GPS-based dynamic monitoring of large-scale structural buildings Cheng Penggen 12 Xiong Zhuguo 1 Han Lihua 3 Xu Yunhe 1 (1. Department of Surveying, East China Institute of Technology, Fuzhou 344000, Jiangxi; 2. National Key for Surveying, Mapping and Remote Sensing Information Engineering of Wuhan University Satellite signals; through the optical cable of the communication system, transmit the satellite information obtained by the base station receiver to the monitoring station in real time at a certain sampling rate (such as 1 Hz); at the monitoring station, receive the signals from the satellite and the information from the base station , Using GPS software for real-time differential processing, the three-dimensional coordinates of the monitoring station can be obtained and sent to the monitoring center at a certain sampling rate; the monitoring center receives the monitoring results of each monitoring point, and further processing and analysis through the data processing software, Parameters such as displacement and rotation angle of a structure in a specific direction can be obtained. For example, the displacement of a cable-stayed bridge in the longitudinal, lateral, and vertical directions of the bridge, and the vibration frequency and amplitude of a high-rise building in a specific direction. All these displacements The information is saved in the database in order to provide a basis for further evaluation of the structure. It should be known For example, in theory, the maximum displacement of the suspension bridge is located in the middle of the bridge span, and the maximum displacement of the high-rise building is at the top of the building. Therefore, for long-span cable-stayed bridges, the monitoring point should be selected at the bridge span. The monitoring points of high-rise buildings should be located at the top of the building at the half, quarter and top of the bridge. The reference point should be selected at a fixed position within a certain range of the structure to be monitored, and Determine its coordinates.
2.4 The purpose of data processing, analysis and monitoring is to obtain the displacement or rotation angle of the point of interest in specific directions such as the longitudinal, lateral and vertical directions of the structure, so as to further analyze the relationship between displacement and temperature, the relationship between displacement and wind speed, and displacement Relationship with structural loads, etc. The data processing work of the structure condition monitoring system includes coordinate transformation, frequency spectrum analysis, monitoring data compression, and structure evaluation.
Because the coordinates of the monitoring points obtained by the GPS displacement real-time monitoring system are WGS 84 coordinates converted into plane coordinates according to the Gaussian projection, and then transformed into coordinates under the local coordinate system of the structure, so that the displacement time history curve of the monitoring point in the direction of the structure axis can be obtained. For example, for a bridge, the X axis of the local coordinate system is the longitudinal direction of the bridge, the vertical axis is the Z axis, and the 84 coordinate is to the feature point of the bridge structure. Different structures reverse the maximum 1 position. The coordinate of the blish part of the system is changed, the wind affects the position of the bridge (the influence of temperature w on the position selection of the bridge 2.3 reference station and monitoring station. Due to the differential GPS measurement, it is affected by climate errors and orbit errors. The distance between the reference station and the monitoring station changes, and the distance between the reference point and the monitoring point should be kept within a certain distance. Under the existing technical conditions, when the distance between the reference point and the monitoring point is within 1 km, the atmosphere The influence of the orbit error can be controlled within the millimeter level. In order to reduce the influence of the multi-path effect during the observation process, it is required that the reference point and the monitoring point should be within the field of view of 15 degrees above the horizontal plane. The reflection effect of the diameter effect. The selection of the monitoring point should consider the importance of the structure, the size of the deformation and the information to be collected. Generally, the monitoring point should be selected at the point of interest, the maximum deformation position or the right-hand rule to get Y axis.
By analyzing the displacement time history curve of the monitoring point, the vibration frequency and amplitude of the structure can be obtained. The spectrum analysis can be carried out by the method of fast Fourier transform, and the power spectrum curve of the monitoring point can be obtained through the spectrum analysis, which can be compared with the designed theoretical value or the power spectrum curve of different periods to diagnose the stability of the structure.
When performing dynamic monitoring on a structure, in addition to measuring the displacement value of the monitoring point, usually parameters such as temperature, wind direction or load on the structure are also required. Combined with these observations, analysis such as the effect of wind on displacement, temperature on displacement, and load on displacement can also be performed.
For example, in a bridge structure dynamic monitoring system, the effect of vertical displacement to be performed, the effect of vehicles on the vertical displacement of the bridge, and frequency spectrum analysis, etc. Based on these analysis results, the bridge can be monitored for wind effect, temperature effect, traffic load effect, and stress monitoring of the main components of the bridge.
Since the original monitoring data collected from the monitoring system is usually relatively large, it is often difficult and sometimes unnecessary to store all of these data. How to extract the information essence that can represent the entire monitoring information from the original monitoring data in order to reduce the storage data capacity is a very meaningful data refining work. In addition, the assessment of structural status and safety based on monitoring information is also the goal of the entire structural health monitoring system.
3 Examples of dynamic monitoring of large structures There are many successful examples of dynamic monitoring of large structures using GPS at home and abroad, mainly divided into real-time dynamic displacement monitoring of high-rise buildings and large bridges. For example, the Calgary Tower in Canada, the Humber Bridge in the United Kingdom, the Kaiyo Bridge in Akashi, Japan, the Third Bridge in the Tsing Ma Control Zone in Hong Kong, the Republic Building in Singapore, and the Humen Bridge in China and the Imperial Building in Shenzhen have all successfully applied GPS technology. Carry out dynamic monitoring.
Canada used the method of differential GPS carrier phase to successfully monitor the dynamic deformation of Calgary Tower in Calgary in 1993. The tower is about 160m high. The reference station is installed on the top of a low-rise apartment building about 1km north of the tower. Two monitoring points (one backup) are installed on the top of the tower. Data collection work was carried out on the morning of November 9, 1993, sampling at 10Hz Synchronized data observation was performed for 15 minutes of frequency. After processing the monitoring results, the vibration frequency of the tower in the east-west and south-north directions is about 0.3Hz, and the amplitudes in the north-south and east-west directions are Â± 15 respectively. The UK used PTK * GPS technology for the Humber Bridge at the mouth of the Humber River Dynamic monitoring works were carried out. 5. The bridge is 2220m long, and the bridge is divided into three spans by two towers with a height of 155.5m. The main span is 1410m. The monitoring point is located in the middle of the bridge and the bridge, and the reference point is located at a distance The bridge is 1.5km away, and its three-dimensional coordinates are accurately determined. The receiver used is AshtechZ * type dual-frequency GPS receiver, the communication system uses RacalDeltaLink type UHF remote sensing link, and the software is Ashtech * sPNAV real-time processing software. The purpose of monitoring is to monitor the displacement of the central position of the bridge in the direction of each axis of the bridge and the displacement of the bridge tower in the southeast, northwest and vertical directions.
Kaiyo Bridge in Akashi, Japan has also installed an advanced monitoring system. It is a three-dimensional coordinate of a tower with a main span of 1991m and a total length of 3910m and the anchor point at one end of the bridge. The coordinates of the anchor point are used as reference. The three-dimensional coordinates of the monitoring point are converted to calculate the displacement in the direction of the bridge axis. At the same time, the temperature and wind direction at the corresponding point are measured to obtain the corresponding relationship between the displacement value and the temperature, and the relationship between the wind speed and the displacement value. The GPS receiver is the LeicaMC 1000 type, and the data sampling frequency during earthquakes and strong typhoons is 20 Hz. The purpose of the monitoring system is to ensure traffic safety and structural stability.
GPS suspension monitoring systems have also been installed on the three suspension or cable bridges in the Tsing Ma Control Area in Hong Kong. The system consists of four parts: GPS measurement system, information acquisition system, data processing system and system operation and control system. The GPS receivers are mainly installed on both sides of the bridge deck and the top of the tower. A total of 27 GPS receivers are installed. The sampling frequency of the data is 10Hz. The three-dimensional coordinates of the monitoring point are obtained by differential GPS real-time dynamic measurement, and transmitted to the information processing and analysis center synchronously through the information collection system. The purpose of monitoring is to obtain the instantaneous displacement of the bridge body and tower in real time, so as to further calculate the pressure of the main structure of the bridge body to evaluate the load capacity, working state and durability of the bridge.
The tallest building in Singapore, Republic Square Building, also uses RTK-GPS technology for real-time dynamic monitoring. The building is 280m high. The reference station is located on a nearby building, and two mobile monitoring stations are installed on the 66th floor of the building. The GPS receiver is a Leica CRS1000 type, which connects the reference station and the central control processing computer through UHF radio communication, and RS-232 connects the monitoring station and the central processing computer. The purpose of the monitoring system is to use GPS technology to obtain centimeter-level displacement measurement accuracy. The sampling frequency of the data is 10 Hz, and the obtained data is the position vector of the relative point. Combined with the data collected by the wind speed and temperature sensors, the wind effect monitoring and temperature effect monitoring of the building are carried out. At the same time, the wavelet transform method is used to perform spectrum analysis.
The suspension cable GPS is used to determine the mid-span of the bridge. The towers are like ink tops. There were some successful examples of GPS technology used for structural dynamic monitoring in Taikulai when GPS technology was used in bookmark4 in mainland China. For example, the real-time dynamic monitoring of Humen Bridge measured the displacement and vibration frequency of the Imperial Building under the effect of typhoon. The main span of Humen Bridge is 15385m. In order to monitor the working status of the bridge in real time under the conditions of typhoon, traffic load and temperature, 7 sets are installed in the middle, quarter, one-eighth of the bridge span and the tower beam GPS receiver. The sampling frequency is 5 Hz, and the safety monitoring of the bridge began in May 2000. Practice shows that the monitoring displacement value obtained by GPS technology can be used for bridge safety analysis. Emperor Building is 324.95m high, the monitoring point is located on the top of the building, the reference point is set in the southwest direction 500m away from the low-rise building movement and vibration frequency analysis, the results show that the positioning accuracy can reach * 5mm, the vibration frequency is 0.4. Visualization In a system for long-term structural dynamic monitoring, because the monitoring data collected from the monitoring system is massive, it is difficult to manage the monitoring data in the form of traditional documents, and certain measures must be adopted. In addition, the statistical data, processing and analysis results from the data processing and analysis subsystem of the monitoring system should also be effectively managed. Database technology is an advantageous tool for managing massive amounts of data. The most effective way is to establish a dynamic database of monitoring data, and can regularly update, backup and restore monitoring data. In order to achieve the sharing of monitoring data, a database management system based on a network environment should be used, such as the SQLSeimOracle database system. In the case of a relatively large monitoring system and a large number of monitoring points, the amount of monitoring data per day is often very large. At this time, the database can be constructed by establishing a database on the monitoring data of one day, one week or one month. This database construction method brings greater convenience to the establishment, backup, restoration or access of the database. For example, when we developed a bridge monitoring information management system, we adopted this method of establishing a database.
Visualization is to display various data on the screen in the form of graphics or images, and it is a powerful method for people to study and analyze massive data intuitively. In the real-time monitoring system of the structure, the visualization of the monitoring data can clearly reflect the dynamic changes of the structure. Therefore, the visualization of the monitoring data is one of the essential functions of the large-scale structure health dynamic monitoring system. Different visualization methods are usually used for different monitoring results. For example, the daily change curve of temperature, the displacement curve of the monitoring point in the three-dimensional direction, the change diagram of the displacement in a specific direction (such as the axial direction), the relationship diagram of temperature and displacement, the relationship diagram of temperature and load, etc. In addition, for a long suspension bridge, the real-time displacement of the bridge deck in the vertical direction is very effective for analyzing the relationship between the bridge change and the load. It is a schematic diagram of real-time dynamic displacement visualization of a suspension bridge deck.
5 Conclusion GPS technology can overcome the shortcomings of traditional structural monitoring methods. It can overcome the limitations of climatic conditions and conduct all-weather observations. Many GPS receivers currently use differential GPS carrier phase measurement to achieve centimeter or even millimeter accuracy, and have a sampling frequency of 10 Hz or even 20 Hz. The GPS positioning measurement can obtain the three-dimensional coordinates of the monitoring points in real time, in particular, it can realize the visualization and automatic management of the real-time dynamic displacement of the multi-point bridge deck with the suspension bridge. All these advantages provide good technical support for real-time dynamic monitoring of large structures. Examples from home and abroad show that GPS technology has broad application prospects in dynamic monitoring of large structures. With the development of GPS technology, computer technology and network technology, the future large-scale structure dynamic monitoring system will be a comprehensive technology system integrating GPS technology, database technology, visualization technology and network technology.
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