Our study experimentally evaluates the structural characteristics of a Cone-Shaped Friction Isolator (CFI) as part of research on sliding bearings. With its relatively simple configuration and effective restoring mechanism, the CFI has significant practical implications for structural engineering. We designed the shape and components of the CFI, and its operation and restoring mechanisms were theoretically reviewed. A prototype of the CFI was developed, and structural characteristic experiments were conducted, focusing on design parameters such as the cone’s inclination angle, the friction coefficient of the contact surface, the magnitude of the vertical load applied to the isolator, and the horizontal loading frequency. The experimental results provide valuable insights into the structural characteristics of devices in terms of critical shear force and restoring shear force.

Most reinforced concrete (RC) school buildings constructed in the 1980s have seismic vulnerabilities due to low transverse reinforcement ratios in columns and beam-column joints. In addition, the building structures designed for only gravity loads have the weak-columnstrong- beam (WCSB) system, resulting in low lateral resistance capacity. This study aims to investigate the lateral resistance capacities of a two-story, full-scale school building specimen through cyclic loading tests. Based on the experimental responses, load-displacement hysteresis behavior and story drift-strain relationship were mainly investigated by comparing the responses to code-defined story drift limits. The test specimen experienced stress concentration at the bottom of the first story columns and shear failure at the beam-column joints with strength degradation and bond failure observed at the life safety level specified in the code-defined drift limits for RC moment frames with seismic details. This indicates that the seismically vulnerable school building test specimen does not meet the minimum performance requirements under a 1,400-year return period earthquake, suggesting that seismic retrofitting is necessary.

This paper aims to quantify the retrofit effect of the Bolt Prefabricated Concrete-Filled Tube reinforcement method on non-seismic school reinforced concrete building through static cyclic loading experiments. To achieve the objective, two-story specimens including a non-retrofitted frame(NRF) and a Bolt Prefabricated Concrete-Filled Tube Reinforcement Frame(BCRF) were tested under static cyclic loading, and the lateral resistant capacities were compared in terms of maximum strength, initial stiffness, effective stiffness, and total energy dissipation. In addition, the load-displacement curves were compared to the story drift limit specified in Seismic Performance Evaluation and Retrofit Manual for School Facilities to investigate if the retrofitted frame was satisfied in target performance(life safety). Experimental results showed that BCRF successfully met the target performance, with a 200% increase in maximum strength and a 300% increase in energy dissipation capacity. Additionally, both initial stiffness and effective stiffness improved by more than 30% compared to NRF. Furthermore, BCRF exhibited an effect that delayed the occurrence of bond failure.

국내 도심지에 적용하고 있는 중앙버스정류장의 포장은 주로 아스팔트 포장으로 시공되어 있으나 중차량인 버스의 하 중으로 인해 포장 파손 사례가 증가하여 시민들의 안전에 악영향을 미치고 있으며 유지보수 비용이 매년 증가하고 있다. 서울시에서는 이러한 문제를 해결하기 위해 국내 최초로 중앙버스정류장 신설 구간에 현장타설 방식으로 연속철근 콘크 리트 포장(CRCP)을 시공하였다. 본 연구에서는 이러한 구간의 연속철근 콘크리트 포장에 대한 이동차량 하중에 의한 동 적 거동 특성을 분석하고자 포장 슬래브에 콘크리트 변형률계를 설치하고 덤프트럭을 통과시키며 동적 하중 재하 실험 을 수행하였다. 실험에서는 이동차량의 속도를 다양하게 변화시켜 차량 속도에 따른 포장 슬래브의 동적 거동을 비교 분 석하였으며 이동차량이 CRCP의 여러 위치에서 정지하도록 하여 정지 위치에 따른 거동도 분석하였다. 실험 결과, 차량 이 CRCP를 통행할 경우 차량 속도 및 정지 위치에 따른 포장 슬래브의 동적 변형률은 매우 유사한 것으로 분석되었다.

In this study, the initial operation characteristics of a multi-type cooling system with three indoor units using an inverter compressor were investigated experimentally using a calorimeter. The operating characteristics of the cooling system were confirmed under the full load condition of simultaneous operation of three rooms and the partial load condition of individual operation of two or one room under the standard cooling conditions. The capacities of A, B and C are 50, 20, and 30% of the total capacity, respectively. The 3 room combination has 100% capacity, the 2 room combination has 50, 70 and 80% capacity, and the 1 room has 20, 30, and 50% capacity. The compressor condensing and evaporating pressures, the electronic expansion valve openings of indoor units A, B, and C, and the compressor operating frequencies were measured for 10 minutes after the cooling system was started. During the initial operation, the changes in the operating time and opening of the electronic expansion valve varied depending on the indoor unit combination and the operating load, and the relationship between the compressor pressure and the operating frequency was found.

For experimental studies on the production of MR fluid for MR dampers, MR fluid with a viscosity of 506 cP and a density of 2.6 g/cc was produced. In order for MR fluid to have suitable performance for MR dampers, it is important to select surfactants, magnetic particles, base oil, and characteristic additives to obtain high damping force and maintain physical and chemical properties. In order to investigate the redispersibility of MR fluid, viscosity, density, saturation magnetic flux density, dispersibility, and temperature effects were evaluated. A particle size distribution meter and a vibrating magnetometer were used, and a yield stress and redispersion device were developed to obtain the yield stress of the MR fluid. The recovery rate of MR fluid was approximately 97% at 0.2% succinic acid coating and 8% anti-settling agent. And when current is applied, the viscosity increases by more than 90% due to magnetic properties.

일반적으로 전기 패널은 용접이나 앵커링을 통해 기초에 설치된다. 콘크리트 기초-앵커 시스템에서 고려해야 할 열화 요인에 는 콘크리트 기초의 균열이 포함된다. 콘크리트 균열은 전기 패널의 앵커에 영향을 미치는 열화 현상 중 하나로 간주될 수 있다. 또한 독립반 및 열반된 전기 패널의 동적 특성은 상당히 다를 수 있다. 그러나 많은 연구자들이 하나의 전기 캐비닛 시편으로 진동대실험을 수행하였다. 따라서 열반 구성을 고려하여 동적 특성을 평가할 필요가 있다. 본 연구에서는 0.5 mm 및 1.0 mm 균열 폭을 고려하여 콘크리트 기초-앵커 시스템을 설계하였다. 콘크리트 기초-앵커 시스템을 진동대에 고정하고 1∼3개의 열반으로 구성된 단순화된 캐비 닛 모델을 설치하였다. 열반 수와 콘크리트 균열을 매개변수로 고려하여 진동대에 의한 공진주파수 검색 실험을 수행했으며 각 실험편 의 공진 주파수를 비교하였다.

Experimental findings pertaining to the frost resistance of calcium sulfoaluminate (CSA) and amorphous calcium aluminate (ACA) cement-based repair mortars incorporated with anhydrite gypsum are described herein. To prepare the mortars, CSA and/or ACA cements were used as binders, and the water–binder ratio was fixed at 0.57. The compressive and bond strengths, chloride-ion penetration resistance, and scaling resistance of the mortars were measured. Based on the ASTM C666 method, the resistance to both frost action and multi-deterioration of chloride and frost attacks on the mortars were experimentally examined. Calcium aluminate-based binders effectively enhanced the compressive and bond strengths of the mortars owing to the formation of C2AH8 and Ye’elimite hydrates. Furthermore, replacing 25% ACA with OPC yielded excellent resistance to both frost attack and multi-deterioration of chloride and frost attacks. Replacing ACA at an appropriate level as a binder effectively improves the durability of concrete road facilities in winter.

The heat transfer characteristics of double-pipe spiral heat exchanger using aluminum oxide nano-fluid were investigated by three different sizes of curvature size, experimentally. Five concentration of nano-fluid as working fluid were made and tested to analyze the heat transfer characteristics. As results, the heat transfer performance was improved at 0.25% of nano-fluid due to high thermal conductivity, however, as the concentration of nanofluid increased (~2.0%), the heat transfer performance deteriorated due to the increase in thermal resistance caused by the sedimentation of particles in the flow path. In addition, the nano-fluid has a higher pressure drop than water due to its high density and viscosity. The optimal range for heat transfer enhancement of nano-fluid was found to be less than 4.0 LPM in flow rate and 0.25% of nano-fluid concentration in this study.

This study analyzed the epilithic diatom community and ecological health of freshwater streams using environmental DNA (eDNA)-based metabarcoding technology. eDNA metabarcoding is a method that analyzes biological communities by performing PCR amplification followed by next-generation sequencing (NGS), offering higher sensitivity and faster results compared to traditional microscopic analyses. The study compared the eDNA metabarcoding results of ribulose bisphosphate carboxylase large chain gene (rbcL) targeting epilithic diatoms according to Taq polymerases (SuperFi II, GainBlue, EzPCR, and AccuPower). SuperFi II and GainBlue yielded the highest number of reads and zOTUs, with GainBlue showing particularly uniform read distribution, allowing for more accurate analysis for community diversity of epilithic diatoms. On the other hand, EzPCR and AccuPower exhibited lower number of reads and zOTUs, making them less suitable for the community diversity. In terms of community similarity analysis, SuperFi II and GainBlue produced highly similar results, while EzPCR and AccuPower showed significant differences. This study demonstrates that PCR Taq polymerases significantly influence community diversity and similarity analyses of epilithic diatoms, with GainBlue providing the most stable and accurate results. Our findings serve as a valuable foundation for improving the accuracy of eDNA-based metabarcoding analyses of diatoms.

본 연구에서는 전하 이동 특성을 가지는 분자[쿠마린(C)-DNP]의 흡수 스펙트럼을 정확하게 예측하기 위해 장거 리 보정 밀도 범함수 이론 (long-range corrected density functional theory, LC-DFT)인 LC-BLYP의 범위 분리 매개변수 (μ)를 여러 가지 피팅 방법을 이용하여 최적화하였다. 기체 상태의 Koopmans 이론을 기반으로 최적화된 μ값은 실험적 흡수 피크에 비해 청색 이동(blue-shift)되는 경향성을, 반대로 용매 환경에서 최적화된 μ값은 과도하게 적색 이동 (red-shift)이 되는 경향성을 보였다. 반면, 실험적 데이터에 맞춰 조정된 μ값은 흡수 스펙트럼의 피크 위치와 세기를 가 장 고정확도로 재현하였으며, 특히 C-DNP와 C-OH 분자에서 나타나는 최대 흡수 피크 에너지의 차이를 잘 예측하였 다. C-DNP의 HOMO와 LUMO 전자 분포는 모든 μ값에서 일정한 모양(shape)을 가지고 있었으며, HOMO에서 LUMO 의 전이는 C에서 DNP로의 분자 내 전하 이동(Intramolecular Charge Transfer, ICT)임을 보였다.

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.

In conventional construction practices, roof-parapet junction structures inevitably disrupt the insulation installation's continuity, leading to energy loss and thermal bridging. To address this issue, parapet thermal breaks were installed to interrupt the heat flow between the roof and the parapet, effectively preventing thermal bridging and energy loss and thereby reducing overall energy loss in buildings. This study equipped three experimental specimens with the developed parapet thermal breaks to verify their structural performance. These specimens were subjected to unidirectional loading under displacement-controlled conditions. The structural performance of these insulation structures was evaluated by comparing and analyzing the test results with corresponding analytical studies conducted using a finite element analysis program. In addition, five analytical models with varying parameters of the parapet thermal breaks were developed and compared against the baseline model. Consequently, the most efficient shape of the parapet thermal break was determined.

In this research, the concrete breakout strength in tension of cast-in-place anchors (CIP) is experimentally investigated to be used as fundamental data for the seismic fragility analysis of equipment in nuclear power plants. Experimental variables are chosen, such as the embedment depth of the anchor, single/group anchor configurations, diameter of the head plate, and crack width. Monotonic and cyclic loading are applied to all types of specimens. As measured from the experiments, concrete breakout strength in tension is 1.5 to 2 times higher than the expected strengths from concrete capacity design (CCD) method-based model equations. In alignment with the model’s predictions, concrete breakout strength increases with deeper embedment depth, and the strength of group anchors also increases based on the expansion of the projected concrete failure area. This study also explores the effects of head plate diameter and crack width, which are not considered in the model equation. Experimental results show that the diameter of the head plate is not directly correlated to the concrete breakout strength, whereas the crack width is. The presence of cracks, with widths of 0.3 mm and 0.5 mm, leads to reductions of approximately 7% and 17%, respectively, compared to single anchors in non-cracked concrete.