Wet pavement friction decreases due to the increase in water film thickness (WFT), leading to a significant increase in vehicle crashes occurrences. The British Pendulum Test described in ASTM E303-93 is one of the methods used to measure pavement friction in wet conditions for the input of geometric design and pavement management systems. The British Pendulum Number (BPN) in wet conditions varies with WFT. Following ASTM E303-93 standard procedures, water film thickness was simulated by spraying water on the pavement surface. However, the measurement of BPN did not include specific information about the thickness of the water film present during testing. To address these issues, WFTs and BPNs were measured using artificial rainfall generated by a rainfall simulator across various intensities, drainage lengths, pavement slopes, and pavement surfaces. This study aims to investigate the influence of water film thickness on BPN for wet pavement friction and provide the WFT corresponding to each BPN measurement for different surface types. BPNs of three test slabs, including a smooth surface and tined surfaces with 16 mm and 25 mm spacing, were measured under wet conditions by spraying water, and by creating water film thicknesses using a rainfall simulator. This study demonstrates that the BPNs of non-tined surfaces and longitudinally and transversely tined surfaces with 25mm spacing exhibit a significant decrease with increasing water film thickness, while those with 16mm spacing show a slight decrease. These findings can be attributed to the lower friction observed in both non-tined and longitudinally tined pavements, in contrast to surfaces with transverse tinning.

PURPOSES : The skid resistance between tires and the pavement surface is an important factor that directly affects driving safety and must be considered when evaluating the road performance. In especially wet conditions, the skid resistance of the pavement surface decreases considerably, increasing the risk of accidents. Moreover, poor drainage can lead to hydroplaning. This study aimed to develop a prediction equation for the roughness coefficient—that is, an index of frictional resistance at the interface of the water flow and surface material—to estimate the thickness of the water film in advance to prevent human and material damage. METHODS : The roughness coefficient can be changed depending on the surface material and can be calculated using Manning's theory. Here, the water level (h), which is included in the cross-sectional area and wetted perimeter calculations, can be used to calculate the roughness coefficient by using the water film thickness measurements generated after simulating specific rainfall conditions. In this study, the pavement slope, drainage path length, and mean texture depth for each concrete surface type (non-tined, and tined surfaces with 25-mm and 16-mm spacings) were used as variables. A water film thickness scale was manufactured and used to measure the water film thickness by placing it vertically on top of the pavement surface along the length of the scale protrusion. Based on the measured water film thickness, the roughness coefficient could be back-calculated by applying Manning's formula. A regression analysis was then performed to develop a prediction equation for the roughness coefficient based on the water film thickness data using the water film thickness, mean texture depth, pavement slope, and drainage path length as independent variables. RESULTS : To calculate the roughness coefficient, the results of the water film thickness measurements using rainfall simulations demonstrated that the water film thickness increased as the rainfall intensity increased under N/T, T25, and T16 conditions. Moreover, the water film thickness decreased owing to the linear increase in drainage capacity as the mean texture depth and pavement slope increased, and the shorter the drainage path length, the faster the drainage, resulting in a low water film thickness. Based on the measured water film thickness data, the roughness coefficient was calculated, and it was evident that the roughness coefficient decreased as the rainfall intensity increased. Moreover, the higher the pavement slope and the shorter the drainage path length, the faster the drainage reduced the water film thickness and increased the roughness coefficient (which is an indicator of the friction resistance). It was also evident that as the mean texture depth increased, the drainage capacity increased, which also reduced the roughness coefficient. CONCLUSIONS : As the roughness coefficient of the concrete road surface changes based on the environmental factors, road geometry, and pavement surface characteristics, we developed a prediction equation for the concrete pavement roughness coefficient that considered these factors. To validate the proposed prediction equation, a sensitivity analysis was conducted using the water film thickness prediction equation from previous studies. Existing models have limitations on the impact of the pavement type and rainfall intensity and can be biased toward underestimation; in contrast, the proposed model demonstrated a high correlation between the calculated and measured values. The water film thickness was calculated based on the road design standards in Korea—in the order of normal, caution, and danger scenarios—by using the proposed concrete pavement roughness coefficient prediction model under rainy weather conditions. Specifically, because the normal and caution stages occur before the manifestation of hydroplaning, it should be possible to prevent damage before it leads to the danger stage if it is predicted and managed in advance.

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.

Since the decrease of skid resistance of the road surface due to the effects of hydroplaning increases the ratio of vehicle crashes significantly, it is important to predict water film thickness (WFT). Tined is one of the widely used textures for concrete pavements. Since previous WFT models have been developed based on the asphalt pavement texture and broom concrete, it may not give reliable predictions for Water film thickness for tinned concrete. Furthermore, surface flow on tined texture may show hydraulically different characteristics due to the geometric characteristics of tined texture. This study aims to propose a reliable water film thickness prediction model for tined concrete. Three test slabs including a smooth surface, a tined surface with 16mm spacing, and a tined surface with 25mm spacing were prepared. WFTs of the test slab were measured for various conditions such as pavement slope (0-10%), rainfall intensity (0-130mm/h), and drainage path length (0-5m). A statistical model was proposed to predict water film thickness (WFT) as a function of pavement slope, rainfall intensity, drainage path length, and mean texture depth. This model exhibits strong agreement with the experimental test results. The GWNU prediction model consistently provides reliable predictions with the actual WFT for tined concrete pavement. Conversely, the previous equation consistently underestimated the water film thickness, notably on tined surfaces with 16 mm and 25 mm spacing, due to the occurrence of viscous flow along the tined lines.

여름철은 타 계절에 비해 장마와 불안정한 대기 등으로 인하여 빗길 교통사고의 위험성이 크게 증대될 수 있으며, 최근 5년 (2018~2022)간 여름철 빗길 교통사고는 전체 빗길 교통사고의 39%를 차지할 정도로 높은 수준이다. 이러한 빗길 운전은 노면의 배수 불량 및 미끄럼 저항 감소 등으로 인하여 수막현상을 발생시키게 된다. 이에 본 연구에서는 우천 시 도로의 안전성 강화 및 사고 위 험을 최소화하기 위한 요소인 수막두께를 산정하기 위하여 Manning의 평균 유속식을 기반으로 콘크리트 노면의 조도계수 예측 모델을 개발하는 것을 목표로 하였다. 조도계수의 영향인자를 고려하기 위하여 실외 강우 모의 장비를 이용하여 콘크리트를 타설한 뒤 실험 인자로 포장 경사, 배수거리, 강우강도, 노면 조직 특성을 고려하였으며, 이 중 노면 조직 특성은 타이닝 처리를 하지 않은 구간만 고 려한 타 연구의 기존 예측 모델 단점을 보완하기 위하여 16, 25mm 간격의 타이닝 표면 처리한 구간을 추가로 고려하였다. 수막두께 측정은 측정 범위 0.3~5mm의 수막두께 측정 게이지를 제작하여 강우가 모사된 조건에서 배수 거리 1~5m 이내 지점의 노면 조직 상 단과 수면이 접하는 수직 높이를 총 3회 측정하여 평균값을 사용하였다. 실측된 수막두께 데이터베이스를 기반으로 Manning 공식을 이용하여 조도계수를 역산한 결과, 강우강도가 증가함에 따라 조도계수는 감소하였으며, 이는 강우의 증가로 인해 물의 흐름과 콘크리 트 노면 사이의 마찰 저항 감소에 기인한 것으로 판단되었다. 또한 포장 경사가 높고 배수 거리가 짧을수록 배수성이 증가하여 마찰 저항의 지표인 조도계수가 증가하는 것으로 확인되었다. 평균 조직 깊이에 따른 조도계수 영향의 경우, 평균 조직 깊이가 증가할수록 콘크리트 표면에 노출되는 표면적이 증가하여 수막두께가 얕게 생성되고, 얕은 수심으로 인해 물의 흐름 저항이 감소하여 조도계수는 감소하는 것으로 산정되었다. 이후 135개의 데이터를 종합하여 조도계수를 종속변수로 하고 강우강도, 포장경사, 배수거리, 평균 조직 깊이, 수막두께를 독립변수로 하는 회귀분석을 수행하여 조도계수 산정식을 개발하였다.

PURPOSES : This study provides fundamental information on the temperature variations in tunnel structures during severe fire events. A fire event in a tunnel can drastically increase the internal temperature, which can significantly affect its structural safety. METHODS : Numerical simulations that consider various fire conditions are more efficient than experimental tests. The fire dynamic simulator (FDS) software, based on computational fluid dynamics (CFD) and developed by the National Institute of Standards and Technology, was used for the simulations. The variables included single and multiple accidents involving heavy goods vehicles carrying 27,000 liters of diesel fuel. Additionally, the concrete material characteristics of heat conductivity and specific heat were included in the analysis. The temperatures of concrete were investigated at various locations, surfaces, and inside the concrete at different depths. The obtained temperatures were verified to determine whether they reached the limits provided by the Fire Resistance Design for Road Tunnel (MOLIT 2021). RESULTS : For a fire caused by 27,000 liters of diesel, the fire intensity, expressed as the heat release rate, was approximately 160 MW. The increase in the carrying capacity of the fire source did not significantly affect the fire intensity; however, it affected the duration of the fire. The maximum temperature of concrete surface in the tunnel was approximately 1400 ℃ at some distance away in a longitudinal direction from the location of fire (not directly above). The temperature inside the concrete was successfully analyzed using FDS. The temperature inside the concrete decreased as the conductivity decreased and the specific heat increased. According to the Fire Resistance Design for Road Tunnel (MOLIT 2021), the internal temperatures should be within 380 ℃ and 250 ℃ for concrete and reinforcing steel, respectively. The temperatures were found to be approximately 380 ℃ and 100 ℃ in mist cases at depths of 5 cm and 10 cm, respectively, inside the concrete. CONCLUSIONS : The fire simulation studies indicated that the location of the maximum temperature was not directly above the fire, possibly because of fire-frame movements. During the final stage of the fire, the location of the highest temperature was immediately above the fire. During the fire in a tunnel with 27,000 liters of diesel, the maximum fire intensity was approximately 160 MW. The capacity of the fire source did not significantly affect the fire intensity, but affected the duration. Provided the concrete cover about 6 cm and 10 cm, both concrete and reinforcing steel can meet the required temperature limits of the Fire Resistance Design for Road Tunnel (MOLIT 2021). However, the results from this study are based on a few assumptions. Therefore, further studies should be conducted to include more specific numerical simulations and experimental tests that consider other variables, including tunnel shapes, fire sources, and locations.

목적 : 본 연구는 RGP 렌즈 착용 상태에서 렌즈후면과 각막전면에 존재하는 눈물층의 두께와 눈물의 굴절력을 측정하였다. 방법 : 본 연구의 대상자는 20명(평균연령 23.02±1.89세)이 참여하였다. 각 참여자는 각막곡률의 측정값에 따 라 피팅상태가 flat fit, alignment fit, steep fit이 되도록 3개의 다른 BC의 RGP를 피팅하였다. RGP렌즈를 착 용한 상태에서 OCT로 눈물층 두께 측정, 자동굴절계를 이용하여 눈물렌즈의 굴절력을 측정하였다. 결과 : 측정결과 베이스 커브에 따라 발생한 렌즈 후면과 각막 간의 눈물층 높이의 평균값은 플랫한 피팅 상태 에서는 6.20±1.06 μm, 정렬된 피팅상태에서는 9.10±1.55 μm, 스팁한 피팅상태에서는 12.5±1.50 μm으로 통 계적으로 유의한 차이가 나타났다(F(2, 57)=103.05, p<0.010). 피팅상태에 따라 생성된 눈물렌즈의 굴절력은 플 랫 피팅인 경우 –0.85±0.75 D, 정렬된 경우 –0.48±0.85 D, 스팁 피팅인 경우 +1.56±0.77 D로 통계적 으로 유의하게 나타났다(F(2, 57)=53.71,p<0.010). 3가지 피팅에 따라서 RPG 렌즈 후면과 각막전면의 있는 눈 물 렌즈의 두께와 눈물 렌즈로 생성된 굴절력과의 상관관계 분석에서 r=0.58로 다소 높은 상관관계를 보였다. 결론 : 본 연구에서는 정렬된 피팅이 된 경우, 최소의 굴절력 조정이 요구되며, 반면 스팁한 피팅인 경우 더 많 은 조정이 필요하다.

콘크리트 충전강관은 국부좌굴을 방지하고 내화성이 향상되기 때문에 건설현장에서 많이 적용되며 휨성능을 향상시 키기 위해 강관 내부에 철근을 보강하여 사용한다. 그러나 철근은 부식되며 내구성이 저하되기 때문에 이를 대신할 소재에 대 한 연구가 진행되고 있다. 탄소섬유보강근은 철근에 비해 경량이며 고강도와 내부식성이 우수하다는 이점이 있다. 그러나 임계 온도가 250℃로 철근의 임계온도인 538℃에 비해 현저히 낮기 때문에 내화피복이 필요하다. 따라서 열전달해석을 통해 탄소섬 유보강근을 사용하였을 때 온도분포를 확인하고 P-M상관도를 도출하여 적용 가능여부를 확인하고자 한다. 해석결과 내화성능을 확보하기 위해 콘크리트 피복두께 40mm, 뿜칠내화피복재 30mm를 적용하거나 콘크리트 피복두께 60mm, 뿜칠내화피복재 20mm 를 적용하면 3시간 내화성능을 만족하는 것으로 평가되었다.

As the demand for appropriate heat dissipation measures to improve product stability and performance continues to increase and product design becomes highly integrated, research to improve heat transfer performance while maintaining the same area or size is required. In this study, the sample-shaped aluminum plate was treated as upper-coating, and the thickness of the coating was divided into 1mm, 2mm, and 3mm, respectively, and the coating material was applied with silver, copper, and graphene. The temperature condition of the heat source was set to 473K, and heat dissipation analysis was performed under natural convection. The thermal performance was compared and analyzed through temperature distribution, flow velocity distribution, and heat flux, and it was confirmed that the high thermal conductivity of graphene compared to other materials had a dominant effect on the increase in the conduction heat transfer rate. And it was confirmed that the high surface temperature of the graphene coating also increased the heat transfer rate by convection, thereby enhancing the heat dissipation effect.

Background: Shoulder impingement syndrome, a major cause of shoulder pain, involves weakness of the scapular retractor muscles. The major scapular retractor muscles are the middle trapezius and rhomboid major muscles; however, the latter is excluded in most studies. Objects: We aimed to measure the thickness of the middle trapezius and rhomboid major muscles using an ultrasonic diagnostic imaging system while performing four different shoulder retraction exercises and comparing the thicknesses and ratio of the thicknesses of these muscles. Methods: The thickness of the middle trapezius and rhomboid major muscles was measured in 24 healthy adults using ultrasound. Muscle thickness was measured three times in the Reference posture and four times while performing four different exercises that involved scapular retraction. The averages and standard deviations of the measured muscle thicknesses were obtained and compared. The ratio of muscle thickness and rate of changes in muscle thickness between the reference posture and the four exercises were compared. Results: For both, male (n = 10) and female (n = 14), there was a significant difference in the thickness of the middle trapezius muscle between the reference posture and the four exercises (p < 0.05) and in the thickness of the middle trapezius and rhomboid major muscles between male and female (p < 0.05); however, there was no significant difference in the ratio of the thicknesses of these muscles. Although a significant difference in the rate of change in muscle thickness during the four exercises was noted, there was no significant difference in the ratio of change in muscle thickness. Conclusion: This study demonstrates the ratio of the thicknesses of the middle trapezius and rhomboid major muscles and the rate of change in their thickness during exercises involving scapular retraction in healthy people in their 20s–30s.

본 연구는 육계사육에서 횃대의 제공효과와 최적 두께를 구명하기 위해 진행하였다. 12일령 육계(RossⅹRoss) 288수를 24개의 독립된 공간(7.3 수/m2)에 균등한 평균 체중으로 분배하여 42일령까지 사양실험을 실시하였다. 그룹은 일반 평사사육(대조구)과 3개의 횃대 처리구(두께: 3, 4 및 5 cm)인 총 4개로 구성하였으며, 각 그룹은 6반복과 반복당 12수씩으로 배치하였다. 각 반복 별로 횃대의 길이는 1.3 m (0.11 m/수)로서 높이 15 cm에 설치하였다. 조사항목으로 육계의 생산성, footpad dermatitis (FPD)과 hock burn (HB) 지표 및 횃대이용성을 확인하였다. 본 연구결과, 육계사육에서 횃대의 유무와 두께에 따른 체중, 증체량, 사료섭취량 및 사료요구율은 통계적 차이가 없었다. FPD는 처리구 간 유의적 차이가 없었으나, HB 지표는 4와 5 cm의 횃대를 제공한 처리구에서 일반 평사와 3 cm 두께의 횃대에서 사육한 육계에 비해 개선되었다(p<0.05). 육계가 횃대를 이용한 시간은 사육전기(12~24일령)에는 차이가 없었으나, 사육후기(25~42일령)에 횃대를 이용한 총 시간은 5 cm 두께에서 3과 4 cm 두께보다 높았으며(p<0.05), 올라간 횟수에 비해서도 더 많은 시간을 보냈다(p<0.05). 그러므로 횃대는 육계의 다리질병을 줄이며, 4~5 cm의 두께를 이용하는 것이 가장 적합할 것으로 사료된다.

This study was performed to evaluate the effect of pork belly thickness on physicochemical and sensory characteristics after pan frying. Pork belly with three different thickness (5, 10, 20 mm) from three different parts (A:thoracic vertebrae no. 5-9, B:thoracic vertebrae 10-14, C:lumbar vertebrae 1-6) was pan grilled with electronic grill until it reached an internal temperature of 71℃. Cooking loss, shear force, sensory characteristics, volatile compounds of cooked pork belly were determined. Electric nose analysis was performed to support descriptive analysis and consumer sensory analysis. The cooking loss of pork belly with 20 mm thickness from all positions was significantly low (p<0.05). Shear force increased with increase in thickness (p<0.05). Electric nose identified major seven volatile compounds such as acetonitrile, (Z)-4-heptenal, 2-octanol, linalool, carbon disulfide, methylcyclohexane, n-nonanal to discriminate those samples. The part of pork belly significantly affected the intensity of volatile compounds rather than thickness. In discriminate analysis, the overall acceptability of pork belly (A and B parts) with 20 mm thickness was higher than that of pork belly with 5 mm thickness. In addition, the overall acceptability by consumers for pork belly with 20 mm thickness from A, B, and C parts was higher than the overall acceptability for pork belly with 5 mm thickness. This preliminary study suggests that it is more desirable to use pork belly with 20 mm thickness from part A when cooking on a pan gril compared with pork belly of 10 mm or 20 mm thickness from part B or C in the meat markets and restaurant.