This PDF file contains the front matter associated with SPIE Proceedings Volume 7292, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing

A class of low-cost, wireless sensor has been developed at the University of Texas at Austin to monitor the performance of reinforced and prestressed concrete members in civil infrastructure systems. The sensors are designed to be interrogated in a wireless manner as part of a routine inspection. The sensors do not require batteries or connections to external power supplies. As such, the sensors are intended to be maintenance free over the service life of the infrastructure system. Research efforts to date have focused on detecting the onset of corrosion. It is envisioned that the sensors would be attached to the reinforcement cages before placement of the concrete. The results of long-term exposure tests will be used in this presentation to demonstrate the potential and reliability of the resonant sensors.

The focus of this paper is on real-time damage detection in reinforcing fiber bundles and composites using high-speed photography and image analysis. In other words, the end of a reinforcing fiber bundle or composite is imaged and the sequence of fiber fracture is monitored using a high-speed camera. These studies were undertaken using as-received and silane-treated custom-made optical fibers of around 12 μm diameter and E-glass fibers of 15 (±3) μm diameter. The first part of this paper reports on the techniques that were developed to produce void-free test specimens and the procedures used for imaging the end of the fiber bundle and composite during tensile loading. Evanescent wave spectroscopy was used to study the effect of silane treatment on the cross-linking kinetics of an epoxy/amine resin system. Conventional piezo-electric acoustic emission (AE) transducers were used to monitor the acoustic events occurring during the tensile test. The signals from the AE transducers were used to trigger the high-speed camera. The second part of this paper presents details of the image analysis routines that were developed to track the light intensity transmitted through individual fibers during tensile loading. Good correlation was observed between the transmitted light intensity and the AE signals.

Elevated civil structure systems, such as communication towers and water tanks, are prone to higher mode vibration and earthquake induced damages. To mitigate damages, however, the structures are retrofitted with conventional (e.g. steel casing) and/or emerging techniques (e.g. smart structures). Smart structure entails integration of system behavior, control design and actuators. In this paper, utility of smart structures is illustrated through an elevated water tank concrete column. The concrete column is modeled as a continuous system, using the Lagrangian formulation, and linear quadratic regulator (LQR) is used for the control system, and shape memory alloy (SMA) for actuation. The water tank is excited with the 1940 El-Centro earthquake record. A sensitivity analysis is performed on the controller error and penalizing constants, as well as actuator location and angle of the connection. The four control variables that can be analyzed for the controller are: R_r, Q_r, R_e, and Q_e, which are the control penalty, error penalty, measurement noise and process noise, respectively. The connection height on the beam and angle of the actuator is also analyzed for optimal performance. From the sensitivity analysis, the most efficient controller configuration is identified for further analysis of the structure. Optimal actuator configuration can be found based on the reduction of displacement versus the amount of energy used. It has been shown that using the SMA, the seismic demand on the concrete column is reduced using the SMA.

In this study, taking advantage of carbon nano-fiber paper's (CNP) small and thin size, high conductivity, rapid increasing temperature in low voltage, higher steady state temperature, electrical and heat, it found out a way that place argentine glue electrode on the CNP's surface and use a kind of transmitting-heat glue fixed thermal couple for testing the temperature change of CNP following by different voltage in room temperature and adiabatic circumstance. The electrode attachment method on the CNP developed. Experimental validation studies have verified that the CNP exhibit highly electrical and heat property and develop a new self-heating concrete using CNP.

Globally, civil infrastructures are deteriorating at an alarming rate caused by overuse, overloading, aging, damage or failure due to natural or man-made hazards. With such a vast network of deteriorating infrastructure, there is a growing interest in continuous monitoring technologies. In order to provide a true distributed sensor and control system for civil structures, we are developing a Structural Nervous System that mimics key attributes of a human nervous system. This nervous system is made up of building blocks that are designed based on mechanoreceptors as a fundamentally new approach for the development of a structural health monitoring and diagnostic system that utilizes the recently developed piezo-fibers capable of sensing and actuation. In particular, our research has been focused on producing a sensory nervous system for civil structures by using piezo-fibers as sensory receptors, nerve fibers, neuronal pools, and spinocervical tract to the nodal and central processing units. This paper presents up to date results of our research, including the design and analysis of the structural nervous system.

This paper addresses the issue of intermittent data loss during transmission of wireless network sensors and the application of the reconstruction signal for damage detection with the damage locating vector (DLV) method. The algorithm makes use of frequencies which contribute significant amount of energy in the signal based on Fourier transform. As the amplitudes are uncertain due to lost data, the Fourier amplitudes are estimated based on least-square fit of only the measured portions of the signal. The lost portions are reconstructed through inverse Fourier transform. The procedure is iterated until the discrepancy between estimated lost portions of two consecutive iterations is below a set threshold. This threshold and the power spectral threshold to demarcate the significant frequencies are selected based on results from numerically simulated signals. The reconstructed signals are used with the DLV method for damage detection to investigate the practicality of this procedure. A cantilever truss structure with a pre-stressed cable was monitored using six wireless sensors. The pre-stressed cable was cut mid-way during random load application and data collection. The results obtained support the use of the reconstructed signal within the framework of the DLV method.

Economic and reliable online health monitoring strategies are very essential for safe operation of civil, mechanical and aerospace structures. Furthermore, a PZT sensor self-diagnostic and validation procedure is quite important issue for successful impedance-based SHM system's implementation. This study presents online sensor self-diagnosis technique over structural health monitoring (SHM) strategies using wireless impedance sensor nodes. The wireless impedance sensor node incorporating a miniaturized impedance measuring chip, a microcontroller, and a radio-frequency (RF) telemetry is equipped with the capabilities for temperature-sensing, multiplexing of several sensors, and local data analysis. A temperature effects-free sensor self-diagnosis algorithm is embedded into the sensor node and its feasibility is examined from the experiments monitoring the integrity of each piezoelectric sensor on a wireless sensor network.

Wireless acquisition and transmission system of the sensing signals of the smart cement-based sensors is designed for stress/strain monitoring of concrete structures, the conception and the sensing principle of smart cement-based sensors are introduced, and the design method is presented based on the characters of the signals of smart cement-based sensors and the modularized program. The operating principle of the wireless acquisition and transmission system is especially analyzed, and the hardware circuit and the integration method are discussed in detail. The experiment of the designed wireless acquisition and transmission system is finished, and the experimental results show that the presented wireless acquisition and transmission system of the sensing signals of smart cement-based sensors has such advantages as simple circuit, easy to realize, high reliability, low cost, convenient setting and good practicability, and it is suitable for application in health monitoring of concrete structures.

Lead zirconate titanate (PZT) based impedance transducers have been widely used in structural health monitoring (SHM). They have shown excellent capabilities in evaluation of structural health in terms of damage, deformation and load monitoring. However, in applications of large scale structures or in the case that structure to be monitored is difficult to access, the accuracy of data acquired is compromised due to long cables used to connect sensors and data acquisition equipment. Wireless technology is therefore desired in controlling health monitoring of aerospace, civil and mechanical structures to solve the problem. This paper presents a newly developed wireless impedance analyzer which is applied to monitor structural damage. The reliability of the wireless data acquisition system is analyzed by comparing signatures acquired using wireless impedance analyzer against those obtained from traditional cable connection.

This paper describes an autonomous wireless system that generates road safety alerts, in the form of SMS and email messages, and sends them to motorists subscribed to the service. Drivers who regularly traverse a particular route are the main beneficiaries of the proposed system, which is intended for sparsely populated rural areas, where information available to drivers about road safety, especially bridge conditions, is very limited. At the heart of this system is the SmartBrick, a wireless system for remote structural health monitoring that has been presented in our previous work. Sensors on the SmartBrick network regularly collect data on water level, temperature, strain, and other parameters important to safety of a bridge. This information is stored on the device, and reported to a remote server over the GSM cellular infrastructure. The system generates alerts indicating hazardous road conditions when the data exceeds thresholds that can be remotely changed. The remote server and any number of designated authorities can be notified by email, FTP, and SMS. Drivers can view road conditions and subscribe to SMS and/or email alerts through a web page. The subscription-only form of alert generation has been deliberately selected to mitigate privacy concerns. The proposed system can significantly increase the safety of travel through rural areas. Real-time availability of information to transportation authorities and law enforcement officials facilitates early or proactive reaction to road hazards. Direct notification of drivers further increases the utility of the system in increasing the safety of the traveling public.

Strain analysis due to vibration can provide insight into structural health. An Extrinsic Fabry-Perot Interferometric (EFPI) sensor under vibrational strain generates a non-linear modulated output. Advanced signal processing techniques, to extract important information such as absolute strain, are required to demodulate this non-linear output. Past research has employed Artificial Neural Networks (ANN) and Fast Fourier Transforms (FFT) to demodulate the EFPI sensor for limited conditions. These demodulation systems could only handle variations in absolute value of strain and frequency of actuation during a vibration event. This project uses an ANN approach to extend the demodulation system to include the variation in the damping coefficient of the actuating vibration, in a near real-time vibration scenario. A computer simulation provides training and testing data for the theoretical output of the EFPI sensor to demonstrate the approaches. FFT needed to be performed on a window of the EFPI output data. A small window of observation is obtained, while maintaining low absolute-strain prediction errors, heuristically. Results are obtained and compared from employing different ANN architectures including multi-layered feedforward ANN trained using Backpropagation Neural Network (BPNN), and Generalized Regression Neural Networks (GRNN). A two-layered algorithm fusion system is developed and tested that yields better results.

Image thresholding in the High Resolution Target Movement Monitor (HRTMM) is examined. The HRTMM was developed at the Missouri University of Science and Technology to detect and measure wall movements in underground mines to help reduce fatality and injury rates. The system detects the movement of a target with sub-millimeter accuracy based on the images of one or more laser dots projected on the target and viewed by a high-resolution camera. The relative position of the centroid of the laser dot (determined by software using thresholding concepts) in the images is the key factor in detecting the target movement. Prior versions of the HRTMM set the image threshold based on a manual, visual examination of the images. This work systematically examines the effect of varying threshold on the calculated centroid position and describes an algorithm for determining a threshold setting. First, the thresholding effects on the centroid position are determined for a stationary target. Plots of the centroid positions as a function of varying thresholds are obtained to identify clusters of thresholds for which the centroid position does not change for stationary targets. Second, the target is moved away from the camera in sub-millimeter increments and several images are obtained at each position and analyzed as a function of centroid position, target movement and varying threshold values. With this approach, the HRTMM can accommodate images in batch mode without the need for manual intervention. The capability for the HRTMM to provide automated, continuous monitoring of wall movement is enhanced.

Recently, system augmentation has been combined with nonlinear feedback auxiliary signals to provide sensitivity enhancement in both linear and nonlinear systems. Augmented systems are higher dimensional linear systems that follow trajectories of a nonlinear system one at a time. These augmented systems are subject to a specialized augmented forcing which enforces the augmented system will exactly reproduce the trajectory of the nonlinear system when projected onto the lower dimensional (physical) system. Augmented systems have additional benefits outside of handling nonlinear systems, which makes them more desirable than regular linear systems for sensitivity enhancing control. One of the key advantages of augmented systems is the complete control over the augmented degrees of freedom, and the additional sensor knowledge from the augmented variables. These sensing and actuation features are very useful when only few physical actuators and sensors can be placed. Such restrictions severely limit the usefulness of traditional linear sensitivity enhancing feedback approaches. Another benefit of the augmentation is that the control exerted on the augmented degrees of freedom does not require any physical energy, rather it is just signal processing. In this work, the benefits of system augmentation are explored by using few actuators and sensors. In addition to increased sensitivity for both global and local parameter changes, a study of increasing the sensitivity of local changes, while decreasing the sensitivity of global changes is conducted. Numerical simulations for a linear cantilevered beam with a single piezo-actuator and two sensors are used to validate the approach and discuss the effects of noise.

Matching pursuit (MP) is an adaptive signal decomposition technique and can be applied to process Lamb waves, such as denoising, wave parameter estimation, and feature extraction, for health monitoring applications. This paper explored matching pursuit decomposition using Gaussian and chirplet dictionaries to decompose/approximate Lamb waves and extract wave parameters. While Gaussian dictionary based MP is optimal for decomposing symmetric signals, chirplet dictionary based MP is able to decompose asymmetric signals, e.g., dispersed Lamb wave. The extracted parameter, chirp rate, from the chirplet MP can be used to correlate with two Lamb wave modes, S0 and A₀.

Image segmentation for quantifying damage based on Bayesian updating scheme is proposed for diagnosis and prognosis in structural health monitoring. This scheme enables taking into account the prior information of the state of the structures, such as spatial constraints and image smoothness. Bayes' law is employed to update the segmentation with the spatial constraint described as Markov Random Field and the current observed image acting as a likelihood function. Segmentation results demonstrate that the proposed algorithm holds promise of searching a crack area in the SHM image and focusing on the real damage area by eliminating the pseudo-shadow area. Thus more precise crack estimation can be obtained than the conventional K-means segmentation by shrinking the fuzzy tails which often exist on both sides of the crack tips.

This paper presents a structural health monitoring system for judging structural condition of metallic plates by analyzing ultrasonic waves. Many critical accidents of structures like buildings and aircrafts are caused by small structural errors; cracks and loosened bolts etc. This is a reason why we need to detect little errors at an early stage. Moreover, to improve precision and to reduce cost for damage detection, it is necessary to build and update the database corresponding to environmental change. This study focuses our attention on the automatable structures, specifically, applying artificial immune system (AIS) algorithm to determine the structure safe or not. The AIS is a novelty computational detection algorithm inspired from biological defense system, which discriminates between self and non-self to reject nonself cells. Here, self is defined to be normal data patterns and non-self is abnormal data patterns. Furthermore, it is not only pattern recognition but also it has a storage function. In this study, a number of impact resistance experiments of duralumin plates, with normal structural condition and abnormal structural condition, are examined and ultrasonic waves are acquired by AE sensors on the surface of the aluminum plates. By accumulating several feature vectors of ultrasonic waves, a judging method, which can determine an abnormal wave as nonself, inspired from immune system is created. The results of the experiments show good performance of this method.

The use of coupled Rayleigh-like waves in aluminum plates has been investigated with a view towards applications for the non-destructive inspection of aircraft structures. Such waves can be generated using standard Rayleigh wave transducers at frequencies, so that the Rayleigh wavelength corresponds to approximately half the plate thickness. The Rayleigh-like wave, which can be interpreted as the superposition of the fundamental Lamb modes, transfers energy between both surfaces with a characteristic distance called the beatlength. Experimentally the reflected wave can be measured using either standard pulse-echo equipment or a laser vibrometer. The energy transfer between the plate surfaces results in a good sensitivity for the detection of small defects on both surfaces. Using a combination of evaluation in the time and frequency domain, the defect location and damaged plate side can be accurately determined. Due to the beating phenomenon, the Rayleigh-like wave can propagate past regions with surface defects or features. This allows for the remote detection of defects in areas where access is restricted by structural features, such as stiffeners and stringers. This has been shown experimentally and verified from Finite Difference simulations.

Guided waves generated and measured using surface-bonded Lead Zirconate Titanate (PZT) transducers have been widely used for structural health monitoring (SHM) and nondestructive testing (NDT) applications. For selective actuation and sensing of Lamb wave modes, the sizes of the transducers and the driving frequency of the input waveform should be tuned. For this purpose, a theoretical Lamb wave tuning curve (LWTC) of a specific transducer size is generally obtained. Here, the LWTC plots each Lamb wave mode' amplitude as a function of the driving frequency. However, a discrepancy between experimental and existing theoretical LWTCs has been observed due to little consideration of the bonding layer and the energy distribution between Lamb wave modes. In this study, calibration techniques for the theoretical LWTCs are proposed. First, a theoretical LWTC is developed when circular shape of PZTs is used for both Lamb wave excitation and sensing. Then, the LWTC is calibrated by estimating the effective PZT size with PZT admittance measurement. Finally, the energy distributions among symmetric and antisymmetric modes are taken into account for better prediction of the relative amplitudes between Lamb wave modes. The effectiveness of the proposed calibration techniques is examined through numerical simulations and experimental estimation of the LWTC using the circular PZT transducers instrumented on an aluminum plate.

This paper presents spectral element formulation which simulates high frequency dynamic responses generated by PZT transducers bonded on a thin plate. A two layer beam model under 2-D plane strain condition is developed to represent fundamental Lamb wave modes induced by a piezoelectric (PZT) layer rigidly bonded on a base plate. Mindlin- Herrmann and Timoshenko beam theories are employed to represent the first symmetric and anti-symmetric Lamb wave modes on a base plate, respectively. The Euler-Bernoulli beam theory and 1-D linear piezoelectricity are used to model the electro-mechanical behavior of a PZT layer. The equations of motions of a two layer beam model are derived through Hamilton's principle. The necessary boundary conditions associated with the electro-mechanical properties of a PZT layer are formulated in the context of dual functions of a PZT layer as an actuator and a sensor. General spectral shape functions of response field and the associated boundary conditions are obtained through equations of motion transformed into frequency domain. Detailed spectral element formulation for composing the dynamic stiffness matrix of a two layer beam model is presented as well. The validity of the proposed spectral element is demonstrated through a numerical example.

Propagation of torsional elastic waves in the clad core is addressed in this paper. The shear velocity of the core is slightly smaller than that in the cladding. Core with cladding of different finite thickness and infinite thickness is investigated. Two types of modes, guided and leaky modes are examined with the discussion of motion in waveguide. Phase, group, and energy velocities, cutoff frequencies are analyzed and the results of first three modes are presented. The change of dispersion curves due to variation of thickness of cladding is discussed and it is found that when the thickness increases the results of finite clad core will approach those of infinite clad core in guided mode, but not in leaky mode. Below cutoff frequencies the wavenumber becomes complex in infinite clad core, while it is pure imaginary in finite clad cores. The group and energy velocity are presented and in leaky mode the group velocity becomes abnormal, while the energy velocity is physically meaningful.

This paper reports a fundamental study of the coupling between highly nonlinear waves, generated in a one dimensional granular chain of particles, with linear elastic media, for the development of a new Non Destructive Evaluation and Structural Health Monitoring (NDE/SHM) paradigm. We design and use novel acoustic actuators to excite compact highly nonlinear solitary waves in a one-dimensional linear elastic rod and investigate the pulse propagation across the interface. To model the actuator and rod system we use Finite Element Analysis (Abaqus) and obtain excellent agreement between the experimental observations and the numerical results. We also study the response of the system to the presence of defects (cracks) in the steel rod, by comparing the wave propagation properties in pristine and cracked test objects. The obtained results encourage the use of highly nonlinear waves as an effective tool for developing a new, viable NDE/SHM method.

In this paper, we present our progress on developing Sonic Infrared (IR) Imaging for structural health monitoring on steel structures. Sonic IR imaging is a fast, wide-area novel imaging NDE/SHM technique. Ultrasonic excitation was used to stimulate heating in defects, combining with Infrared Imaging to identify defects in structures. The whole process takes only about a second. We have been working on some steel specimens used in some typical steel structures. Actual heating patterns are extracted from the IR images and the actual temperature changes are mapped out. Theoretical computing is also carried out to calculate the heating pattern in the specimens with the experimental results as benchmarks.

We present several findings related to acoustic emission detection using a MEMS sensor. The MEMS sensor is a capacitive resonant transducer, fabricated in the PolyMUMPs process, with a resonant frequency near 160 kHz. In this paper, the design, initial characterization, amplification electronics, and packaging of the sensor system are reviewed. We present results from an experiment that compares the MEMS sensor system to a commercial PZT sensor by comparing the response of each sensor to a pencil lead break on a plate. In addition, we describe the noise characterization of the MEMS sensor system, comparing the predicted noise voltage to the measured value. This analysis reveals that the electronic noise from the amplifier is significantly greater than the noise from the sensor, suggesting that an amplifier with less noise would increase the sensitivity of the MEMS sensor system. We describe the design of a new, transimpedance amplifier and its noise characterization, showing the new amplifier design has less noise than the old design. The experiment comparing the commercial PZT sensor and the MEMS sensor system is repeated using the new amplifier, and we present results showing an increase in sensitivity of the MEMS sensor system. Finally, we present results from an experiment comparing the ability of the commercial PZT sensor and the MEMS sensor system with the new amplifier to detect pencil lead breaks performed a large distance from each sensor.

Experimental studies were performed using high-fidelity broadband Glaser-NIST conical transducers to quantify stress waves produced by the elastic collision of a tiny ball and a massive plate. These sensors are sensitive to surface-normal displacements down to picometers in amplitude, in a frequency range of 20 kHz to over 1 MHz. Both the collision and the resulting transient elastic waves are modeled with the finite element program ABAQUS and described theoretically through a marriage of the Hertz theory of contact and a full elastodynamic Green's function found using generalized ray theory. The calculated displacements were compared to those measured through the Glaser-NIST sensors.

The installation of a structural monitoring system on a medium- to large-span bridge can be a challenging undertaking due to high system costs and time consuming installations. However, these historical challenges can be eliminated by using wireless sensors as the primary building block of a structural monitoring system. Wireless sensors are low-cost data acquisition nodes that utilize wireless communication to transfer data from the sensor to the data repository. Another advantageous characteristic of wireless sensors is their ability to be easily removed and reinstalled in another sensor location on the same structure; this installation modularity is highlighted in this study. Wireless sensor nodes designed for structural monitoring applications are installed on the 180 m long Yeondae Bridge (Korea) to measure the dynamic response of the bridge to controlled truck loading. To attain a high nodal density with a small number (20) of wireless sensors, the wireless sensor network is installed three times with each installation concentrating sensors in one portion of the bridge. Using forced and free vibration response data from the three installations, the modal properties of the bridge are accurately identified. Intentional nodal overlapping of the three different sensor installations allows mode shapes from each installation to be stitched together into global mode shapes. Specifically, modal properties of the Yeondae Bridge are derived off-line using frequency domain decomposition (FDD) modal analysis methods.

This paper describes the design and testing of a wireless sensor network based on the SmartBrick, a low-power SHM device developed by the authors. The SmartBrick serves as the base station for the network, which utilizes additional sensor nodes to periodically evaluate the condition of the structure. Each node measures vibration, tilt, humidity, and strain, and is designed for easy interfacing of virtually any other analog or digital sensor. The sensor nodes use Zigbee to transmit their data to the base station, which in turn uses the GSM cellular phone network to provide long-range communication and support for remote control. The system has been designed from the outset to minimize power consumption, and is projected to operate autonomously for up to four years without any on-site maintenance, due largely to the minimal power consumption and rugged design. Remote calibration over the GSM network further increases the autonomy of the system. Most importantly, it can perform all requisite actions with no cables for power or communication. The focus of this paper is the addition of short-range wireless communication over Zigbee. This allows a network of several devices to be used to monitor larger structures, such as multi-span bridges. Results of laboratory testing are included and discussed in detail, demonstrating the unique capabilities of the proposed SHM system.

Understanding the dynamic behavior of civil engineering structures is important to adequately resolve problems related to structural vibration. The dynamic properties of a structure are commonly obtained by conducting a modal survey that can be used for model updating, design verification, and improvement of serviceability. However, particularly for largescale civil structures, modal surveys using traditional wired sensor systems can be quite challenging to carry out due to difficulties in cabling, high equipment cost, and long setup time. Smart sensor networks (SSN) offer a unique opportunity to overcome such difficulties. Recent advances in sensor technology have realized low-cost smart sensors with on-board computation and wireless communication capabilities, making deployment of a dense array of sensors on large civil structures both feasible and economical. However, as opposed to wired sensor networks in which centralized data acquisition and processing are a common practice, the SSN requires decentralized algorithms due to the limitation associated with wireless communication; to date such algorithms are limited. This paper proposes a new decentralized hierarchical approach for modal analysis that reliably determines the global modal properties and can be implemented on a network of smart sensors. The efficacy of the proposed approach is demonstrated through several numerical examples.

Acceleration and impedance signatures extracted from a structure are appealing features for a prompt diagnosis on structural condition since those are relatively simple to measure and utilize. However, the feasibility of using them for damage monitoring is limited when their changes go undisclosed due to uncertain temperature conditions, particularly for large structures. In this study, temperature effect on hybrid damage monitoring of prestress concrete (PSC) girder bridges is presented. In order to achieve the objective, the following approaches are implemented. Firstly, a hybrid monitoring algorithm using acceleration and impedance signatures is proposed. The hybrid monitoring algorithm mainly consists of three sequential phases: 1) the global occurrence of damage is alarmed by monitoring changes in acceleration features, 2) the type of damage is identified as either prestress-loss or flexural stiffness-loss by identifying patterns of impedance features, 3) the location and the extent of damage are estimated from damage index method using natural frequency and mode shape changes. Secondly, changes in acceleration and impedance signatures were investigated under various temperature conditions on a laboratory-scaled PSC girder model. Then the relationship between temperatures and those signatures is analyzed to estimate and a set of empirical correlations that will be utilized for the damage alarming and classification of PSC girder bridges. Finally, the feasibility of the proposed algorithm is evaluated by using a lab-scaled PSC girder bridge for which acceleration and impedance signatures were measured for several damage scenarios under uncertain temperature conditions.

A glulam beam retired from the field and without visible indications of wood decay was used. Towards detection and assessing wood decay, X-ray computer tomography and ultrasonic measurements were carried out. It was observed that decrease in mass density with increasing levels of wood decay affects x-rays attenuation and allows radioscopy to detect and assess wood decay. To detect and assess decay when only one lateral side of the beam is available, a modified impulse-echo was developed. The modified impulse-echo approach is based on observing the dynamic response of the glulam beams to the drop of a steel sphere onto a steel plate coupled to the glulam beam lamina. It was observed that monitoring certain frequency bands allows detection and assessment of wood decay. The selection of these frequency bands requires knowledge of the nominal beam transverse dimensions. Because of the high ultrasonic material attenuation values of decayed wood as compared with those of sound wood, the area under the power spectral density in these frequency bands is smaller in regions of decayed wood. Results show that results from both X-ray computer tomography and impulse-echo measurements are consistent with each other and can be used to detect and assess wood decay in structural lumber.

An acoustic emission (AE) approach to evaluate low temperature cracking susceptibility of asphalt binders is presented. Thin films of asphalt binders were bonded to granite substrates and exposed to temperatures ranging from 15°C to - 50°C. Differential thermal contraction between granite substrates and asphalt binders induces progressively higher thermal stress in the binders resulting in thermal crack formation, which is accompanied by a release of elastic energy in the form of transient waves. Using piezoelectric sensors (Digital Wave, Model B-1025), a four-channel acoustic emission system was used to record the acoustic emission activity during the binder/granite cooling process. Assuming the cracking temperature (Tcr) to be the temperature at which the AE signal energy exceeds a pre-selected threshold energy level, this AE testing approach was found to be sensitive and repeatable for predicting cracking temperatures (Tcr) in four SUPERPAVE core asphalt binders. These AE-based Tcr predictions showed strong correlation (R2 = 0.9) with predictions based on either AASHTO TP1 or MP1A protocols. Unlike TP1 and MP1A protocols, the presented AE approach does not require the use of sophisticated software for predicting thermal stresses, and no assumption is required regarding the testing cooling rate and the binder coefficient of thermal contraction.

We propose a novel approach for optimal actuator and sensor placement for active sensing-based structural health monitoring (SHM). Of particular interest is the optimization of actuator-sensor arrays making use of ultrasonic wave propagation for detecting damage in thin plate-like structures. Using a detection theory framework, we establish the optimum configuration as the one which minimizes Bayes risk. The detector incorporates a statistical model of the active sensing process which accounts for both reflection and attenuation features, implements pulse-echo and pitchcatch actuation schemes, and takes into account line-of-site. The optimization space was searched using a genetic algorithm with a time varying mutation rate. For verification, we densely instrumented a concave-shaped plate and applied artificial, reversible damage to a large number of randomly generated locations, acquiring active sensing data for each location. We then used the algorithm to predict optimal subsets of the dense array. The predicted optimal arrangements proved to be among the top performers when compared to large sets of randomly generated arrangements.

A steel box beam in a monorail application is constructed with an epoxy grout wearing surface, precluding visual inspection of its top flange. This paper describes a sequence of experimental research tasks to develop an ultrasonic system to detect flaws (such as fatigue cracks) in that flange, and the results of a field test to demonstrate system performance. The problem is constrained by the fact that the flange is exposed only along its longitudinal edges, and by the fact that permanent installation of transducers at close spacing was deemed to be impractical. The system chosen for development, after experimental comparison of alternate technologies, features angle-beam ultrasonic transducers with fluid coupling to the flange edge; the emitting transducers create transverse waves that travel diagonally across the width of the flange, where an array of receiving transducers detect flaw reflections and flaw shadows. The system rolls along the box beam, surveying (screening) the top flange for the presence of flaws. In a first research task, conducted on a full-size beam specimen, we compared waves generated from different transducer locations, either the flange edge or the web face, and at different frequency ranges. At relatively low frequencies, such as 100 kHz, we observed Lamb wave modes, and at higher frequency, in the MHz range, we observed nearlylongitudinal waves with trailing pulses. In all cases we observed little attenuation by the wearing surface and little influence of reflection at the web-flange joints. At the conclusion of this task we made the design decision to use edgemounted transducers at relatively high frequency, with correspondingly short wavelength, for best scattering from flaws. In a second research task we conducted experiments at 55% scale on a steel plate, with machined flaws of different size, and detected flaws of target size for the intended application. We then compared the performance of bonded transducers, fluid-coupled transducers, and angle-beam (wedge) transducers; from that comparison we made the design decision to use wedges, which beam the wave to increase the scattering from flaws. We also compared the performance of wired transducers using fluid coupling to that of wireless (inductively coupled) transducers mounted permanently. Although the wireless transducers achieved flaw detection, the necessary spacing (determined experimentally) would have required an impractical number of transducers. Therefore, we made the design decision to use wedge transducers with fluid coupling. In a third research task we developed and tested a rolling system with a water channel for acoustic coupling, including a study of its sensitivity to misalignment, and in a fourth task we devised a data display to create a pattern of reflections or shadows that could be easily interpreted as evidence of a flaw. Finally, we conducted a field test on the full-size system in a region containing bolt holes, which act as a physical simulation of a flaw, and show successful detection of reflections and shadows from those holes.

Critical buildings such as hospitals and police stations must remain functional immediately following a major earthquake event. Due to earthquake effects, they often experience large strains, leading to progressive collapses. Therefore, monitoring and assessing the large strain condition of critical buildings is of paramount importance to post-earthquake responses and evacuations in earthquake-prone regions. In this study, a novel large strain sensor based on the long period fiber grating (LPFG) technology is proposed and developed. CO2 laser induced LPFG sensors are characterized for such mechanical properties as strain sensitivity in extension and flexure, sensor stability, and measurement range. For practical applications, the need for LPFG sensor packaging is identified and verified in laboratory implementations. By introducing various strain transfer mechanisms, the strain sensitivity of LPFG sensors can be customized for different applications at corresponding strain transfer ratios.

Significant progress has been made in recent years on the design and deployment of optical fibre-based sensors to monitor the cross-linking (cure) reactions in thermosetting resins. In the current study, the following sensor designs were used to study cross-linking reactions of an epoxy/amine resin system: (i) intensity-based Fresnel sensors, (ii) extrinsic fibre Fabry-Perot interferometic (EFPI) sensors, (iii) fibre Bragg grating (FBG) sensors and (iv) sensor designs to enable transmission, reflection and evanescent wave spectroscopy. This paper presents a detailed study on a comparison of the above-mentioned techniques for a commercially available epoxy/amine resin system. Conventional Fourier transform infrared spectroscopy was used as the reference method for obtaining quantitative data on the cross-linking kinetics. The shrinkage of the resin during cross-linking was monitored using EFPI and FBG sensors. This paper also discusses the cross-linking data obtained using optical fibre-based evanescent wave spectroscopy.

Sensing techniques based on Optical Fiber Bragg Grating (FBG) has been increasingly applied in civil engineering structures. However, it is still lacking of a reliable FBG based accelerometer for structural vibration measurement. In this study, a novel FBG accelerometer was developed. The developed sensor has high sensitivity for acceleration measurement especially in low frequency range where the natural modes of civil engineering structures are usually concerned. Furthermore, the temperature influence can be self-compensated. This paper described the principle of the sensor and the parameter optimization for improving the sensor's sensitivity in its measurement ranges of magnitude and frequency. A prototype sensor was manufactured; the optimal viscosity of the damping liquid filled in the sensor was selected experimentally. The amplitude-frequency relationship, the sensitivity and the linearity of the sensor were gained through calibration tests. The results of the tests showed that the feasibility of the FBG accelerometer developed are satisfactory for low frequency vibration measurement.

This paper introduces the concept and development of a strain sensing system for structural application based on the properties of photonic crystals. Photonic crystals are artificially created periodic structures, usually produced in the thinfilm form, where optical properties are tailored by a periodicity in the refractive index. The idea of using the crystal as a sensor is based on the observation that a distortion in the crystal structure produces a change in the reflected bandwidth. When a photonic crystal is designed to operate in the visible part of the spectrum, a permanent distortion of the film results in a change in its apparent color. This property makes photonic crystals suitable for permanent monitoring of structural elements, as any critical changes in the strain field can be promptly and easily detected by visual inspection. A simple and low-cost example of photonic crystals consists of opals synthesized by vertical deposition. In this contribution we introduce a target application for the fatigue monitoring of wind turbines, and then provide the reader with some basic information concerning modeling of the crystal architecture and fabrication of these structures. Next we discuss their application to strain measurement, specifying how reflection and transmission properties of the opals have to be designed to satisfy the expected strain response of the sensor. Finally, we present the preliminary results of a laboratory validation carried out on thin films applied to a rubber support.

A nanostructured sensor based on double wall carbon nanotubes (DWNTs) was fabricated and assessed for hydrogen gas detection. DWNT networks were used as an active substrate material evaporated with layers of palladium nanoparticles of three thicknesses 1, 3 and 6 nm. The electrical resistance change of nanosensor with hydrogen gas exposure in compressed air at room temperature was monitored. The nanostructures were characterized using high resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM). Hydrogen concentrations as low as 0.05 vol% (500 ppm) can be detected at room temperature. Sensitivity values as high as 65% and response times of about 3 seconds were obtained. The results indicate that DWNT- based sensors exhibit comparable performance as that for SWNT-based high performance hydrogen sensors, but with potential improvement in mechanical and thermal resistance associated with the double layer structure.

Anodized aluminum oxide (AAO) membranes are fabricated under different anodization potentials in dilute sulfuric acid. Here we report the growth of AAO under 10, 15, 20, and 25V. These AAO membranes consist of nanopores with pore-to-pore distance from 35 to 69 nm. When AAO membranes are kept thin (less than ~500 nm), together with the unreacted aluminum substrate, interference colors are observed. The inference color of the membrane is changed by its thickness and the pore-to-pore distance, which is controlled by the anodization time and voltage, respectively. By using thin film interference model to analyze the UV-Vis reflectance spectra, we can extract the thickness of the membrane. Thus the linear growth of AAO membrane in sulfuric acid with time during the first 15 minutes is validated. Coating poly (styrene sulfonate) (PSS) sodium salt and poly (allylamine hydrochloride) (PAH) layer by layer over the surface of AAO membrane consistently shifts the interference colors. The red shift of the UV-Vis reflectance spectrum is correlated to the number of layers. This color change due to molecular attachment and increasing thickness is a promising method for chemical sensing.

This paper describes the application of a novel actuator/sensor technology for the generation and detection of stress waves in structural materials like concrete. The technology is aimed at developing an innovative NDE scheme based on the generation of highly nonlinear solitary waves (HNSWs). HNSWs are stress waves that can form and travel in highly nonlinear systems (i.e. granular, layered, fibrous or porous materials) with a finite spatial dimension independent on the wave amplitude. Compared to conventional linear waves, the generation of HNSWs does not rely on the use of electronic equipment (such as an arbitrary function generator) and on the response of piezoelectric crystals or other transduction mechanism. The results of using these new actuator/sensors to test concrete slabs are presented and discussed.

This paper presents a biologically inspired sensor network framework for autonomous structural health monitoring (SHM). The presented sensor network framework transforms desirable characteristics and effective defense mechanisms of the natural immune system to wireless sensor networks for SHM. The autonomous structural health monitoring is achieved through an integrated sensor network framework consisting of high computational power sensors, a mobileagent- based sensor network middleware, and artificial immune pattern recognition (AIPR) methodology for structure damage detection and classification. An AIPR-based structure damage classifier (AIPR-SDC) has been developed, which incorporates several novel characteristics of the natural immune system. The performance of the AIPR-SDC has been validated using a benchmark structure proposed by the IASC-ASCE (International Association for Structural Control - American Society of Civil Engineers) SHM Task Group. The validation results show a better classification success rate comparing to some of other classification algorithms. The further study of unsupervised structure damage classification is also conducted by integrating data clustering techniques and the AIPR method.

Damage detection in engine bladed disks is an extremely important task. While current ultrasonic and eddy current damage detection techniques are reliable, they are also expensive in cost and cannot be used for in-situ monitoring. Although global vibration-based damage detection techniques can overcome these challenges, they may not be accurate due to its low sensitivity to damage. On the other hand, for a periodic structure such as the bladed disk, due to its unique dynamic characteristics, there is great potential in utilizing a vibration-response-based concept to effectively and accurately detect damage. The goal of this research is to advance the state-of-the-art of damage detection of bladed disks by exploring a piezoelectric circuitry network design methodology to enhance the structural vibration damage sensitivity, particularly through the introduction of intentional circuitry mistuning. Additionally, this research aims to investigate intentional circuitry mistuning as an alternative to intentional blade mistuning for forced response localization reduction so that a single design configuration can be adapted to both applications. The effectiveness of the network on inherently mistuned bladed disks is explored using Monte Carlo simulations, where promising results are illustrated.

The impedance-based damage detection has been recognized to be sensitive to small-sized damage due to its highfrequency measurement capability. Low-cost impedance measurement circuit has been explored to extract the piezoelectric impedance/admittance curves by using a resistor that is serially connected with the piezoelectric transducer, which enables a self-contained sensor unit. In this research, an innovative impedance-based damage detection scheme is proposed, which combines the key features of the low-cost impedance measurement circuit with those of the piezoelectric circuitry dynamics. In the new scheme, the piezoelectric transducer is integrated with an inductive circuit. The resonant effect of the inductive circuitry can greatly increase the measurement amplitude. Moreover, when the inductance is properly tuned, very significant dynamic interaction between the mechanical structure being monitored and the electrical circuitry will occur. This results in an order-of-magnitude amplification of the admittance change upon the occurrence of damage, which can yield much increased damage detection sensitivity. Extensive numerical and experimental investigations are carried out to demonstrate the new sensing system development.

In this paper, we present a wireless sensing prototype for condition monitoring using acoustic emission signals. It consists of a 4-member microphone array, a 4-channel 16-bit analog-to-digital converter (ADC) and a wireless node. The prototype will serve as a platform for sensor and algorithm developments for gearbox condition monitoring. In the TinyOS operation system, software interfaces are written in the nesC language to link the hardware with high-level programs. The prototype will eventually collect acoustic emission signals from the microphone array, convert them into digital data using the ADC, perform local signal processing and transmit the results to another wireless node or a base station. Two TinyOS programs are also written to test the functionality of the ADC and the wireless nodes. The programs also demonstrate that data collection and transmission for the one-channel case has been accomplished, though the four-channel case is still under development. Preliminary results and analysis are presented in the paper. Future improvements would involve microphone array filtering/denoising, four-channel data transfer, signal processing and decision making algorithms, and a high-level wireless transmission protocol.

This paper presents the numerical simulation and experimental verification of a semi-active cable vibration control system. The finite-element analysis "ABAQUS" is used to design and simulate the dynamic characteristics of a cable structure. The system matrixes 'M', 'C' and 'K' of the simplified cable model is then generated from the finite element model. A 3 kN MR damper, made by Lord co., is connected to the cable to reduce the vibration. Through a systematic performance test and system identification procedure, the modified Bou-Wen model is generated to represent the nonlinear behavior of the MR damper. According to the simplified cable model and MR damper model, the LQG with continuously-optimal control is used to design the semi-active control system. The scaled-down cable structure is design and builds according to the finite-element model in ABAQUS. Suitable mass and cable force are added to make the cable vibration more realistic. A small shaker is designed and mounted onto the cable to generate the excitations with different amplitudes and frequencies. Both passive and semi-active control cases have been tested. Through the numerical simulation and experimental test results, the semi-active cable vibration control system with MR damper can reduce the cable vibration well under different kinds of excitations. This investigation demonstrates the feasibility and capabilities of a cable vibration control system with MR damper.

Modeling and re-analysis techniques are proposed for predicting the dynamic response of complex structures that have suffered damage in one or more of their components. When such damages are present, the model of the healthy structure may no longer capture the system-level response or the loading from the rest of the structure on the damaged components. Hence, novel models that allow for an accurate re-analysis of the response of damaged structures are needed in important applications, including damage detection. Herein, such models are obtained by using a reduced order modeling approach based on component mode synthesis. Because the resonant response of a complex structure is often sensitive to component uncertainties (in geometric parameters such as thickness, material properties such as Young's modulus, etc.), novel parametric reduced order models (PROMs) are developed. In previous work, PROMs have been applied for handling uncertainties in a single substructure. Herein, PROMs are extended to the general case of multiple substructures with uncertain parameters or damage. Two damage cases are considered: severe structural deformation (dents), and cracks. For the first damage case, an approximate method based on static mode compensation (SMC) is used to perform fast re-analysis of the vibration response of the damaged structure. The re-analysis is performed through a range of locations and severity levels of the damage. For selected damage locations and levels, the SMC approximation is compared to full finite element analysis to demonstrate the accuracy and computational time savings for the new method. For the second damage case (cracks), the vibration problem becomes nonlinear due to the intermittent contact of the crack faces. Therefore, to estimate the resonant frequencies for a cracked structure, the bi-linear frequency approximation (BFA) is used for cracks of various lengths. Since BFA is based on linear analyses, it is fast and particularly well suited for implementation with PROMs for structural re-analysis. In contrast, most other nonlinear techniques for predicting the dynamic response are computationally intensive and cumbersome. For validating the proposed PROMs, resonant frequencies predicted using BFA and PROMs are shown to agree very well with results obtained using a much more expensive commercial finite element tool.

In light of the efforts to improve the performance of micromachined gyroscopes, this paper presents an investigation of energy loss mechanisms in a SOI-based tuning-fork gyroscope, since these loss mechanisms dictate the value of the mechanical Quality factor (Q) that has been identified as a critical determinant for achieving high-precision performance. The numerical models of thermoelastic damping (TED) and anchor loss in the tuning-fork gyroscope design are created in a FEM software, ANSYS/Multiphysics, according to a thermal-energy method and a separationand- transfer method, respectively. The calculated results indicate that thermoelastic damping is the dominant loss while anchor loss is negligible for the gyroscope design. In order to validate the created models, an experimental study on the Q of the SOI-based tuning-fork gyroscope is consequently conducted. Comparison between the calculated results and the measured data not only validates the numerical models, but also demonstrates the significant effect of fabrication process on the final achievable Q values of the fabricated gyroscopes.

Smart materials when interact with engineering structures, should have the capability to sense, measure, process, and detect any change in the selected variables (stress, damage) at critical locations. These smart materials can be classified into active and passive depending on the type of the structure, variables to be monitored, and interaction mechanism due to surface bonding or embedment. Some of the prominent smart materials are piezoelectric materials, micro fiber composite, polymers, shape memory alloys, electrostrictive and magnetostrictive materials, electrorheological and magnetorheological fluids and fiber optics. In addition, host structures do have the properties to support or repel the usage of smart materials inside or on it. This paper presents some of the most widely used smart materials and their interaction mechanism for structural health monitoring of engineering structures.

In this paper, a variable camber wing, which comprises a flexible skin, a metal sheet, and a honeycomb structure, is presented. Shape memory polymer (SMP) is selected for the use of flexible skins. Embedded heating wire springs act as the activation system for the SMP. Experimental result shows that the inherent separation does not occur between the heating elements and SMP upon elongation because of elasticity of wire springs. The deformation of SMP skins at different temperature conditions is analyzed in order to establish the relationship between the deformation of the skin and pre-strain applied in the SMP skin. Fibre Bragg Grating (FBG) sensors, with flexibility and small size, are bonded on the surface of the metal sheet to measure the deflection on the some certain points. The relation of the strain on the upper surface of metal sheet and the deflection of the trailing-edge is established to ensure the position of the bonded FBG sensors. The curve shape of the bending metal sheet can be reconstructed using the calibration information.

A key objective of the NASA exploration missions is to explore the Solar System and beyond in an implementation that is safe, sustainable and affordable. One of the major enabling technologies for meeting this objective is the development of effective autonomous sampling systems for robotic in-situ analysis and scientific experiments for life and water detection as well as the potential to conduct materials characterization and mineralogy. Rapid sampling techniques with minimum deterioration of the sample and the potential to capture volatiles have long been an objective of the planetary science community. Tethered penetrator sampling whether the penetrator is driven by gravity [Jones et al. 2006], chemical means [Jones et al. 2006], mechanical springs [Backes et al. 2008] or air guns [Lorenz and Shandera 2000] has the potential to meet this objective. In this paper we present the development of a tethered harpoon sampling and sample handling system operated from an aerial platform for in-situ astrobiological investigations. The harpoon system can be driven into the sample using gravity, pyro, spring or compressed gas mechanisms and is retrieved using a spooling mechanism. The system description and preliminary test results are presented.

Several researchers are actively studying Ionomeric polymer transducers (IPT) as a large strain low voltage Electro- Active Polymer (EAP) actuator. EAPs are devices that do not contain any moving parts leading to a potential large life time. Furthermore, they are light weight and flexible. IPT have the ability to generate bending strains on the order 5% when +2V potential is applied across its thickness. As sensors however, IPTs are proven to be superior compared to any other EAP material when a charge amplifier is used as a signal conditioner. Furthermore, researchers has developed miniature sensors from IPTs that could be flush mounted to a surface and measure shear stresses due to fluid flow at even low Reynolds numbers. Sensor resolution is on the order of 10 mPa enables it to be useful as a wall shear stress sensor for several aero/hydrodynamic and biomedical applications. In this paper a new signal conditioning circuit is designed with superior sensing capabilities compared to the old circuit. In the new circuit the IPT is biased with a small voltage on the order of 5mV to 25 mV. Initial experimental results demonstrated 30% enhancement in signal to noise ratio compared to the old circuit. Furthermore, this circuit enables the use of IPT polymers with larger capacitance compared to the previous circuits. Akle et al. demonstrated that the capacitance of an ionic polymer transducer is proportional to transducer performance. Ionic polymers are generally made of an ion exchange membrane, typically Nafion, coated with a flexible electrode. In this study the Direct Assembly Process (DAP) is used for the fabrication of IPT. The DAP consists of mixing a metal particulate with an ionomer solution and spraying it directly on a diluent saturated ion conducting membrane. The thickness of the electrode is controlled by altering the amount of the ionomer/metal mix sprayed on the membrane. Thicker electrodes provide IPT with a larger capacitance, and hence larger sensitivity is obtained using the new circuit. It was impossible to use the previous signal conditioning circuit for high capacitance sensors. Finally an attempt to model these sensors along with the circuit is provided. By understanding the interaction between the IPT and the signal conditioning circuit we can create devices with even higher sensitivity. The presented circuit will help in modeling and predicting the response of the sensor.

Fatigue cracks initiating at fastener hole locations in metallic structure are among the most common form of airframe damage. Current methods for inspecting airframes for these cracks are manual, whereby inspectors rely on nondestructive inspection equipment or hand-held probes to scan over areas to be monitored. Use of this equipment often demands disassembly of the airframe to search appropriate hole locations for cracks, which elevates the complexity and cost of maintenance inspections. In this study an Additive, Interleaved, Multi-layer Electromagnetic (AIME) sensor was developed and integrated with the shank of a fastener to form a Structural Health Monitoring Fastener, a new technology targeted at insitu detection of fastener hole cracks. The major advantages of the Structural Health Monitoring (SHM) Fastener over other SHM technologies are its installation, which does not require joint layer disassembly, its capability to detect inner layer cracks in a multi-layer joint, and its capability to operate in a continuous monitoring mode. The AIME sensor design, SHM Fastener, and complete SHM system are presented along with experimental results from a series of single-layer and bolted double lap-joint aluminum specimens to validate the capability of these sensors to monitor metallic joints for fastener hole cracks and loads. Fatigue cracks were successfully tracked to over 0.7 inches from the fastener hole in these tests. Sensor output obtained from single-layer fatigue specimens was compared with analytical predictions for fatigue crack growth versus cycle number showing a good correlation in trend between sensor output and predicted crack size.

We present an SHM system integrating both the impedance and the Lamb wave propagation method on a single board, while sharing the same DSP (Digital Signal Processing) processor and the piezoelectric patches. Three functional blocks, such as signal excitation/generation, signal sensing, and data processing, were implemented to incorporate the Lamb wave method into our existing impedance-based SHM system. Both pitch-and-catch and pulse-and-echo schemes were implemented for damage detection and location, respectively. Through synergetic integration of the two methods, our SHM system can detect various types of simulated damages on aluminum plates.

Structural health monitoring (SHM) is an emerging field in which smart materials interrogate structural components to predict failure, expedite needed repairs, and thus increase the useful life of those components. Piezoelectric wafer active sensors (PWAS) have been previously adhesively-bonded to structures and demonstrate the ability to detect and locate cracking, corrosion, and disbonding through use of pitch-catch, pulse-echo, electro/mechanical impedance, and phased array technology. The present research considers structurally-integrated PWAS that can be fabricated directly to the structural substrate using thin-film nano technologies (e.g., pulsed-laser deposition, sputtering, chemical vapor deposition, etc.) Because these novel PWAS are made up of nano layers they are dubbed nano-PWAS. Nano-PWAS research consists of two parts, thin-film fabrication and nano-PWAS construction. The first part is how to fabricate the piezoelectric thin-film on structure materials. In our research, ferroelectric BaTiO3 (BTO) thin films were successfully deposited on structure material Ni and Ti by pulsed laser deposition under the optimal synthesis conditions. Microstructural studies revealed that the as-grown BTO thin films have the nanopillar structures and the good interface structures with no inter-diffusion or reaction. The dielectric and ferroelectric property measurements exhibit that the BTO films have a relatively large dielectric constant, a small dielectric loss, and an extremely large piezoelectric response with a symmetric hysteresis loop. The second part is nano-PWAS construction and how they are related to the active SHM interrogation methods. Nano-PWAS architecture achieved through thin-film deposition technology and its potential application for SHM were discussed here. The research objective is to develop the fabrication and optimum design of thin-film nano-PWAS for structural health monitoring applications.

The stress-strain relationship and phase transformation behavior of shape memory alloy (SMA) in pure shear state are investigated by using Zhou's SMA micromechanical constitutive equation of 3-dimension and Zhou's SMA phase transformation equation of 1-diemsion respectively. Then thermo-mechanical model describing thermo-mechanical behaviors of SMA torque thin-walled tube is established based on the stress-strain relation and phase transformation model of SMA in pure shear state. The relations of torque vs. rotation, recovery rotation vs. temperature and recovery torque vs. temperature of the torque tube are numerically simulated by using the thermo-mechanical model.

This study deals with new generation composite systems which apart from the primary reinforcement at the typical fiber scale (~10 μm) are also reinforced at the nanoscale. This is performed via incorporation of nano-scale additives in typical aerospace matrix systems, such as epoxies. Carbon Nanotubes (CNTs) are ideal candidates as their extremely high aspect ratio and mechanical properties render them advantageous to other nanoscale materials. The result is the significant increase in the damage tolerance of the novel composite systems even at very low CNT loadings. By monitoring the resistance change of the CNT network, information both on the real time deformation state of the composite is obtained as a reversible change in the bulk resistance of the material, and the damage state of the material as an irreversible change in the bulk resistance of the material. The irreversible monotonic increase of the electrical resistance can be related to internal damage in the hybrid composite system and may be used as an index of the remaining lifetime of a structural component.

The purpose of this research is to evaluate three polymer electroding techniques in developing a novel in situ sensor for an RO system using the electrical response of a thin film composite sensor. Electrical impedance spectroscopy (EIS) was used to measure the sensor response when exposed to sodium chloride solutions with concentrations from 0.1 M to 0.8 M in both single and double bath configurations. An insulated carbon grease sensor was mechanically stable while a composite Direct Assembly Process (DAP) sensor was fragile upon hydration. Scanning electron microscopy results from an impregnation-reduction technique showed gold nanoparticles were deposited most effectively when presoaked in a potassium hydroxide solution and on an uncoated membrane; surface resistances remained too high for sensor implementation. Through thickness carbon grease sensors showed a transient response to changes in concentration, and no meaningful concentration sensitivity was noted for the time scales over which EIS measurements were taken. Surface carbon grease electrodes attached to the polyamide thin film were not sensitive to concentration. The impedance spectra indicated the carbon grease sensor was unable to detect changes in concentration in double bath experiments when implemented with the polyamide surface exposed to salt solutions. DAP sensors lacked a consistent response to changes in concentration too. A reverse double bath experiment with the polysulfone layer exposed to a constant concentration exhibited a transient impedance response similar to through thickness carbon grease sensors in a single bath at constant concentration. These results suggest that the microporous polysulfone layer is responsible for sensor response to concentration.

The objective of this study is the application of finite-element based damage detection techniques to identify the damage severity of reinforced concrete structures subject to different intensity level of earthquake excitation. The damage detection procedure consists of two parts: (1) identify the system dynamic characteristics using the system identification technique (subspace identification, SI) from direct input/output measurements, (2) develop damage assessment of structural members (joints) based on the progressive finite element model and large-scale optimization with nonlinear least-square technique. To verify the proposed method, first, four specimens of two-bay one-story reinforced concrete frame and one two-story reinforced frame structure, with the same design detail and same construction material properties, are tested on the shaking table with different intensity level of earthquake excitations. Integrate the Subspace Identification method and the Finite-element based model updating, damage identification of the structures are investigated. The proposed finite-element based damage identification method were found to be a very effective method for damage assessment of frame structure.

We have recently developed a prototype SHM system consisting of smart sensors, database and MATALB servers. In preceding efforts, we demonstrated the usefulness of analyzing and publishing the data on the web. However, the effective data management and automatic analysis had not been provided. In this study, the data model for easy and flexible data management and automatic configuration of the smart sensors are proposed and their feasibility is demonstrated. In addition, an automatic analysis tool based on ARX models is introduced for practical application. The prototype SHM system is in operation for more than two months without any troubles. To incorporate many needs from different stakeholders, we formed a consortium called K-SHM last year at Keio University. At present, 16 companies joined the consortium consisting of 11 construction companies, 3 large design firms, a sensor maker and a system integration company as members. The consortium will continue improving this system for real application.

Fibre Bragg grating (FBG) sensors continue to be used extensively for monitoring strain and temperature in and on engineering materials and structures. Previous researchers have also developed analytical models to predict the loadtransfer characteristics of FBG sensors as a function of applied strain. The general properties of the coating or adhesive that is used to surface-bond the FBG sensor to the substrate has also been modelled using finite element analysis. In this current paper, a technique was developed to surface-mount FBG sensors with a known volume and thickness of adhesive. The substrates used were aluminium dog-bone tensile test specimens. The FBG sensors were tensile tested in a series of ramp-hold sequences until failure. The reflected FBG spectra were recorded using a commercial instrument. Finite element analysis was performed to model the response of the surface-mounted FBG sensors. In the first instance, the effect of the mechanical properties of the adhesive and substrate were modelled. This was followed by modelling the volume of adhesive used to bond the FBG sensor to the substrate. Finally, the predicted values obtained via finite element modelling were correlated to the experimental results. In addition to the FBG sensors, the tensile test specimens were instrumented with surface-mounted electrical resistance strain gauges.

This paper gives insight to the ultrasonic wave propagation in arbitrary cross section waveguides such as a rail. Due to the geometrical complexity of the rail cross section, the analytical solution to the wave propagation in the rail is not feasible. A Semi Analytical Finite Element method is described as an alternative yet still robust approach to get the solution of the problem. The free-vibration solution (unforced) and the forced solution to a laser excitation, are shown for the case of an undamped rail up to a frequency of 500 kHz. The effects of different loading patterns are discussed, while experimental results are provided. A mode selection is performed, in accordance to the sensitivity of each mode to the different types of defect that can occur in a rail.

The performance of reverse path methods applied to identify the underlying linear model of base-isolated structures is investigated. The nonlinear rubber bearings are considered as nonlinear components attached to an underlying linear model. The advantage of reverse path formulation is that it can separate the linearity and nonlinearity of the structure, extract the nonlinearity and identify the underlying linear structure. The difficulty lies in selecting the nonlinearity function of the hysteretic force due to its multi-valued property and path-dependence. In the thesis, the hysteretic force is approximated by the polynomial series of displacement and velocity. The reverse path formulation is solved by Nonlinear Identification through Feedback of Output (NIFO) methods using least-square solution. Numerical simulation is carried out to investigate the identification performance.

Recent collapse of the I-35W bridge in Minneapolis on August 1, 2007 raised public concern enormously regarding the structural safety of highway bridges. However, the maintenance, which is mostly performed by visual inspection, is very expensive and labor intensive process. The structural health monitoring system has been developed to monitor the integrity of those structures effectively. Although the two-dimensional numerical simulation has been widely used for the last decade, the three-dimensional simulation is indispensable for the development of a Lamb wave phased array system. We develop a virtual Lamb wave phased array considering three-dimensional coupled numerical models of metal plates and PZT patch arrays using finite element methods. The optimized geometry and operation techniques are investigated for the focusing of Lamb waves by Lead-Zirconate-titanate (PZT) arrays.

Many bridges, including 90% of the California inventory, are post-tensioned box-girders concrete structures. Prestressing tendons are the main load-carrying components of these and other post-tensioned structures. Despite their criticality, much research is needed to develop and deploy techniques able to provide real-time information on the level of prestress in order to detect dangerous stress losses. In collaboration with Caltrans, UCSD is investigating the combination of ultrasonic guided waves and embedded sensors to provide both prestress level monitoring and defect detection capabilities in concrete-embedded PS tendons. This paper presents a technique based on nonlinear ultrasonic guided waves in the 100 kHz - 2 MHz range for monitoring prestress levels in 7-wire PS tendons. The technique relies on the fact that an axial stress on the tendon generates a proportional radial stress between adjacent wires (interwire stress). In turn, the interwire stress modulates nonlinear effects in ultrasonic wave propagation through both the presence of finite strains and the interwire contact. The nonlinear ultrasonic behavior of the tendon under changing levels of prestress is monitored by tracking higher-order harmonics at (nω) arising under a fundamental guided-wave excitation at (ω). Experimental results will be presented to identify (a) ranges of fundamental excitations at (ω) producing maximum nonlinear response, and (b) optimum lay-out of the transmitting and the receiving transducers within the test tendons. Compared to alternative methods based on linear ultrasonic features, the proposed nonlinear ultrasonic technique appears more sensitive to prestress levels and more robust against changing excitation power at the transmitting transducer or changing transducer/tendon bond conditions.

Recently, a reference-free damage detection technique that does not rely on baseline data has been proposed for plate-like structures by the author's research group. If Lamb waves traveling along a thin plate encounter damage such as crack and corrosion, mode conversions occur. Using the previously developed reference-free technique, it has been shown that the mode conversion due to damage formation can be detected without using baseline data. In this study, the previous technique is further advanced so that it can be applied to structures with complex geometries such as a stiffener and thickness variations. First, the applicability of the proposed technique to a plate with a stiffener is tested. Due to the stiffener in the wave path, mode conversion is produced even in the absence of damage. Next, the effect of the plate thickness variation is investigated. When Lamb waves propagate along a symmetrically tapered section, mode conversion can be also produced. However, due to symmetry of waveguide, converted modes cancel out each other and no special treatment is necessary. On the other hand, non-symmetric thickness variation can cause the mode conversion even in the absence of the defect. Since feature observed from the non-symmetrically tapered plate is the most complex to analyze, this case is highlighted in this study. Furthermore, an instantaneous damage classification method has been developed. Experimental studies as well as numerical simulations are executed to investigate the effectiveness of the proposed technique.

To increase the efficiency of in-situ casting or precast of concrete, determining the optimal time of demolding is very important for concrete suppliers. In the first few hours after mixing, the fresh concrete gradually achieves solid properties with reasonable compressive strength. Due to different type and amount of cementitious materials, concrete additives (e.g. retarders) and curing temperature, different rates of hardening are expected. In addition, some other factors like the quality of the cementitious materials further increase the uncertainty in determining appropriate time for demolding of concrete. Electro-mechanical impedance (EMI) based lead zirconate titanate (PZT) sensors have been used for damage detection and structural identification for various engineering structures. In this work, a reusable PZT sensor for monitoring initial hydration of concrete is developed, where a piece of PZT is bonded to a piece of metal with two bolts tightened inside of the holes drilled in the metal. An impedance analyzer is used to acquire the signature of this reusable sensor. During the concrete casting, the bolts and the bottom surface of the metal is set to penetrate part of the fresh concrete. At different stages of the first 48 hours after casting, the PZT signatures are acquired. A statistical analysis technique is employed to associate the change in concrete strength with the changes in the PZT admittance signatures. The results show that the developed sensor is able to effectively monitor the initial hydration of concrete, and can be detached from the concrete for future use.

Various nondestructive monitoring techniques have been explored and developed for predicting strength gain of concrete. Important issues in the implementation of any nondestructive techniques are practicality and reliability of measurements. Recently, the applicability of electro-mechanical impedance (EMI) sensing technique utilizing piezoelectric materials has been extended to monitoring of concrete strength. This technique shows a strong correlation between resonant frequency shift of the measured EMI spectrum of a surface bonded piezo-impedance transducer and compressive strength of concrete. In the present study, the application of EMI sensing technique for monitoring strength development of concrete was performed using an impedance analyzer. The effect of mix proportion of concrete on the EMI spectrum was investigated.

A lack of safety and the reliability of the existing metallic structure can threaten people's lives today. It is getting stronger to demand to ensure reliable safety in society. Non Destructive Testing(NDT) can support to public safety with finding damaged structure. Eddy Current Testing (ECT) is a one of NDT for metallic or conductive materials. It already plays an important role in very wide field such as airline and power plants for maintenance, ironworks for production. Though ECT is considered as a finished testing method,it has the unwanted property that flaw blur in ECT signal.This defect partly comes from the essential principle of ECT. In order to obtain fine image of flaw, the authors proposed a method with signal processing to reconstruct more finer image of flaw from ECT signal. The method is based on simple relationship that signal are expressed as a convolution of response function and flaw shape. Many obtained results, more fine images of points flaw and both short and long line flaw than images of those ECT signal were reconstructed, show validity of the method for those flaws. Nevertheless its aim was fundamental survey on validation of the method so that tested flaws were limited in shape.In this paper,beyond that limitation, the authors wish to report the results of applications to complex shape flaws that are likely to be found in actual inspection site. The obtained reconstructed images show notable results indicate that the validity is kept even for complex flaw.

This paper presents an easy method of embedding piezoceramic transducer (PZT) and its implementation in electromechanical (EM) impedance based health monitoring of concrete structures. The basic principle used in this monitoring is to record EM admittance signatures acquired from the actuations of PZT transducer in the presence of electric field. Any deviations in these signatures during the monitoring period indicate disturbance/ damage in the structure. The PZT can be either surface bonded or embedded, however the important features of embedding PZT inside the host structure are durability and protection from surface finish, vandalism and environment attacks. The embedment of PZT in the structure is not as simple as surface bonding because there are several issues such as bonding between PZT and host structure. Moreover, it should withstand the curing pressures and temperatures of the host material. This paper is also expected to be useful for monitoring embeddable composite structures.

The technique of structure health monitoring (SHM) has become a reaching hotspot in civil engineering field at present. The successful application of smart materials in this field has greatly promoted the development of the SHM. Among the smart materials, the piezoelectric material has been paid much attention for its good characteristic and low price. The well competitive properties have had a wide application prospect in SHM field. In this paper, the crack monitoring technique for concrete columns using piezoceramic transducers was experimentally developed. In the experiment, the piezoceramic transducers were embedded into two concrete columns under the large and small eccentric compression loads, respectively. The acoustic emission was used for the identification of the crack generation and development. For the detection of the crack level, a wave-based method for the damaged columns was used and the damage level was determined by compare of the health and damage signals. The experimental results show that acoustic emission based on piezoceramic transducers can be used in the crack monitoring of reinforced concrete structure.

Impedance-based structural health monitoring (SHM) technique has been developed using piezo-ceramic (PZT) transducers either by surface bonding or embedding inside the structure to detect damage at the earliest possible stage using signatures. However, this technique requires PZT to be permanently attached to the structures. Furthermore permanent attachment will influence the appearance of the host structure and during replacement of faulty transducer, the use of de bonding tools may spoils the surface and beneath. Hence the present study is aimed to fabricate a portable structure, where PZTs are bonded on it and later the portable structure is attached to the host structure. This portable structure is easy to install during monitoring period and uninstall after recording the monitoring signatures of the host structure. This method protects the surface of the host structure to be monitored and will have same efficiency as that of permanently attached PZTs.

This paper presents recent developments in an extremely compact, wireless impedance sensor node for combined use with both impedance method and low-frequency vibrational data acquisition. The sensor node, referred to as the WID3 (Wireless Impedance Device) integrates several components, including an impedance chip, a microcontroller for local computing, telemetry for wireless data transmission, multiplexers for managing up to seven piezoelectric transducers per node, energy storage mediums, and several triggering options into one package to truly realize a self-contained wireless active-sensor node for SHM applications. Furthermore, we recently extended the capability of this device by implementing low-frequency A/D and D/A converters so that the same device can measure low-frequency vibration data. The WID3 requires less than 60 mW of power to operate and is designed for the mobile-agent based wireless sensing network. The performance of this miniaturized device is compared to our previous results and its capabilities are demonstrated.

This paper presents a method for detecting and locating structural damages in local elements or regions of a structural system by directly utilizing structural vibration measurements. A previously developed damage diagnosis technique is enhanced by including a simplified lumped-mass model, which is equivalent to the complex frame structure. The parameters derived from the simplified lumped-mass model are used in the damage diagnosis algorithm, while the actual dynamic responses measured from the frame structure under seismic excitation are used as the inputs. The dynamic responses measured from different floors can be decoupled by implementing the proposed damage diagnosis algorithm. As a result, damages in the frame structure can be detected and located. Numerical examples of a three-story-one-bay steel frame model and a benchmark-liked four-story-two-bay steel frame model are considered to demonstrate and evaluate the effectiveness of the present method.

Health monitoring of defective beams is achieved through the use of a distributed network of sensors that can map the deflection profile of these beams. The mapped deflection profiles are then used to extract the structural power flow as an effective criterion for identifying the exact location of the defects. In this paper, emphasis is placed on demonstrating the accuracy and the effectiveness of the power flow maps in identifying the location and the extent of small defects. The presented concepts can be easily employed in health monitoring of more complex and critical structures such as aircraft fuselages and bridges where small defects can be detrimental to their safe operation and their locations can not be easily identified by conventional modal identification methods.

The current NASA Decadal mission planning effort has identified Venus as a significant scientific target for a surface in-situ sampling/analyzing mission. The Venus environment represents several extremes including high temperature (460°C), high pressure (~9 MPa), and potentially corrosive (condensed sulfuric acid droplets that adhere to surfaces during entry) environments. This technology challenge requires new rock sampling tools for these extreme conditions. Piezoelectric materials can potentially operate over a wide temperature range. Single crystals, like LiNbO3, have a Curie temperature that is higher than 1000°C and the piezoelectric ceramics Bismuth Titanate higher than 600°C. A study of the feasibility of producing piezoelectric drills that can operate in the temperature range up to 500°C was conducted. The study includes the high temperature properties investigations of engineering materials and piezoelectric ceramics with different formulas and doping. The drilling performances of a prototype Ultrasonic/Sonic Drill/Corer (USDC) using high temperate piezoelectric ceramics and single crystal were tested at temperature up to 500°C. The detailed results of our study and a discussion of the future work on performance improvements are presented in this paper.

Piezoceramic transducers (PZTs) have been successfully employed for electromechanical impedance (EMI) technique based models of structural health monitoring (SHM) in the recent past. In the EMI models, the PZTs are generally surface bonded or embedded inside the host structure, and then subjected to actuation so as to interrogate the structure for the desired frequency range. The interrogation results in the prediction of electro-mechanical (EM) admittance signatures. These EM signatures serve as indicator of the health/integrity of the structure. However to effectively monitor structural health, understanding interaction mechanism of PZT with host structure is essential. Interaction of surface bonded PZT is different from that of an embedded PZT. This paper presents an over view of all the one, two and three dimensional interaction mechanisms considering different actuation of the PZT in the presence of electric field. Additionally it presents the existing single and multiple PZTs and their mathematical relationships.

A hybrid approach involving both analytical computations and measurement data is proposed for designing optimal actuators for piezoelastic structures. The analytical part comprises the linear mathematical structure of models of beams, plates or membranes which are appropriately described by mode shapes and modal paramters, i.e. eigenfrequencies, modal gains and modal damping. Also, the governing differential equation for perfect compensation of external loads due to piezoelectric actuation is applied. The measurement part relies on identification of mode shapes and parameters under an external load using experimental modal analysis. The real-world data is fed into the analyical part with the ultimate goal of achieving a match between the modal gains due to external loading and piezoelectric actuation. The algorithm which can be extended to various mathematical models of piezoelastic structures, is evaluated on a beam structure which is clamped at both ends.

An asymptotically correct analysis is developed for Macro Fiber Composite unit cell using Variational Asymptotic Method (VAM). VAM splits the 3D nonlinear problem into two parts: A 1D nonlinear problem along the length of the fiber and a linear 2D cross-sectional problem. Closed form solutions are obtained for the 2D problem which are in terms of 1D parameters.

In the past years parallel robots demonstrated their capability in applications with high-dynamic trajectories. Smart-structures offer the potential to further increase the productivity of parallel robots by reducing disturbing vibrations caused by high dynamic loads effectively. To investigate parallel robots and their applications, including suitable control concepts for smart-structures, the Collaborative Research Center 562 was founded by the German Research Council (DFG). The latest prototype within this research center is called Triglide. It is a four degree of freedom (DOF) robot with three translational and one rotational DOF. It realizes an acceleration of 10 g* at the effector. In the structure of the robot six active rods and a tri-axial accelerometer are integrated to control effector vibrations in three translational DOF. The main challenge of this control application is the position dependent vibration behavior. A single robust controller is not able to gain satisfying performance within the entire workspace. Therefore a strategy for describing the vibration behavior by linearization at several operating points is developed. Behavior in-between is approximated by a linear approach. On a trajectory robust controllers in all operating points are smoothly switched by robust gain-scheduling. The scheduling parameters are fast varying and though a suitable stability proof is defined, based on Small-Gain approach. Several transformations enhance the results from Small-Gain Theorem and reduce the usual conservatism. Experimental data is used to show the improvements made.

An image-processing approach is described that detects the position of a vehicle on a bridge. A load-bearing vehicle must be carefully positioned on a bridge for quantitative bridge monitoring. The personnel required for setup and testing and the time required for bridge closure or traffic control are important management and cost considerations. Consequently, bridge monitoring and inspections are good candidates for smart embedded systems. The objectives of this work are to reduce the need for personnel time and to minimize the time for bridge closure. An approach is proposed that uses a passive target on the bridge and camera instrumentation on the load vehicle. The orientation of the vehicle-mounted camera and the target determine the position. The experiment used pre-defined concentric circles as the target, a FireWire camera for image capture, and MATLAB for computer processing. Various image-processing techniques are compared for determining the orientation of the target circles with respect to speed and accuracy in the positioning application. The techniques for determining the target orientation use algorithms based on using the centroid feature, template matching, color feature, and Hough transforms. Timing parameters are determined for each algorithm to determine the feasibility for real-time use in a position triggering system. Also, the effect of variations in the size and color of the circles are examined. The development can be combined with embedded sensors and sensor nodes for a complete automated procedure. As the load vehicle moves to the proper position, the image-based system can trigger an embedded measurement, which is then transmitted back to the vehicle control computer through a wireless link.

Using direct and inverse piezoelectric effects of high-polymer piezoelectric films simultaneously, flexible structures are expected to be realized which possess vibration damping ability and are able to behave actively and autonomously such as biological systems. However, conventional studies have been limited to either developing high order controller in conjunction with sensor/actuator of basic shaping or developing sensor/actuator of complicated shaping function in conjunction with simple controller. In this paper, a new shaping design method of distributed piezoelectric film sensor/actuator for vibration control of flexible beams is proposed. At first, fundamental equations are derived, and a new shaping method in which the shaping function is described by the superposition of the modal strain functions is proposed. In the proposed method, the weighting coefficient is determined by a reciprocal of the cube of wavenumber. It is proved that in the case of simply supported beam, one example of the proposed shaping function is reduced to the conventional triangular shaping function. Numerical examples of designed shaping function for a simply supported beam and a cantilever beam are shown for single mode, multi mode and all mode sensor/actuator.

In this paper, a new design concept for multifunctional fasteners using smart materials is presented. The proposed piezoelectric devices, named 'smart fasteners,' can be fabricated by modifying the design of ordinary fasteners such that they have a piezoelectric element and a control unit embedded in their body. These smart fasteners can not only clamp structural members like ordinary fasteners but also measure the response of the structure and generate forces to enhance the dynamic performance of the structure. Due to their fastener-type design, they are more convenient to install onto or remove from structures compared to conventional piezoceramic patch actuators for which a bonding epoxy layer needs to be applied. In order to demonstrate their applicability in active vibration controls, a simulation study was conducted on a fixed-fixed beam structure. Since the control force is applied at the boundary of the structure where the smart fasteners are attached, a new control algorithm called Active Boundary Control (ABC) was developed using the Lyapunov's direct method. The simulation results show that smart fasteners can be used to suppress vibration of the beam by applying the Lyapunov-based Active Boundary Control algorithm.

This paper describes a mechanical horizontal monolithic sensor for geophysical applications developed at the University of Salerno. The instrument is basically a monolithic tunable folded pendulum, shaped with precision machining and electric-discharge-machining, that can be used both as seismometer and, in a force-feedback configuration, as accelerometer. It is a very compact instrument, very sensitive in the low-frequency seismic noise band, with a very good immunity to environmental noises, whose main characteristics are the tunability of the resonance frequency and the integrated laser optical readout, consisting of an optical lever and an interferometer. The theoretical sensitivity curves are in a very good agreement with the measurements. A direct comparison of its performances with the STS-2 ones shows that better performances have been reached with the interferometric readout (≈ 10^-12 m/ √ Hz in the band 10^-1 ÷ 10Hz as seismometer. Finally, the first results as accelerometer (force feed-back configuration) are also presented and discussed.

Light-weight and multiplexable, Fiber Bragg Grating (FBG) optical sensors allow the integration of many sensors along a single electrically passive and electromagnetic interference immune optical fiber. In this paper, we describe the use of multiple FBGs for monitoring and early stage detection of fatigue crack growth. We provide experimental results over a range of temperatures for fatigue crack monitoring in titanium alloy specimens subjected to periodic loading for tens of thousands of cycles and demonstrate detection of early-stage fatigue crack extension.

Immune to electromagnetic interference, Fiber Bragg Grating (FBG) optical sensors are multiplexable, highly sensitive to minute strains, and can facilitate maximum smart structure functionality, with minimum weight and size. In conjunction with advanced damage characterization algorithms, FBG sensor systems are expected to play an increasing role in extending the life and reducing costs of new generations of civil, mechanical and aerospace systems. In this paper, we discuss the development of fast parallel processing FBG interrogation systems. Comparison with other structural health monitoring systems demonstrates better signal-to-noise, high-speed multi-sensor support and damage detection potential.

In this article, the equivalent two-degree-of-freedom (2-DOF) model for the hypersensitive ear of fly Ormia ocharacea is revisited. It is found that in addition to the mechanical coupling between the ears, the key to the remarkable directional hearing ability of the fly is the proper contributions of the rocking mode and bending mode of the ear structure. This can serve as the basis for the development of fly-ear inspired directional microphones. New insights are also provided to establish the connection between the mechanics of the fly ear and the prior biological experiments, which reveals that the fly ear is a nature-designed optimal structure that might have evolved to best perform its localization task at 5 kHz. Based on this understanding, a new design of the fly-ear inspired directional microphone is presented and a corresponding normalized continuum mechanics model is derived. Parametric studies are carried out to study the influence of the identified non-dimensional parameters on the microphone performance. Directional microphones are developed to verify the understanding and concept. This study provides a theoretical guidance to develop miniature bio-inspired directional microphones, and can impact many fronts that require miniature directional microphones.

Mass deposition influence on natural frequencies of nonuniform cantilever resonator sensors of linear and parabolic thickness is investigated in this paper. Resonator sensitivity, defined as a fraction of change in frequency per deposited mass, is found. Constant thickness mass deposition on all four lateral surfaces of the cantilever of rectangular crosssection was assumed. The Euler-Bernoulli theory was used under the assumption that the beams are slender. Mass deposition on the free end surface of the beams was neglected. The deposition thickness was considered uniform and very small compared to any beam dimension. The deposited mass had no contribution to the stiffness, only to the mass. Results show that when compared to the sensitivity of uniform resonator, the sensitivity of linear thickness resonator and parabolic thickness resonator are in the first mode 6 times and 3 times higher, respectively.

A study was conducted of socks fitted with thin flexible conductive polymer sensors for the potential use as a smart sock for monitoring foot motion. The thin flexible sensors consisted of a conductive polymer applied on an elastic textile substrate that exhibited a resistance change when strained. Quasi-static response tests of the basic sensor over a static load range of a few Newtons were conducted and showed a time varying response as observed by previous investigators. Dynamic testing through an electrodynamic shaker shows good dynamic response at a low frequency range, less than 4Hz. Strips of 12 cm x 1 cm of the sensor on fabric showed a reproducible basal resistance on the order of 10KOhms. Other geometries of the continuous sensors and correlation of strain to resistance variation were studied. Similar tests were performed on different textile substrates which vary in composition and microstructure, i.e. woven, knitted, nylon%, polyester%, etc... These sensors were integrated into socks and preliminary results indicate that distinct responses to different foot motion patterns are detected in sensors placed at different joint locations on the foot. Further processing of strain results from smart socks should provide information about the kinematics and dynamics of the human foot.

In recent decades, optical fiber has proven useful for many sensor applications. Specifically, fiber Bragg grating (FBG) sensors have shown great utility for integrity management and environmental sensing of composite structures. One major drawback of FBG sensors, however, is the lack of a robust, non-"pigtail" technique for coupling the embedded FBG sensor to an external optical interrogation device. In this paper, a novel method of free space passive coupling of light into FBG sensors has been investigated. Angled 45-degree mirrors integrated directly into fibers were used as an input coupling technique. The approach was applied to both single mode and multimode glass fibers containing FBG's. For multimode investigations, mirrors were integrated into graded-index multimode fiber by polishing the end face to a 45-degree angle. In single mode investigations, a novel method of coupling to the sensor via splicing and fusing a multimode fiber to a single mode FBG was explored. Associated transmission spectra are shown for each method.

A computer-vision monitoring system is demonstrated that automatically detects the presence and location of people. The approach investigated the potential for real-time, automated surveillance and tracking in a realistic environment. Economy was obtained by the use of gray-scale, fixed perspective images and efficiency was obtained by the use of selected object features and a neural-network-processing algorithm. The system was applied to pedestrian traffic on an outdoor bridge and consequently had to handle complex images. Image sequences of single and multiple people were used with differences in clothing, position, lighting, season, etc. A two-stage algorithm was implemented in which (1) new objects were identified in a highly variable scene and (2) the objects were classified with a back-propagation neural network. The image processing techniques included segmentation and filtering and the neural network used fourteen object features as inputs. The implementation had excellent people-discrimination accuracy despite the noise in the images and had low computational complexity with respect to alternative techniques.

The currently project is focused on monitoring the reliability, the static and dynamic conditions of the Pedestrian Olympic Bridge in Torino, Italy. Smart sensors based on fiber optic sensors, realized by University of Illinois at Chicago, were installed on the cables. In parallel new low-cost accelerometers and inclinometers sensors, realized by the ChiLab (Italy), were installed on the bridge deck to control statically but also dynamically its behaviour. Acquisition system to collect the data through a continuous monitoring platform, able to pre-process the data, was integrated to manage it locally or in remote way. The performance and reliability of civil infrastructure systems such as bridges are governed by a number of factors including the actual operating and loading environments, complex interactions between structural members and systems, and defect, deterioration and damage mechanisms. These factors are studied dynamically with structural identification of various levels of uncertainty which can be attributed to the fabricated-constructed-erected nature of these systems, variability in site characteristics and conditions, material properties and service loads, and direct exposure to the environment over long life-cycles that are often many decades in length.

In this study, a system using autonomous smart sensor nodes is developed for bridge structural health monitoring (SHM). In order to achieve the research goal, the following tasks are implemented. Firstly, acceleration-based and impedancebased smart sensor nodes are designed. Secondly, an autonomous operation system using smart sensor nodes is designed for hybrid health monitoring using global and local health monitoring methods. Finally, the feasibility and applicability of the proposed system are experimentally evaluated in a lab-scaled prestressed concrete (PSC) girder for which a set of damage scenarios are experimentally monitored by wireless sensor nodes and embedded software.

External bonding of PZT patches to host structures as sensors and actuators has emerged as a popular method in smart structural applications such as structural health monitoring and vibration and shape control. Due to the strong material mismatches between the PZT patch and host structure, severe stress concentration can be induced along the PZT-host structure interface, which can lead to interface debonding and premature failure of the smart structure. For this reason, stresses along the PZT-host structure interface are of great research interest. To find the interface stresses, existing studies commonly adopted a one-way coupling model to simulate the behavior of the piezoelectric patch, in which the electric displacement field is assumed to be uniform through the thickness of the piezoelectric patch. In this study, however, a two-way coupling model for the electrical and mechanical field interaction is proposed. The electrical displacement field in the thickness direction of the piezoelectric patch is assumed to have a parabolic distribution. Closed-form solutions of interface stresses and electric field are obtained. To verify the model and for comparison purpose, a numerical example is calculated with different models, along with the numerical solution from finite element analysis (FEA).

The objective of this paper is to develop a novel sensing system which can conduct continuous monitoring of a building structure and generate a monitoring report. The building monitoring data will focus on the ambient vibration responses. Two servers are used in this SHM system: 1) wireless measurement server which takes care of measuring and archiving all the structural responses and environmental situation, and 2) analysis server which conducts the signal processing on the received signals. The measurement server is in charge of the collection of signals and broadcast wirelessly from all sensors to the analysis server. Dominant frequencies and mode shapes of the building will be estimated in the analysis server from the continuous monitoring of the ambient vibration data (velocity) of the building by using AR-Model, Frequency Domain Decomposition and Stochastic Subspace Identification methods. The proposed continuous monitoring system can effectively identify the building current health condition and generate a report to the owner.

As a first step to realizing "Biofication of Living Space" that needs spatial recognition for accommodation and evolution, a new human identification system was developed. The system can identify human activities using information from multiple sensors. Acceleration sensors, pyroelectric infrared sensors and microphone were adopted in this study. And these sensors' information was fused and handled together. Therefore, the system recognized 10 persons with up to 91.3 percent accuracy by 21 dimensional feature quantities. And also, it was confirmed that by combination of multiple sensors' information, the false discrimination rate was reduced by about half compared to single sensor's information. Simultaneous identification of multi persons was performed. Using the extracted feature quantities, the discrimination rate was calculated in 3 settings of learn data. When learn data was extracted data of measurement that tested 4 persons walked alone, the system recognizes 4 persons with up to 80 percent accuracy. Moreover, even in situation that lacked data from some sensors human identification can be achieved with more than 80 percent accuracy.

In this paper, a non-contact dynamic displacement measurement method based on video motion detection (VMD) technique and a structural modal identification technique based on the principal component analysis (PCA) is proposed for vibration tests and modal identification of frame structures. Relying on the instant digitized image acquiring using a digital video recorder and image processing based on the close-range photogrammetry theory, the dynamic deformation of a structure can be measured. The PCA is then employed to decompose the correlated structural deformation measurements into statistically uncorrelated ones. Under the condition of small damping, these uncorrelated data can be shown to be related to modal responses and can be used to estimate the modal parameters of a structure. To demo the process and validate its accuracy, a dynamic test on a scaled frame structure is conducted in the lab. Dynamic responses at given target point were obtained and structural modal parameters were estimated. Compared with the modal parameters obtained from the eigenvalue analysis of a FEM model, the proposed method is of enough precision for vibration tests and modal identification of frame structures.

The civil infrastructures deteriorate over time and their reliability is time variant. To mitigate the deterioration of structures, the maintenance, monitoring, inspection, etc. are needed. To optimize the cost of structure, life-cycle design of structure is urgently needed. Different from current structure design theories, the design index of life-cycle design should be able to reflect the time variation of structure directly and provide reference for making maintenance decisions, but the performance indices of current design theories can't meet these requirements. For the deficiencies above, life-cycle design is introduced herein and life index of structure is defined. The properties, functions and determination principles of the structural life index are concluded as well. An example is also presented, in which the process of obtaining life index is demonstrated. The freeze-thaw action spectrum of Harbin is utilized and the life index of certain common concrete under freeze-thaw action in Harbin is obtained herein. The result shows that the life index of that concrete is only 6 years. The investigation will be helpful for controlling the structure life-cycle cost, and can promote the development of life-cycle design.

An early detection of structural damages is critical for the decision making of repair and replacement maintenance in order to guarantee a specified structural reliability. Consequently, the structural damage detection, based on vibration data measured from the structural health monitoring (SHM) system, has received considerable attention recently. The traditional time-domain analysis techniques, such as the least square estimation (LSE) method and the extended Kalman filter (EKF) approach, require that all the external excitations (inputs) be available, which may not be the case for some SHM systems. Recently, these two approaches have been extended to cover the general case where some of the external excitations (inputs) are not measured, referred to as the LSE with unknown inputs (LSE-UI) and the EKF with unknown inputs (EKF-UI). Also, new analysis methods, referred to as the sequential non-linear least-square estimation with unknown inputs and unknown outputs (SNLSE-UI-UO) and the quadratic sum-square error with unknown inputs (QSSE-UI), have been proposed for the damage tracking of structures when some of the acceleration responses are not measured and the external excitations are not available. In this paper, these newly proposed analysis methods will be compared in terms of accuracy, convergence and efficiency, for damage identification of structures based on experimental data obtained through a series of experimental tests using a small-scale 3-story building model with white noise excitation. The capability of the LSE-UI, EKF-UI, SNLSE-UI-UO and QSSE-UI approaches in tracking the structural damages will be demonstrated.

Nowadays, Structural Health Monitoring (SHM) is essential in order to prevent damages occurrence in civil structures. This is a particularly important issue as the number of aged structures is increasing. Damage detection algorithms are often based on changes in the modal properties like natural frequencies, modal shapes and modal damping. In this paper, damage detection is completed by using Artificial Immune System (AIS) theory directly on acceleration data. Inspired from the biological immune system, AIS is composed of several models like negative selection which has a great potential for this study. The negative selection process relies on the fact that T-cells, after their maturation, are sensitive to non self cells and can not detect self cells. Acceleration data were provided by using the numerical model of a 3-story frame structure. Damages were introduced, at particular times, by reduction of story's stiffness. Based on these acceleration data, undamaged data (equivalent to self data) and damaged data (equivalent to non self data) can be obtained and represented in the Hamming shape-space with a binary representation. From the undamaged encoded data, detectors (equivalent to T-cells) are derived and are able to detect damaged encoded data really efficiently by using the rcontiguous bits matching rule. Indeed, more than 95% of detection can be reached when efficient combinations of parameters are used. According to the number of detected data, the localization of damages can even be determined by using the differences between story's relative accelerations. Thus, the difference which presents the highest detection rate, generally up to 89%, is directly linked to the location of damage.

A statistical vibration-based damage identification algorithm to assess the stability of the measurement data, detect and locate damage in civil structures, where variability in response and modal parameters due to measurement noise and environmental influence is often inevitable, is presented in this paper. The algorithm utilizes the statistical correlation of the magnitudes of frequency response function (FRF) of target sensors relative to a reference sensor to assess the consistency of the data while the slopes of lines of fit are exploited for damage localization. Through numerical simulation and experimental investigation of a flexural structure using accelerometers and "point" strain gauges, and long gauge fiber Bragg gratings (FBG) sensors, the importance of the technique for civil SHM is established and presented in an easy-to-interpret graphical format for effective implementation of results. The proposed method using long-gauge FBG sensors is suitable for practical civil SHM with limited number of sensors and where variability in response and modal parameters due to measurement noise and environmental influence is often inevitable. Also, the ability to effectively manage and make sense of enormous amounts of data collected under continuous monitoring process for an effective diagnostic and/or prognostic system is an added advantage.

The water leakage leads to deficient water supplies, roads caving in, leakage in buildings, and secondary disasters. In this study, we propose the PCA-based automatic water leakage detection method considering complex Fourier components. The water leakage sounds and pseudo sounds, such as gas flow sounds, water usage sounds etc., are collected by microphone put on the ground. The Fourier spectra are obtained through the short-time Fourier transform (STFT). Then the principal component analysis (PCA) is applied to complex Fourier components of each collected sound data. The contribution ratio and the kurtosis of the eigenvector of the first principal component show the good ability to distinguish the water leakage sounds from the pseudo sounds. Therefore, the feature vectors are created from these PCA parameters. Based on them, the Support Vector Machine (SVM) is built. The results show that the classification can reach a very high accuracy. At last, applicability of the proposed water leakage detection method is well demonstrated.

Identification of structural parameters under ambient condition is an important research topic for structural health monitoring and damage identification. This problem is especially challenging in practice as these structural parameters could vary with time under severe excitation. Among the techniques developed for this problem, the stochastic subspace identification (SSI) is a popular time-domain method. The SSI can perform parametric identification for systems with multiple outputs which cannot be easily done using other time-domain methods. The SSI uses the orthogonal-triangular decomposition (RQ) and the singular value decomposition (SVD) to process measured data, which makes the algorithm efficient and reliable. The SSI however processes data in one batch hence cannot be used in an on-line fashion. In this paper, a recursive SSI method is proposed for on-line tracking of time-varying modal parameters for a structure under ambient excitation. The Givens rotation technique, which can annihilate the designated matrix elements, is used to update the RQ decomposition. Instead of updating the SVD, the projection approximation subspace tracking technique which uses an unconstrained optimization technique to track the signal subspace is employed. The proposed technique is demonstrated on the Phase I ASCE benchmark structure. Results show that the technique can identify and track the time-varying modal properties of the building under ambient condition.

Based on the bridge health monitoring data, the traffic-load effect model for arch bridge suspender was set up using direct statistical method. Firstly, the Bridge Health Monitoring System (BSHM) set up on the Ebian Dadu River Bridge in Sichuan province to obtain daily traffic-load effect of suspenders was introduced. Secondly, the section distribution of suspender traffic-load effect was researched by statistical approach using monitoring data. Finally, the probability distribution of maximum traffic-load effect during design period was given. The statistical result shows that the section distribution of suspender traffic-load effect follows lognormal distribution and the probability distribution of maximum traffic-load effect during design period follows generalized extreme-value distribution. The traffic-load effect model of suspender was different with the design code given which may underestimates the real load effect level. It's the first time in China to determine the traffic-load effect probability model for arch bridge suspenders based on actual acquired monitoring data using statistical and probabilistic approach.

Various uncertainties involved in the structural modeling and experiment processes greatly limit the application of the system identification (St-Id) technology on the real-life structural health monitoring and risk-based decision making. An efficient St-Id method is proposed to accurately identify structural modal parameters by using ambient test data with various uncertainties. The random decrement technique is first applied to reduce random errors by averaging the test data. Subsequently, a high order Vector Backward Auto-Regressive (VBAR) model is proposed to identify structural modal parameters. The merit of the VBAR model is that it awards a determine way to separate the system modes consisting of structural parameters and the extraneous modes arising due to uncertainties. The ambient vibration data from a cantilever beam experiment is employed to demonstrate the effectiveness of the proposed St-Id method.

This paper reports on the design, fabrication, and testing of a SOI-based tuning-fork gyroscope with high Quality factors (Qs). A tuning-fork structure with high Qs is designed and is integrated with on-chip electrostatic transducers for excitation and detection. With a one-mask fabrication technology, this gyroscope design is fabricated on a SOI wafer with a 30μm-thick device layer. The fabricated devices are further tested for their preliminary performance characterization. The measured Qs of a fabricated gyroscope are 162,060 for the drive mode and 85,168 for the sense mode at 16.8kHz. In order to enhance its rate sensitivity, the frequency of the sense mode is tuned using electrostatic tuning toward that of the drive mode and a minimum frequency split of 6Hz between the two modes is demonstrated. Under this nearly matched-mode condition, a prototype device shows a measured rate sensitivity of 0.02mV/°/sec. The theoretical mechanical resolution due to Brownian noise is 0.3°/hr/√Hz.

The structural control can provide the potential protection through passive and active control techniques. Structures with base isolations have been successfully implemented and proven effective in the vibration mitigation. To enhance the functionality of base isolations, a hybrid control system can be considered using a combination with active control devices. This research applies the hybrid control technique to a three-story two-bay steel building. The base isolation is installed under the structural base, and three actuators are placed at the lowest level. The control objective is to reduce the structural responses in the motion of three directions. First, the control system has been identified through the proposed system identification technique and considered with the control-structure interaction. Different controllers are designed to examine the performance under different types of excitation. Finally, this control system is tested on the shake table for evaluation of the controllers, and the two-dimensional control strategy is also realized through the whole procedures.

The present paper deals with a self-deployable graphite/epoxy composite structure using a partially flexible composite (PFC) with shape memory alloy wires. The present paper introduces the fabrication processes of the PFC. Two different matrices are used for the PFC: epoxy resin for the normal main part, and silicone rubber for the folding line. Since the fibers are continuous in the structure, the PFC has the same tensile strength as a normal composite. We investigate graphite fiber breakages during the folding process by considering changes in electrical resistance. An SMA wire is embedded in the PFC to keep the folded configuration without loading and self-deployment is achieved using Joule heating. The results confirm that a flexible part of adequate length enables foldable composite structures without causing carbon fiber breakages. The embedded SMA wire realizes compactly folded composite panel structures without loading and Joule heating of the SMA wires enables self-deployable composite structures.

Sensors constructed with single-crystal PMN-PT, i.e. Pb(Mg_1/3Nb_2/3)O3-PbTiO₃ or PMN, are developed in this paper for structural health monitoring of composite plates. To determine the potential of PMN-PT for this application, glass/epoxy composite specimens were created containing an embedded delamination-starter. Two different piezoelectric materials were bonded to the surface of each specimen: PMN-PT, the test material, was placed on one side of the specimen, while a traditional material, PZT-4, was placed on the other. A comparison of the ability of both materials to transmit and receive an ultrasonic pulse was conducted, with the received signal detected by both a second surface-bonded transducer constructed of the same material, as well as a laser Doppler vibrometer (LDV) analyzing the same location. The optimal frequency range of both sets of transducers is discussed and a comparison is presented of the experimental results to theory. The specimens will be fatigued until failure with further data collected every 3,000 cycles to characterize the ability of each material to detect the growing delamination in the composite structure. This additional information will be made available during the conference.

Structural Health Monitoring (SHM) is required for early detection of damage in structural components to improve the safety, reduce the cost, and increase the performance and efficiency of aircrafts. Currently available techniques have a number of deficiencies prohibiting wide spread of SHM in aerospace applications. In this contribution we will present the initial results of development at Luna Innovations of an all-fiber optic ultrasonic airframe SHM system that will be able to address the deficiencies of solutions suggested/developed to date. In this contribution we will present the details on design, development and testing of the prototype fiber optic SHM system.

The paper parametrically explores the design sensitivity of a fiber optic pressure sensor (FOPS), based on the potential failure mechanisms expected in the sensor diaphragm. The product under study is a miniature FOPS that can be embedded in, or installed on, a structure for pressure monitoring applications. The field operating conditions are defined in terms of temperature, pressure, and vibration loading. The FOPS probe has a Fabry-Perot cavity, with the fiber tip and a miniature diaphragm acting as the two mirrors. The cavity length changes when the diaphragm deflects under pressure. However, due to field operating conditions, several failure mechanisms may affect the structural and optical characteristics of the sensor, such as cracks in the diaphragm and/or high residual stresses in the optical fiber. With the aid of finite element analysis, this article investigates conflicting design constraints due to structural failure mechanisms in the diaphragm and elaborates on the severity of each one by parametric design sensitivity studies.

For monitoring of railway structures, optical fiber sensors are very convenient. The fiber sensors are very small and do not disturb the structural properties. They also have several merits such as electro-magnetic immunity, long signal transmission, good accuracy and multiplicity of one sensor line. Strain measurement technologies with fiber optic sensors have been investigated as a part of smart structure. In this paper, we investigated the possibilities of fiber optic sensor application to the monitoring of railway structures. We expect that the fiber optic sensors have much less noises than electrical strain gauges because of electro-magnetic immunity while railways operate electric power of 22000 volts. Fiber optic sensors showed good durability and long term stability for continuous monitoring of the railway structures as well as good response to the structural behaviors during construction.

Optical fibers can be used as a promising sensors in smart structures thanks to their novel characteristics. In particular, its immunity to electromagnetic interference (EMI) makes the sensor suitable for use in electronic environments. In order to inspect the reliability of a structure, it is essential to characterize the dynamic responses of the structure. An accelerometer associated with optical fiber makes it possible to conduct real-time structural health monitoring under high electromagnetic environments. This paper describes an optimal design of a novel fiber optic accelerometer using one grating panel for the application to civil engineering structures. The fiber optic sensor design was optimized to have the best sensitivity to the motion of the reflective grating using two optical fibers in the quadrature. The reflected optical signal of the sensor is influenced by the reflective grating pattern and optical fiber-grating distance. In this paper, several simulations and experiments were carried out to evaluate the characteristics of the output signals according to the grating pattern and the distance between the optical fiber and the grating for a fixed fiber core diameter. Through comparison of the results between the simulations and the experiments, the optimum design of the grating-pattern was determined to obtain a stable and periodic sine wave as the output signal. Furthermore, it was demonstrated that the output signals reflected by one grating panel could be used for the final parameter-measurement.

A simple interrogation technique is presented which relies on a characteristic specific to saturated fibre Bragg gratings (i.e. gratings where most of the energy at the Bragg wavelength has been reflected prior to the incident light reaching the far end of the grating). In this regime, when the grating is illuminated by a broadband source a change in pitch within a region of the grating will result in the emergence of reflected energy in other spectral regions without significant loss in power from the main Bragg peak. Hence there will be an increase in the overall integrated power reflected from the grating, which is a function of the degree of strain gradient experienced by the grating. This allows the degree of strain gradient to be directly converted to an intensity measurement without the need for an optical filter. Because environmental temperature effects would generally not be localised along the short physical length of the grating, any temperature changes will typically shift the reflection spectrum in the wavelength domain rather than alter the amount of reflected light, which renders the measurement effectively temperature-insensitive. Experimental data is presented demonstrating the application of this sensing approach to the detection of growth of cracks in metallic structures and disbonds in composite repairs. Some of these experiments were carried out during environmental thermal cycling to demonstrate the temperature independence of the measurement technique.

With the popular use of wireless sensor networks, the replacement of the batteries becomes more concerned in the research communities. Piezoelectric materials (PZT) can be used to convert ambient vibration energy into electrical energy for use in powering microelectronics. Because the generated power and voltage depend on not only the amplitude and frequency of the ambient vibration, but also the geometric configuration of the piezoelectric bimorph generator, it is of great interest to study the relationships between the harvester's geometric configuration and its resonant frequency, and between the driving frequency and the harvested voltage and power. In this paper, a piezoelectric bimorph cantilever beam with a proof mass on the free end is adopted as the basic configuration, since it is simple and widely used as a low resonance frequency energy harvester. The previous model in the literature is described at the beginning, and then the Euler-Bernoulli beam model is created and calculated numerically. ANSYS simulation is performed to compare the results of the two different models. The results show that the Euler model has better predication of the resonant frequency of the PEH than the model in the literature. Finally, the design optimization of PEH is presented.

Noncontact measurements of flexible and moving structures have the challenge of obtaining high speed, accurate and registered data over a long range. Many noncontact measurement methods are based on the object staying aligned with the sensor. Yet sometimes the desired loading is a result of the motion interacting with structural dynamics as is the case with aeroelasticity. Triangulation of video data can capture large scale motion, but limits the speed and accuracy of the measurement. Laser vibrometry can capture minute, structural vibrations but must be aligned to the point of interest. This paper presents a method of registering a laser vibrometer steering system to a motion capture system. The basis of calibration lies on determining the location of the laser steering system through the videogrammetry capture volume for dynamic in-flight tracking and measurement. A method for using video capture of the laser is presented to determine registered lines through the capture volume. Results of the calibration are sufficient to have the laser track within half a degree for distances over 4m. The laser is then able to be open-loop steered with static and dynamic accuracies presented. This system can provide real-time structural awareness enabling active control.

This paper deals with the problem of damage localization and quantification using the Frequency Response Function (FRF) subjected to earthquake ground excitation. The damage identification equation is derived from the motion equation of the system before and after damage. The FRFs of the intact and damaged system as well as the system matrices of the intact system are required to solve the damage identification equation. The system matrices can be obtained from the state matrices identified by subspace identification technique. According to the numerical study of a frame structure, only a few discrete frequencies from the FRFs which are close to the system natural frequencies are sufficient to achieve a satisfactory precision of damage extent. The proposed technique was applied to an experimental data of a 6-story steel frame structure and its efficiency was confirmed.

In this paper, a wavelet entropy based damage identification method is experimentally validated using wireless smart sensor units (Imote2) with TinyOS-based firmware. Recently, the wireless smart sensor network has drawn significant attention for applications in Structural Health Monitoring (SHM). Wavelet entropy is considered to be a damagesensitive signature that can be obtained both at different spatial locations and time stations to indicate changes in dynamic responses of structures. Compared to metrics based on the Fourier Transform, metrics based on wavelets require much simpler mathematics, with no complex numbers. Thus wavelet-based SHM methods would be easier to embed on motes. Wavelets can have other (mathematical) advantages when the structures are complex and the dynamic signals are non-stationary. Particularly, use of the relative wavelet entropy (RWE) has been extensively explored for use in damage detection using wireless smart sensors. First, sensor validation tests have been conducted using wireless and wired sensors. To verify an off-line time synchronization technique and the feasibility of using acceleration data from wireless sensors, modal identifications have been conducted using the ERA technique. Finally, the wavelet entropy based damage detection method has been demonstrated using Imote2 wireless smart sensors.

Recent advances in fibre Bragg grating (FBG) and piezoceramic lead zirconate titanate (PZT) sensors have enhanced their applicability in structural health monitoring (SHM). FBG belongs to fine class of fibre optical sensors which are extensively used in noise and vibration control and SHM of engineering structures. FBG sensors utilize intensity modulation or phase modulation techniques for sensing. On the other hand, PZT impedance sensors work on the principle of electromechanical impedance (EMI). In the EMI technique, PZT works as both sensor and actuator. When an electric field is applied on PZT, it vibrates the local area of the structure where the PZT is bonded. These vibrations are then captured by the sensing capability of PZT in terms of EMI signatures. The present paper examines the combination of FBG and PZT sensors for load monitoring. A number of FBG and PZT sensors are experimentally tested for load monitoring on various metallic specimens. The two types of sensor were bonded to a protective mounting instead of being directly bonded to host structure such that they can be removed after test and used for future application. The results are compared using statistical indices like root mean square deviation index.

A new kind of self-sensing fiber reinforced polymer (FRP)-concrete composite beam, which consists of a FRP box beam combined with a thin layer of concrete in the compression zone, was developed by using two embedded FBG sensors in the top and bottom flanges of FRP box beam at mid-span section along longitudinal direction, respectively. The flexural behavior of the proposed self-sensing FRP-concrete composite beam was experimentally studied in four-point bending. The longitudinal strains of the composite beam were recorded using the embedded FBG sensors as well as the surfacebonded electric resistance strain gauges. Test results indicate that the FBG sensors can faithfully record the longitudinal strain of the composite beam in tension at bottom flange of the FRP box beam or in compression at top flange over the entire load range, as compared with the surface-bonded strain gauges. The proposed self-sensing FRP-concrete composite beam can monitor its longitudinal strains in serviceability limit state as well as in strength limit state, and will has wide applications for long-term monitoring in civil engineering.

Determination of structural seismic damage mechanisms and post-seismic damage assessment remains a major challenge for civil engineers. One of the main reasons is that traditional sensors cannot serve for such a long term to capture a destructive earthquake and the seismic damage cannot definitely be predicted in advance. In this paper, a smart distributed fiber optic monitoring method based on OTDR technology is developed for steel structure seismic damage identification. Geopolymer is used as a "smart material" to couple the sensing optic fiber with the structure of interest. It not only functions as the adhesive for bonding the optic fiber to the structure and protecting it, but also works as the sensing material by forming cracks when the pre-defined damage state occurs, which introduce optic power loss into the optic fiber. The power loss is able to be monitored through optic time domain reflectrometry (OTDR). Tentative tests are conducted to decide the composition of geopolymer. It is found that the Si/Al ratio of 3.8 provided cracking strains of about 1300 micro strain, which is desirable for monitoring the yielding of steel. Monotonic, cyclic and buckling loading tests on steel specimen were conducted to verify the efficiency of the proposed system in monitoring seismic damage mechanism.

Accurate measurement of strain variation and effective prediction of failure within models has been a major objective for strain sensors in dam model tests. In this paper, a FBG strain sensor with enhanced strain sensitivity and packaged by two gripper tubes is presented and applied in the seismic tests of a small scale dam model. This paper discusses the principle of enhanced sensitivity of the FBG strain sensor. Calibration experiments were conducted to evaluate the sensor's strain transferring characteristics on plates of different material. This paper also investigates the applicability of the FBG strain sensors in seismic tests of a dam model by conducting a comparison between the test measurements of FBG sensors and analytical predictions, monitoring the failure progress and predicting the cracking inside the dam model. Results of the dam model tests prove that this FBG strain sensor has the advantages of small size, high precision and embedability, demonstrate promising potential in cracking and failure monitoring and in identification of the dam model.

Magnetorheological (MR) damper-based semiactive control systems can be considered as one of the most advantageous control systems for natural hazard mitigation in the field of civil engineering because MR dampers have many good features such as small power requirement, reliability, and low price to manufacture. Those systems require feedback control and power supply parts to efficiently reduce the structural responses. The control system becomes complex when a lot of MR dampers are applied to large-scale civil structures, such as cable-stayed bridges and high-rise buildings, resulting in difficulties in its implementation and maintenance. To overcome the above difficulties, a new-class MR damper-based control system was recently proposed by replacing feedback control and power supply parts with an electromagnetic induction (EMI) part consisting of permanent magnets and a coil. According to the Faraday's law of electromagnetic induction, an EMI part produces electrical energy (i.e., electromotive force or induced voltage) from mechanical energy (i.e., reciprocal motions of an MR damper), which is proportional to the rate of the change of the movement of a damper. From this characteristic of an EMI part, it might be used as a response sensing device as well as an alternative power supply. In addition, some control algorithms used in the MR damper-based semiactive control systems require the measurement information on the response related to the relative velocity of the damper. In this study, the sensing capability of an EMI part is preliminarily examined for an application to the MR damper-based semiactive control system. To this end, experimental tests are carried out using the real-scale stay cable employing an MR damper with an EMI part. It is demonstrated from the tests that an EMI part could exactly extract the dynamic characteristics of the stay cable so that it might be used as a sensing device for estimating the tension force of the stay cable. In addition, numerical simulations are performed to verify the control performance of the MR damper-based semiactive control system adopting an EMI part as a power supply as well as a velocity sensor and the maximum energy dissipation algorithm, which requires the information on the relative velocity, as a control algorithm. The numerical result validates that the proposed control system can reduce the vibration of the stay cable effectively.

In this paper, experimental investigation on vibration control is carried out on a stay cable model incorporated with one small size magnetorheological fluid (MR) damper. The control efficiency of the MR dampers to reduce the cable vibration under sinusoidal excitation using passive control strategy is firstly tested. The dynamic coupling between the cable and MR damper with the passive control strategy is obviously observed. Dynamic coupling models between stay cable and MR damper with constant and fluctuating current input are proposed respectively. The proposed dynamic coupling model corresponding to the MR damper with constant current input is validated by the numerical simulations of the measured experimental data. Furthermore, using the proposed dynamic coupling corresponding to the MR damper with fluctuating current input, experimental investigation on the cable vibration control subjected to sinusoidal excitation using semi-active control strategy is then conducted. Experimental results demonstrate that the semi-active MR damper can achieve much better mitigation efficacy than the passive MR dampers with different constant current inputs due to negative stiffness provided by the semi-active MR damper.

A new self-powered and sensing semi-active control system based on magnetorheological (MR) damper is presented. The system includes four key parts: a rack and pinion mechanism, a linear permanent magnet DC generator, a current adjustment MR damper, and a control circuit. Numerical simulations for seismic protection of elevated bridges equipped with this system excited by two historical earthquakes are conducted. Linear quadratic regulator (LQR) is used for the design of ideal active control system. LQR-based clipped optimal control as well as skyhook control is used to command a MR damper in both the semi-active control with external power and self-powered semi-active control. It is shown that five strategies (ideal active control, two semi-active controls and two self-powered semi-active controls) have similar control performance in pier response as well as bearing response. It is noticed that only one accelerometer is needed to monitor the response of the deck to realize the self-powered skyhook control, which greatly simplifies the classical semiactive vibration control system based on MR damper.

This paper proposes a neuro-fuzzy model of NiTi shape memory alloy (SMA) wires that is capable of capturing behavior of superelastic SMAs at different temperatures and at various loading rates while remaining simple enough to realize numerical simulations. First, in order to collect data, uniaxial tensile tests are conducted on superelastic wires in the temperature range of 0 ºC to 40 ºC, and at the loading frequencies of 0.05 Hz to 2 Hz that is the range of interest for seismic applications. Then, an adaptive neuro-fuzzy inference system (ANFIS) is employed to construct a model of SMAs based on experimental input-output data pairs. The fuzzy model obtained from ANFIS training is validated by using an experimental data set that is not used during training. Upon having a model that can represent behavior of superelastic SMAs at various ambient temperature and loading-rates, nonlinear simulation of a multi-span continuous bridge isolated by rubber bearings that is equipped with SMA dampers is carried out. Response of the bridge to a historical earthquake record is presented at different ambient temperatures in order to evaluate the effect of temperature on the performance of the structure. It is shown that SMA damping elements can effectively decrease peak deck displacement and the relative displacement between piers and superstructure in an isolated bridge while recovering all the deformations to their original position.

This paper addresses tracking-control of hysteretic systems using a gain-scheduled (GS) controller. Hysteretic system with variable stiffness and damping is represented as a quasi linear parameter varying (LPV) system. Designed controller is scheduled on the measured/estimated stiffness and damping in real-time. GS controller is constructed from the parameter dependent Lyapunov matrices, which are obtained as optimal solutions of linear matrix inequalities (LMIs) that ensures the feasibility solution for closed loop system performance. The proposed method is worked on semiactive independently variable stiffness (SAIVS) device. It is shown that the gain-scheduled controller developed for the quasi-LPV system results in excellent tracking performance even in the cases where robust-H∞ controller failed to function.

A fuzzy logic control (FLC) algorithm optimized by the genetic algorithm (GA) is developed in the paper for the benchmark problem application regarding the vibration control of tall buildings under along wind excitation. The adopted control scheme consists of an MR damper which the control action is achieved by a Fuzzy Controller. The fuzzy rules for the controller are optimized by the genetic algorithm to enhance the efficiency of the control system. A fuzzy strategy of two-input and single-output variables is adopted in the control system. The fuzzy subset and rules base for the controller are optimized by the genetic algorithm to further decrease the responses of the controlled structure. The robustness of the controller has been demonstrated through the uncertainty in stiffness (15% and -15% variations from initial stiffness) of the building. The results of the simulation show a good performance by the fuzzy controller for all tested cases.

Laser interferometry is one of the most sensitive methods for small displacement measurement for scientific and industrial applications. Interferometric techniques have been already successfully applied also to the design and implementation of very sensitive sensors for geophysical applications, like monolithic accelerometers. In this paper we describe the architecture and the expected theoretical performances of a laser interferometric velocimeter for seismic waves measurement. We analyze and discuss the experimental performances of the interferometric system, comparing the experimental results with the theoretical predictions and with the performances of a state-of the art commercial accelerometer. The results obtained are very encouraging, such as the sensitivity and stability of the interferometric system, that have been improved.

In this paper, we describe the development of a viscosity sensing system using a simple and low-cost long-period fiber grating (LPFG) sensor. The LPFG sensor was extremely sensitive to the refractive index of the medium surrounding the cladding surface of the sensing grating, thus allowing it to be used as an ambient index sensor or chemical concentration indicator. Viscosity can be simply defined as resistance to flow of a liquid. We have measured asphalt binder, 100-190000 centistokes, in comparison with optical sensing results. The system sensing asphalt binders exhibited increase trend in the resonance wavelength shift when the refractive index of the medium changed. The prototype sensor consisted of a LPFG sensing component and a cone-shaped reservoir where gravitational force can cause asphalt binders flow through the capillary. Thus the measured time for a constant volume of asphalt binders can be converted into either absolute or kinematic viscosity. In addition, a rotational viscometer and a dynamic shear rheometer were also used to evaluate the viscosity of this liquid, the ratio between the applied shear stress and rate of shear, as well as the viscoelastic property including complex shear modulus and phase angle. The measured time could be converted into viscosity of asphalt binder based on calculation. This simple LPFG viscosity sensing system is hopefully expected to benefit the viscosity measurement for the field of civil, mechanical and aerospace engineering.

In this paper, the technique recently proposed by the authors for the detection of structural local damage in large size linear structures is extended to explore the detection of local damage in some complex nonlinear structures. The technique is based on substructural approach in which a complex nonlinear structure is decomposed into substructures Interaction effect between adjacent substructures is accounted by considering the interaction forces at substructural interfaces as the 'unknown inputs' to the substructures. An algorithm utilizing the classical Kalman extended estimator and the recursive least squares estimation for the unknown inputs is proposed to identify structural parameters at element level and the 'unknown inputs' to the substructure. Two cases that measurements at the substructure interfaces are available or not available are considered. Structural local damage is estimated from the change of structural parameters, such as the degradation of the stiffness, at element level. The technique enables distributed identification of local damage in complex nonlinear structures utilizing only a limited number of measured acceleration responses. Performance of proposed technique is illustrated by a numerical example of detecting local damage in a multi-story hysteretic building. It is shown that the proposed technique can be used for detecting structural local damage in some complex nonlinear structures.

To investigate the influence of shape memory alloys (SMAs) on the dynamic properties (mainly refers to the frequency and the damping ratio) of concrete columns, the vibration curves of the concrete column reinforced with steel wire and SMA wires with different phase were measured through initial displacement method. In this study, the experiment included two parts. One is the free vibration test, which utilized the active property tuning (APT) principle, i.e. the passive damping, of SMAs to change the vibration performance of the concrete columns. The results show that SMAs can increase the damping ratio of the concrete column due to its high damping and decrease the frequency owing to its lower stiffness. The other is the vibration test with electrical current activation, the active strain energy tuning (ASET) principle, i.e. the active damping, was applied to alternate the vibration performance of the concrete columns. In this test, martensitic SMA wires were strained up to 4% and were heated with a current of 40A. The test results show that with increasing of the temperature, the frequency of the concrete column decreases, while its damping ratio increases. Comparing the results of these two tests, the influence of two tuning principles, APT principle and ASET principle, on the damping ratio of concrete columns is almost the same. However, for the frequency of the concrete columns, the influence of ASET principle is larger than that of APT principle.

Fiber Bragg grating (FBG) sensors demonstrate great potentials for structural health monitoring of civil structures to ensure their structural integrity, durability and reliability. The advantages of applying fiber optic sensors to a tall building include their immunity of electromagnetic interference and multiplexing ability to transfer optical signals over a long distance. In the work, FBG sensors, including strain and temperature sensors, are applied to the construction monitoring of an 18-floor tall building starting from its construction date. The main purposes of the project are: 1) monitoring the temperature evolution history within the concrete during the pouring process; 2) measuring the variations of the main column strains on the underground floor while upper 18 floors were subsequently added on; and 3) monitoring the relative displacements between two foundation blocks. The FBG sensors have been installed and interrogated continuously for more than five months. Monitoring results of temperature and strains during the period are presented in the paper. Furthermore, the lag behavior between the concrete temperature and its surrounding air temperature is investigated.

As a first step for the safety network integration, test bed bridge was integrated by using the FBG sensor system. For the operating efficiency of the bridge monitoring system, software which can control the conventional sensor system and fiber optic sensor system concurrently was developed. Measuring item was limited to the strain, and the other measuring items such as acceleration or displacement will be applied to the bridge next research period. Beside these items, image processing device was installed to the test bed bridge, and the applicability of these data was considered. As a result of strain measurement, the data from fiber optic sensor system were high stable and reliability, and the problems or advanced parts will be suggested during the test bed bridge operation in the future.

The methods for investigation of the element under vibration of smart structures is proposed. The first eigenmodes of bending vibrations of a circular pezoceramic plate with fixed internal radius are determined and it is assumed that vibrations take place according to the eigenmode. The stresses in the coating are calculated by using the procedure of conjugate approximation. Then the relative error norms for the finite elements are determined. They are used in the proposed procedure of adaptive conjugate approximation with smoothing. From the presented results it is shown that the adaptively smoothed image is advantageous when compared with the conventionally smoothed images. Thus the proposed procedure of adaptive conjugate smoothing builds the ground for realistic reconstruction of experimentally produced photo-elastic fringes and effective application of digitally reconstructed images in hybrid numerical - experimental procedures. Analysis is performed using a plate bending element assuming that a coating has no effect to the motion of a plate. Relative error norms for the finite elements are determined. They are used in the procedure of adaptive conjugate approximation with smoothing.

This paper reports the experimental results that we have achieved from the tests of characterization of an Adaptive Optics (AO) Prototype implemented in our laboratory in compliance with the statements of the design previously carried out. Our purpose is to check the operation of the AO system that is expected to perform laser beam jitters reduction in the bandwidth of interest of interferometric Gravitational Wave (GW) antennas. Using the correspondence between Hermite Gauss polynomials and Zernike modes that alternatively represent the laser beam perturbations as demonstrated in our previous works, we have designed and implemented an AO system that extracts error signals in terms of Hermite Gauss coefficients and then corrects the wavefront through driver commands sent to the deformable mirror in terms of Zernike profiles. The results here reported confirm effectiveness and robustness of the Prototype which exhibits significant reduction of first and second order laser beam jitters. In particular we have measured the decrease of astigmatism and defocus modes of 60 dB at low frequency below 1 Hz and of 20 dB up to 200 Hz, which at the best of the present technology fulfils the requirements for noise reduction of the interferometric GW detectors.

A streaming potential method for modeling the electromechanical responses due to imposed deformation of ionic polymer transducers (IPTs) is presented. It has been argued that imperfect ion pairing results in the availability of free counterions within the hydrophilic regions, thereby resulting in the presence of an electrolyte within these regions in the hydrophobic polymer matrix. When there is a net relative motion of this electrolyte with respect to the electrode, a streaming potential should result. It is hypothesized that a streaming potential mechanism within the electrode regions should be able to predict sensing responses for all modes of deformation. Based on a recently introduced parallel waterchannel morphology in Nafion® membrane, this model successfully addresses the physics of sensing in IPT bending. A linear relationship between the tip deflection of an IPT cantilever beam and the current generated in the IPT is achieved. The result trends show a good agreement with the experimental measurements. While this work studies the bending mode, it is able to be adapted for the other three sensing modes.

An eddy current testing (ECT) and an electromagnetic acoustic testing (EMAT) employ electromagnetic methods to induce an eddy current and to detect flaws on or within a sample without directly contacting it. ECT produces Lissajous curves, and EMAT gives us a time series of signal data, both of which can be directly displayed on nondestructive testing (NDT) equipment screens. Since the interpretation of such output is difficult for untrained persons, images need to be properly reconstructed and visualized. This could be carried out by single-probe 2/3D scanners with imaging capabilities or with array probes, but such equipment is often too large or heavy for ordinary on-site use. In this study, we introduce a flexible scanning tablet for on-site NDT and imaging of detected flaws. The flexible scanning tablet consists of a thin film or a paper with a digitally encoded coordinate system, applicable to flat and curved surfaces, that enables probe positions to be tracked by a specialized optical reader. We also discuss how ECT and EMAT probe coordinates and measurement data could be simultaneously derived and used for further image reconstruction and visualization.