During the operation of Pressurized Heavy Water Reactor (PHWR), corrosion oxide layers are formed on the surface of carbon steel SA 106 Grade B (GR.B), primary coolant system material. These oxide layers can be effectively removed using the common chemical decontaminant, oxalic acid (OA). However, the base metal of the structural material may also undergo corrosion, increasing the concentration of metal ions, such as ferrous ions, in the decontamination solution. The increased concentration of metal ions leads to an increased use of cation exchange resins in wastewater treatment, thereby increasing the amount of secondary wastes. Therefore, minimizing the corrosion of the base metal during chemical decontamination is crucial. In this study, imidazole (IM) and 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) were selected for their effectiveness in reducing carbon steel corrosion in acidic environments. Their efficiency as corrosion inhibitors was evaluated under actual decontamination conditions in OA solution. When [BMIM]Cl was added to OA, the corrosion depth of carbon steel decreased from 0.641 μm to 0.406 μm, and the corrosion rate decreased from 1.924 μm/h to 1.218 μm/h, both representing a reduction of 36.7%. In conclusion, this study suggests that [BMIM]Cl is a good candidate as a corrosion inhibitor to be further evaluated under chemical decontamination process.

본 연구에서는 2009년부터 2024년까지 발생한 수도관 파손 사례 29건(DCIP 16건, SP 13건)을 직접 조사하여 파손의 원인을 규명하였다. DCIP의 파손 유형은 주로 종방향 균열 또는 파손(62.5%, 10건)이었고, 그외 파손 유형으로는 홀(Hole) 발생(18.8%), 원주방향 균열 (12.5%), 접합부 부식으로 인한 누수(6.3%)이었다. SP는 5건의 홀 발생(38.5%), 그외 종방향 균열과 원주방향 균열은 각각 30.8%로 나타났다. 이러한 파손의 원인으로 DCIP는 제조상(관두께 부족, 편차, 몸통 기공, 표면 결함 등)이나 재질 결함(화학적 성분, 금속 구조, 인장강도 등)이 DCIP의 파손에 가장 큰 영향을 미쳤으며, 부식과 관련된 매설 환경과 관 하부 기초 시공(자갈, 보 등)과 관련된 사항이 영향을 주었던 것으로 나타났다. SP는 부식, 관의 처짐을 유발하는 매설 환경이나 시공 관련 요인이 SP에 가장 큰 영향을 미쳤고, 일부 롤벤딩으로 제작된 SP는 종방향 용접 결함(부분 용접 등)으로 인한 반복적인 파손 사고를 유발하는 것으로 나타났다. 마지막으로, DCIP와 SP의 파손 사고는 단일 원인이라기보다는 상기의 다양한 요인들이 복합적으로 작용하여 발생한 것으로 판단된다. 그러나 관의 파손에는 관 제조상, 재료 결함, 시공 요인들이 큰 영향을 주고 있어 상수도 관 진단 시 더욱 집중적으로 조사해야 할 영역으로 판단된다.

Due to the limited experimental data on the seismic performance of concrete-encased steel columns, standardized guidelines for nonlinear modeling parameters and acceptance criteria have not yet been developed. This study utilized analytical and numerical methods to predict the nonlinear behavior of concrete-encased steel columns with H-shaped steel sections. The findings of this study have direct and practical implications for the design and evaluation of concrete-encased steel columns. For instance, for concrete-encased steel columns constructed with normal-strength concrete and subjected to low-to-moderate axial load ratios, the yield rotation angle can be determined through fiber-based section analysis and analytical equations, and the nonlinear modeling parameter can be evaluated based on section analysis and the proposed empirical equation. For concrete-encased steel columns with high-strength concrete or high axial load ratios, inconsistencies between section analyses and experimental results are observed. Accordingly, the nonlinear modeling parameter a can be evaluated using the proposed empirical equation. The empirical equation was conservatively developed based on the modeling parameter criteria for reinforced concrete columns in ASCE 41-13.

In the United States, seismic design standards are crucial in classifying buildings into Risk Categories I to IV. These categories are based on the buildings' occupancy type and the potential risk they pose to public safety, the protection of human life, and the socioeconomic consequences of structural collapse in the event of an earthquake. As the risk category increases, a higher seismic importance factor and more stringent drift limits are imposed on the respective building. This results in enhanced lateral strength and stiffness of the seismic force-resisting system. This study, which compares the seismic demands of special moment frame buildings assigned to high-risk categories, focusing on static system overstrength, ductility, and collapse risk, provides practical insights for structural engineers and architects. For this purpose, nonlinear static and dynamic analyses are performed to quantify the seismic demands of 18 steel frame buildings assigned to Risk Categories II, III, and IV. The findings indicate that buildings in Risk Category II do not meet the target collapse risk of 1% in 50 years, as specified in ASCE/SEI 7. For buildings in higher risk categories, the equivalent lateral force method for estimating seismic base shear is deemed more effective in ensuring adequate seismic performance.

본 연구는 바이오차를 혼입한 콘크리트를 구조용 재료로 활용할 가능성을 검토하기 위해, 보강근의 종류에 따른 부착 성능 차이를 실험적으로 분석하였다. 이를 위해 직접 인발 실험을 수행하였으며, 실험 변수로는 콘크리트의 종류(일반/바이오차), 보강근의 종류(철근/GFRP), 보강근 직경(D13/D16)을 설정하였다. 실험 결과, 일반 철근을 적용한 실험체에서는 바이오차 혼입이 부착강도 저 하를 유발하였으며, 특히 D13 보강근에서 약 30%의 감소가 확인되었다. 반면, GFRP 보강근을 적용한 실험체에서는 바이오차 콘크리 트를 적용한 경우 부착성능이 소폭 향상되는 경향을 보였다. 또한 보강근의 직경이 증가할수록 최대 인발하중 및 평균 부착강도가 증가하는 양상이 일관되게 관찰되었다. 이러한 결과는 GFRP 보강근과 바이오차 콘크리트의 조합이 기계적 결합력 증대를 통해 긍정적인 구조 성능을 발휘할 수 있음을 시사하며, 향후 지속가능한 콘크리트 구조물의 보강설계에 기초자료로 활용될 수 있을 것으로 기대된다.

본 연구는 고속철도 궤도 구조의 핵심 부재인 상부 콘크리트층(TCL)에 GFRP 보강근을 적용하여 기존 철근을 대체한 구조의 비선형 동적 거동 특성을 규명하였다. GFRP는 비도전성, 내식성, 경량성과 같은 특성을 갖추고 있어 철도 신호 간섭 방지와 내구성 향상에 적합하다. 국내외 설계기준은 정적 하중 중심이어서 GFRP 적용 구조의 동적 응답과 균열 거동에 대한 연구가 부족한 상황이다. 이에 본 연구에서는 동적 비선형 3차원 유한요소해석을 수행하여 GFRP 보강 TCL 구조와 기존 철근 보강 구조의 하중-변위, 균열폭, 응력 분포를 비교하였다. 분석 결과, 철근 적용 구조는 높은 연성으로 인해 반복 재하에 따른 균열 확대가 크지만 GFRP 적용 구조는 취성적 파괴 양상을 보이며 균열폭이 작고 안정적이었다. 두 구조 모두 허용기준 내의 성능을 만족하였으며, GFRP 보강 구조는 특히 반복 하중에 대한 안정성과 구조 신뢰성에서 우수한 결과를 나타냈다. 본 연구는 GFRP 보강근을 활용한 철도 구조물의 설계 및 유지관 리 측면에서 실용적 근거를 제시하며, 향후 설계기준 수립에 기여할 수 있을 것이다.

This study investigated the ultra-low-temperature (4.2 K) tensile properties and deformation mechanisms of stainless steel 304L manufactured via laser powder bed fusion (LPBF). The tensile properties of LPBF 304L were compared to those of conventional 304L to assess its suitability for cryogenic applications. The results revealed that LPBF 304L exhibited a significantly higher yield strength but lower ultimate tensile strength and elongation than conventional 304L at 4.2 K. The temperature dependence of the yield strength also favored LPBF 304L. Microstructural analysis demonstrated that LPBF 304L features a high density of dislocation cells and nano-inclusions, contributing to its greater strength. Furthermore, strain-induced martensitic transformation was observed as a key deformation mechanism at cryogenic temperatures, where austenite transformed into both hexagonal-closed packed (HCP) and body-centered cubic (BCC) martensite. Notably, BCC martensite nucleation occurred within a single HCP band. These findings provide critical insights into the mechanical behavior of LPBF 304L at cryogenic temperatures and its potential for applications in extreme environments.

Metal additive manufacturing (AM) facilitates the production of complex geometries with enhanced functionality. Among various AM techniques, laser powder bed fusion (LPBF) is distinguished by its precision and exceptional mechanical properties achieved via laser fusion deposition. Recent advancements in AM have focused on combining LPBF with post-processing methods such as cold rolling, high-pressure torsion, and forming processes. Therefore, understanding the forming behavior of LPBF-processed materials is essential for industrial adoption. This study investigates the stretch-flangeability of LPBF-fabricated 316L stainless steel, emphasizing its anisotropic microstructure and mechanical properties. Hole expansion tests were employed to assess stretch-flangeability in comparison to wrought 316L stainless steel. The results demonstrate that LPBF-processed samples exhibit significant anisotropic behavior, demonstrating the influence of microstructural evolution on formability. These findings contribute valuable insights into optimizing LPBF materials for industrial forming applications.

In this study, the molten steel flow inside the mold according to the shape change of the submerged entry nozzle (SEN) was simulated in the continuous casting process, and the effects of the immersion depth and long side length of the mold on the molten steel flow were compared and analyzed. The heat flow analysis was performed using the ANSYS Fluent software, and the turbulence model used the standard k-ε model. Based on the analysis results, the meniscus velocity decreased with deeper immersion depth, but it was slightly faster with lower immersion depth. In addition, the flow velocity of the molten steel of the outlet was increased because the molten steel exiting the upper outlet spread directly without colliding with the short side of the mold when the long side of the mold length was increased.

This study explores the seismic performance of steel diaphragm walls in underground structures, a critical aspect of structural engineering. The study focuses on the effects of slab diaphragm flexibility, an often overlooked factor in seismic design. Traditional seismic designs often assume the slab acts as a rigid diaphragm, leading to inaccuracies in predicting how forces are distributed between the slab and walls during an earthquake. To address this, the authors model steel diaphragm walls using equivalent cross-sections and analyze shear forces in both rigid and semi-rigid diaphragm scenarios. Results show that semi-rigid diaphragms reduce the shear forces on the exterior walls while increasing them on the internal core, thereby affecting the overall stiffness of the structure. The study emphasizes the importance of considering diaphragm flexibility in seismic design to achieve more accurate predictions of structural behavior and improve construction efficiency.

While the subduction zone earthquakes have long ground motion durations, the effects are also not covered in seismic design provisions. Additionally, the collapse risk of steel frame buildings subjected to long-duration ground motions from subduction earthquakes remains poorly understood. This paper presents the influence of ground motion duration on the collapse risk of steel frame buildings with special concentrically braced frames in chevron configurations. The steel buildings considered in this paper are designed at a site in Seattle, Washington, according to the requirements of modern seismic design provisions in the United States. For this purpose, the nonlinear dynamic analyses employ two sets of spectrally equivalent long and short-duration ground motions. Based on the use of high-fidelity structural models accounting for both geometric and material nonlinearities, the estimated collapse capacity for the modern code-compliant steel frame buildings is, on average, approximately 1.47 times the smaller value when considering long-duration ground motion record, compared to the short-duration counterpart. Due to the sensitivity to destabilizing P-Delta effects of gravity loads, the influence of ground motion duration on collapse risk is more profound for medium-to-high-rise steel frame buildings compared to the low-rise counterparts.