been actively studied in structural engineering. In particular, reinforcement learning (RL) has attracted attention as a framework in which an agent interacts with an environment to autonomously search for optimal design solutions in complex design spaces. This study proposes an automated design model for rectangular reinforced-concrete (RC) columns based on a multi-agent Double Deep Q-Network (Double DQN). Extending prior RL-based automation developed for RC beam design to column members, the proposed environment explicitly incorporates key column-specific behaviors, including axial force–bending moment (P–M) interaction and moment magnification due to column buckling. Four agents independently determine the section width (b), section depth (h), number of longitudinal bars (n), and bar size. The reward function combines (i) penalty terms for violations of ACI 318-19 design constraints and (ii) an economic reward defined relative to an approximate optimal cost predicted by a quadratic regression model. After training for approximately 10,000 episodes, the proposed multi-agent Double DQN consistently generated ACI-compliant column designs across all test load cases and produced solutions with improved cost efficiency compared with the approximate optimal baseline. These results demonstrate the feasibility and practical potential of multi-agent RL for automated RC column section design.

In this study, a non-welded beam-to-column connection applicable to the extension and renovation of pipe-rack structures was proposed. The structural performance of the proposed connection was verified at the component level through preliminary finite element analyses. In order to verify structural performance of beam-to-column connection implementing panel zone reinforcing elements, full-scale quasi static test was conducted. As a result, the specimen incorporating box-type panel zone reinfocing element exhivited maximum strength approaximatly 1.3 times higher than that of the specimen with existing connection detail of which structural behavior was governed by weak panel zone deformation. However, the specimen with suggested detail shows stable ductile behavior due to reduction of stress concentrated on the beam-to-column connection since the applied forces were distributed through the yielding of the beam end plate and the reinforcing element inserted into the panel zone.

본 연구는 3차원 비선형 유한요소해석을 이용하여 고속도로 2주형 교각 코핑부에서 철근을 유리섬유보강폴리머(GFRP) 보강 근으로 대체하는 경우를 평가하였다. 콘크리트의 균열, 손상 및 보강근 응답을 모사하기 위해 콘크리트 손상소성(CDP) 모델을 적용하 였다. 단조하중 조건에서 철근 기준 Case와 다수의 GFRP Case를 비교하였다. 주요 변수로는 GFRP의 강성, 콘크리트와의 부착계수 영향, 그리고 수직 전단보강근 상세 배근을 포함하였다. 수치해석 모델은 실험 경향과의 비교를 통해 검증되었으며 전반적인 거동이 일관되게 나타났다. GFRP로의 대체는 철근 대비 강성과 하중 전달 메커니즘을 변화시켰다. 또한 콘크리트 손상이 전체 응답과 파괴 진행을 지배하는 주요 요인으로 나타났다. GFRP 강성이 높고 부착성능이 우수할수록 구조 효율과 상세설계의 실현성이 향상되었다. 적절한 설계가 전제될 경우 전단보강근의 양은 전체 거동에 미치는 영향이 제한적인 범위에서 최적화가 가능하였다. 이상의 결과는 GFRP 적용의 실무적 가능성을 뒷받침하는 동시에, GFRP의 선형탄성ㆍ취성 거동과 국부 응력집중 가능성을 고려할 필요가 있음을 시사한다.

본 연구는 고속도로 다주식 교각 두부보를 대상으로 철근 보강과 철근 대체 GFRP 보강의 균열 손상 거동을 3차원 유한요소 해석으로 비교ㆍ평가하였다. 콘크리트는 ABAQUS의 CDP 모델을 적용하고, 균열 분포는 인장 손상 변수를 핵심 지표로 사용하였다. 선형해석 결과, 두부보 중앙 상단부의 압축 응력 지배 구간과 중앙 하단부 및 접합부 주변의 인장ㆍ전단 영향 구간이 명확히 구분되었 으며, 향후 실험 계측 위치 선정에 활용 가능한 정보를 제공하였다. 비선형 해석 결과, 전반적으로 각 Case의 최초 균열하중 및 최대하 중, 균열 발생 시 변위 및 최대 변위는 큰 차이 없이 유사 범위에 분포하였으며, 균열 면적과 분포 형상 역시 대체로 유사하여 GFRP 보강 두부보의 구조적 안정성이 확인되었다. 특히 일부 Case는 초기 강성과 파괴 저항 측면에서 철근 보강 대비 경쟁력 있는 결과를 보여, 실무적 대체 가능성을 뒷받침하였다.

This study investigates the seismic performance of beam-column connections using Thin-Walled Steel Composite (TSC) beams and Prestressed Reinforced Concrete (PSRC) columns. TSC beams are constructed from U-shaped thin steel plates that are filled with concrete, allowing for composite action with slabs through the use of shear connectors. They are widely applied in industrial buildings due to excellent strength, stiffness, and constructability. However, slender web plates are prone to local buckling, which may compromise their performance during seismic events. To mitigate this issue, internal supports have been introduced to enhance web stability and concrete confinement. Cyclic loading tests on three specimens—with and without internal supports—demonstrated that the supports increased moment capacity, improved energy dissipation, and effectively reduced buckling. Even slender sections demonstrated performance comparable to that of compact sections. All specimens reached peak strength at a 2.44% rotation angle, with damage localized near the supports. A practical connection detail was also proposed, taking into account constructability and structural reliability. The results provide valuable guidance for the seismic design of composite systems in large-scale structures.

Existing reinforced concrete building structures have seismically-deficient details on columns and beam–column joints; therefore, accurate modeling of structural behavior is required for reliable seismic performance assessment. This study aims to investigate the differences in dynamic responses resulting from modeling variations through developing four distinct numerical models. Separate models were established to simulate flexural and shear failures of columns and beam–column joints. Using these component-level models, a structural analysis model of the target building was constructed, and nonlinear time-history analyses were performed to evaluate seismic performance. Based on the simulated dynamic behavior of the target building, soft-story mechanisms were identified, and it was identified and confirmed that column behavior plays a dominant role in governing the overall structural response.

This study proposes empirical formulas for predicting the nonlinear behavior of GIR beam-to-column connections in timber structures to evaluate their structural performance. A database comprising 59 experimental results of GIR connections was collected, and the normality of data distribution was verified. Statistical analysis were conducted to investigate the correlations between input and output parameters. Based on input parameters with high correlation, derived variables were formulated and utilized in a multiple regression analysis to develop empirical formulas for moment capacity and rotation. The R-squared values of the proposed formulas exceeded 0.9, and the predicted initial stiffness and strength closely matched those of experimental results not used in the regression analysis. So the suggested empirical formulas exhibit excellent predictive performance for the nonlinear behavior of GIR beam-to-column connections in timber structures.

There have been meaningful changes in column stirrup spacing by KDS 41 20 00 in 2022, which is to decrease one of the spacing limits from the minimum section dimension to half of the minimum section dimension. Decreased column stirrup spacing increases the seismic shear resistance of columns and the seismic performance of the entire building. Among the effects of the column stirrup spacing change, this study focused on deformation compatibility in the seismic design of building frame system buildings with ordinary shear walls for seismic design category D. The beams and columns in building frame systems shall satisfy moment and shear strength, or deformation capability induced by seismic design displacement for satisfaction of the deformation compatibility. The commentary of KDS 41 17 00 describes that the deformation compatibility check can be ignored if the members in moment frames are upgraded to intermediate section details. The study showed that the deformation compatibility of columns was satisfied without additional consideration if the building frame systems were designed by the decreased column spacing in KDS 41 20 00. However, beams adjacent to walls needed further consideration, such as the recommendation of commentary in the code.

Reinforced concrete (RC) moment frames are widely used to resist lateral loads associated with wind and earthquakes. However, most older RC moment frames performed poorly against past earthquakes. In moment frames, beam-column connections play a crucial role in system performance. Among the connections, corner connections are more vulnerable because they are restrained by only two beams and are affected most strongly by bidirectional loading. High-performance fiber-reinforced cementitious composites (HPFRCC) were used in previous studies to improve the seismic performance of older beam-column connections. This study aims to evaluate the level of improvement of seismic behavior of older beam-column connections under bidirectional loading after retrofitted with HPFRCC by comparing the seismic behavior of the HPFRCC connections to beam-column connections used in intermediate (IMF) and special moment frames (SMF). Test results revealed that the seismic behavior of the HPFRCC connections was almost close to that of SMF connections.

The purpose of this study is to experimentally analyze the seismic performance of a vertical irregular beam-column specimen reinforced with RBS (Replaceable Steel Brace System), a steel brace system. To evaluate the seismic performance of RBS, three specimens were manufactured and subjected to cycle loading tests. The stiffness ratio of beam-upper column of the non-retrofitted specimen was 1.2, and those of the two retrofitted specimens were 1.2 and 0.84. The stiffness ratio of the beam-lower column of all specimens was 0.36. And the stiffness ratio were used for variable. As a result of the experiment, the specimen retrofitted with RBS showed improved maximum load, effective stiffness and energy dissipation capacity compared to the non-retrofitted specimen with the same beam-upper column stiffness ratio. The specimen with 0.84 beam-upper column stiffness ratio showed improved performance compared to the specimen with 1.2 stiffness ratio.

This study proposes an economically affordable method for retrofitting non-seismic detailed roof reinforced concrete beam-column joints (BCJs). The proposed method presents an innovative arrangement of steel plates designed to delay the propagation of joint shear cracks by externally applying compressive stress to the area surrounding the BCJs. Two full-scale sub-assemblage specimens for each exterior and interior roof BCJ, i.e., control and retrofitted specimens, were subjected to reversed cyclic loading to evaluate the proposed method. The retrofitted specimens displayed a preferable ductile behavior to the corresponding control specimen, with an enhancement in lateral strength by at least 100%. Furthermore, retrofitted specimens dissipated up to 13 times more energy than the control specimen by initiating a plastic hinge on beams or columns. These results indicated the effectiveness of the proposed method in preventing joint shear failure and improving the seismic behavior of roof BCJs.

The economical manufacturing of high-quality graphene has been a significant challenge in its large-scale application. Previously, we used molten Sn and Cu as the heat-transfer agent to produce multilayer graphene on the surface of gas bubbles in a bubble column. However, element Sn and Cu have poor catalytic activity toward methane pyrolysis. To further improve the yield of graphene, we have added active Ni into Sn to construct a Sn–Ni alloy in this work. The results show that Sn–Ni alloy is much more active for methane pyrolysis, and thus more graphene is obtained. However, the graphene product is more defective and thicker because of the faster growth rate. By using 300 ml molten Sn–Ni alloy (70 mm height) and 500 sccm source gas ( CH4:Ar = 1:9), this approach produces graphene with a rate of 0.61 g/hr and a conversion rate of methane to carbon of 37.9% at 1250 ℃ and ambient pressure. The resulting graphene has an average atom layer number of 22, a crumpled structure and good electrical conductivity.

본 연구에서는 콘크리트 구조물의 내구성 고도화를 위하여 고속도로용 교각 기둥부에 대하여 내부 식성이 우수한 GFRP 보강근 적용하였으며, 설계적 분석, 축소모형 시험체 제작 및 성능 시험을 통하 여 실용화의 타당성를 검증하였다. 설계적으로 교각의 기둥부는 축방향 주철근을 GFRP 보강근으로 대체하였다. 일반적으로 GFRP는 압축부에 취약한 것으로 알려져 있으며, 국외 기준의 경우는 압축부 에 대하여 GFRP 보강근은 저항력이 없는 것으로 가정하고 있다. 본 연구에서는 탄성 교각에 대하여 기존 철근을 대체할 수 있는 GFRP 보강근의 설계적 방안 제시 및 실물 시험을 통한 성능 검증을 수 행하여 결과를 제시하였다. 본 연구 결과는 고속도로용 탄성 교각 기둥의 내구성 증진을 위한 설계 및 실용화에 있어 가능한 가이드라인을 제시할 것으로 기대된다. 다만, 본 연구에서 다룬 기둥부는 주철 근만을 GFRP 보강근으로 대체한 것으로, 향후 GFRP 나선형 보강근 등의 적용, GFRP의 축하중 분담 률 및 건조수축 크리프 특성, 기둥부의 최소 보강근비 산정 그리고 GFRP 보강근의 압축강도 측정법 등 상세 사항에 대한 추가적인 연구가 필요할 것이다.

Existing reinforced concrete buildings with seismically deficient column details affect the overall behavior depending on the failure type of column. This study aims to develop and validate a machine learning-based prediction model for the column failure modes (shear, flexure-shear, and flexure failure modes). For this purpose, artificial neural network (ANN), K-nearest neighbor (KNN), decision tree (DT), and random forest (RF) models were used, considering previously collected experimental data. Using four machine learning methodologies, we developed a classification learning model that can predict the column failure modes in terms of the input variables using concrete compressive strength, steel yield strength, axial load ratio, height-to-dept aspect ratio, longitudinal reinforcement ratio, and transverse reinforcement ratio. The performance of each machine learning model was compared and verified by calculating accuracy, precision, recall, F1-Score, and ROC. Based on the performance measurements of the classification model, the RF model represents the highest average value of the classification model performance measurements among the considered learning methods, and it can conservatively predict the shear failure mode. Thus, the RF model can rapidly predict the column failure modes with simple column details.

The purpose of this study is to experimentally analyze the seismic performance of beam-column specimens with vertical irregular, which were reinforced with RHS (Replaceable steel haunch system). a steel haunch system. To evaluate the seismic performance of the RHS, three specimens were manufactured and subjected to cycle loading tests. Retrofitted specimens have different beam-upper column stiffness ratio as a variable. The stiffness ratio of beam-upper column were considered to be 1.2 and 0.84. As a result of the test, the specimen reinforced with RHS showed improved maximum load and effective stiffness, and energy dissipation capacity compared to the non-retrofitted specimen with same beam-upper column stiffness ratio. The specimen with 0.84 beam-upper column stiffness ratio showed improved performance than the specimen with 12.

A provision crane is installed on the stern deck of the ship to load or unload ship supplies. In this study, a ventilation hole capable of circulating internal flow was installed to reduce dew condensation by reducing the temperature difference between the inside and outside of the cylindrical column supporting the provision crane installed at the stern of the training ship. In order to reduce the temperature difference between the inside and the outside, an anti-sweat covering work was carried out by adding insulation material. By reducing dew condensation, we aim to improve the insulation of the electric motor installed inside the cylindrical column and improve the usability of the provision crane