Real-time wireless vibration monitoring for operational modal analysis of an integral abutment highway bridge

Remote structural health monitoring systems employing a sensor-based quantitative assessment of in-service demands and structural condition are perceived as the future in long-term bridge management programs. However, the data analysis techniques and, in particular, the technology conceived years ago that are necessary for accurately and efficiently extracting condition assessment measures from highway infrastructure have just recently begun maturation. In this study, a large-scale wireless sensor network is deployed for ambient vibration testing of a single-span integral abutment bridge to derive in-service modal parameters. Dynamic behavior of the structure from ambient and traffic loads was measured with accelerometers for experimental determination of the natural frequencies, damping ratios, and mode shapes of the bridge. Real-time data collection from a 40-channel single network operating with a sampling rate of 128 Hz per sensor was achieved with essentially lossless data transmission. Successful acquisition of high-rate, lossless data on the highway bridge validates the proprietary wireless network protocol within an actual service environment. Operational modal analysis is performed to demonstrate the capabilities of the acquisition hardware with additional correlation of the derived modal parameters to a Finite Element Analysis of a model developed using as-built drawings to check plausibility of the mode shapes. Results from this testing demonstrate that wireless sensor technology has matured to the degree that modal analysis of large civil structures with a distributed network is a currently feasible and a comparable alternative to cable-based measurement approaches.     

Mobile Agent Computing Paradigm for Building a Flexible Structural Health Monitoring Sensor Network

Abstract: Wireless structural health monitoring research has drawn great attention in recent years from various research groups. While sensor network approach is a feasible solution for structural health monitoring, the design of wireless sensor networks presents a number of challenges, such as adaptability and the limited communication bandwidth. To address these challenges, we explore the mobile agent approach to enhance the flexibility and reduce raw data transmission in wireless structural health monitoring sensor networks. An integrated wireless sensor network consisting of a mobile agent‐based network middleware and distributed high computational power sensor nodes is developed. These embedded computer‐based high computational power sensor nodes include Linux operating system, integrate with open source numerical libraries, and connect to multimodality sensors to support both active and passive sensing. The mobile agent middleware is built on a mobile agent system called Mobile‐C. The mobile agent middleware allows a sensor network moving computational programs to the data source. With mobile agent middleware, a sensor network is able to adopt newly developed diagnosis algorithms and make adjustment in response to operational or task changes. The presented mobile agent approach has been validated for structural damage diagnosis using a scaled steel bridge.     

Vibration testing of a steel girder bridge using cabled and wireless sensors

Being able to significantly reduce system installation time and cost, wireless sensing technology has attracted much interest in the structural health monitoring (SHM) community. This paper reports the field application of a wireless sensing system on a 4-span highway bridge located in Wayne, New Jersey in the US. Bridge vibration due to traffic and ambient excitation is measured. To enhance the signal-to-noise ratio, a low-noise high-gain signal conditioning module is developed for the wireless sensing system. Nineteen wireless and nineteen cabled accelerometers are first installed along the sidewalk of two neighboring bridge spans. The performance of the wireless sensing system is compared with the high-precision cabled sensing system. In the next series of testing, 16 wireless accelerometers are installed under the deck of another bridge span, forming a 4 × 4 array. Operating deflection analysis is successfully conducted using the wireless measurement of traffic and ambient vibrations.     

Sensor Attitude Correction of Wireless Sensor Network for Acceleration‐Based Monitoring of Civil Structures

Wireless sensors are now becoming practical alternatives to traditional wired sensors in monitoring civil structures. Though many have been reported on acceleration‐based monitoring of civil structures using wireless sensor networks, sensor attitude that may be different from instrumentation plan has been a seemingly overlooked issue behind performance validation of the network. In this article, a technique to correct the sensor attitude is proposed for the wireless sensor network that measures 3D acceleration of civil structures. Six simple formulas to assess the well‐known 3D Euler angles (i.e., roll, pitch, and yaw) are derived using the gravity extracted from measured 3D acceleration and nonchanging direction of sensors on a stationary structure. The proposed technique is validated at a large‐scale wireless sensor network with 22 sensors in the respective attitudes on a truss bridge. First, attitudes assessed by the proposed method are compared with instrumentation plan. Then, mode shapes obtained before and after the correction are compared with those from finite element model. Comparison shows that quality of the mode shapes improves significantly by small amount of attitude correction less than 7°.     

大体积混凝土结构长期应变监测系统

桥梁健康监测系统是近年应用于桥梁管理与维护的一项新技术,具有重要的工程价值。无线振弦传感器具有抗干扰强,精度高,传输距离远等特点,广泛应用于大体积混凝土结构中振动、应力等动态物理量监测。本文主要论述了桥梁无线应变监测系统结构、无线振弦传感器工作原理,设计了振弦传感器内部的激振电路及测频电路,以及无线通讯模块,同时给出了内部软件的设计,分析了无线振弦传感器的特性。无线的设计极大的方便了振弦传感器的使用,通过工程实际应用显示,本文设计的基于正弦传感器的桥梁无线应变监测系统稳定、质量可靠、测量数据迅速准确。     

基于自适应动态惩罚遗传算法的桥梁监测无线测点优化研究

针对桥梁监测的无线测点优化布置问题,提出一种基于自适应动态惩罚函数的改进广义遗传算法。首先针对无线传感器数量固定和通信距离有限的典型特征将桥梁监测无线测点优化布置表达为约束优化问题,无线传感器的数量和极限传输距离作为优化问题的约束;其次构建了一种能够根据解的偏离程度和种群中高适应度个体数量自动调整惩罚力度的自适应动态惩罚函数;然后采用精英保存机制和末位淘汰策略对基于二重结构编码的广义遗传算法进行了改进;最后利用一大跨悬索桥对该方法进行了验证,并进一步讨论了自适应动态惩罚函数对解的有效性和收敛速度的影响。结果表明:提出的自适应动态惩罚函数能够根据种群的特征自动改变惩罚尺度,保证无线传感器之间的距离小于极限通信距离,同时将无线数据传输距离对桥梁监测信息获取的影响降到最低;改进的广义遗传算法具有很强的全局快速寻优能力,能够快速搜索到全局最优解,优化结果不仅能够满足无线传感网络数据传输距离的要求,还能最大化无线测点的信息获取能力。     

Measuring and modelling the thermal performance of the Tamar Suspension Bridge using a wireless sensor network

A study on the thermal performance of the Tamar Suspension Bridge deck in Plymouth, UK, is presented in this paper. Ambient air, suspension cable, deck and truss temperatures were acquired using a wired sensor system. Deck extension data were acquired using a two-hop wireless sensor network. Empirical models relating the deck extension to various combinations of temperatures were derived and compared. The most accurate model, which used all the four temperature variables, predicted the deck extension with an accuracy of 99.4%. Time delays ranging from 10 to 66 min were identified between the daily cycles of the air temperature and of the structural temperatures and deck extension. However, accounting for these delays in the temperature–extension models did not improve the models' prediction accuracy. The results of this study suggest that bridge design recommendations are based on overly simplistic assumptions which could result in significant errors in the estimated deck movement, especially for temperature extremes. These findings aim to help engineers better understand the important aspect of thermal performance of steel bridges. This paper also presents a concise study on the effective use of off-the-shelf wireless technology to support structural health monitoring of bridges.     

基于Imote2无线传感器的拱桥模型动力试验

介绍了Imote2高性能无线传感器的性能和特点,并利用Imote2建立了无线信号采集系统,解决了在数据采集和处理过程中传感器的时间不能同步等问题;通过在钢管混凝土拱桥模型上的试验测试,得到了拱桥模型的动力特性,并和有线传感器的测试结果进行了比较,利用频谱分析技术和频率稳定图方法验证了试验结果的准确性。结果表明：Imote2无线传感系统能够成功应用在土木工程结构监测中。     

Long-Term Monitoring and Identification of Bridge Structural Parameters

Abstract:   Vibration of a new concrete bridge was monitored and change in the bridge structural stiffness was identified accordingly over a 5-year period. This three-span 111-m long bridge is instrumented with 13 acceleration sensors at both the superstructure and the columns. The sensor data are transmitted to a server computer wirelessly. Modal parameters of the bridge, that is, the frequencies and the modal shapes were identified by processing 1,707 vibration data sets collected under traffic excitations, based on which the bridge structural parameters, stiffness and mass, and the soil spring values were identified by employing the neural network technique. The identified superstructure stiffness at the beginning of the monitoring was 97% of the stiffness value based on the design drawings. In the identified modal frequencies, a variation from −10% to +10% was observed over the monitoring period. In the identified stiffness values of the bridge superstructure, a variation from −3% to +3% was observed over the monitoring period. Based on the statistical analysis of the collected data for each year, 5% decrease in the first modal frequency and 2% decrease in the superstructure stiffness were observed over the 5-year monitoring period. Probability density functions were obtained for stiffness values each year. Stiffness threshold values for the collapse of the bridge under the operational loading can be determined. Then the number of years can be assessed for which the area under the proposed probability density functions is greater than the threshold value. So the information obtained in this study is valuable for studying aging and long-term performance assessment of similar bridges.     

Testing and long-term monitoring of a curved concrete box girder bridge

Capital investment in national infrastructure is significant. The need to maintain and protect critical infrastructure links has led in recent years to significant developments in the area of structural health monitoring. The objective is to track a structure’s long-term performance, typically using sensors, and to successively compare the most recently measured responses with prior response history. During construction of the West Street On-Ramp, a curved concrete box girder bridge, located in the city of Anaheim (California), eleven accelerometers were permanently installed on its bridge deck. The associated data acquisition system was configured to record once a specified threshold acceleration response was exceeded; during the period 2002-2010 a total of 1350 datasets including six earthquakes, for each of the eleven sensors, were acquired. This automatically acquired data was supplemented, during the summer of 2009, with responses measured during controlled vehicle tests. Six accelerometers were additionally installed on the frame of the weighed test vehicle. This paper presents the findings of the analyses of these measured data sets and serves to inform owners and managers as to the potential feedback from their instrumentation investment. All response histories were analyzed using frequency domain techniques for system identification. Extraction of the modal characteristics revealed a continuous reduction, of approximately 5%, in the first three natural frequencies over the period of the study. The measured responses from the vehicle sensors are discussed in the context of identifying the potential for bridge frequency measurement using instrumented vehicles.     

A preliminary research on wireless cantilever beam vibration sensor in bridge health monitoring

According to specific bridge environment, optimal design piezoelectric cantilever beam structure by using results of theoretical calculations and simulation, verify natural frequencies of piezoelectric cantilever beam and production ability of data by experiment, thus formed a complete set of design method of piezoelectric cantilever beam. Considering natural frequency of vibration and intensity of the beam body, design a new type of piezoelectric cantilever beam structure. Paper analyzes the principle of sensor data acquisition and transmission, design a hardware integration system include signal conversion module, microcontroller module and wireless transmission module, test local read and wireless transmission for the combination structure of cantilever beam and data collection card, experimental verification of the radio piezoelectric vibrating cantilever vibration response is intact, the beam produced signal by vibration, acquisition card converts and wireless transmit data, this proved a good and intuitive linear response in simulation of bridge vibration test. Finally, the paper designed a kind of new wireless sensor of vibration cantilever beam, suitable for small bridge health monitoring based on Internet of things.     

无线传感器网络在智能建筑中的应用

无线传感器网络系统非常适用于对布线困难、人员不能到达的区域和临时状况远程监测。介绍了无线传感器网络的概念,体系结构及节点组成,组网过程。展望了无线传感器网络在HVAC系统、照明系统、信息传输领域及环境监测等系统中的应用。最后介绍了ZigBee无线传感器网络技术和无线传感器网络应用案例。     

Web-Based Structural Health Monitoring of an FRP Composite Bridge

Abstract:   To develop an understanding of the long-term performance of fiber reinforced polymer (FRP) composite bridge structures, a health monitoring scheme utilizing wireless technology was implemented on the Kings Stormwater Channel Bridge. The bridge, which is located on a major state highway in California, utilizes FRP composite girders and deck panels. The data collected by a comprehensive array of sensors are transmitted wirelessly, and processed in real-time remotely. Computer-based automated analysis algorithms process the incoming data to provide an assessment of structural response. Effects, due to time-based deterioration, and irregularities are determined using modal parameters, in terms of damage localization indices and an estimated damage severity. The results, made available via a web-based interface, enable appropriate action to be authorized for preliminary maintenance or emergency response prior to actual on-site inspection. It is expected that such systems will not only give engineers a valuable tool in monitoring the structural performance of critical bridge systems, but will also provide important information related to durability, design criteria, and long-term response of FRP composite structures.     

缩短郊区排水压力管爆管位置发现时间的措施

为了准确及时地获取郊区污水管道压力数据,从郊区管道压力采集设备长时间供电、预防自然灾害、提高数据可靠性入手,经过调研和改进,将太阳能供电设备、GPRS无线传输设备以及压力传感器有效组合在一起,安装在部分建设年份较长、管道压力较高、爆管事故时有发生的排水管线上,实现了郊区重要压力管线压力数据的实时监控,达到了在爆管初期及时发现险情,并在最短的时间内找出爆管发生位置、及时进行抢修的目的。     

Deployment of a dense hybrid wireless sensing system for bridge assessment

Discussed in this paper is the deployment of a dense wireless sensor system on a short span integral abutment bridge superstructure located in St. Lawrence County, New York. The Wireless Sensor Solution (WSS) is designed specifically for diagnostic bridge monitoring providing independent conditioning for accelerometers and strain transducers. During deployment, strain measurements are obtained in real-time under ambient environmental and traffic loading. Strain transducers are placed at various locations along the girders, including the top and bottom flanges of a heavily instrumented interior girder at the mid-span and the abutment ends where the neutral axis location, section modulus, and girder moments are obtained. Results from the strain data analysis aid in quantifying the bridge response; notably, detection of end fixity, load distribution, and composite action between the girders and bridge deck. The measured responses are illustrated to propose a deterioration profile based on the level of capacity and demand.     

Structural Health Monitoring System for the Shandong Binzhou Yellow River Highway Bridge

Abstract:   Structural health monitoring (SHM) provides a useful tool for ensuring safety and detecting the evolution of damage and performance deterioration of civil infrastructures. A great number of civil infrastructures under construction can be used as test beds for SHM systems. The Binzhou Yellow River Highway Bridge is a cable-stayed bridge in Shandong Province, China. An SHM system has been implemented on this bridge during its construction for monitoring its health status and assessing its safety for long-term services. The system includes a sensor module, a data acquisition module, a wired and wireless data transmit module, a structural analysis module, a database module, and a warning module. It is integrated by using LabVIEW software and can be remotely operated via Internet. The database is available freely to all scientists and engineers in the SHM research area. This article introduces the deployment and functions of this system, and presents the measured responses of the bridge subjected to moving vehicle loads.     

Prediction of WSN placement for bridge health monitoring based on material characteristics

WSN signal obstruction from various bridge components, including girders, bracings and connectors, can affect the performance and reliability of wireless communication. Although the placement of sensor nodes is essential for forming a mesh or ad-hoc network, there are no quantitative approaches related to the optimal separation distance of each node and the corresponding signal quality. This paper reports the results of an experimental evaluation of the WSN performance in the obstructed environment of a bridge structure. The performance criteria, such as thickness of bridge components, material types and location, were analyzed to determine quantitatively the packet reception rate and allowable separation distance during wireless communication. In addition, a case study was conducted to identify the practical implication that an obstructed environment degrades the communication range and WSN reliability according to the performance criteria. The results show that the WSN placement mainly depends on the material type and object thickness.     

Landscape of connectivity. Measuring and representing fluctuations in wireless network traffic in space

Measuring and understanding the propagation of wireless network signals in buildings is an important task for the planning of both architecture and wireless networks. This article documents an approach to understanding the wireless network traffic load in a location-specific manner, based on the users. The traffic counting system enables relating of traffic load (both cellular and Wi-Fi) to a position in space, using Connect or Not smartphone application. Positioning tracking is based on two technologies: Wi-Fi fingerprints, created using existing networking infrastructure and Bluetooth beacons installed at testing locations. The positioning system is able to track movement through space to a satisfactory level.The system was tested in the context of interactive installations as well as long-term observations of user behaviour in space. These experiments facilitate the conceptualization of a communication landscape, highlighting the activity of people and devices in the network layer. The system can, thus, be useful for post-occupancy evaluations. Moreover, it enables a profound understanding of signal propagation and use patterns in space. We argue that the compound measurement of these two phenomena, which are rarely related, forms a productive base for understanding the relevance of built architecture for the design of wireless infrastructures, and vice versa.     

混凝土徐变对重庆石板坡长江大桥长期服役性能的影响

混凝土徐变对预应力混凝土连续刚构桥梁长期服役下的变形及受力有非常重要的影响。本文以重庆石板坡长江大桥为工程背景,采用CEB-FIP(MC90)的徐变模型,对成桥十年后该桥的徐变效应引起的桥梁变形、内力和预应力损失进行了计算分析,分析结果对该类桥梁的施工分析及设计具有一定的借鉴作用。     

A Synchronized Wireless Sensor Network for Experimental Modal Analysis in Structural Health Monitoring

Abstract: Structural health monitoring aims to provide an accurate diagnosis of the condition of civil infrastructures during their life span using data acquired by sensors. Wireless sensor networks represent a suitable monitoring technology to collect reliable information about the structure's condition, replacing visual inspections, and reducing installation and maintenance time and costs. This article introduces a time synchronized and configurable wireless sensor network for structural health monitoring enabling a highly accurate identification of the modal properties of the monitored structure. The wireless sensor nodes forming the network are equipped with a 3‐axis digital accelerometer and a temperature and humidity sensor. The implemented Medium Access Control layer time synchronization protocol (μ‐Sync) ensures a highly accurate synchronicity among the samples collected by the nodes, the absolute error being constantly below 10 μs, also when high sampling frequency (up to 1 kHz) and extended sampling periods (up to 10 minutes) are applied. The experimental results obtained on a wooden model bridge, compared with those derived from acceleration signals acquired by high‐quality wired sensors, show that the so synchronized wireless sensor nodes allow a precise identification of the natural frequencies of vibration of the monitored structure (1% maximum relative difference).