As one of the four ancient civilizations, China has a long and splendid culture. In the field of bridge engineering, during the Zhou and Qin dynasties in China, three bridge types, beam-cable-floating, were basically available; In the Han Dynasty, trestle construction was the mainstay. During the Sui and Tang Dynasties, technology became more and more mature and reached a leap. During the Song Dynasty, it was carried out in an all-round way and on a large scale. During the Yuan, Ming and Qing Dynasties, it became increasingly prosperous, and technology began to fall behind in the middle and late Qing Dynasty. Compared with the world level in the same period, China has been at the advanced level in the world for a long historical period, with numerous bridges built and a large number of outstanding works handed down from generation to generation.
Zhao Zhouqiao, which was founded in 605-6 16, is not only China, but also the earliest and best-preserved hollow stone arch bridge in the world, which has had a far-reaching impact on bridge construction in the future generations of the world. Crossing the Weihe River in Zhao County, it is an open-shouldered single-hole arc stone bridge with large arches superimposed on small arches at both ends, which is used for diversion. It consists of 28 stone arches side by side. Its architectural structure is peculiar, and it has been known as "the best in the world" since ancient times. 199 1 year, Zhao Zhouqiao was selected as the 12 "International Civil Engineering" by American Society of Civil Engineers. Anping Bridge has the reputation of "the longest bridge in the world", which was built in the Southern Song Dynasty more than 800 years ago, with a total length of more than 2,000 meters. It is not only the longest Liang Shi Bridge in China, but also the longest Liang Shi Bridge in the world. There is Lugou Bridge, which ranks first among the three famous ancient bridges in China. Luoyang Bridge (also known as Wan 'an Bridge) is the first to use raft foundation and oyster solid foundation in the history of bridge building in the world. Luding Bridge, span103m; Guangji Bridge, the earliest stone bridge with movable switch in China and even in the world, and so on.
At this time, the modern Qiantang River Bridge, Wuhan Yangtze River Bridge and Nanjing Yangtze River Bridge sounded the clarion call for China to March into a modern bridge country. According to incomplete statistics, by the end of 2009, the total number of highway, railway and public railway bridges in China has reached more than 600,000, and there are more than 250 bridges on the Yangtze River and the Yellow River alone. Among them, the Yangtze River and its tributaries Tuotuo, Tongtianhe and Jinshajiang have nearly 130, and the Yellow River has more than 120. Among the completed cable-stayed bridges, suspension bridges, arch bridges and beam bridges, 24 are among the top ten bridges of the same type in the world, accounting for 60%. There are 6 cable-stayed bridges, among which Sutong Yangtze River Bridge (steel box with main span 1088m) and Stonecutters Bridge in Hong Kong (separated steel box with main span 10 18m) rank first and second respectively. Four suspension bridges, Zhoushan Xihoumen Bridge (split steel box with main span 1650m; The world's first) and Runyang Yangtze River Bridge (main span 1490m steel box) ranked second and fourth respectively; There are 8 arch bridges, Chongqing Chaotianmen Yangtze River Bridge (continuous steel truss tied arch with main span of 552m) and Shanghai Lupu Bridge (tied arch with steel box and basket with main span of 550m) rank first and second respectively. There are 6 beam bridges, and Chongqing Shibanpo Yangtze River Bridge (a continuous steel-concrete mixed rigid frame with a main span of 330m) ranks first. The total length of Hangzhou Bay Bridge in Ningbo is 36 kilometers, which is the highest in the world. The total length of Donghai Bridge is 32.5Km；; Zhoushan Continental Link Island Project is 54.68 kilometers long; ; Shanghai Yangtze River Tunnel Bridge Project-South Tunnel North Bridge, with a tunnel length of 8.9Km and a bridge length of 10.3Km, is by far the largest tunnel-bridge combination project in the world.
No matter what kind of bridge, most of its basic materials can be classified as stone, wood, concrete, steel and other types, and these materials have different degrees of durability problems, which need special attention. Therefore, with the arrival of the climax of bridge construction in China, it is more and more urgent to monitor the operation of important bridges in real time. Under the guidance of the latest development trend in the international bridge field, bridge health monitoring has increasingly become a hot spot in domestic development.
Brief introduction to the development of bridge health monitoring system
Although health monitoring is a technical direction that has only appeared in the last twenty years, we find that the concept of structural monitoring has existed since ancient times: in China, bells are usually installed on ancient pagodas, which have the early warning function of reminding tourists to evacuate when the structure shakes strongly. In addition, China's monitoring and sensing technology has a long history: there are records of atmospheric temperature and wind speed and direction measurement in ancient books of Han Dynasty. 1969, the paper written by Lifshitz and Rotem is regarded as the first paper to explain the concept of modern structural health monitoring-evaluating the structural health status through dynamic response monitoring; Therefore, bridge health monitoring is developing vigorously in the world.
Engineering field: 1987 Sensors were laid on the foyle Bridge, a three-span continuous steel box girder bridge with a total length of 522 meters, to monitor the vibration, deflection and strain response of the main girder under the action of vehicles and wind loads during the bridge operation. This system is one of the earliest relatively complete health monitoring systems. Monitoring systems have also been installed on long-span bridges, such as the Skamsundet cable-stayed bridge in Norway, the Faroe cross-sea cable-stayed bridge in Denmark and the Great Belt East suspension bridge with a main span of 1624m, the Confederate continuous rigid-frame bridge in Canada and the Akashi Strait Bridge in Japan. During the period of 1997, wind and structural monitoring systems were installed on three bridges in Hong Kong, namely, Qingma Bridge, Jishuimen Bridge and Tingjiu Bridge. Subsequently, structural monitoring systems of different scales were established in Donghai Bridge, Humen Bridge, Xupu Bridge and Jiangyin Yangtze River Bridge in mainland China.
In academic field: At the 9th World Earthquake Engineering Conference (9WCEE) held in Tokyo, Japan from 65438 to 0988, the active control of civil engineering was discussed for the first time in the world. 1994, the international society for structural control (IASC) was formally established, and the first international conference on structural control (1ST world conf. Structural control) was held in the same year. In order to meet the needs of the development of the situation, after 2006, the meeting of the International Society for Structural Control (IASC) was renamed World CONF. Structural control and monitoring.
Main research progress of health monitoring
Looking at the development history and present situation of bridge health monitoring, there are mainly the following technical problems and research progress:
Firstly, the overall design of health monitoring system. The general design principles of health monitoring system include the following: (1) Arrange monitoring points according to the results of vulnerability analysis of bridge structure and the requirements of maintenance management; (2) From the requirements of structural safety, durability and availability, the structure is monitored, and the work is completed with the least number of sensors and data by combining real-time monitoring with regular monitoring; (3) Structural displacement monitoring is the main method, supplemented by force, stress and modal analysis. The monitoring contents mainly include load source, system characteristics and structural response. At present, the design of health monitoring system is mainly based on the limitation of experience and project funds, but there is no clear standard for the design of sensor system. At the same time, there is no clear method to obtain the data that plays a key role in structural state evaluation through health monitoring system.
Second, sensing transmission technology. The shortcomings of traditional sensing technology, such as easy interference and long transmission line, have not adapted to the development requirements of bridge health monitoring. With the support of modern science and technology, many new sensing technologies have been developed in recent years, among which optical fiber sensing, wireless sensing, GPS technology and Internet data communication technology are the main technical representatives. The optimal placement of sensors has attracted more and more attention. The type, number and location of sensors have a great relationship with the monitoring effect. Under objective conditions, the number of sensors is always limited. How to arrange the limited sensors reasonably to maximize their efficiency is one of the key technologies of health monitoring and one of the development directions in the future.
Third, data fusion technology. Multi-sensor data fusion technology can effectively monitor and diagnose structural systems because of its powerful space-time coverage ability and comprehensive processing ability of multi-source uncertain information. At present, the developed data fusion technologies mainly include: weighted average, Kalman filter, Bayesian estimation, statistical decision theory, evidence theory, fuzzy reasoning and neural network. Most of the existing health monitoring systems stay in the stage of data collection and simple data analysis, and the bridge health monitoring system will produce a large number of test data. It is still very difficult to integrate and interpret these test data and information and make a reasonable evaluation of the real state of the structure.
Fourthly, research on system and damage identification theory. At present, the main research methods are structural damage identification method and model updating method based on vibration. As an important part of structural state assessment, structural damage identification is one of the research hotspots in health monitoring in recent years, and a series of damage identification methods such as structural frequency, displacement mode, strain mode, curvature mode, strain energy, stiffness, flexibility, energy method and frequency response function have appeared. The model updating method is mainly based on the optimization of motion equation, test results and structural constraints of finite element model, and constantly corrects the distribution of structural stiffness, mass and damping to make its response as close as possible to the actual response. Structural model updating can provide a benchmark model for health monitoring, and also provide a good foundation for structural damage identification and performance simulation based on the inversion of test results.
Fifth, structural health assessment. The structural state evaluation method mainly uses the possible internal information reflecting the structural performance to evaluate the working state of the structure, such as construction and operation. At present, there are reliability theory, analytic hierarchy process, fuzzy theory, neural network and expert system. The structural state evaluation of health monitoring system needs to extract features that can reflect the structural characteristics from a large number of data of structural monitoring, so as to complete the real-time and regular evaluation of the structure, which inevitably involves feature extraction, data fusion and performance decision-making of structural data. But at present, little work has been done in this area.
An example of bridge health monitoring-Donghai Bridge
Donghai Bridge officially started construction on June 26th, 2002. After 35 months of hard construction, structural connectivity was achieved on May 25th, 2005. It is the first truly sea-crossing bridge in China. Donghai Bridge starts from Luchaogang, Nanhui District, Shanghai, connects hulu expressway in the north, crosses the northern waters of Hangzhou Bay in the south, and reaches Xiaoyangshan Island, Shengsi County, Zhejiang Province, with a total length of about 32.5 kilometers, of which the onshore section is about 3.7 kilometers, the offshore section from the new levee of Lu Chao Port to Tortoise Island is about 25.3 kilometers, and the connecting section between Tortoise Island and Xiaoyangshan Island is about 3.5 kilometers. The bridge is designed according to the highway standard of two-way six-lane and emergency parking zone. The width of the bridge is 3 1.5m, the design speed is 80km, the design load is checked according to the dense arrangement of heavy containers, and it can resist typhoon of magnitude 12 and earthquake of magnitude 7, and the design reference period is 100. Donghai Bridge is an important supporting project of the first phase of Yangshan Deepwater Port Area of Shanghai International Shipping Center, which provides container land transportation, water supply, power supply and communication services for Yangshan Deepwater Port Area. The completion and opening of Donghai Bridge has laid a solid foundation for the completion and further development of Yangshan Deepwater Port and the acceleration of the construction of Shanghai International Shipping Center. Donghai Bridge was listed as "No.1 Project" by the Shanghai Municipal Government at that time, and its importance is self-evident. At the same time of structural construction, the layout of health monitoring system has also been put on the agenda. From June 5, 2006 to 2006 10, the monitoring system of Donghai bridge was successfully arranged and put into use in 2007.
The monitoring contents of Donghai Bridge mainly include environmental parameters, structural static and dynamic response and structural durability. Among them, environmental parameters mainly include wind speed, earthquake, waves and scouring. Structural response mainly includes deformation of pylon, deflection of continuous beam, deformation of dampers and expansion joints, damage of main girder, vibration of main girder and pylon and stress of stay cables. Structural durability monitoring includes fatigue of steel structure and chronic corrosion of concrete structure.
The basic monitoring methods adopted by Donghai Bridge include: measuring stress and temperature with FBG sensor; Monitoring structural deformation with global positioning system: measuring bridge fatigue with fatigue sensor. The whole bridge * * * uses 478 sensors, of which the main span uses 169 sensors.
The data evaluation system is divided into online evaluation and offline evaluation. Network monitoring is an automatic monitoring system, which can not only judge the safety of the structure, but also analyze the collected data. The automatic monitoring system can also automatically decide whether it is necessary to warn managers and immediately start off-line evaluation. The off-line evaluation system can carry out some more advanced analysis, such as structural static analysis, modal analysis, bridge mechanical behavior and environmental factor correction analysis. This system needs a lot of structural analysis and judgment by experts, and then gives a comprehensive evaluation of the bridge state.
The monitoring data of bridge structure includes not only the normal operation state, but also the response of bridge structure under extreme loads (such as typhoon, earthquake, explosion, ship collision, etc.). ). After getting a lot of monitoring data, it needs more in-depth analysis and sorting. First of all, we should distinguish which parts of the data are caused by environmental changes and which are caused by structural damage, and then show the inherent laws and changes contained in the data through charts and other forms, and then evaluate the overall situation of the structure.
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