• International Journal of Concrete Structures and Materials
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• 제9권3호
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• pp.369-379
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• 2015

Friction in a post-tensioning system has a significant effect on the distribution of the prestressing force of tendons in prestressed concrete structures. However, attempts to derive friction coefficients using conventional electrical resistance strain gauges do not usually lead to reliable results, mainly due to the damage of sensors and lead wires during the insertion of strands into the sheath and during tensioning. In order to overcome these drawbacks of the existing measurement system, the Smart Strand was developed in this study to accurately measure the strain and prestressing force along the strand. In the Smart Strand, the core wire of a 7-wire strand is replaced with carbon fiber reinforced polymer in which the fiber Bragg grating sensors are embedded. As one of the applications of the Smart Strand, friction coefficients were evaluated using a full-scale test of a 20 m long beam. The test variables were the curvature, diameter, and filling ratio of the sheath. The analysis results showed the average wobble and curvature friction coefficients of 0.0038/m and 0.21/radian, respectively, which correspond to the middle of the range specified in ACI 318-08 in the U.S. and Structural Concrete Design Code in Korea. Also, the accuracy of the coefficients was improved by reducing the effective range specified in these codes by 27-34 %. This study shows the wide range of applicability of the developed Smart Strand system.

• Smart Structures and Systems
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• 제19권5호
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• pp.463-472
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• 2017

In a previous study, the potential of damping suspension bridges with active stay cables has been evaluated on a numerical model of a suspension bridge, and demonstrated experimentally on a laboratory mockup. In this paper, we extend our study to explore two different configurations of the active stay-cables: one classical configuration, corresponding to attaching the active stay-cables between the top of the pylons and the deck (configuration I) and, another configuration, consisting of attaching the stay-cables between the base of the pylons and the catenary (configuration II). The analysis confirmed that both configurations are effective with a slight superiority of the second configuration. The study is conducted numerically and experimentally on a suspension bridge mock-up, by considering two types of active stay-cables. The experimental results confirmed the numerical predictions, and demonstrated the effectiveness of the second configuration.

• 패션비즈니스
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• 제26권2호
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• pp.129-142
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• 2022

The purpose of this study is to develop socks to check the range of ankle movement during squats for men in their late 20s. Sensors of 6, 8, and 12 mm were selected, and each sample was impregnated 1 to 3 times. It was prepared using a CNT dispersion, and the GF value was measured using UTM. Among them, the sample with 2 impregnation showed the best GF value. As a result of applying each sample to the socks, the 12 mm sensor was wider than the area of the Achilles tendon, resulting in noise, and the 8 mm sensor was higher than the tensile strength of the socks, resulting in a decrease in the graph. Therefore, testing was performed using a 6 mm sensor. In order to determine the effectiveness of the sensor, the normal operating range was checked through squats, and significant changes were confirmed when the operating range was checked again through squats by performing operations that can increase the operating range through Gastrocnemius, Soleus stretching, and low lunge. Using the results of this study, it is expected that the average value of the ankle movement range of the user is checked prevent injury, to be provided as basic data for the production of shoe products and the promotion of physical health.

• Smart Structures and Systems
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• 제25권2호
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• pp.229-240
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• 2020

In this research, toggled actuator forces were examined. For achieving to this object, an actuator was installed in a toggle pattern in a S.D.O.F frame and actuator forces were investigated thru a numerical analysis process. Within past twenty years, researchers tried to use strong bracing systems as well as huge dampers to stabilize tall buildings during intensive earthquakes. Eventually, utilizing of active control systems containing actuators to counter massive excitations in structures was emerged. However, the more powerful earthquake excitations, the more robust actuators were required to be installed in the system. Subsequently, the latter process made disadvantage to the active control system due to very high price of the robust actuators as well as their large demands for electricity. Therefore, through a numerical process (Part I), influence of toggled actuator pattern was investigated. The algorithm used in the system was LQR and ATmega328 was selected as a control platform. For comparison, active tendon control system was chosen. The final results show clearly that using the toggle pattern mitigates the required actuator forces enormously leading to deploy much lighter actuators.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2011년도 정기 학술대회
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• pp.178-181
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• 2011

본 연구에서는 광섬유센서를 내장한 스마트강연선을 이용하여 초고성능콘트리트로 제작된 하이브리드 사장교 세그먼트의 횡방향 도입 긴장력을 계측하고 세그먼트 내부의 프리스트레스를 계측하여 즉시손실에 해당하는 정착장치 활동에 의한 손실과 마찰손실을 도로교설계기준(2005)의 설계 마찰손실과 비교하였다. 제작된 2개의 UHPC 사장교 세그먼트는 횡방향 길이 16.7m, 종방향 길이 1.75m, 높이 1.5m이며 각 시험체의 1/4, 1/2, 3/4지점에 긴장력을 계측하기 위해 3개의 FBG센서를 배치하였다. 긴장력은 유압잭을 이용하여 5개의 강연선에 동시에 순차적으로 도입되었으며, 단부에서 최대 도입 긴장력은 세그먼트 1은 734kN, 세그먼트 2는 639kN이었다. 도로교설계기준에 제시된 마찰계수의 중간값(파상마찰계수=0.00405, 곡률마찰계수=0.20)을 사용하여 FBG센서 위치에서 계산된 긴장력은 계측치와 5% 이내의 차이를 보였으며, 정착장치 활동에 의한 순간손실은 긴장단에서 최대 12.8%로 계측되었다. 이로부터 이 연구에서 제시하는 긴장력계측방법의 적용성을 입증할 수 있었으며, 향후 이 방법은 프리스트레스트 콘크리트 교량의 설계기준 마찰계수 개정을 위한 연구에 좋은 도구로 활용될 수 있을 것으로 기대된다.

• Smart Structures and Systems
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• 제5권1호
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• pp.81-94
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• 2009

A vibration-impedance-based monitoring method is proposed to predict the loss of prestress forces in prestressed concrete (PSC) girder bridges. Firstly, a global damage alarming algorithm using the change in frequency responses is formulated to detect the occurrence of damage in PSC girders. Secondly, a local damage detection algorithm using the change in electro-mechanical impedance features is selected to identify the prestress-loss in tendon and anchoring members. Thirdly, a prestress-loss prediction algorithm using the change in natural frequencies is selected to estimate the extent of prestress-loss in PSC girders. Finally, the feasibility of the proposed method is experimentally evaluated on a scaled PSC girder model for which acceleration responses and electro-mechanical impedances were measured for several damage scenarios of prestress-loss.

• 한국전산구조공학회논문집
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• 제28권6호
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• pp.707-714
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• 2015

본 논문에서는 프리텐션된 고강도 콘크리트 부재에서의 전달길이를 측정하기 위해 FBG 센서가 기입된 스마트 강연선을 활용하여 실험을 수행하였다. 전달길이 측정을 위해 길이 3m, 단면 $150{\times}150mm$의 고강도 콘크리트 시험체를 총 5개 제작하였으며, 프리텐션 도입 시 콘크리트 압축강도는 58MPa로 측정되었다. 실험 결과 콘크리트 표면에 부착하는 기존의 전기 저항식 게이지보다 FBG 센서로부터 보다 정밀하고 신뢰성있는 강연선의 전달길이를 계측할 수 있는 것으로 나타났다. 계측결과로부터 산정된 강연선 전달길이를 기존의 여러 모델들과 비교하였으며, 이를 통해 고강도 콘크리트 부재에서의 전달길이 산정에 대한 기존 모델들의 적용성을 분석하였다. 본 연구 내용은 향후 강연선의 부착 특성 분석 등의 관련 분야 연구 등에 유용할 것으로 기대된다.

• Smart Structures and Systems
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• 제17권1호
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• pp.107-122
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• 2016

We propose an effective methodology using electromechanical impedance characteristics for estimating the remaining tensile force of tendons and simultaneously detecting damages of the anchorage blocks. Once one piezoelectric patch is attached on the anchor head and the other is bonded on the bearing plate, impedance responses are measured through these two patches under varying tensile force conditions. Then statistical indices are calculated from the impedances, and two types of relationship curves between the tensile force and the statistical index (TE Curve) and between statistical indices of two patches (SR Curve) are established. Those are considered as database for monitoring both the tendon and the anchorage system. If damage exists on the bearing plate, the statistical index of patch on the bearing plate would be out of bounds of the SR curve and damage can be detected. A change in the statistical index by damage is calibrated with the SR curve, and the tensile force can be estimated with the corrected index and the TE Curve. For validation of the developed methodology, experimental studies are performed on the scaled model of an anchorage system that is simplified only with 3 solid wedges, a 3-hole anchor head, and a bearing plate. Then, the methodology is applied to a real scale anchorage system that has 19 strands, wedges, an anchor head, a bearing plate, and a steel duct. It is observed that the proposed scheme gives quite accurate estimation of the remaining tensile forces. Therefore, this methodology has great potential for practical use to evaluate the remaining tensile forces and damage status in the post-tensioned structural members.