In the fabrication of curved steel plates for shipbuilding, post line-heating is widely used to induce plastic deformation by applying local heat and controlling residual stress. However, the process is still dependent on skilled labor and empirical methods, making it difficult to ensure consistent quality and precision. To improve the automation and standardization of the post line-heating process, this study aims to investigate the relationship between heating conditions and the resulting deformation behavior of marine structural steel plates. Experiments were conducted on AH36 steel specimens under 24 different heating conditions, including three plate thicknesses (12mm, 16mm, 20mm), two heating speeds, two gas flow ratios, and two torch tip types. Maximum deformation was measured across 15 locations per case. The results showed that thinner plates exhibited greater deformation, and higher heat input—such as slower heating speed and higher gas flow—led to increased deformation. The 800-type torch tip, with a narrower flame focus, also induced larger deformation than the 1000-type. These findings provide fundamental data for optimizing post line-heating parameters and establishing automated correction processes in shipbuilding applications.

This study investigates the deformation behavior of AH32 steel plates under various line heating conditions in the post line-heating process. A total of 24 experimental cases were conducted by varying material thickness (12mm, 16mm, 20mm), heating speed, oxygen and acetylene flow rates, and torch tip size. Deformation was measured at 35 points per specimen, with emphasis on the maximum deformation at the 300mm X-axis location. The deformation results were classified into three groups: high (≥4.0mm), medium (2.0–3.9mm), and low (≤1.0mm). The results confirmed that material thickness had the greatest effect on deformation, followed by heat input parameters such as heating speed and gas flow rate. High deformation occurred under low heating speed and high flow rate conditions, while low deformation was observed in thick plates with fast heating and low flow rates. These findings highlight the importance of controlling heat input and geometric factors for deformation correction. The data acquired from this study can be utilized as a reference for optimizing automated post line-heating processes in shipbuilding.

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.

X-ray diffraction is widely used as a non-destructive method for measuring residual stress in crystalline materials, and is particularly useful as a technique for controlling residual stress that has been introduced during the heat treatment or surface treatment of metallic materials. Neutron stress measurement is gaining attention as an internal material measurement method. It complements the demerits of the X-ray method in that it measures stress in a very thin surface layer. The neutron stress measurement method, like the X-ray method, is based on the principle of crystal diffraction, and its penetration depth is about 1,000 times greater than that of the X-ray method and is suitable for measuring the inside of a material. This study investigated the residual stress measurement method using the sin2ψ method using shot-peened mechanical structural carbon steel. The non-destructive measurement using high-energy X-rays was compared with the residual stress measured using conventional laboratory X-rays, and the following results were obtained. The high intensity diffraction angles using highenergy X-rays are low, but can be measured with sufficient precision. Interpreting the three diffractions 633, 552, and 721 as a single diffraction profile allowed stress measurements to be made, and the calculated value was close to the weighted average of the intensity ratios. The results of the high-energy X-ray residual stress measurements were in good agreement with the results from laboratory X-rays, confirming the usefulness of this method as a non-destructive method of assessing stress deep inside materials.

본 연구에서는 센싱 기반 모니터링 스마트 파이프 개발 연구의 일환으로 화학적 전처리된 코팅 강관에 대한 유한요소해석을 실시 하였다. 개발된 코팅 강관은 내･외면 개질 폴리에틸렌으로 화학적 코팅 전처리 과정을 수행하였으며, 확관 시 표면 코팅 손상을 최소 화하기 위한 연결 부속을 사용한 코팅 강관의 해석을 수행하였다. 다양한 하중에 대한 구조성능 평가를 위해 토압 하중에 의한 정적 구 조해석, 차량 하중에 의한 피로수명 평가, 인장 및 압축 하중에 의한 누수 저항성의 4가지 하중 조건을 설정 및 조사하였다. 해석 결과, 기존 에폭시 코팅 및 조인트 사용 강관 대비 개발 강관에서 개선된 피로 수명이 산출되었으며, 동일 직경의 조건에서 평균 56.1%의 최 대 변위 감소와 61.2% 최대 응력이 감소함을 통해 개발 코팅 강관과 연결 부속의 안전성을 검증하였다. 이에 더하여 응력 분포 분석을 통해 체결부의 누수 저항성 역시 강관 중앙면 대비 우수함을 확인하였다.

본 연구에서는 강합성라멘교의 벽체 배면 철근 커플러 적용 여부에 따른 두 실험체를 제작하여 하 중가력 실험을 수행하였다. 그 결과 공법에 적용된 주요 기술에 대한 구조적 안전성 및 적정성을 확인 하였으며, 실험체는 설계 내하력 대비 충분한 안전성을 확보하고 있음이 확인되었다. 또한, 경간장 17.3m, 교폭 3.0m, 높이 3.25m의 실험체에 대한 정적성능실험 및 동특성 측정 실험을 수행하였으며, 그 결과 설계 내하력 대비 충분한 안전성을 확보하고 있는 것으로 나타났다.

This study systematically investigated the efficacy of incorporating graphene/cerium hydroxide (GH) composite material into epoxy-modified polyurethane resin coatings for enhancing the corrosion resistance of Q690qE steel within polluted marine atmospheric conditions. The research encompassed a range of electrochemical assessments and analyses. Notably, the E/GH-0.3% coating displayed a substantially positive open-circuit potential (OCP) and prominently reduced corrosion current density, leading to annual corrosion rates of 2.72 mm/a following 25 days of immersion. Electrochemical impedance spectroscopy (EIS) elucidated the superiority of the E/GH-0.3% coating, characterized by the highest impedance modulus |Z| at 0.1 Hz, indicative of robust corrosion protection. Remarkably, the self-healing performance of E/GH-0.3% and E/ GH-0.5% coatings was evidenced by the formation of a composite passivation layer at scratch sites, particularly pronounced after 40 days of immersion. These findings underscore the promising potential of the GH composite as an effective corrosion inhibitor, holding significant promise for the advancement of protective coatings in harsh coastal industrial environments.

In this study, we designed and manufactured a large angular contact ball bearing (LACBB) with low deformation using JIS-SUJ2 steel and analyzed changes in its structural characteristics and chemical composition upon heat treatment. The bearing was produced by hot forging and heat treatment including a quenching and tempering (Q/T) process, and its properties were analyzed using 4 mm thick specimens. A difference in the size distribution of the carbide in the outer and inner parts of the bearing was observed and it was confirmed that large and non-uniform carbide was distributed in the inner part of the bearing. After heat treatment, the hardness value of the outer part increased from 13.4 HRC to 61 HRC and the inner part increased from 8.0 HRC to 59.7 HRC. As a result of X-ray diffraction (XRD) measurements, the volume fraction of the retained austenite contained in the outer part was calculated to be 3.5~4.8 % and the inner part was calculated to be 3.6~5.0 %. The surface chemical composition and the content of chemical bonds were quantified through X-ray photoelectron spectroscopy (XPS), and a decrease in C=C bonds and an increase in Fe-C bonds were confirmed.

In this study, alternative seismic force-resisting systems for plant structure supporting equipment were designed, and the seismic performance thereof was compared using nonlinear dynamic analysis. One alternative seismic force-resisting system was designed per the requirement for ordinary moment-resisting and concentrically braced frames but with a reduced base shear. The other seismic force-resisting system was designed by accommodating seismic details of intermediate and unique moment-resisting frames and special concentrically braced frames. Different plastic hinge models were applied to ordinary and ductile systems based on the validation using existing test results. The control model obtained by code-based flexible design and/or reduction of base shear did not satisfy the seismic performance objectives, but the alternative structural system did by strengthened panel zones and a reduced effective buckling length. The seismic force to equipment calculated from the nonlinear dynamic analysis was significantly lower than the equivalent static force of KDS 41 17 00. The comparison of design alternatives showed that the seismic performance required for a plant structure could be secured economically by using performance-based design and alternative seismic-force resisting systems adopting minimally modified seismic details.

It is effective to apply hybrid damping device that combine separate damping device to cope with various seismic load. In this study, HRS hybrid damper(hybrid rubber slit damper) in which high damping rubber and steel slit plate are combined in parallel was proposed and structural performance tests were performed to review the suitability for seismic performance. Cyclic Loading tests were performed in accordance with criteria presented in KDS 41 17 00 and MOE 2019. As a result of the test, the criteria of KDS 41 17 00 and MOE2019 was satisfied, and the amount of energy dissipation increased due to the shear deformation of the high-damping rubber at low displacement. Result of performing the RC frame test, the allowable story drift ratio was satisfied, and the amount of energy dissipation increased in the reinforced specimen compared to the non-reinforced specimen.

모듈러 건축물은 철근콘크리트 및 철골 구조물에 비하여 상대적으로 경량이고, 단위 모듈간 기둥의 일체성을 기대하기 어려운 구조적 특성을 가진다. 이와 같은 구조적 특성은 모듈러 건축물의 높이가 높아짐에 따라 바람 및 지진과 같은 횡력저항성능에 직접적인 영향을 미친다. 본 연구에서는 횡력저항성능을 향상시키기 위해 긴장재를 활용한 모듈러 구조시스템을 제안하였다. 모듈러 구조시스템을 구성하는 주요 요소인 포스트텐션 기둥-바닥 접합부는 셀프 센터링 거동을 유도하기 위한 형상 및 상세를 가진다. 포스트텐션 기 둥-바닥 접합부의 이력 거동을 상세히 파악하기 위해 유한요소해석을 수행하였으며, 그 결과 초기 긴장력 및 보-기둥 접합부의 접합 조건에 따라 이력 거동은 확연한 차이를 보이는 것으로 나타났다.

본 연구에서는 H-Beam 부재에 TRM(Total Reinforced Member)공법의 적용을 통한 부재의 구조성능개선에 대하여 분석하였다. TRM공법은 가교의 성능개선을 위해 적용되는 여러 공법 중 프리스트레스 도입을 통해서 H-Beam 부재의 구조성능을 개선하는 공법이다. 우선 본 연구에서는 해석적인 시뮬레이션을 통해서 TRM공법의 적용 가능성을 확인하였다. 1차적으로 수치 해석을 통해서 프리스트레스 도입을 위한 선행하중을 결정하고, 순수 H-Beam 부재와 L형 강재가 용접된 부재 그리고 TRM공법이 적용된 3가지의 부재에 대한 구조성능 변화를 해석을 통해서 확인하였다. 그리고 해석적인 결과의 검증 및 공법의 현장적용 가능성을 평가하기 위하여 순수 H-Beam 부재와 TRM공법이 적용된 2가지의 부재에 대한 3점 굽힘 시험을 수행하였다. 실험을 통하여 TRM공법이 적용된 부재에서 순수 H-Beam 부재대비 하부 플랜지의 발생응력 및 최대처짐이 각각 20.60%, 16.87% 감소 하는 결과를 확인하였다.

본 논문에서는 도서 지역 화물 및 승객 운송을 맡은 연안 항해용 친환경 차도선을 개발하면서, 검토된 주요 결과들에 대해서 논의한다. 시장에서의 경제성을 확보하기 위하여, 폭 19 m를 최종 개발모델 및 갑판면적에 많은 차량이 배치되도록 고려하였다. 조파저항 감소를 위해 선형 형상은 “V”에 선수벌수를 접목하였으며, 수치해석을 통해 개발 선박의 유체역학적 성능을 확인하였다. 선가를 직접 결정짓는 선각 중량을 감소하기 위하여, 최적화 전문 프로그램에 내재된 다목적 최적화 방법인 파레토 시뮬레이트 어닐링을 활용하여 약 3.9 %의 중량 절감을 달성하였다. 본 연구를 통해서 도출된 주요 결과들은 추후 쌍동형 차도선 관련 연구를 수행하는 엔지니어와 관련 산 업에 좋은 선례가 될 것으로 기대한다.

U-flanged truss beam is composed of u-shaped upper steel flange, lower steel plate of 8mm or more thickness, and connecting lattice bars. Upper flange and lower plate are connected by the diagonal lattice bars welded on the upper and lower sides. In this study, the details of delayed buckling of lattice members were developed through reinforcement of the end section, in order to improve structural capacity of U-flanged Truss Steel Beam. To verify the effects of these details, the simple beam experiment was conducted. The maximum capacity of all the specimens were determined by the buckling of the lattice. The vertical reinforced details of the ends with steel plates, rather than the details reinforced with steel bars, are confirmed to be a valid method for enhancing the structural capacity of the U-flanged Truss beam. In addition, U-flanged Truss Steel Beam with reinforced endings with steel plates can exhibit sufficient capacity of the lattice buckling by the formulae according to Korean Building Code (KBC, 2016) and Eurocode 3.

일반적인 구조용 강재의 경우 항복변형률의 이상의 변형을 경험한 이후에 하중을 제거하면 재가력되는 시점에 따라 서 재료의 항복강도는 증가하고 연성이 감소하는 현상을 보인다. 원형강관의 경우 철판을 말아서 제작하는 과정에서 철판의 두 께와 원형강관의 직경에 따라서 항복변형률이상의 큰 변형을 경험하게 되고 이러한 변형은 제작된 강관의 구조적인 성능에 많 은 영향을 미친다. 이러한 이유에서 제작과정에 발생하는 변형이 원형강관의 구조성능에 미치는 영향을 파악할 필요가 있다. 따 라서, 이 연구에서는 원형강관을 제작하는 경우에 발생하는 변형에 의한 철판의 항복강도, 인장강도 및 연성 등의 영향을 파악 하기 위해서 강관의 직경 및 두께와 시험편을 채취한 방향을 변수로 다수의 인장실험을 수행하고 이를 분석하였다. 실험 결과 를 바탕으로 원형강판에서 채취한 시험편은 코일에서 채취한 시험편에 비해 항복강도와 인장강도가 더 높았고, 연신율은 낮아 진 것으로 나타났다.

This study was carried out to standardize the material properties of roll-over protective structure (ROPS) for agricultural tractor. The material properties which were obtained from stress-strain curve, a result of tensile test stress, were used to apply to the virtual test and varied from one production lot to the other and from one manufacturer to the other. And the finite element analysis was performed on the ROPS according to the OECD code. The results show that the load-displacement curves of virtual test were approximately equal to the actual test curves. The manufacturer or lot has been shown to have little effect on the properties of the material. Therefore, it is expected that the representative values that can be used in the finite element analysis can be determined by averaging the property values.