Showing papers on "Structural health monitoring published in 2013"

Carbon nanotube cement-based transducers for dynamic sensing of strain

Abstract: A new type of sensor for structural health monitoring (SHM) has emerged since the birth and development of nanotechnology and is based on cementitious materials additioned with carbon nanoparticles that can provide measurable electrical responses to applied strain. The response of similar transducers was mainly investigated under slowly varying strains while applications in dynamics have not been yet documented. This paper is aimed at exploring the applicability of carbon nanotube–cement based sensors for measuring dynamically varying strain in concrete structures. Experiments are presented to investigate the electrical response of prismatic specimens made of carbon nanotube–cement composite when subjected to sinusoidal stress–strains in the typical frequency range of large civil structures. The results demonstrate that the sensors’ output retains all dynamic features of the input thus providing useful information for SHM and encouraging the transformation of structures into infinite sets of potential sensors with enhanced durability and limited access issues.

Low Power Wireless Sensor Network for Building Monitoring

Abstract: A wireless sensor network is proposed for monitoring buildings to assess earthquake damage. The sensor nodes use custom-developed capacitive microelectromechanical systems strain and 3-D acceleration sensors and a low power readout application-specified integrated circuit for a battery life of up to 12 years. The strain sensors are mounted at the base of the building to measure the settlement and plastic hinge activation of the building after an earthquake. They measure periodically or on-demand from the base station. The accelerometers are mounted at every floor of the building to measure the seismic response of the building during an earthquake. They record during an earthquake event using a combination of the local acceleration data and remote triggering from the base station based on the acceleration data from multiple sensors across the building. A low power network architecture was implemented over an 802.15.4 MAC in the 900-MHz band. A custom patch antenna was designed in this frequency band to obtain robust links in real-world conditions. The modules have been validated in a full-scale laboratory setup with simulated earthquakes.

A Wireless Sensor Network‐Based Structural Health Monitoring System for Highway Bridges

Abstract: An integrated structural health monitoring (SHM) system for highway bridges is presented in this article. The system described is based on a customized wireless sensor network platform with a flexible design that provides a variety of sensors that are typical to SHM. These sensors include accelerometers, strain gauges, and temperature sensors with ultra-low power consumption. A S-Mote node, an acceleration sensor board, and a strain sensor board are developed to satisfy the requirements of bridge structural monitoring. The article discusses how communication software components are integrated within TinyOS operating system to provide a flexible software platform whereas the data processing software performs analysis of acceleration, dynamic displacement, and dynamic strain data. The prototype system comprises a nearly linear multi-hop topology and is deployed on an in-service highway bridge. Data acquired from the system are used to examine network performance and to help evaluate the state of the bridge. Experimental results presented in the article show that the system enables continuous or regular interval monitoring for in-service highway bridges.

System and method for time reversal data communications on pipes using guided elastic waves

Abstract: Embedded piezoelectric sensors in large civil structures for structural health monitoring applications require data communication capabilities to effectively transmit information regarding the structure's integrity between sensor nodes and to the central processing unit. Conventional communication modalities include electromagnetic waves or acoustical waves. While guided elastic waves can propagate over long distances on solid structures, their multi-modal and dispersive characteristics make it difficult to interpret the channel responses and to transfer useful information along pipes. Time reversal is an adaptive transmission method that can improve the spatiotemporal wave focusing. The present disclosure presents the basic principles of a time reversal based pulse position modulation (TR-PPM) method and demonstrates TR-PPM data communication by simulation. The present disclosure also experimentally demonstrates data communication with TR-PPM on pipes. Simulated and experimental results demonstrate that TR-PPM for data communications can be achieved successfully using guided elastic waves.

Structural health monitoring of the Tamar suspension bridge

Abstract: This paper presents experiences and lessons from the structural health monitoring practice on the Tamar Bridge in Plymouth, UK, a 335-m span suspension bridge opened in 1961. After 40 years of operations, the bridge was strengthened and widened in 2001 to meet a European Union Directive to carry heavy goods vehicles up to 40 tonnes by a process in which additional stay cables and cantilever decks were added and the composite deck was replaced with a lightweight orthotropic steel deck. At that time, a structural monitoring system comprising wind, temperature, cable tension and deck level sensors was installed to monitor the bridge behaviour during and after the upgrading. In 2006 and 2009, respectively, a dynamic response monitoring system with real-time modal parameter identification and a robotic total station were added to provide a more complete picture of the bridge behaviour, and in 2006 a one-day ambient vibration survey of the bridge was carried out to characterize low-frequency vibration modes of the suspended structure. Practical aspects of the instrumentation, data processing and data management are discussed, and some key response observations are presented. The bridge is a surprisingly complex structure with a number of inter-linked load–response mechanisms evident, all of which have to be characterized as part of a long-term structural health monitoring exercise. Structural temperature leading to thermal expansion of the deck, main cables and additional stays is a major factor on global deformation, whereas vehicle loading and wind are usually secondary factors. Dynamic response levels and modal parameters show apparently complex relationships among themselves and with the quasi-static load and response. As well as the challenges of fusing and managing data from three distinct but parallel monitoring systems, there is a significant challenge in interpreting the load and response data firstly to diagnose the normal service behaviour and secondly to identify performance anomalies. Copyright © 2012 John Wiley & Sons, Ltd.

Compressive sampling–based data loss recovery for wireless sensor networks used in civil structural health monitoring

Abstract: In a wireless sensor network, data loss often occurs during the data transmission between the wireless sensor nodes and the base station. In the wireless sensor network applications for civil structural health monitoring, the errors caused by data loss inevitably affect the data analysis of the structure and subsequent decision making. This article explores a novel application of compressive sampling to recover the lost data in a wireless sensor network used in structural health monitoring. The main idea in this approach is to first perform a linear projection of the transmitted data x onto y by a random matrix and subsequently to transmit the data y to the base station. The original data x are then reconstructed on the base station from the data y using the compressive sampling method. The acceleration time series collected by the field test on the Jinzhou West Bridge and the Structural Health Monitoring System on the National Aquatics Center in Beijing are employed to validate the accuracy of the propos...

Summary Review of GPS Technology for Structural Health Monitoring

Abstract: Over the last two decades, global positioning system (GPS) technology has been developed rapidly and recently applied to civil structures for appropriate monitoring of structural performance. Currently, the GPS technique can only be applied to flexible structures having lower modal frequency ranges, and it still has remaining issues when it comes to obtaining accurate measurements. However, the application of GPS is promising as a monitoring tool because it can measure dynamic characteristics and static displacements in real time, whereas the conventional monitoring system using accelerometers cannot measure static and quasi-static displacements. Furthermore, rapid advancements in GPS devices and algorithms can mitigate erroneous sources of GPS data, and integrated systems using GPS receivers with other supplement sensors are capable of providing accurate measurements. Therefore, GPS technology can provide accurate displacements of structures in real time, and stress and strain conditions of the structures can be computed using finite-element models and numerical analyses. It is also expected that damage localization and severity can be identified using the dynamic characteristics of structures obtained from GPS. This paper summarizes the use of GPS technology for structural health monitoring.

Damage classification in structural health monitoring using principal component analysis and self-organizing maps

Abstract: SUMMARY Damage classification is an important issue within SHM going beyond the purely damage detection. This paper proposes a data-driven statistical approach for damage classification, which is constructed over a distributed piezoelectric active sensor network for excitation and measurement of vibrational structural responses. At different phases, a single piezoelectric transducer is used as actuator, and the others are used as sensors. An initial baseline model for each phase for the healthy structure is built by applying PCA to the data collected in several experiments. In addition, same experiments are performed with the structure in different states (damaged or not), and the dynamic responses are projected into the different baseline PCA models for each actuator. Some of these projections and damage indices are used as input features for a self-organizing map, which is properly trained and validated to build a pattern baseline model. This baseline is further used as a reference for blind diagnosis tests of structures. Both training/validation and diagnosis modes are experimentally assessed using an aluminum plate instrumented with four piezoelectric transducers. Damages are simulated by adding mass at different positions. Results show that all these damages are successfully classified both in the baseline pattern model and in further diagnosis tests. Copyright © 2012 John Wiley & Sons, Ltd.

Robust Flexible Capacitive Surface Sensor for Structural Health Monitoring Applications

Abstract: Early detection of possible defects in civil infrastructure is vital to ensuring timely maintenance and extending structure life expectancy. The authors recently proposed a novel method for structural health monitoring based on soft capacitors. The sensor consisted of an off-the-shelf flexible capacitor that could be easily deployed over large surfaces, the main advantages being cost-effectiveness, easy installation, and allowing simple signal processing. In this paper, a capacitive sensor with tailored mechanical and electrical properties is presented, resulting in greatly improved robustness while retaining measurement sensitivity. The sensor is fabricated from a thermoplastic elastomer mixed with titanium dioxide and sandwiched between conductive composite electrodes. Experimental verifications conducted on wood and concrete specimens demonstrate the improved robustness, as well as the ability of the sensing method to diagnose and locate strain.

Model-based imaging of damage with Lamb waves via sparse reconstruction.

Abstract: Ultrasonic guided waves are gaining acceptance for structural health monitoring and nondestructive evaluation of plate-like structures. One configuration of interest is a spatially distributed array of fixed piezoelectric devices. Typical operation consists of recording signals from all transmit-receive pairs and subtracting pre-recorded baselines to detect changes, possibly due to damage or other effects. While techniques such as delay-and-sum imaging as applied to differential signals are both simple and capable of detecting flaws, their performance is limited, particularly when there are multiple damage sites. Here a very different approach to imaging is considered that exploits the expected sparsity of structural damage; i.e., the structure is mostly damage-free. Differential signals are decomposed into a sparse linear combination of location-based components, which are pre-computed from a simple propagation model. The sparse reconstruction techniques of basis pursuit denoising and orthogonal matching pursuit are applied to achieve this decomposition, and a hybrid reconstruction method is also proposed and evaluated. Noisy simulated data and experimental data recorded on an aluminum plate with artificial damage are considered. Results demonstrate the efficacy of all three methods by producing very sparse indications of damage at the correct locations even in the presence of model mismatch and significant noise.

Toward Data-Driven Structural Health Monitoring: Application of Machine Learning and Signal Processing to Damage Detection

Abstract: A multilayer data-driven framework for robust structural health monitoring based on a comprehensive application of machine learning and signal processing techniques is introduced. This paper focuses on demonstrating the effectiveness of the framework for damage detection in a steel pipe under environmental and operational variations. The pipe was instrumented with piezoelectric wafers that can generate and sense ultrasonic waves. Damage was simulated physically by a mass scatterer grease-coupled to the surface of the pipe. Benign variations included variable internal air pressure and ambient temperature over time. Ultrasonic measurements were taken on three different days with the scatterer placed at different locations on the pipe. The wave patterns are complex and difficult to interpret, and it is even more difficult to differentiate the changes produced by the scatterer from the changes produced by benign variations. The sensed data were characterized by 365 features extracted from a variety of...

Recent Developments on Wireless Sensor Networks Technology for Bridge Health Monitoring

Abstract: Structural health monitoring (SHM) systems have shown great potential to sense the responses of a bridge system, diagnose the current structural conditions, predict the expected future performance, provide information for maintenance, and validate design hypotheses. Wireless sensor networks (WSNs) that have the benefits of reducing implementation costs of SHM systems as well as improving data processing efficiency become an attractive alternative to traditional tethered sensor systems. This paper introduces recent technology developments in the field of bridge health monitoring using WSNs. As a special application of WSNs, the requirements and characteristics of WSNs when used for bridge health monitoring are firstly briefly discussed. Then, the state of the art in WSNs-based bridge health monitoring systems is reviewed including wireless sensor, network topology, data processing technology, power management, and time synchronization. Following that, the performance validations and applications of WSNs in bridge health monitoring through scale models and field deployment are presented. Finally, some existing problems and promising research efforts for promoting applications of WSNs technology in bridge health monitoring throughout the world are explored.

Wind Effects on Cable-Supported Bridges

Abstract: This book provides readers with an overview of the effects of wind on cable-supported bridges. Topics include: types of wind storms and types of cable-supported bridges; profiles of winds in atmospheric boundary layer; mean wind load; vibration and vibration control; cable vibrations; wind-road-vehicle-bridge interactions; computational fluid dynamics (CFD) simulations; wind tunnel studies and simulation of typhoon wind; structural health monitoring and fatigue analysis; and buffeting response. Two bridges, Stonecutters cable-stayed bridge and Tsing Ma suspension bridge, serve as case studies to illustrate subject matter.

New trends in structural health monitoring

Abstract: A motivation for structural health monitoring.- Structural health monitoring of aircraft structures.- Vibration-based damage diagnosis and monitoring of external loads.- Statistical time series methods for vibration based structural health monitoring.- Fiber optic sensors.- Damage localisation using elastic waves propagation methods experimental techniques.- Application for wind turbine blades.

Soft Elastomeric Capacitor Network for Strain Sensing Over Large Surfaces

Abstract: Field applications of existing sensing solutions to structural health monitoring (SHM) of civil structures are limited. This is due to economical and/or technical challenges in deploying existing sensing solutions to monitor geometrically large systems. To realize the full potential of SHM solutions, it is imperative to develop scalable cost-effective sensing strategies. We present a novel sensor network specifically designed for strain sensing over large surfaces. The network consists of soft elastomeric capacitors (SECs) deployed in an array form. Each SEC acts as a surface strain gage transducing local strain into changes in capacitance. Results show that the sensor network can track strain history above levels of 25 μe using an inexpensive off-the-shelf data acquisition system. Tests at large strains show that the sensor's sensitivity is almost linear over strain levels of 0-20%. We demonstrate that it is possible to reconstruct deflection shapes for a simply supported beam subjected to quasi-static loads, with accuracy comparable to resistive strain gages.

Neutral axis as damage sensitive feature

Abstract: Structural health monitoring (SHM) is the process of continuously or periodically measuring structural parameters and the transformation of the collected data into information on real structural conditions. The centroid of stiffness is a universal parameter and its position in a cross-section can be evaluated for any load-carrying beam structure as the position of the neutral axis under conveniently chosen loads. Thus, a change in the position of the neutral axis within a cross-section can indicate a change in the position of the centroid of stiffness, i.e., unusual structural behaviors. This paper proposes a novel monitoring method based on deterministic and probabilistic determination of the position of the neutral axis under conveniently chosen conditions. Therefore, the method proposed in this paper is potentially applicable to a large variety of beam-like structures. Data from two existing structures were used to validate the method and assess its performance: Streicker Bridge at Princeton University and the US202/NJ23 highway overpass in Wayne, NJ. The results show that the neutral axis location is varying even when damage is not present. Reasons for this variation are determined and the accuracy in the evaluation assessed. This paper concludes that the position of the neutral axis can be evaluated with sufficient accuracy using static and dynamic strain measurements performed on appropriate time-scales and indicates its potential to be used as a damage sensitive feature.

A Review of Passive Wireless Sensors for Structural Health Monitoring

Abstract: Wireless sensors for Structural Health Monitoring (SHM) is an emerging new technology that promises to overcome many disadvantages pertinent to conventional, wired sensors. The broad field of SHM has experienced significant growth over the past two decades, with several notable developments in the area of sensors such as piezoelectric sensors and optical fibre sensors. Although significant improvements have been made on damage monitoring techniques using these smart sensors, wiring remains a significant challenge to the practical implementation of these technologies. Wireless SHM has recently attracted the attention of researchers towards un-powered and more effective passive wireless sensors. This article presents a review of some of the underlying technologies in the field of wireless sensors for SHM - with a focus on the research progress towards the development of simple, powerless, yet effective and robust wireless damage detection sensors. This review examines the development of passive wireless sensors in two different categories: (1) use of oscillating circuits with the help of inductors, capacitors and resistors for damage detection; and (2) use of antennas, Radio Frequency Identification (RFID) tags and metamaterial resonators as strain sensors for wireless damage monitoring. An assessment of these electromagnetic techniques is presented and the key issues involved in their respective design configurations are discussed.

SmartSync: An Integrated Real-Time Structural Health Monitoring and Structural Identification System for Tall Buildings

Abstract: This study introduces a unique prototype system for structural health monitoring (SHM), SmartSync, which uses the building’s existing Internet backbone as a system of virtual instrumentation cables to permit modular and largely plug-and-play deployments. Within this framework, data streams from distributed heterogeneous sensors are pushed through network interfaces in real time and seamlessly synchronized and aggregated by a centralized server, which performs basic data acquisition, event triggering, and database management while also providing an interface for data visualization and analysis that can be securely accessed. The system enables a scalable approach to monitoring tall and complex structures that can readily interface a variety of sensors and data formats (analog and digital) and can even accommodate variable sampling rates. This study overviews the SmartSync system, its installation/operation in the world’s tallest building, Burj Khalifa, and proof-of-concept in triggering under dual e...

Spatial Sensing Using Electrical Impedance Tomography

Abstract: The need for structural health monitoring has become critical due to aging infrastructures, legacy airplanes, and continuous development of new structural technologies. Based on an updated structural design, there is a need for new structural health monitoring paradigms that can sense the presence, location, and severity with a single measurement. This paper focuses on the first step of this paradigm, consisting of applying a sprayed conductive carbon nanotube-polymer film upon glass fiber-reinforced polymer composite substrates. Electrical impedance tomography is performed to measure changes in conductivity within the conductive films because of damage. Simulated damage is a method for validation of this approach. Finally, electrical impedance tomography measurements are taken while the conductive films are subjected to tensile and compressive strain states. This demonstrates the ability of electrical impedance tomography for not only damage detection, but active structural monitoring as well. This paper acts as a first step toward moving the structural health monitoring paradigm toward large-scale deployable spatial sensing.

Particle filter scheme with mutation for the estimation of time-invariant parameters in structural health monitoring applications

Abstract: SUMMARY In this study, a novel method is presented for non-linear, non-Gaussian online state and parameter identification, developed for use in structural health monitoring (SHM) problems. The algorithm consists of a particle filter (PF) that combines the use of the standard PF with mutation operators. The algorithm aims at alleviating the sample impoverishment problem, which is a well-known limitation of the standard PF, yielding it inefficient for demanding non-linear identification problems. To overcome this hurdle, we introduce here an alternative approach, influenced by the principles of evolutionary computation. After the standard PF steps are performed to a point where the sample diversity drops below some threshold, the unfit particles are replaced by either the fittest particles or the current weighted estimate of the state. Next, the time-invariant components of the particles are mutated under some mutation probability, and the new sample is then propagated to the next time step. This process is well suited for joint state and parameter estimation problems, as is usually the case in SHM techniques. As a result, the loss of diversity associated with the standard PF is overcome, and the new PF with mutation is shown to outperform the standard PF and the unscented Kalman filter for the case of high process noise. The method is validated through an established benchmark problem found in the literature, lying outside of the structural identification concept, and a previously referenced 3DOF structural system with hysteresis elaborating the SHM aspect. Copyright © 2012 John Wiley & Sons, Ltd.

Development of a FBG based distributed strain sensor system for wind turbine structural health monitoring

Abstract: The development of a fiber Bragg grating (FBG) based distributed strain sensor system for real time structural health monitoring of a wind turbine rotor and its validation under a laboratory scale test setup is discussed in this paper. A 1 kW, 1.6 m diameter rotor, horizontal axis wind turbine with three instrumented blades is used in this study. The sensor system consists of strain sensors, surface mounted at various locations on the blade. At first the sensors are calibrated under static loading conditions to validate the FBG mounting and the proposed data collection techniques. Then, the capability of the sensor system coupled with the operational modal analysis (OMA) methods to capture natural frequencies and corresponding mode shapes in terms of distributed strains are validated under various non-rotating dynamic loading conditions. Finally, the sensor system is tested under rotating conditions using the wind flow from an open-jet wind tunnel, for both a baseline wind turbine and a wind turbine with a structurally modified blade. The blade was modified by attaching a lumped mass at the blade tip simulating structural damage or ice accretion. The dynamic characteristics of the baseline (healthy) blade and modified (altered) blade are compared to validate the sensor system's ability for real time structural health monitoring of the rotor.