The IoT-based sensor network is one of the methods that can be efficiently applied to maintain the facilities, such as bridges, at a low cost. In this study, based on LoRa LPWAN, one of the IoT communications, sensor board for cable tension monitoring, data acquisition board for constructing sensor network along with existing measurement sensors, are developed to create bridge structural health monitoring system. In addition, we designed and manufactured a smart sensor node for LoRa communication and established a sensor network for monitoring. Further, we constructed a test bed at the Yeonggwang Bridge to verify the performance of the system. The test bed verification results suggested that the LoRa LPWAN-based sensor network can be applied as one of the technologies for monitoring the bridge structure soundness; this is excellent in terms of data rate, accuracy, and economy.

국내 고도성장기 이후 본격 건설되기 시작한 사회 기반 시설물은 노후화가 빠르게 진행되고 있다. 특히 사고 발생 시 대량 인명 피해로 직결될 수 있는 교량, 터널 등의 대형 구조물에 대한 안전성 평가가 필요하다. 하지만 기존의 유선 센서 기반의 Structural Health Monitoring(SHM)을 개선한 무선 스마트 센서 네트워크는 짧은 신호 도달거리로 인해 경제적이고 효율적인 시스템 구축이 힘들다. 따라서 LoRa LPWAN 시스템은 사물인터넷의 확산과 더불어 저전력 장거리 통신이 각광을 받고 있으며, 이를 구조 건전성 모니터링에 응용함으로써 경제적이면서도 효율적인 모니터링 시스템 구축이 가능하다. 본 연구에서는 LoRa LPWAN 기반의 무선 계측센서 기술 동향을 조사하였으며, LoRa LPWAN 기반의 무선 계측센서 설치 및 유지관리 방안을 제안한다.

Wireless sensors are more favorable in measuring structural response compared to conventional sensors in terms of them being easier to use with no issues with cables and them being considerably cheaper. Previous tests have been conducted to analyze the performance of MEMS (Micro Electro Mechanical Systems) sensor in sinusoidal excitation tests. This paper analyzes the performance of in-built MEMS sensors in devices by comparing with an ICP sensor as the reference. Earthquake input amplitude excitation in shaking table tests was done. Results show that MEMS sensors are more accurate in measuring higher input amplitude measurements which range from 100gal to 250gal than at lower input amplitudes which range from 10gal to 50gal. This confirms the results obtained in previous sinusoidal tests. It was also seen that natural frequency results have lower error values which range from 0% to 3.92% in comparison to the response spectra results. This also confirms that in-built MEMS sensors in mobile devices are good at estimating natural frequency of structures. In addition, it was also seen that earthquake input amplitudes with more frequency contents (Gyeongju) had considerably higher error values than Pohang excitation tests which has less frequency contents.

Recently, measuring instruments for SHM of structures has been developed. In general, the wireless transmission of sensor signals, compared to its wired counterpart, is preferable due to the absence of triboelectric noise and elimination of the requirement of a cumbersome cable. However, the low-cost wireless MEMS sensor has high noise density and transmits the signal wirelessly, so data transmission delay occurs during measurement. Therefore, the footbridges that was previously measured by a mobile phone in 2014 was remeasured using G-Link-200, iPad and iPhone to compare their performance.

A wireless sensor network is emerging technology and intelligent wireless communication paradigm that is dynamically aware of its surrounding environment. It is also able to respond to it in order to achieve reliable and efficient communication. The dynamical cognition capability and environmental adaptability rely on organizing dynamical networks effectively. However, optimally clustering the cognitive wireless sensor networks is an NP-complete problem. The objective of this paper is to develop an optimal sensor network design for maximizing the performance. This proposed Ranking Artificial Bee Colony (RABC) is developed based on Artificial Bee Colony (ABC) with ranking strategy. The ranking strategy can make the much better solutions by combining the best solutions so far and add these solutions in the solution population when applying ABC. RABC is designed to adapt to topological changes to any network graph in a time. We can minimize the total energy dissipation of sensors to prolong the lifetime of a network to balance the energy consumption of all nodes with robust optimal solution. Simulation results show that the performance of our proposed RABC is better than those of previous methods (LEACH, LEACH-C, and etc.) in wireless sensor networks. Our proposed method is the best for the 100 node-network example when the Sink node is centrally located.

Wireless sensors are more favorable in measuring structural response compared to conventional sensors. This is because they are easier to use with no issues with cables and are considerably cheaper. There are several applications that can be used in recording and analyzing data from MEMS sensor installed on an iPhone. The Vibration App is one of the applications used and there has not been adequate research conducted in analyzing the performance of this App. This paper analyzed the performance of the Vibration App by comparing it with the performance of an ICP sensor. Results show that natural frequency results are more accurate (error less than 5%) in comparison to the amplitude results. This means that built- in MEMS sensor in smartphones are good at estimating natural frequency of structures. In addition, it was seen that the results became more accurate at higher frequencies (5.0Hz and 10.0Hz).

Recently, measuring instruments for SHM of structures has been developed. In general, the wireless transmission of sensor signals, compared to its wired counterpart, is preferable due to the absence of triboelectric noise and elimination of the requirement of a cumbersome cable. However, in extreme environments, the sensor may be less sensitive to temperature changes and to the distance between the sensor and data logger. This may compromise on the performance of the sensor and instrumentation. Therefore, in this paper, free vibration experiments were conducted using wireless MEMS sensors at an actual site. Measurement was assessed in time and frequency domain by changing the temperature variation at(- 8℃, - 12℃ and - 16℃) and the communication distance (20m, 40m, 60m, 80m).

Recently, measuring instruments for SHM of structures had being developed. In general, the wireless transmission of sensor signals, compared to its wired counterpart, is preferable due to its absence of triboelectric noise and elimination of the requirement for cumbersome cable. However, the research on the tall buildings with relatively small vibration levels is insufficient. Therefore, in this paper, we used the wireless MEMS sensor and iPad to compare and analyze the vibration measurements of three tall buildings and two towers.

Wireless MEMS sensors have common features such as wireless communication, data measurement, embedded processing, battery-based self-power, and low cost, and increased measurement effectiveness. Wireless MEMS sensors enable efficient SHM without interfering with location because there is no requirement for triboelectric noise and cumbersome cables. However, there is little research on the communication distance with sensors and data. For instance, existing researches have limited communication distance experiments in civil engineering bridges. It is also necessary to investigate the characteristics of dynamic behavior and the communication distance of architectural structures with different wireless transmission/reception environments. Therefore, in a building structure with walls and slabs instead of open spaces, MEMS sensors and data loggers were used as distance experiments where communication disturbance between the vertical slab and the horizontal wall could actually be communicated.

Recently, measuring instruments for SHM of structures had being developed. In general, the wireless transmission of sensor signals, compared to its wired counterpart, is preferable due to its absence of triboelectric noise and elimination of the requirement for cumbersome cable. Preliminary studies on the continuous vibration measurement of high-rise buildings using MEMS sensors have been carried out. However, the research on the low-rise buildings with relatively small vibration levels is insufficient. Therefore, in this paper, we used the wireless MEMS sensor to compare and analyze the vibration measurements of three low-rise buildings.

선박 및 해양구조물의 화물 중 많은 수가 가연성, 휘발성의 석유 및 석유 가공 화물이다. 뿐만 아니라 컨테이너 박스, 벌크화물, 차량 등의 중량 화물이 그 나머지를 차지한다. 게다가 선박은 파랑, 해류 등의 하중을 주기/비주기적으로 받기 때문에 화물의 위치 및 이동 가능성이 존재한다. 그렇기 때문에 선상 사고 위험은 육상의 산업현장 보다 훨씬 크다. 선박 및 해양구조물은 화물 및 화물의 영향으로 인한 사고 위험성이 항시 존재하기 때문에 그 모니터링과 대비가 반드시 필요하다. 이에 본 연구에서는 선상에서 선원 및 작업자의 안전을 보장하기 위해 무선센서네트워크를 도입하여 모니터링 시스템을 구축하기 위한 연구를 진행하였다.

PTEF membranes are used for roofing materials of membrane structures. PTEF is the abbreviation of Poly-tetra Fluotide-ethylene. These materials are consisted of fiberglass weave and polyetrfluoroethylene coating. Also, PTEF membranes have some problems of structural capacity by wind or snow load, etc. In this study, sensor housings using lead switches are bonding in PTFE membranes, Monitoring to changes tension and tear damages are studied using radio frequency. If tension is received on edged membranes, bonded lead switches of sensor housings will be destroyed by changes tension, and these become to send signals of damages at the connected radio frequency system with increased tension. Study of these functional membrane materials will be contributed to prevent water leakage and long-term maintenance of membrane structures.

본 연구에서 리드스위치를 이용한 정적변위센서를 무근과 철근 콘크리트 보에 부착하고 균열손상의 모니터링을 위해 무선주파수를 이용하였다. 무근 콘크리트 보와 철근 콘크리트 보에 외력이 작용하면 균열손상이 발생하고 균열의 증진으로 정적변위센서가 파괴되면 이와 연결되어 있는 무선주파수 발신자가 손상신호를 외부로 발신하게 된다. 이러한 기능성 건축부재에 대한 연구는 이상 기후 현상과 지진 등으로부터 건축물이나 주요구조물을 보호하는데 중요한 역할을 담당할 것으로 사료된다.

케이블 교량에서 케이블은 가장 중요한 구조부재의 하나이며, 케이블의 내부 장력을 모니터링하는 것은 케이블 교량 유지 관리에서 필수적이다. 본 연구에서는 케이블 장력을 효율적으로 모니터링하기 위한 무선센서 기반의 장력추정 자동화 시스템을 개발하였다. 무선센서에 포함된 가속도계를 통해 케이블의 진동을 계측하고, 진동기반 장력추정법을 통해 케이블의 장력을 추정하였다. 장력추정 절차를 자동화하기 위해 가장 널리 사용되고 있는 기계학습법의 하나인 합성곱 신경망을 도입하였다. 개발된 자동화 기법은 싱글보드 컴퓨터의 하나인 라즈베리파이3 모델B+에 구현하였으며, 실험실에서 모형 케이블을 이용하여 성능을 검증하였다. 케이블의 장력이 바뀌는 경우에도 개발된 시스템은 자동으로 변화된 장력의 크기를 잘 계측할 수 있는 것을 확인하였다.

The wireless sensor prototype was developed and the field test result, natural frequencies of each mode in stay-cable, showed 0.5% difference compared to the wired sensor. Also, the cable tension derived by the vibration method was 1.177% difference. As a sensor for managing cable tension, the applicability to bridges was confirmed. In the next study, LoRa LPWAN technology will be applied to various sensors used in structures.

Prediction of compressive strength of concrete by Maturity Method is applied in construction site. However, due to the use of wired type high-priced equipment, economic efficiency and workability are falling. In this study, a newly developed concrete embedded wireless sensor is used to perform a mock-up test. Next, the concrete compressive strength of the Maturity Method is predicted using Saul and Plowman's function as measured temperature data. The predicted concrete strength at the beginning of the age was the actual strength and stiffness, but the error rate was less than 1% at 28th day.

Prediction of the compressive strength of the maturity method has been studied by several researchers and has been applied to the construction of concrete structures. In order to apply the maturity method, which is a function related to temperature and time, it is important to measure the accurate temperature inside the concrete during the curing period. The purpose of this study is to verify the performance by analyzing sensitivity, measurement and transmission accuracy by exposing wireless embedded sensor to various curing environment.

In this study, concrete slab with insulation and non-insulated formwork was used to monitor and control its strength using a wireless sensor network with equivalent age method. As a result, the temperature and compressive strength of the structures were monitored without any problems, which revealed a good management tool.

In this study examined the strength of wall concrete using insulated molds and non-insulated forms by monitoring the strength of the structure using a wireless sensor network by maturity method. It was confirmed that the temperature and compressive strength of the structures are monitored in real time, along with effective strength control.