본 연구는 50 GPa 이상의 탄성계수를 갖는 GFRP 보강근을 적용한 콘크리트 보의 장기 거동에 대한 실험적 분석을 수행하 였다. ACI 440.11-22 및 CSA S806-12를 포함한 현행 설계 규정은 철근 콘크리트 부재의 설계 방식을 준용하여, 단기 처짐에 경험적 계수를 곱하는 방식으로 장기 처짐량을 산정한다. 그러나 이러한 계수들은 과거의 저탄성계수 GFRP 보강근 데이터를 기반으로 도출되 었으므로, 최근 사용되는 고탄성계수 보강근에 이를 그대로 적용하는 것은 적합하지 않다. 이러한 한계를 극복하기 위해 본 연구에서는 하중 단계, 보강비, 보강근의 직경을 주요 변수로 설정하여 GFRP 보강 콘크리트 보에 대한 장기 하중 가력 실험을 진행하였다. 이를 통해 부재의 크리프와 휨 강성 변화를 정량화하였으며, 현행 설계 기준의 정확성을 평가하고 보강재의 강성이 장기 거동에 미치는 영향을 분석하였다. 실험 결과, 기존의 장기 처짐 계수는 높은 하중 수준에서 고탄성계수 GFRP 보강 콘크리트 보의 시간 경과에 따른 처짐을 정확하게 예측하지 못하는 것으로 나타났다. 따라서 본 연구는 고탄성계수 GFRP 보강 부재의 거동 특성을 반영한 새로운 장기 처짐 예측 모델의 필요성에 대한 근거를 제시한다.

철근 콘크리트의 부식으로 인해 비부식성 대체재의 채택이 촉진되었으며, GFRP 철근은 가장 널리 채택된 경제적이고 균형 잡힌 성능 옵션 중 하나이다. GFRP 철근의 탄성 계수는 강철보다 낮아 완전한 대체가 어렵다. 하지만 최근 GFRP의 탄성 계수는 국제 기준 30∼40 GPa에서 약 60 GPa(국외 생산 기준), 50 GPa(국내 생산 기준)로 증가했습니다. 그러나 대부분의 설계 방정식은 기존의 저탄성계수 GFRP를 기준으로 보정되었다. 본 연구에서는 고탄성계수 GFRP 보강근으로 보강된 두 개의 콘크리트 보의 휨 거동을 분석하며, 실험 하중-변위 응답을 Adam, ACI 440.1R-06, CSA S806-12 및 최신 ACI 440.11-22의 예측값과 비교한다. 이 모델들은 모두 비균열 영역의 초기 경사와 일치하지만, 저탄성계수 GFRP를 사용한 보정으로 인해 실제 강성을 과소평가하고 처짐 을 과대 예측하는 경향이 있습니다. 균열 발생 후 편차가 증가하며, 이때, Adam 방정식이 가장 큰 편차를 보인다. 이는 기존 모델의 한계를 보여주며, 변위 제어가 매우 중요한 경우 기존 모델의 사용에 신중해야 함을 보여준다.

중대재해처벌법 시행 이후에도 고소작업에서의 추락 사고는 여전히 높은 비율로 발생하 고 있으며, 이로 인한 사망 사고는 기업경영의 리스크로 작용하고 있다. 추락재해를 예방 하기 위해 안전대를 착용하도록 하고 있는데 안전대를 거는 수평 생명줄의 적절한 설치와 처짐 길이를 고려하지 않을 경우 작업자의 생명에 직접적인 위협이 될 수 있다. 본 연구는 섬유로프를 이용한 수평 생명줄의 처짐 길이를 실험적으로 분석하고, 이를 바탕으로 고소 작업 시 안전한 고정점 높이를 제시하는 데 목적을 두었다. 연구에서는 폴리프로필렌(P.P) 및 폴리에틸렌(P.E) 로프를 사용하여 하중을 가한 상태에서 로프의 처짐 길이를 측정하고, 그 결과를 바탕으로 고정점 높이를 산출하였다. 실험 결과, 로프의 규격에 따라 처짐 길이 가 상이하게 나타났으며, 고정점 높이를 설정할 때 이를 충분히 고려해야만 안전한 작업 환경이 조성될 수 있음을 확인하였다. 본 연구는 ESG(환경, 사회, 지배구조) 관점에서 기업의 안전 관리 중요성을 제시하고 수평 생명줄의 처짐으로 인한 사고 예방을 강화하기 위한 방안을 제언하였다. 연구 결과를 활용하여 고소작업에서의 추락 사고 예방을 위한 실질적인 지침을 제공하고 기업의 안전 관리를 강화하는데 기여할 것으로 기대한다.

The amount of deflection that affect deflection caused by the load of steel board used to support concrete blocks were analyzed. By eliminating the central area of the cross section of board, it was possible to design a new board that reduces the weight of the board by about 50% while increasing the deflection by only about 10% for 5000N load. Since the deflection of the board is inversely proportional to the moment of inertia for area, it is most important to increase the cross-sectional height of the board to reduce the deflection, followed by the thickness of the upper and lower plates, and the thickness of the internal forming material played the smallest role. The other parts, the side supporting parts and reinforcing parts, were found to play a negligible role in preventing deflection. Applying the results of this study, we can predict the amount of board deflection and find the effective cross-sectional design of board without exceeding the deflection limit.

PURPOSES : The purpose of this study is to investigate the tendency of material property estimation under different concrete distress conditions and curling conditions when non-destructive tests such as rebound hammer and surface deflection test are applied to concrete pavement. METHODS : Nondestructive tests using Schmidt hammer and Falling Weight Deflectometer were performed to inspect the expressway concrete pavements constructed more than 20 years ago. Some results were compared with core tested elastic modulus and compressive strength. RESULTS : As a result of the rebound test, the section with Alkali-Silica Reaction(ASR) distress was outside the range of the existing estimation formula, but the control section was found to be within the range of the existing estimation formula. As a result of the physical property estimation through deflection test, the section with ASR distress showed greater fluctuations in the estimated material properties and deflection ratio compared to the control section, showing that the ASR damage seems to affect the slab deflection behavior. CONCLUSIONS : The rebound test may not sufficiently reflect the decline in material properties due to concrete damage. The deflection test can obtain results that reflect the deterioration of material properties, but it was confirmed that significant variability may occur, so it seems to necessary to perform complementary indoor core tests with nondestructive testing(NDT) tests.

Background: Foot drop is a common symptom in stroke patients. Tape applications are widely used to manage foot drop symptoms. Previous studies have evaluated the effects of static and dynamic balance and gait on foot drop using kinesiology tape; however, only few studies have used dynamic tape application in stroke patients with foot drop. Objects: The purpose of this study was to investigate the immediate effects of dynamic taping, which facilitates the dorsiflexor muscle, on static and dynamic balance and gait speed in stroke patients with foot drop. Methods: The study included 34 voluntary patients (17 men, 17 women) with stroke. The patients were randomly assigned to the experimental group (n = 17), wherein dynamic taping was used to facilitate the dorsiflexor muscle, or the control group (n = 17), wherein kinesiology taping was used. Before the taping application, velocity average, path-length average, Berg balance scale, and timed up and go test (TUG) were recorded to measure static and dynamic balance, whereas the 10-meter walk test (10MWT) was used to measure gait speed. After the taping application, these parameters were re-evaluated in both groups. Repeated measure analysis of variance was used. Statistical significance levels were set to α = 0.05. Results: Except for the 10MWT scores in the control group, significant differences were noted in all the parameters measured for static and dynamic balance and gait speed between the pre and post-test (p < 0.05). However, the parameters showed significant interaction effects between group and time in the TUG and 10MWT (p < 0.01). Conclusion: These results indicate that compared with kinesiology taping, dynamic taping used in chronic stroke patients with foot drop had a more significant effect on dynamic balance and gait speed.

승객에게 편안한 승차감을 제공할 수 있도록 자기부상열차 차체 연직가속도의 진동크기에 대한 기준을 제시하고 이를 만족하는 가이드웨이 구조물의 처짐한계를 제안한다. 차량-구조물 상호작용을 고려한 해석기법을 사용하여 자기부상열차 시스템의 매개변수 해석을 수행하고, 차체 연직가속도에 대한 기준을 만족할 수 있는 가이드웨이 구조물의 처짐한계를 L/1300 로 제안한다. 이를 실제 자기부상열차 시스템의 동적 해석에 적용하여 제안한 처짐한계의 적절성을 검토한다. 기존의 자기부상철도 가이드웨이 구조물의 설계 기 준과 비교하였을 때, 이 연구에서 제안한 처짐한계를 적용하면 경제적인 가이드웨이 구조물의 설계와 시공이 가능할 것으로 기대된다.

PURPOSES: The objective of this study is to evaluate and compare the stiffness characteristics and seasonal variation in surface deflections of block and asphalt pavements using the light weight deflectometer (LWD) and falling weight deflectometer (FWD). METHODS: LWD and FWD testing was conducted on block and asphalt pavement sections in a low-impact development facility, to evaluate the structural capacity and seasonal variation in asphalt pavements. To analyze the seasonal variation in stiffness characteristics, this testing was performed in October 2016, January 2017, and March 2017 in the same drop locations. RESULTS : It was found from that the average center deflections in the asphalt and block pavements were 218 ㎛ and 2974 ㎛, respectively. The center deflections measured using FWD testing in block pavement are 15 times those measured in asphalt pavement. It was also observed that LWD deflections in block pavements were decreased by approximately 65-90% as the air temperature dropped from 20 to 4℃. The degree of reduction in block pavement was significantly higher when compared with asphalt pavement, which showed a 25- 50% reduction in deflection. CONCLUSIONS: When using block pavements for roadways, the structural capacity of the pavement system should be considered during the design and construction stages. In block pavements, the use of low-quality material and insufficient compaction in the base and subgrade layers can induce a reduction in structural capacity, which would lead to the need for frequent repair work. A reinforcement underneath the block layer would be an appropriate measure for improving the structural support and extending the service life.

In this study, we analyzed the structural safety and vibration characteristics of rotational drive in 3D CT scan equipment using finite element analysis. The analysis results showed a safety factor of 9.2 and a left and right vertical deflectional deviation of 0.24mm from the maximum equivalent stress. After applying weight compensation of 27.7kgf, the structural analysis reduced the safety factor to 7.6, but the deflectional deviation of the left and right structure was reduced to 0mm. Also, we presented the optimum design of rotational drive through the vibration analysis.

PURPOSES: The purpose of this study is to evaluate and improve the potential risk of road cave-ins due to subsurface cavities based on the deflection ratio measured with light falling weight deflectometer (LFWD) tests. METHODS : A cavity database for Seoul was developed and sorted. LFWD tests based on the database were conducted on pavement sections with and without road cavities detected by ground-penetrating radar (GPR) tests; after excavating the area, the cavity sizes were measured. The deflection ratio was applied and analyzed by cavity management grade methods of Japan and Seoul. RESULTS : The results of comparative analysis show that the deflection method can detect road cavities in areas of the narrow road (or in narrow areas of the road). The average deflection ratio of the cavity sections to the robust sections were 2.48 for high-risk cavities, 1.85 for medium-risk level cavities, and 1.49 for low-risk cavities. Risk levels in Japan and Seoul were reclassified according to the deflection ratios. CONCLUSIONS : LFWD test results can be applied to verify and improve the subsurface cavity risk level by comparing maximum deflection and deflection ratio between cavity area and non-cavity area at the loading center. LFWD devices also have more advantages compared with larger NDT(Nondestructive test) because FWD and GPR encounter difficulties in traffic control and they could not get in a narrow roads.