1. Health monitoring status of urban bridges
More than 60 large bridges in China have installed bridge health monitoring systems, including some urban bridges. These health monitoring systems consist of as few as 50 sensors and as many as 500 sensors, accounting for about 0.5-2.0% of the total cost of the bridge. However, according to the two standards of functional requirements and benefit-cost analysis, the system still has the following problems.
1) The monitoring range can't meet the demand. The monitoring scope is small, and generally only focuses on large rivers. With the development of urban bridges, the maintenance tasks of urban main roads and bridges are becoming increasingly heavy.
2) Only for specific bridges or a few bridges, it can only be regarded as a single "information island", which is not integrated into a unified platform from the perspective of urban bridge management, information is not shared, and there is a lack of organic connection with other management systems.
3) Lack of guidance and planning, the system function is not comprehensive enough, and the design scheme that pays attention to monitoring content and technology while ignoring test data processing and evaluation is increasingly unacceptable to bridge owners. After the system is put into use, subsequent upgrading and secondary development are difficult.
4) The software and hardware development platforms are not unified. Because there are many types of urban bridges and different monitoring items, developing a set of special monitoring software for each specific bridge has some shortcomings, such as long development cycle, poor code portability and non-repetition, which leads to an increase in human resources and development costs.
5) Due to the short monitoring time, the current health monitoring system has not made full use of the information contained in monitoring data of various time scales to realize the long-term mechanism of mining data evolution laws, nor has it been able to upgrade the health monitoring of bridge structures to the tracking monitoring of the whole life process of structures, thus achieving the purpose of guiding maintenance management.
2. The content and design of urban bridge cluster monitoring system
2. 1 Key factors of cluster monitoring system design
Urban bridge cluster monitoring system is an "open" system, and its establishment and improvement is a huge project. The following key factors should be considered in system design and planning:
1) fund planning
At present, the investment in large-scale bridge construction in China is huge, and the development of health monitoring system has sufficient financial support, which is also the main source of funds for establishing health monitoring system at present. However, the investment in the maintenance and management of bridges in large cities in service is seriously insufficient. Therefore, it is difficult for R&D to raise funds for urban bridge cluster monitoring system at one time. It is more practical to advocate the distributed mode of "overall planning and step-by-step implementation" at this stage.
2) Technical planning
Technically speaking, because the problems faced by health monitoring can not be solved overnight, the research and application of high-tech and automation equipment has just started in China, and many key technologies have yet to be broken. There is still a big gap between theoretical research and practical application, which needs to be gradually developed and improved in practice to achieve the best results.
3) Bridge life
For newly-built bridges, the safety conditions at the initial stage of construction are mostly good. At this time, the establishment of health monitoring system is mainly to accumulate important original data for the bridge and monitor the response of the structure under sudden accidents (earthquake, impact, etc.). ), so you only need to arrange measuring points at key positions.
4) instrument life
The bridge health monitoring system itself also has the problems of service life and service life, and because the system mostly uses electronic equipment, it is more likely to be damaged in harsh environment. According to the actual situation of the bridge, the phased implementation scheme can not only save costs, but also extend the service life of the system.
2.2 Cluster monitoring system and its function analysis
The bridge cluster monitoring system comprises a vertical pole installed on a bridge, a camera is installed on the vertical pole, a power supply device and a wireless transmitter matched with the camera are also installed on the vertical pole, and the camera transmits a video signal to a wireless receiver matched with the wireless transmitter through the wireless transmitter. The wireless receiving device is connected with the primary visual alarm terminal or the secondary visual alarm terminal in a wired or wireless way; The intelligent acousto-optic alarm device installed on the first-level visual alarm terminal is connected with the first-level alarm terminal in a wired or wireless way. The utility model has short response time for receiving police, and can send out police in time, thus avoiding the false alarm of police destination and improving the efficiency of sending out police.
On the basis of studying the design criteria of bridge health monitoring system at home and abroad, the urban bridge cluster monitoring system is based on the urban bridge management system based on GIS, and three core components, namely distributed remote bridge monitoring system, data transmission network system and system integrated management platform, are added, which are composed of different modules. The electronic map technology of GIS system relates the attributes of bridges, which is convenient to master the distribution and attributes of bridges in the whole city.
2.2. 1 distributed remote bridge monitoring system
It mainly includes sensor module, data dynamic acquisition module and remote data transmission module. Among them, the sensor module is composed of various sensors and secondary instruments, which mainly monitors the load change, the environmental change of the structure and the actual working state of the structure; The data acquisition module is mainly composed of data acquisition instruments controlled by microcomputer. Its function is to collect the original signals sent by sensors, preprocess the signals according to the functional requirements of the system, and decompose and transform the data to obtain the required parameters. The data transmission module is mainly to establish a communication link for remote transmission and realize network transmission. Distributed remote bridge monitoring system is the most advanced and basic system in cluster monitoring system.
2.2.2 Data transmission network system
It is mainly composed of local area network module of monitoring system, connecting module with other local area networks or backbone networks and remote control module, which realizes the functions of data remote communication, transmission and remote control, and is a bridge connecting distributed remote bridge monitoring system and system cluster management platform.
2.2.3 System Cluster Management Platform
The system cluster management platform consists of central database management module, data analysis and processing module, structural state evaluation module, decision support module and monitoring system control management and maintenance module.
The above three components run in different software and hardware environments and undertake different functions. The cooperative work between them will realize the online monitoring and evaluation function of the urban important bridge cluster monitoring system.
3 Conclusion
In order to ensure the safety of urban bridges, this paper puts forward the concept of urban bridge cluster monitoring system. By using modern information technology, the system constructs a remote online monitoring system for structural safety covering important bridges in the city, which is of great significance and value to ensure the safe and smooth traffic in the city. With the deepening of research, bridge management will be gradually informationized and scientific.
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