LONG TERM STRUCTURAL HEALTH MONITORING SYSTEM FOR CABLE STAYED BRIDGE IN VIETNAM Dr. Eng. Luong Minh Chinh 1 Abstract: Structural Health Monitoring System (SHMS) has been applied and developed in recent years. Most of the major bridges in the world, especially cable-stayed bridge, are installing the Structural Health Monitoring Systems to continuously monitoring and collecting data (the physical quantity) during the operation and exploitation time. In U.S., Japan and Europe, the Structural Health Monitoring System applied and developed very effectively. This article introduces an overview of monitoring systems and devices of SHMS, also shows the necessity of a SHMS system for major bridge projects in Vietnam such as the cable-stayed bridge, serving for the management, rehabilitation and maintenance of bridge works. Based on the documents and research results, the article aim to provide directions for establishing and training qualified staffs and experts in this field of structural health monitoring in Vietnam. Keywords: Structural Health Monitoring System, SHMS, Long bridge, Cable-Stayed Bridge, Measurement, data collection maintenance, 1. General 1 In the design of construction works in general and bridge design in particular, the offering assumptions to simplify the theoretical compute model shall lead to inadequate reflection of operation status and behavior in normal operation condition and during exploitation stage. Dispite of many computer methods or software which sharply developed in recent time, for example, the application 3D calculation method (within non-linear surface feature), but received theoretical calculation result only indicated approximately relative to actual behavior of structure. One of method brink to many potentials to evaluate operation and exploitation process of bridges is installation devices on several equipment or elements of bridge such as monitoring devices, displacement sensors, continuous measurement sensors for physical values of structure: from deformation state to stress state in structure components [1]. Pic. 1 Can Tho Bridge [foto. Internet] 1 Water Resources University.TIE/ HOA PHONG E&C The structural Health Monitoring System (SHMS) has been started to apply and develop in the world in recent years. The majority of bridges in the world have been installed various monitoring systems to monitor and collect data (physical figures) during operation and exploitation stage of bridge. The monitoring systems have been applied widely and effectively in United State, Japan and Europe. In Vietnam there are several of cable-stayed bridges have been installed monitoring systems such as Binh Bridge (Hai Phong), Rao II Bridge (Hai Phong), Nguyen Van Troi - Tran Thi Ly Bridge (Da Nang), Bai Chay Bridge (Quang Ninh) and Can Tho Bridge. Can Tho is one of the long span bridges installed BRIMOS monitoring system provided by NTT Data Company (Japan) [10]. 2. Bridge monitoring system A long span bridge usually have complex structure, long span, result to a significant impact of temperature change, especially for Vietnam s temperature condition with its temperature may reach 40 o C at several regions in the summer, besides, wind effect (especially for Cable-Stayed bridge, Suspension bridge with high tower) is also significant so that the setting up a general monitoring system as well as the collection of data, physical figures shall very necessary. To satisfy above, the general monitoring system shall be consisted of features as bellow: KHOA HỌC KỸ THUẬT THỦY LỢI VÀ MÔI TRƯỜNG - SỐ 44 (3/2014) 11
- Monitoring system of structure condition (stress, displacement) - Monitoring system of meteorological parameters (temperature, humidity, wind direction and wind speed ) - Camera monitoring system (traffic camera monitoring for bridge operation) - Monitoring system of displacement and deformation. Monitoring the structure status Data transmission (to all computer) Via GPRS, Internet or LAN Meteorological monitoring Image monitoring - F - Cable tension sensor - Tt - Angular deformation sensor - S - Structural deformation sensor - A - Acceleration sensor -CGD - Data collection and transmission server - RD - Rainfall sensor - TH - Temperature sensor - An - Wind speed and direction sensor - VS - Sight distance sensor - RS - Road sensor - MS - Meteorological station - VP - Monitoring Camera - VA - Video-recording device - EN - Power supply Figure1. The structure of the monitoring system and associated equipment [3] The collected data providing from monitoring equipment and sensors to be recorded by server installed on bridge, then transfer to Internet or GSM (GPRS) storage center. The structure of the monitoring system shall be set up as Figure 1. 2.1. Monitoring system of structural status Figure 2. Installed position diagram of sensors For monitoring system of bridge, the structural status monitoring system is most important and complicate. The change in physical figure relating to operation status and behaviors of structure under effect both of dead load and live load on basis of recalculation at some of measurement points by measurement of sensors. The physical figures in majority of bridges are: stress, deformation, displacement and acceleration, temperature change, wind speed, humidity [7].. One of monitoring system SHMS tasks are support to engineers and experts who being monitored structural status at execute time during the normal operation and exploitation state of structure and evaluate the extreme states such as impact of whirlwind, overload and oversize truck impact or traffic accident occurred on bridge. Therefore, the selection points (location) to install monitoring devices and selection of value needs to monitor and measure at its position should be thoroughly calculated and analyzed as well as consideration of impact and effect to structures due to many calculated models and combination of various loads [Figure3]. It is necessary to pay special attention to extreme conditions [6] and effect of outside temperature and weather change. Therefore, all sensors and devices especially for sensors installed inside the bridge must have durability longer than 30 years. All equipment of sensor shall be kept in closed box and have ability to transfer the signal via 5km optic fiber cable [Figure 3]. These advantages make wire sensor were widely applied in long-term monitoring of bridge [4]. The changing of wire s strain in sensor lead to vary the vibration frequency of wire and allow to measure and monitor a lot of physical values which needed to evaluate the operation of structures in operation and exploitation stage. 12 KHOA HỌC KỸ THUẬT THỦY LỢI VÀ MÔI TRƯỜNG - SỐ 44 (3/2014)
ELECTROMAGNET THERMISTOR MONITORING SIGNAL VIBRATION SENSOR WIRE MAGNETIC FIELD Pic. 2. Wire sensor kept in Geocon Figure 3. Working structure of wire sensor [5]. closed box. Normally, 2 deformation sensors and 2 temperature sensors [8] will be installed at every monitoring position. This duplication of sensors Recorded in a certain period of time, for example from every 10 seconds to every 60 minutes, acquired parameters and datum from will assure accuracy and reliability of inclinometers will be sent to the server of the monitoring results of the system. pylon-based host computer, where they will be In order to measure and monitor angular transformed into necessary datum for deformations of constructions, inclinometers with high accuracy will be installed. They are able to measure angular deformations at ±10 seconds 0,5mm/1000m [Picture 3]. In addition, these inclinometers can be installed at bridges, where vibration sensors [Picture 4] are necessary to be installed at a range of positions, in order to define effects of dynamic loads and natural vibration frequency of structures, they, will also be used to carry out monitoring by special software [Picture 5], [8].. All computers and servers installed should meet serious requirements on quality and durability for equipment operating in extremely severe environment. Temperature inside pylon may reach 60 Celsius degree and humidity may be very high in hot summer days; therefore temperature sensors and humidity sensors should be adapted to computers and ventilation fans should be installed to cool computers. modal analysis tests of structures Pic. 3. Inclinometer installed on bridge. Recorded monitoring and measurement datum will be sent from this structure-based server to a saving and monitoring center, where they will be previewed, analyzed and estimated by experts in real time in order to assure accuracy and identify timely problems in operation and usage of the structure. Current systems allow expert to create system accounts in order to access and monitor datum as well as Pic. 4. Vibration sensors after installation Pic. 5: A server of host computer is installed inside the pylon. receiving technical analysis and report. The system also creates tables and charts for every recorded physical quantity at any time in order to supply managers with more general view on operation and usage process of the structure [2]. Maximum and minimum values will be set up for every recorded physical quantity in order to predict exceeding status of calculated values. KHOA HỌC KỸ THUẬT THỦY LỢI VÀ MÔI TRƯỜNG - SỐ 44 (3/2014) 13
timely draw the effective treatment. The image monitoring system consist of high resolution performance of monitoring camera which allow to monitor both in night and day with all the weather conditions, monitoring camera of water level, devices to collect and reserve monitoring image. Once monitored physical quantities exceed permitted limits, the system will warn management and maintenance unit via emails on the internet or SMS on mobile networks [5]. 2.2. Meteorological monitoring system The function of the system is provide meteorological and weather data of structural area, notice temperature indicator of deck slab, amount of rainfall to adjust speed and volume of traffic to ensure traffic safety on bridge. The main devices of monitoring system includes thermometer, anemometer, rain gauge, road surface sensor, road s temperature gauge, road s humidity gauge and meteorological station with data transmission and collection device via cable. Picture 8. The screen display the camera monitor images of the Rao II cable-stayed bridge Hai Phong 2.4. Deformation and displacement monitoring system (geomatic monitoring) Figure 4. The GPS/GNSS monitoring system of Leica Geosystems was installed on Can Tho bridge [10]. Picture 7. The screen display parameters of direction, wind speed and weather conditions Rao II Cable stayed bridge in Hai Phong. 2.3. Image monitoring system (monitoring via image) The function of the system is transferring recorded images of structure to center of operation and data reservation base on camera monitoring system. The image monitoring allows coordinating the traffic more effectively and detecting the violation as well as accident to 14 The most different of geomatic monitoring and the other normal monitoring is allowed to evaluate the dynamic changing process of structure and determine effect of phenomenon simultaneously. Therefore, it controlled whole structure with ability of analysis and emulation when incident occurred. These were many different geomatic monitoring systems in the world, the application of the system is also different and base on property as well as various distinction KHOA HỌC KỸ THUẬT THỦY LỢI VÀ MÔI TRƯỜNG - SỐ 44 (3/2014)
of each structure. One kind of this system is GPS/GNSS [Figure 4], [9] of Leica GeoSystem. In order to operate accurately and effectively, the system shall be configured, then adjusted and programmed accurately for each measurement time. It shall be analyzed and evaluated objectively and accurately the received datum Table 1. List and function of sensor ussually used in cable sayed bridge No. Sensor Position Monitoring items 1 GPS 1.Pylon tops 2.Midpoint of main span girder 3.Basic point (reference) Displacement types 2 Wind gauge 4.Pylon top 5.Midpoint of main span girder Velocity/ wind direction 3 Udometer 6.Midpoint of main span girder Precipitation 4 Cable accelerometer 7.Longest cable Cable force 5 Cable force meter 8.Mobile equipment Cable force 6 Deformeter 9.The edge of pylon base Pylon stress 10.Midpoint of main span girder Deck slab stress 7 Smart camera 11.Cross beam on pylon top Bridge condition 8 Water level camera 12.Pylon edge Water level 9 Seismometer 13.Pylon leg Seismic impact 10 Joint gauge 14.Expansion joint Expansion due to temperature 11 Thermometer 15.Pylon top 16.Midpoint of main span girder 17.Inside fake cable 18.Inside pylon 19.Midpoint of main span girder Air temperature Air temperature Fake cable temperature Temperature in pylon Temperature in deck slab 12 Cable in anchorage pylon dynamometer 20.Cable in anchorage pylon Cable in anchorage pylon force 13 1 axial accelerometer 21.Midpoint of main span girder Deck slab vibration 14 2 axial accelerometer 22.Midpoint of main span deck slab Deck slab vibration 23.Top of pylons Pylon vibration 15 Multi-dimension shape sensor 24.Inside pylons Pylon shape 3. Actual application of monitoring system Monitoring system is designed for each bridge based on structure properties of each construction, required financial situation of Client. Bridge monitoring system must have high durability; ensure high accuracy during exploitation time. The cost of whole monitoring system is not big when compare with total cost of bridge construction, it s about 0.3% - 1.5% total investment value of bridge construction depends on the complexity of monitoring system [6]. Management and operation cost for monitoring system is not big in compared with total cost of construction maintenance, but monitoring system request very high requirements on human and experience of management experts. The biggest advantage of bridge monitoring system is that it can continuously monitor activities and changing of structure for safety and efficient in exploitation and operation. Based on data analyzing and evaluating, we can make correct decision for bridge maintenance. Monitoring results allow us to evaluate the correction of assumptions which were shown in design and construction procedure. The frequency of monitoring allows us to control the behavior of construction under different load combination impact; helps experts determine aging procedure of structures to make solution for avoiding and rising life exploitation of bridge construction. 4. Conclusion Bridge monitoring system is a complex system combined of many elements from construction structure monitoring, aerograph monitoring, image monitoring to geomathematics monitoring. To integrate above elements to a finish system, ensure in supplying accurate data for management, operation and exploitation phase in effective way with low KHOA HỌC KỸ THUẬT THỦY LỢI VÀ MÔI TRƯỜNG - SỐ 44 (3/2014) 15
cost and rising construction durability we need the cooperation of many experts in different sector, with deep and wide knowledge in construction. Monitoring work play an important role in erection, construction and operation procedure; it allows verifying assumptions which were shown in design phase and can be impact in implementation cost of construction. So that, the development and application of modern methods, advanced techniques to monitor bridge construction for implementation, study and manage, operate construction in safety and efficiency way is very necessary and imperative. References: Żółtowski K.: Współczesne możliwości analizy statycznej i dynamicznej mostów stalowych. Mosty stalowe. Projektowanie, technologie budowy, utrzymanie. Dolnośląskie Wydawnictwo Edukacyjne, Wrocław 2008. Biliszczuk J., Hildebrand M., Barcik W., Hawryszuków P.: System obserwacji ciągłej mostu podwieszonego przez Wisłę w Płocku. Inżynieria i Budownictwo, nr 7-8/2006. Żółtowski K., Malinowski M., Hildebrand M.: Monitoring mostów podwieszonych. Mosty, nr 3/2009. Biliszczuk J., Barcik W., Toczkiewicz R.: Projekt techniczny systemu monitoringu elektronicznego konstrukcji mostu przez Wisłę w Puławach. Instytut Inżynierii Lądowej Politechniki Wrocławskiej, Wrocław, 10/2008. Sieńko R.: Systemy monitorowania obiektów mostowych, Materiały Budowlane, nr 4/2008. Biliszczuk J., Sieńko R.: System monitorowania mostu w Puławach. Mosty, materiały i technologie. 2011. Zhishen Wu, Koichi Yokoyama: Sensors and bridge monitoring system. Department of Urban and Civil Engineering, Ibaraki University, Japan. Roger W. Lockhart: Bridge Structural Monitoring System - Distributed Synchronous Ethernet Data Acquisition System Satisfy Demanding I35W St. Anthony Falls Bridge Health Measurements. DATAQ Instruments. Leica Geo-system True Story - Automated Deformation Monitoring Apollo Bridge, Bratislava, Slovakia. Akira TAKAUE: Real time structural health monitoring system for a long span cable stayed bridge Can Tho Bridge. Chodai, Co., Ltd., Japan (email: takaue-a@nifty.com). 2012. Tóm tắt HỆ THỐNG QUAN TRẮC LÂU DÀI CÁC CÔNG TRÌNH CẦU GIẢI PHÁP CHO CÁC CẦU DÂY VĂNG Ở VIỆT NAM Hệ thống quan trắc công trình cầu bắt đầu được đưa vào ứng dụng và phát triển trên thế giới từ những năm gần đây. Phần lớn các công trình cầu lớn, cầu dây văng quan trọng trên thế giới đều được lắp đặt những hệ thống quan trắc khác nhau nhằm liên tục theo dõi và thu thập các dữ liệu (các đại lượng vật lý) trong suốt quá trình hoạt động và khai thác của cầu. Mỹ, Nhật và ở châu Âu là những nơi mà các hệ thống quan trắc được đưa vào ứng dụng rộng rãi và rất hiệu quả. Bài viết này giới thiệu tổng quan về hệ thống giám sát và các thiết bị của hệ thống SHMS, đồng thời cũng cho thấy sự cần thiết của một hệ thống quan trắc SHMS cho các dự án cầu lớn ở Việt Nam như cây cầu dây văng để phục vụ cho công tác quản lý, bảo dưỡng và duy tu công trình cầu. Dựa trên các tài liệu và kết quả nghiên cứu, bài viết nhằm mục đích cung cấp hướng dẫn cho việc thiết lập và đào tạo đội ngũ nhân viên và các chuyên gia có trình độ trong lĩnh vực quan trắc trạng thái kết cấu công trình cầu ở Việt Nam. Từ khóa: SHMS quan trắc, trạng thái, kết cấu, cầu lớn, cầu dây văng, bảo dưỡng duy tu, thu thập dữ liệu. Người phản biện: GS.TS. Vũ Đình Phụng BBT nhận bài: 19/2/2014 Phản biện xong: 25/2/2014 16 KHOA HỌC KỸ THUẬT THỦY LỢI VÀ MÔI TRƯỜNG - SỐ 44 (3/2014)