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.     

Toward an Integrated Smart Sensing System and Data Interpretation Techniques for Pavement Fatigue Monitoring

Abstract: Currently, pavement instrumentation for condition monitoring is done on a localized and short‐term basis. Existing technology does not allow for continuous long‐term monitoring and network level deployment. Long‐term monitoring of mechanical loading for pavement structures could reduce maintenance costs, improve longevity, and enhance safety. In this article, on‐going research to develop and validate a smart pavement monitoring system is described. The system mainly consists of a novel self‐powered wireless sensor based on the integration of piezoelectric transduction with floating‐gate injection capable of detecting, storing, and transmitting strain history for long‐term monitoring and a novel passive temperature gauge. A technique for estimating full‐field strain distributions using measured data from a limited number of implemented sensors is also described. The ultimate purpose is to incorporate the traffic wander effect in the fatigue prediction algorithms. Preliminary results are shown and limitations are discussed.     

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).     

Multi‐objective Optimization of Sensor and Excitation Layouts for Frequency Response Function‐Based Structural Damage Identification

Abstract: The accuracy of many damage identification methods depends significantly on the quality of measurements collected by sensors, such as accelerometers, concerning the response characteristics of a structure. Often the number of sensors used to collect measurements is limited due to available funds, equipment, and access. In addition, the excitation location can significantly affect a sensor's ability to collect quality measurement information. Therefore, both the location and number of sensors and the location of the excitation must be optimized to maximize the quality of information collected. A multi‐objective optimization approach is presented that minimizes the number of sensors specified while maximizing the sensitivity of the frequency response functions (FRFs) collected at each specified sensor location with respect to all possible damaged structural elements. The multiple Pareto‐optimal sensor/excitation layouts obtained aid in determining the number of sensors required to obtain an effective level of measurement information. The benefit of using Pareto‐optimal sensor/excitation layouts is investigated by using the optimized layouts to collect measurement information for a FRF‐based structural damage identification method. Trial results confirm that an increase in damage identification accuracy and efficiency is achieved when Pareto‐optimal sensor/excitation layouts are used instead of nonoptimal layouts. In addition, the Pareto‐optimal layouts improved damage identification accuracy in noisy measurement environments due to increasing the quality of measurements collected.     

Long-term performance assessment of the Telegraph Road Bridge using a permanent wireless monitoring system and automated statistical process control analytics

The purpose of this study is to advance wireless sensing technology for permanent installation in operational highway bridges for long-term automated health assessment. The work advances the design of a solar-powered wireless sensor network architecture that can be permanently deployed in harsh winter climates where limited solar energy and cold temperatures are normal operational conditions. To demonstrate the performance of the solar-powered wireless sensor network, it is installed on the multi-steel girder bridge carrying northbound I-275 traffic over Telegraph Road (Monroe, Michigan) in 2011; a unique design feature of the bridge is the use of pin and hanger connections to support the bridge main span. A dense network of strain gauges, accelerometers and thermometers are installed to acquire bridge responses of interest to the bridge manager including responses that would be affected by long-term bridge deterioration. The wireless monitoring system collects sensor data on a daily schedule and communicates the data to the Internet where it is stored in a curated data repository. Bridge response data in the repository are autonomously processed to extract truck load events using machine learning, compensate for environmental variations using nonlinear regression and to quantitatively assess anomalous bridge performance using statistical process control.     

Monitoring of rocks using smart sensors

This paper examines the feasibility of employing the new generation fibre optic and piezoelectric sensor systems for comprehensive monitoring of rocks, covering load history monitoring/retrieval as well as damage assessment. A detailed experimental study was conducted on the Bukit Timah granite rock samples obtained from a cavern site in Singapore. The rock specimens were subjected to cyclic loading and their conditions were continuously monitored using such smart sensors. Optical fibres with multiplexed fibre Bragg gratings (FBGs), surface bonded on the rock specimens, were used as strain and temperature sensors. Their performance was compared with the conventional electric strain gauges (ESGs). Piezo-electric ceramic patches made up of lead zirconate titanate (PZT) were employed as piezo-impedance transducers for detecting the onset of damages. These typically employed high frequencies of the order of kHz to extract impedance information of the specimens. Typically, the piezo-impedance transducers detected cracks even before they reached macroscopic dimensions. The results of this experimental study demonstrate the superior performance and cost-effectiveness of the new generation smart technologies as compared to the conventional sensor systems for monitoring rock-structures such as caverns and tunnels.     

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.     

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°.     

Gage‐Free Stress Estimation of a Beam‐like Structure Based on Terrestrial Laser Scanning

Abstract: Terrestrial laser scanning (TLS) is a technique that remotely obtains the three‐dimensional (3D) coordinates of an object using laser pulses. It is advantageous when used to obtain the 3D coordinates of the overall shape as well as any particular area or point of a target object. In addition, using TLS for the stress monitoring of structures will not require the installation of a sensor on the target structure whose structural response will be assessed. Thus, TLS can resolve the limitations of conventional sensors based on strain monitoring. This article presents a computational model for the automatic estimation of the stresses of beam structures using TLS in association with a finite element method. The method is experimentally applied to the stress estimation of a simply supported steel beam subjected to a concentrated load. In this experimentation, the maximum and minimum errors between the estimated stresses using TLS and directly measured stresses from electrical strain gages are found to be 7.2% and 2.2%, respectively.     

Applications of FBG-based sensors to ground stability monitoring

Over the past few decades, many optical fiber sensing techniques have been developed. Among these available sensing methods, optical fiber Bragg grating(FBG) is probably the most popular one. With its unique capabilities, FBG-based geotechnical sensors can be used as a sensor array for distributive(profile) measurements, deployed under water(submersible), for localized high resolution and/or differential measurements. The authors have developed a series of FBG-based transducers that include inclination, linear displacement and gauge/differential pore pressure sensors. Techniques that involve the field deployment of FBG inclination, extension and pore-pressure sensor arrays for automated slope stability and ground subsidence monitoring have been developed. The paper provides a background of FBG and the design concepts behind the FBG-based field monitoring sensors. Cases of field monitoring using the FBG sensor arrays are presented, and their practical implications are discussed.     

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。     

基于物联网技术的土石坝安全监测自动化系统研究

构建了基于物联网技术的土石坝安全监测自动化系统,利用无线传感网芯片CC2530和GPRS模块完成了传感器节点、路由器节点、协调节点的硬件和软件设计,集成无线传感网和地理信息系统。实现对土石坝大坝变形、渗流、应力应变以及环境气象等各种因子进行全天候的实时监测、采集和控制,并在专家知识库辅助下,实现对土石坝安全性状的智能化、科学化管理。     

Hybrid wireless hull monitoring system for naval combat vessels

There is increasing interest by the naval engineering community in permanent monitoring systems that can monitor the structural behaviour of ships during their operation at sea. This study seeks to reduce the cost and installation complexity of hull monitoring systems by introducing wireless sensors into their architectural designs. Wireless sensor networks also provide other advantages over their cable-based counterparts such as adaptability, redundancy, and weight savings. While wireless sensors can enhance functionality and reduce cost, the compartmentalised layout of most ships requires some wired networking to communicate data globally throughout the ship. In this study, 20 wireless sensing nodes are connected to a ship-wide fibre-optic data network to serve as a hybrid wireless hull monitoring system on a high-speed littoral combat vessel (FSF-1 Sea Fighter). The wireless hull monitoring system is used to collect acceleration and strain data during unattended operation during a one-month period at sea. The key findings of this study include that wireless sensors can be effectively used for reliable and accurate hull monitoring. Furthermore, the fact that they are low-cost can lead to higher sensor densities in a hull monitoring system thereby allowing properties, such as hull mode shapes, to be accurately calculated.     

大体积混凝土结构长期应变监测系统

大体积混凝土结构长期应变监测系统是近年应用于建筑工程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长期应变的测量。本文主要论述了大体积混凝土结构长期应变监测系统结构和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,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大体积混凝土结构长期应变监测系统稳定、质量可靠、测量数据迅速准确。     

Pavement performance assessment using a cost‐effective wireless accelerometer system

Pavement condition monitoring is required to identify pavements in need of maintenance or rehabilitation. Early identification of reduction in pavement's structural resistance and improving the structural resistance by minor repairs can lead to significantly lower maintenance costs for transportation agencies. In this study, a cost‐effective wireless sensor that can be embedded in the road to measure the transient vibrations due to different applied loads was tested to determine its effectiveness in terms of pavement displacement measurements. Test results show that the vibration sensor, combined with the algorithms, can be embedded in new or existing pavements and used as an accurate wireless displacement sensor. The low cost of the sensor system allows the use of these sensors at high densities for monitoring the performance of an entire road network. Outputs from the developed system can be directly used to evaluate the condition and performance of pavement structure (increasing displacement over time indicating increasing pavement damage). In addition, displacement data from the system can be used to backcalculate pavement layer stiffnesses, which can be used to predict long‐term performance of the pavement structure. Reduction in pavement layer stiffness over time can be used to determine long‐term damage accumulation.     

Integrated multi‐type sensor placement and response reconstruction method for high‐rise buildings under unknown seismic loading

Structural health monitoring system has been implemented on high‐rise buildings to provide real‐time measurement of structural responses for evaluating their serviceability, safety, and sustainability. However, because of the complex structural configuration of a high‐rise building and the limited number of sensors installed in the building, the complete evaluation of structural performance of the building in terms of the information directly recorded by a structural health monitoring system is almost impossible. This is particularly true when seismic‐induced ground motion is unknown. This paper thus proposes an integrated method that enables the optimal placement of multi‐type sensors on a high‐rise building on one hand and the reconstruction of structural responses and excitations using the information from the optimally located sensors on the other hand. The structural responses measured from multi‐type sensors are fused to estimate the full state of the building in the modal coordinates using Kalman filters, from which the structural responses at unmeasured locations and the seismic‐induced ground motion can be reconstructed. The optimal multi‐type sensor placement is simultaneously achieved by minimizing the overall estimation errors of structural responses at the locations of interest to a desired target level. A numerical study using a simplified finite element model of a high‐rise building is performed to illustrate the effectiveness and accuracy of the proposed method. The numerical results show that by using 3 types of sensors (inclinometers, Global Positioning System, and accelerometers), the proposed method offers an effective way to design a multi‐type sensor system, and the multi‐type sensors at their optimal locations can produce sufficient information on the response and excitation reconstruction.     

混凝土结构埋入式光纤应变传感器的耐用性解决方案

埋入式光纤应变传感器在混凝土结构的健康监测中应用日益广泛,但其有效寿命远低于结构的使用寿命,不能实现对结构的全周期监测。基于可更换的思路,提出了一种新型的传感器设计方案,通过对老化的主要应变传感部件(光纤光栅、基底和传输光纤)进行更新来使应变监测得以长期连续进行,从而简便可靠地解决了埋入式光纤应变传感器的耐用性问题。     

Wireless sensor networks as part of a web-based building environmental monitoring system

The presented research shows how advanced wireless sensor technology can be used by engineers to monitor conditions in and around buildings. The objective is split into three different tasks. First, wireless sensor hardware is programmed to process signals from sensors and transmit the data in a suitable format. This task was accomplished through an open-source operating system and a programming language designed specifically for wireless sensor hardware. The second task involved the processing of signals sent by the wireless sensor nodes. In this application, a Java program was written that deciphered messages transmitted from a wireless receiver over a computer's serial port and then placed the data in a database. The structure of that database is discussed to help identify the key pieces of information that are needed to make use of the data. The third piece of the proposed monitoring system is an interface to review the data. A Web-based system was developed that allows a user to mine the database using parameters such as the type of data, location of sensor, and the time of data acquisition. It is anticipated that this research will demonstrate the potential of using wireless sensor networks for monitoring buildings.     

基于LoRa技术的云平台楼宇火警监测系统设计

为了解决传统楼宇火警监测系统布线复杂、传输距离短、智能化程度低等问题,结合物联网技术,设计一种基于LoRa技术的云平台楼宇火警监测系统。该系统利用LoRa技术构建无线传感网络,实现监测信息的远距离传输,包含一个汇聚节点和多个终端节点。终端节点通过多种传感器对环境信息进行监测,汇聚节点接收所有终端节点的数据,并经由EC20 4G通信模块上传至云平台。系统测试结果表明,该云平台能够实时准确地展示环境数据,异常时终端节点和云端均能及时告警,具有覆盖范围广、功耗低、成本低以及部署方便等优点。     

Health monitoring of flexural steel structures based on distributed fibre optic sensors

In our previous study, a distributed long-gauge fibre optic sensing system (with the ability to obtain effective average strain, or macro-strain, distributions) for practical adaptation in civil structural health monitoring was developed and verified. The present paper is devoted to proposing an integrated health monitoring scheme for elastic beam-like structures, where flexure dominates structural responses, based on static testing and measurements using the developed sensors. A series of experimental investigations on steel beams with different levels of damage are first carried out. The static strain measurements from distributed sensors are characterised and some concerns on the data processing and feature extraction are discussed. On the basis of the extracted features, structural health monitoring (SHM) investigations are deployed in three parts: damage identification with no requirement for a structural analytical model, parametric estimation based on finite element (FE) models, and evaluation of structural global behaviour. By comparing to traditional transducers such as linear variable displacement transducers (LVDTs) and foil ‘point’ strain gauges, the ability and ascendancy of the sensors developed here for SHM purposes are verified. A comprehensive health monitoring strategy for steel flexural structures based on the distributed strain sensors array is proposed finally.