The optimal design of steel plate girders has traditionally relied on meta-heuristic techniques, such as Genetic Algorithms (GA), to handle discrete design variables and complex non-linear constraints, including shear buckling and section classification. However, these methods suffer from high computational costs as they require repetitive re-optimization for every new load condition. To address this limitation, this study proposes a highly efficient Sequential Multi-Agent Reinforcement Learning (MARL) framework based on the Agent-Environment Cycle (AEC) architecture. Unlike parallel one-shot approaches, the proposed model effectively learns the dependencies between design variables by determining them sequentially. Furthermore, to maximize cost efficiency during the inference phase, we introduce an Adaptive Inference Chain combined with a deterministic DCR-based Shrink-Refine algorithm. Experimental results on 100 diverse load cases demonstrate that the proposed method achieves an average cost reduction of 8.2% compared to the GA baseline while maintaining 100% feasibility. With an inference time reduced to approximately 76 ms, the model demonstrates significant potential for real-time automated design. Additionally, an in-depth analysis of cases where the Demand-Capacity Ratio (DCR) fell short of the target clarifies the exploration limits within the discrete design space and validates the robustness of the algorithm.

To mitigate power transmission losses between power plants and consumers, Medium-Voltage Direct Current (MVDC) systems, which transmit power as DC and convert it back to AC at the destination, are increasingly being developed. However, these MVDC conversion systems, which are rich in semiconductor devices, generate significantly more heat than conventional transformers. Consequently, the thermal management capabilities of traditional air-cooling methods are proving insufficient, necessitating the adoption of liquid cooling systems. This study aims to optimize the energy efficiency of MVDC liquid cooling systems. Finally, we demonstrated a optimized system that minimizes the pump's power consumption by dynamically adjusting the coolant flow rate to each thermal module based on the automatic control valve system.

In this study, a new Lattice integrated Rib-Type Deck Plate system is proposed to enhance the flexural stiffness and strength. This system integrated a rib-type corrugated deck with a steel wire lattice designed for short spans, which is placed on top of the corrugated deck. To validate the flexural performance of the proposed system, experimental programs were conducted for both the construction stage and the composite stage. Construction stage test results showed that all specimens exhibited deflections less than 13mm under the construction load, satisfying the maximum deflection limit of 19mm. Composite stage test results indicated that increasing the amount of tension and compression reinforcement led to improvements in initial stiffness, yield strength, and maximum strength. Furthermore, specimens with reinforcement in the compression zone demonstrated superior ductility. The flexural strength of all tested specimens was confirmed to be safely evaluated by the flexural strength equation specified in the Korea Design Standard.

Active electronically scanned array (AESA) multi-function radars (MFRs) comprise numerous transmit/receive modules (TRMs) whose maximum temperature and temperature uniformity must be tightly controlled. This study proposes a new liquid-cooling-plate flow-channel design for an X-band AESA MFR: a two-layer straight channel incorporating multiple fins irregularly spaced along the flow channel. The proposed design (Type-4) is compared with three baseline channel designs. At the same coolant flow rate, Type-4 reduces the TRM maximum temperature by 28.2 K and the maximum inter-module temperature difference by 19.7 K relative to Type-1. However, the pressure drop increases by 726% because of the added internal surfaces and fins which are flow obstructions. A comprehensive thermo-hydraulic comparison, including pumping power criteria, is conducted over multiple flow-rate conditions. Overall performance was highest for Type-4, followed by Type-2, Type-3, and Type-1. When designs achieve similar maximum temperature and temperature difference with various coolant flowrate condition, Type-2 requires 83.6% less pumping power than Type-1, and Type-4 requires 33.8% less pumping power than Type-2.

본 연구에서는 Plate Count Agar (PCA; 48시간 배양)와 MC-Media Pad A.C+ (MMPAC+; 24시간 배양)의 검출 효 율과 정량 정확도를 비교하여 건조필름의 배양시간 단축 가능성을 평가하였다. 샐러드 60건에 대한 검출 효율 실 험에서 PCA는 6.1±1.0 log CFU/g, MMPAC+은 6.3±1.1 log CFU/g의 결과를 나타냈다. PCA와 MMPAC+의 P-value 는 0 .3 3 5로 유의적인 차이를 나타내지 않았다. 상관계수 (R2)는 0.5545로 상당한 상관관계를 보였다. 샐러드에 일 반세균을 저농도로 접종한 결과 PCA의 경우 3.3±0.1 log CFU/g, MMPAC+의 경우 3.4±0.1 log CFU/g로 나타났고 P-value는 0.251로 유의적인 차이를 나타내지 않았다. 고 농도로 접종한 결과 PCA의 경우 8.9±0.2 log CFU/g, MMPAC+의 경우 9.0±0.3 log CFU/g로 나타났고, P-value 는 0.561로 유의적인 차이를 나타내지 않았다. 따라서 PCA(48시간 배양)와 더불어 MMPAC+ 건조필름을 24시 간 배양하여 일반세균 실험에 사용할 수 있을 것으로 판 단되었다.

When manufacturing a square plate with a pinhole, the following conclusions were obtained as a result of analyzing the effect of changes in the size of the grid filling the inside of the plate and the presence or absence of a pinhole on the stress concentration factors. 1. It can be seen that in the case where there is a pinhole, the overall stress concentration factors is twice as high as in the case where there is no pinhole. In addition, in the case where there is no pinhole, it can be seen that the stress concentration factors fluctuates at a certain standard depending on the position of the pinhole and the internal grid, and in the case where there is a pinhole, it decreases at a certain point and then increases again. 2. In the case where there is no pinhole, when the L/H ratio increases from 0.1 to 0.3, the Kt value increases from 1.8 to 2.7, an increase rate of approximately 50%. Similarly, in the case of a pinhole, when the L/H ratio increases from 0.1 to 0.4, the Kt value increases from 2.0 to 3.0, an increase rate of about 50%.

도심지에서는 증가하는 교통량으로 인해 지상에서 지하로 교통 시설을 확대하고 있다. 지하에 교통 시설물을 시공할 경 우 기존 도로를 굴착한 후에 지하 시설물을 시공하는 동안에 임시통행판을 사용하여 기존 도로의 역할을 대체하도록 하 고 있다. 이러한 임시통행판은 대부분 철재를 사용하고 있으며 표면에 아스팔트, 콘크리트 등 다양한 재료를 적용하여 사용하기도 한다. 본 연구에서는 콘크리트 슬래브를 임시통행판으로 적용하고 있는 사례를 조사하기 위해 미국 로스앤젤 레스 지역의 콘크리트 임시통행판이 설치된 구간에 대한 현장 조사를 실시하였으며 구성 요소와 손상 유형을 분석하였 다. 콘크리트 임시통행판의 주요 구성 요소로는 각각의 임시통행판을 연결해주는 연결부와 프리캐스트 콘크리트 임시통 행판을 인양할 수 있는 인양장치 체결부 등을 들 수 있다. 조사 구간은 하부의 보 구조 위에 프리캐스트 콘크리트 임시 통행판을 배치하였으며 연결부와 인양 장치 체결부를 그라우트로 채우는 방식으로 시공된 것으로 분석되었다. 손상 유형 을 분석한 결과, 차량 통행으로 인해 연결부와 인양장치 체결부의 그라우트 재료가 탈락되어 빈 공간이 보이는 부분이 많았으며 이러한 부분을 아스팔트 혼합물로 충진하여 사용하고 있었다. 또한, 콘크리트 임시통행판에 균열이 발생한 경 우도 조사되었다.

For the commercialization of bipolar plates, several properties must be considered together. Electrical conductivity, corrosion resistance, contact resistance, mechanical strength, and light weight are essential evaluation factors, with corrosion resistance and durability being significant for unitized regenerative fuel cells (URFCs), which must operate in electrolysis and fuel cell mode. However, improving both properties is challenging, since corrosion resistance is largely inversely proportional to conductivity. In this study, to improve both properties together, composites composed of Pb and Zn with excellent conductivity and corrosion resistance were prepared with graphite powder and formed as a coating layer on the surface of 304 stainless steel (SS304) and evaluated for electrical conductivity and corrosion resistance. Among the ZnPb/C composites prepared at various ratios, Zn8Pb2/C exhibited the lowest transmittance resistance of 1.566 Ω, and improved electrical conductivity and durability compared to bare SS304.

In this study, when manufacturing a rectangular plate with a pinhole, the following conclusions were obtained as a result of analyzing the shape characteristics of the unit cell that fills the interior of the plate and the effect of changes in the size of the pinhole on the stress concentration coefficient. 1. The stress value generated in the case of the completely empty model was 13.9 MPa, which is an 18.8% increase in stress compared to the stress value 11.7 MPa generated in the fully filled model. However, since the weight of the empty model is 43.6% lower than that of the filled model, it is believed to be very advantageous in terms of cost. 2. The stress concentration coefficient value is lowest for the solid model and highest for the hollow model at the same d/H value. In other words, you can see that the values are changing within the boxes of the solid model and hollow model. However, the grid matching model is closest to the solid model and the filling rate is as low as 33.4-9.1%, showing the most stable strength when filling empty space.

This study proposes a steel plate retrofit method and a polyurea method to improve the structural stability and usability of a factory floor slab with a thickness of 120mm. To assess vibration changes, vibrations were measured before and after retrofit. A numerical analysis model was also developed to evaluate improvements in structural safety and usability. The natural frequency increased from 11.4Hz to 17Hz through steel plate reinforcement, confirming an increase in slab stiffness. The damping ratio increased from 2.3% to 3.2% with polyurea reinforcement, indicating improved vibration reduction. Additionally, numerical analysis modeling showed that the natural frequency increased from 13.9Hz to 16.2Hz due to the steel plate reinforcement, enhancing the dynamic characteristics of the floor slab and confirming the reliability of the analysis model.

국내에서는 고속도로에는 콘크리트 포장을 적용하고 있지만 도심지에서는 콘크리트의 양생기간으로 인해 장기간 교통차단이 필요없 는 아스팔트 포장을 주로 적용하고 있다. 그러나 아스팔트 포장은 공용수명이 길지 않아 잦은 유지보수 작업으로 인해 사용자들의 불 편을 초래하고 있다. 본 연구에서는 현장타설 콘크리트 포장 공법을 적용하더라도 즉시 통행이 가능한 포장 임시보호판 개발을 위하 여 임시보호판의 하부 지지보 설치 간격 최적화를 목적으로 3차원 유한요소해석 프로그램을 이용하여 차륜 하중에 대한 응력분포를 분석하였다. 해석에 사용된 임시보호판은 길이 6m, 폭 3m, 두께 0.3m의 콘크리트 슬래브로 구성하였으며, 임시보호판의 하부 지지보 간격을 0.5m, 1m, 1.5m, 3m, 6m로 구성하였다. 하중 조건은 중차량인 버스를 고려하여 타이어 접지 면적당 33,540N의 분포하중을 지지 보 사이에 적용하여 분석하였다. 해석 결과, 하부 지지보 사이의 간격이 좁아질수록 응력이 감소하는 것을 확인하였다.

Recently, the floor construction method of buildings is rapidly being replaced by the steel deck construction method of factory products from the past cast-in-place formwork method in order to shorten construction period, reduce labor costs, and improve constructability. In this study, the bending capacity of a newly developed lattice integrated rib-type deck plate that is economical and constructible was evaluated through a simple beam test. As a result of the experiment, the lattice integrated rib-type deck installed by adding rib to the existing flat deck had excellent initial rigidity and maximum load-bearing ability, confirming the feasibility of practical use. In addition, the test specimen in which the tensile rebar is not integrated with the lattice and deck has very low initial stiffness, which is insufficient to support the load at the construction stage, and new details need to be developed to overcome this.

In this study, a new model using artificial neural networks is proposed to improve the thickness error between the plates, which occurs when the rolling conditions change a lot during the thick rolling. The model was developed by using Python, and the input values are the change in the finish rolling temperature between the plates, the change in target tensile strength, the change in target thickness, and the change in rolling force. The new model is 31.76% better than the existing model based on the standard deviation value of the thickness error. This result is expected to reduce quality costs when applied to online models at actual production sites in the future.

This paper introduces a study on measuring the 3D vibration displacement of plate structure using Digital Image Correlation (DIC) applied to stereo digital continuous camera images. The proposed method is a non-contact 3D displacement measurement method that does not require physical sensors to be attached to the structure, and it has the advantage of simultaneously measuring dynamic displacements at multiple points on the structure. Theoretically, multiple cameras can be used, but in this study, two cameras were used to capture continuous images of the vibrating structure, and the image coordinates of multiple tracking points at arbitrary positions on the structure were measured using correlation matching. Using these image coordinates as input data, the dynamic 3D positions were calculated through Space intersection, successfully determining the 3D dynamic displacements. The measured dynamic displacements were validated for accuracy by comparing them with values measured by laser displacement sensors. And frequencies of measured data were validated by comparing with computational modal analysis by Finite Element Model (FEM).