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.

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.

국내의 도심지 도로는 대부분 아스팔트 포장으로 시공되어 있으며 아스팔트 포장의 공용수명은 콘크리트 포장의 공용 수명에 비해 짧아 잦은 재시공 및 유지보수 작업이 필요하다. 도심지 특성상 포장 재시공 및 유지보수를 실시할 경우 작 업 시간 동안 교통차단을 유발하여 도로 이용자의 불편을 초래하게 된다. 따라서 서울특별시에서는 신설구간인 헌릉로의 중앙버스정류장 구간에 도심지 최초로 현장타설 방식의 연속철근 콘크리트 포장을 시공하였다. 본 연구에서는 중앙버스 정류장 구간에 시공한 연속철근 콘크리트 포장의 철근 거동에 대한 분석을 수행하여 철근의 응력이 가장 크게 발생하는 균열부에서의 철근 응력의 적정성을 분석하였다. 분석 결과, 균열부에서 멀어질수록 철근의 변형률이 뚜렷하게 감소하는 것을 확인하였으며 균열부에서 약 15cm 정도만 이격되어도 철근의 변형률이 급격하게 감소하여 철근과 콘크리트 간의 부착이 적절한 것으로 분석되었다. 또한, 균열부에서 발생한 철근의 변형률을 응력으로 환산하면 약 50MPa 정도로 철근 의 항복강도인 400MPa에 비해 매우 작아서 연속철근 콘크리트 포장의 우수한 공용성을 확보한 것으로 분석되었다.

본 연구에서는 본선차로와 접속차로가 동일한 연속철근 콘크리트 포장(CRCP: Continuously reinforced concrete pavement)일 경우에 접속차로 CRCP의 종방향 철근의 거동을 분석하기 위해 창녕밀양건설사업단 1공구에서 시험시공을 수행하였다. 시험시공 구간에 균열유도장치와 철근 변형률계를 설치하여 접속차로 CRCP의 종방향 철근 거동을 분석하 였다. 분석 결과, 철근의 변형률은 균열부에서 가장 크게 발생하며 균열로부터 멀어질수록 감소하는 것을 확인하였다. 또 한, 변형률을 응력으로 환산할 경우 항복강도보다 현저히 낮아 접속차로 CRCP의 철근 배근은 우수한 공용성에 기여할 것으로 분석되었다. 이러한 결과를 통해 본선차로와 접속차로가 동일한 CRCP로 시공될 경우 포장 공용성을 보다 향상 시킬 수 있을 것으로 분석되었다.

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.

This study employed a cross-rolling process to fabricate oxide dispersion strengthened (ODS) steel plates and investigated their microstructures and mechanical properties. The 9Cr-1W ODS ferritic steel was fabricated using mechanical alloying and hot isostatic pressing. The hot cross-rolling process produced thick ODS ferritic steel plates with a well-extended rectangular shape. The working direction greatly affected the grain structure and crystal texture of the ODS ferritic steel. Cross-rolled plates showed fine micro-grains with random crystal orientation, while unidirectionally rolled plates exhibited a strong orientation with larger, elongated grains. Transmission electron microscopy revealed a uniform distribution of nano-oxide particles in both rolling methods, with no major differences. Tensile tests of the ODS ferritic steel plates showed that the unidirectional rolled plates had anisotropic elongation, while cross-rolled plates exhibited isotropic behavior with uniform elongation. Cross-rolling produced finer, more uniform grains, reducing anisotropy and improving mechanical properties, making it ideal for manufacturing wide ODS steel components.

This study investigated the effect of the hatch spacing parameter on the microstructure and mechanical properties of SA508 Gr.3 steel manufactured by laser powder bed fusion (L-PBF) for a nuclear pressure vessel. Materials were prepared with varying hatch spacing (0.04 mm [H4] and 0.06 mm [H6]). The H4 exhibited finer and more uniformly distributed grains, while the H6 showed less porosity and a lower defect fraction. The yield strength of the H4 material was higher than that of the H6 material, but there was a smaller difference between the materials in tensile strength. The measured elongation was 5.65% for the H4 material and 10.41% for the H6 material, showing a significantly higher value for H6. An explanation for this is that although the H4 material had a microstructure of small and uniform grains, it contained larger and more numerous pore defects than the H6 material, facilitating stress concentration and the initiation of microcracks.

본 연구는 강재 보행자용 방호 울타리 고정부 부식에 따른 유효단면적 감소로 인한 강성 저하를 해결하기 위해 내부식성이 뛰어난 GFRP, CFRP를 볼트에 적용하여 설계하중에서의 적용성을 검증하였다. 강재에서 유효단면적은 부식이 20년 진행 되었을 때 1.4mm 감소하여 기둥 변위는 28.65mm로 측정되어 부식의 심각성을 인지하였다. FRP 적용 시 평가는 파손 지수(DI)를 통하였고 CFRP 고정부 앵커에서 최대 성능의 30% 수준을 사용하여 설계하중에 만족함을 보였다. 또한, 콘크리트 연석에 가하는 쪼갬 인장응력 이 강재 대비 0.93배로 확인되었다. 이는 FRP 볼트 적용 시 강재와 동일한 방법으로 연석을 검토할 수 있을 것으로 판단된다. 결론적 으로 강재 부식에 따른 강성 저하는 구조물의 심각한 영향을 주어 부식 저항성이 높은 재료의 대체는 필수적이며, 동시에 보행자용 방호 울타리의 설계하중에 대한 연구가 추가적으로 수행 되어야한다.

Friction Stir Spot Welding (FSSW) is a solid-state welding technology that is rapidly growing in the automotive industry. Achieving superior welding characteristics requires the proper selection of tool geometry and process conditions. In this study, FSSW was performed on dissimilar materials comprising AA5052-HO/hot-melt aluminum alloy sheets and Steel Plate Cold Rolled for Deep Drawing Use(SPCUD) steel sheets. The effects of tool geometry, plate arrangement, and tool plunge depth on the welding process were investigated. At the joint interface between the aluminum alloy and the steel sheet, new intermetallic compounds (IMCs) were observed. As the plunge depth increased, thicker and more continuous IMC layers were formed. However, excessive plunge depth led to discontinuous layers and cracking defects. An analysis of the IMCs revealed a correlation between the IMC thickness and the shear tensile load. Furthermore, compared to the conventional Al-Top arrangement, the St-Top arrangement exhibited reduced deformation and superior shear tensile load values. These findings indicate that plate arrangement significantly influences the mechanical properties of the joint.

As global greenhouse gas reduction regulations are strengthened and the demand for eco-friendly energy increases, renewable energies, including offshore wind power, are growing rapidly. Unlike onshore wind power generation, offshore wind power is located in the ocean. As a result, the offshore wind power substructure is exposed to low temperatures, corrosion, and continuous fatigue loads. Therefore, selecting appropriate materials and welding techniques is crucial for durability. In this study, FCAW welding was performed on S355ML steel (EN10025) for offshore wind power applications. After the welding process, the mechanical properties of the welded joint were evaluated through tensile, low-temperature impact, and hardness tests to assess the welding condition. The study revealed that the tensile and yield strength of the welded joint were superior to those of the base material. Additionally, the impact strength at low temperatures was confirmed to exceed the standard.