PURPOSES : The adhesive bonding strength of the grid between asphalt pavements is critical in pavement performance. The study is to compare and evaluate the interlayered bonding strength of asphalt mixture specimens with fiber-glass grid (FG) reinforcement and different tack coating materials based on the test results of the shear bonding test. METHODS : Asphalt mixtures were molded with FG reinforcement using various tack coating materials namely RSC4 and D/B coat. The adhesive shear-bond strength was measured by inducing a monotonic shear loadnig rate of 5 mm/min at 20℃. RESULTS : As expected, the asphalt mixture with non-reinforced FG exhibited the highest adhesive shear-bond strength, followed by that of the FG with D/B coating. The ranking order of superiority is as follows: Control (RSC4) > D/B+FG > RSC4+FG. CONCLUSIONS : The results of this experimental study indicate that FG with RSC4 and D/B tack coats can be successfully used in asphalt concrete overlay construction with superior field performance. Based on the test results and literature review, the field bonding strength should exceed 300kPa in grid reinforced asphalt pavement.

최근 국내에서 토목 및 건축구조물의 노후화 및 성능저하에 따른 사회적인 우려가 발생하고 있다. 일반적으로 노후 구조물의 보수보강 방법으로는 외부 부착공법이 가장 많이 사용되고 있으며 시공 용이성을 위하여 GFRP나 CFRP Sheet나 Plate를 활용한 부착 보강방법이 활발히 적용되고 있다. 그러나 이들 방법은 온도에 취약하며 탄소섬유의 경우 경제성이 낮다는 우려가 발생한다. 본 연구에서는 친환경적이고 내열성이 상대적으로 우수한 현무암 섬유(BFRP)를 활용하여 온도변화 및 콘크리트 표면 내 균열발생에 따른 BFRP-콘크리트의 인장 부착성능 및 파괴 패턴을 실험적으로 평가하였다. 그 결과 구조물의 온도가 상승함에 따라 BFRP-콘크리트 계면의 부착성능은 약 30%정도 감소하는 것으로 나타났으며 내열성 수지를 사용한 보강재의 경우 일반 함침용 에폭시 수지보다 부착성능이 다소 우수한 것으로 평가되었다. 콘크리트 표면 내 균열 발생된 경우 균열의 폭이 증가함에 따라 부착 성능은 약 20%씩 감소하는 것으로 나타났다. 하지만 균열보수제로 보강 후 계면에서의 부착성능의 경우, 보강 전 대비 약 30% 정도의 개선효과를 나타내었다.

최근에 국내에는 다양한 원인에 의한 구조물의 안정성을 우려하는 사회적인 관심이 생겼으며 이에 따른 구조물의 보수·보강에 다양한 연구가 진행되고 있다. 우리나라는 4계절이 뚜렷하며 특히 겨울과 봄에는 일교차가 심하게 발생하는 특징이 있다. 이러한 날씨는 철근콘크리트 구조물에게 동결융해작용을 발생시켜 성능저하의 원인이 되며 구조물의 안정성을 위협할 수 있다. 현재 구조물 보수·보강 방법으로는 탄소섬유나 유리섬유로 FRP(Fiber Reinforced Polymer)를 활용하여 Plate나 Sheet 형태의 부착 보강하는 방법이 일반화 되어있다. 하지만 다소 고가이며 유리섬유는 인체에 유해하다는 연구결과가 있다. 때문에 본 연구에서는 친환경적이고 내열성이 우수한 현무암섬유(Basalt Fiber)를 활용하여 동결융해 작용에 의한 콘크리트의 성능저하를 조건으로 BFRP-콘크리트의 부착성능 및 파괴패턴을 비교 분석하였다. 동결융해시험에 따른 부착강도평가는 동일한 섬유와 수지가 함침된 BFRP를 활용하여 동결융해Cycle(0, 100, 200, 300)과 콘크리트 압축강도(24MPa, 30MPa)를 변수로 부착성능을 평가하였으 며 Case1(선 부착 후 동결융해)과 Case2(선 동결융해 후 부착)로 나누어 진행하였다. Case1과 2 모두 콘크리트 파괴의 형태를 보 였으며 Case2의 경우 Case1에 비하여 부착강도가 감소됨을 나타내었고 동결융해 Cycle이 진행될수록 콘크리트 계면의 성능은 저하되고 부착강도는 평균 약 25%정도 감소하는 것을 확인하였다.

Ice accumulation on Aluminum Conductor Steel Reinforced(ACSR) cable during winter is an important matter in terms of safety, economy, and efficient power supply. In this work, the ice adhesion strengths of ACSR cable oxidized during different periods(7 years oxidized and 15 years oxidized) are evaluated. At first, a plate type dry oxidation standard specimen, whose surface characteristics are similar to those of ACSR cable, is prepared. Dry oxidation standard specimens are heat-treated at 500 °C for 20, 60, and 120 minutes in order to obtain different degrees of oxidation. After the dry oxidation, surface properties are analyzed using contact angle analyzer, atomic force microscopy, spectrophotometer, and gloss meter. The ice adhesion strengths are measured using an ice pull-off tester. Correlations between the surface properties and the ice adhesion strength are obtained through a regression analysis indicating a Boltzmann equation. It is revealed that the ice adhesion strength of 15- year oxidized ACSR cable is approximately 8 times higher than that of ACSR-bare.

Background: Knee osteoarthritis (OA) diagnosis using Kellgren-Lawrence scores is commonly used to help decision-making during assessment of the severity of OA with assessment of pain, function and muscle strength. The association between Kellgren-Lawrence scores and functional/clinical outcomes remains controversial in patients with knee OA. Objects: The purpose of this study was to examine the relationships between Kellgren-Lawrence scores and knee pain associated with OA, function during daily living and sports activities, quality of life, and knee muscle strength in patients with knee OA. Methods: We recruited 66 patients with tibiofemoral knee OA and determined knee joint Kellgren-Lawrence scores using standing anteroposterior radiographs. Self-reported knee pain, daily living function, sports/recreation function, and quality of life were measured using the knee injury and OA outcome score (KOOS). Knee extensors and flexors were assessed using a handheld dynamometer. We performed Spearman’s rank correlation analyses to evaluate the relationships between Kellgren-Lawrence and KOOS scores or muscle strength. Results: Kellgren-Lawrence scores were significantly negatively correlated with KOOS scores for knee pain, daily living function, sports/recreation function, and quality of life. Statistically significant negative correlations were found between Kellgren-Lawrence scores and knee extensor strength but not flexor strength. Conclusion: Higher Kellgren-Lawrence scores were associated with more severe knee pain and lower levels of function in daily living and sports/recreation, quality of life, and knee extensor strength in patients with knee OA. Therefore, we conclude that knee OA assessment via self-reported KOOS and knee extensor strength may be a cost-effective alternative to radiological exams.

최근 국내에서는 고층 벽식 아파트 건설 시, 하부 주차공간과 공용공간 확보를 위하여 RC 전이슬래브 시스템을 사용하는 경우가 증가하고 있다. 하지만 두께가 얇은 RC 무량판 슬래브를 위해 개발된 설계방법 및 구조성능평가 방법을 두께가 매우 두꺼운 전이슬래브 구조설계에 그대로 사용하고 있다는 문제점이 있다. 따라서 합리적인 전이슬래브의 구조설계를 위해서는 RC 전이슬래브 시스템의 2면 전단거동 양상에 대한 명확한 분석이 필요하다. 이에 따라 본 연구에서는 전이슬래브의 두께, 콘크리트 강도, 전단경간비, 철근비 등 다양한 설계변수에 따라 비선형 FEM을 이용하여 전이슬래브의 2면 전단거동을 분석 하였다. 또한 비선형 FEM 해석결과와 기존의 2면 전단강도 평가식으로 예측한 전단강도를 비교분석하여 기존 평가식의 전이슬래브 2면 전단강도 평가 유효성을 검토하였다.

PURPOSES : The main purpose of this study is suggest of field bond strength evaluation method for more objective evaluation method through Evaluation of Bond Strength Properties with changing aspect ratio and temperature. METHODS : The evaluation is laboratory bond strength test. Using the core machine, the pull-off test method ; the bond strength test of interface layer the universal testing machine. RESULTS: As a result of the laboratory bond strength evaluation, it was verified that the bond strength by aspect ratio decreases linearly with increasing aspect ratio and the bond strength properties by temperature change existed at high and low temperature condition relative to odinary temperature condition. CONCLUSIONS: According to the results of laboratory bond strength evaluation, the field bond strength evaluation results suggest applying the proposed correction factor (0.8, 1.0, 1.4, 1.9) according to aspect ratio(0.5, 0.1, 1.5, 2.0), For more objective evaluation of the bond strength, it is analyzed that the evaluation value is within 6 ~ 32℃ and the result can be obtained within 5% of the coefficient of variation.

Synthetic wood has been widely used in place of wood such as the building exterior materials and/or the floor plate of moving path. However, it has many disadvantages such as relatively low strength, low durability, and heavy weight, etc. In this study, the synthetic wood deck combined with an aluminum profile was suggested to overcome these disadvantages. The flexural strength of the aluminum-synthetic wood deck was obtained through the theoretical equations under three-point bending conditions. In addition, the finite element analyses were also conducted to evaluate the flexural strength of the aluminum-synthetic wood deck.

Polymer electrolyte membrane (PEM) is one of key elements to determine both electrochemical performances and lifetimes of fuel cell electric vehicles (FCEVs). PEM is exposed to a variety of dynamic stimuli (e.g., temperature, humidity, pressure, fuel gases and so on) under their operation conditions and meets unavoidable mechanical damages derived from unequal pressure difference between anode and cathode feed gases. Even though there have been approaches to evaluate the mechanical strength of PEM materials, most of the trials could provide static information on their mechanical strength. In this study, a pressure-loaded blister hybrid system connected with gas chromatography was developed to disclose the efficacy of the system as an evaluation tool of dynamic PEM strength under realistic FCEV operation conditions.

In the present study, FE analysis was performed for characterising structural strength of a seat frame w.r.t. varying sectional shapes as well as different materials of the seat back frame based on the FMVSS 207 regulation in order to obtain the design outline of a lightweight seat frane structure. Four types of materials, i.e., SAPH440, Al7021, Al6082 and carbon/epoxy composites were applied to the seat back frame type beams and their bending behaviours were compared by three point bending FE analysis. Consequently, the lightweight structure of seat back frame with the equivalent strength characteristics of conventional frame was suggested.

HYB(FRP Hybrid Bar) is composite structural material that combines reinforced bar and FRP. HYB has high elastic modulus and after-yield-hardening properties, despite its corrosion resistance and light weight. HYB under development has relatively stable corrosion durability. This study performs fundamental experiments for the long period UV exposed HYB, and carries out pull-out test for the freezing-thawing exposed specimens of ordinary reinforced bar, HYB, and UV exposed HYB. The effect of UV exposure and freezing-thawing did not affect the tensile property and strength of HYB. However, the bond strength reduction on the environment of accelerated corrosion should be considered in further study.

Tensile strength was investigated for hybrid bar (HYB), in this study. HYB is made of both steel reinforcement and glass fiber. Cross section of HYB has a shape in which steel reinforcement wrapped with glass fiber. For the production of HYB, rebar of SD400 class and glass fiber of E class are used as main materials. Vinyl ester resin is used to harden a glass fiber. In order to evaluate for tensile strength of HYB, the direct tensile test was performed about total ten specimens. The length of total specimens is 2,200 mm including the grip. Diameter of HYB according to core diameter was considered as a test variable. Direct tensile test for HYB was performed using a UTM with a capacity of maximum 1,000 kN. Tensile strength and strain were measured for each specimen during the test. From the test results, tensile strength and elastic modulus were 317 ~ 341 MPa, 103 ~ 107 GPa, respectively. Especially, elastic modulus of HYB was improved in comparison with usual GFRP bars such as the Aslan 100 or the V-rod.

PURPOSES:The objectives of this study are to evaluate moisture sensitivity of various asphalt mixtures and to suggest an alternate method for the dynamic immersion test, which is used to determine the application of anti-stripping agent, by analyzing bond strength.METHODS:The bond strength of various asphalt mixtures such as hot mix asphalt, warm mix asphalt, and polymer-modified asphalt was evaluated by the ABS test. In order to characterize moisture sensitivity at different temperatures of the mixtures, the ABS test was conducted at -10°C, 5°C, 20°C, 40°C, and 54°C under both dry and wet conditions. The concept of the bond strength ratio was applied for objective moisture sensitivity analysis. Moreover, the bond strength characteristic was compared to the dynamic immersion test to suggest an alternate method to determine the application of anti-stripping agent.RESULTS AND CONCLUSIONS :Overall, the polymer-modified asphalt demonstrates the highest bond strength characteristic regardless of moisture condition and temperature. The bond strength characteristic displays a highly reliable linear relationship from 5°C to 40°C, and the relationship could be used to predict bond strength at any intermediate temperature. Based on the analysis of bond strength and retained asphalt ratio, the bond strength value of 1254 kPa could be applied as a criterion for anti-stripping agent.