This paper provides an overview of ongoing laser ultrasonics based structural health monitoring (SHM) activities being performed by the author. Particular focus is given to (1) the development of a fully noncontact laser ultrasonic system that can easily visualize defects with high spatial resolution, (2) laser based wireless power and data transmission schemes for remote guided waves and impedance measurements, (3) minimization of false alarms due to varying operational and environmental conditions, and (4) extension to embedded laser ultrasonic excitation and sensing. SHM examples ranging from bridges to airplanes, as well as nuclear power plants, high-speed rails and wind turbines are also presented.

In this paer the application of output-only system identification technique, known as Stochastic Subspace Identification (SSI) algorithms, for civil infrastructures is carried out. The ability of covariance driven stochastic subspace identification (SSI-COV) was proved through the analysis of the ambient data of an arch bridge under operational condition. A newly developed signal processing technique, Singular Spectrum analysis (SSA), capable to smooth noisy signals, is adopted for pre-processing the recorded data before the SSI. The conjunction of SSA and SSICOV provides a useful criterion for the system order determination. With the aim of estimating accurate modal parameters of the structure in off-line analysis, a stabilization diagram is constructed by plotting the identified poles of the system with increasing the size of data Hankel matrix. Identification task of a real structure, Guandu Bridge, is carried out to identify the system natural frequencies and mode shapes. The uncertainty of the identified model parameters from output-only measurement of the bridge under operation condition, such as temperature and traffic loading conditions, is discussed.

High tensile strength steel strands are widespread load carrying structural components in civil structures. Due to their critical role, several researchers have investigated nondestructive techniques to assess the presence of damage such as corrosion or the change in prestress level (prestress loss). Ultrasonic Guided Waves are known to be an effective approach for defect detection in components with waveguide geometry such as strands. However, Guided Wave propagation (dispersion properties) in steel strands is fairly complex partially due to the strand helical geometry and the influence of axial prestress. For instance, the strand axial stress generates a proportional radial stress between adjacent wires (interwire stress) that is responsible for inter-wire coupling effects. While experimental and numerical investigations have attempted to study and predict wave propagation in axially loaded strands, the propagation phenomenon is not yet fully understood. The present paper intends to improve the knowledge of dispersion properties in progressively loaded seven wire strands accounting for helical geometry and interwire contact forces. Full three dimensional Finite Element simulations as well as Semi-Analytical Models will be used to predict the dispersion curves in strands as a function of the axial stress.

This paper introduces a damage diagnosis algorithm for civil structures that uses a sequential change point detection method for the cases where the post-damage feature distribution is unknown a priori. This algorithm extracts features from structural vibration data using time-series analysis and then declares damage using the change point detection method. The change point detection method asymptotically minimizes detection delay for a given false alarm rate. The conventional method uses the known pre- and post-damage feature distributions to perform a sequential hypothesis test. In practice, however, the post-damage distribution is unlikely to be known a priori. Therefore, our algorithm estimates and updates this distribution as data are collected using the maximum likelihood and the Bayesian methods. We also applied an approximate method to reduce the computation load and memory requirement associated with the estimation. The algorithm is validated using multiple sets of simulated data and a set of experimental data collected from a four-story steel special moment-resisting frame. Our algorithm was able to estimate the post-damage distribution consistently and resulted in detection delays only a few seconds longer than the delays from the conventional method that assumes we know the post-damage feature distribution. We confirmed that the Bayesian method is particularly efficient in declaring damage with minimal memory requirement, but the maximum likelihood method provides an insightful heuristic approach.

The motivation of this work is the installation of a monitoring system on a new cable-stayed bridge spanning the Adige River 10 km north of the town of Trento. This is a statically indeterminate structure, having a composite steel-concrete deck of length 260 m overall, supported by 12 stay cables, 6 per deck side. These are full locked steel cables of diameters 116 mm and 128 mm, designed for operational loads varying from 5000 to 8000 kN. The structural redundancy suggests that plastic load redistribution among the cables can be expected in the long term. To monitor such load redistribution, the owner decided to install a monitoring system to measure cable stress; the precision specified was of the order of few MPa. However no cable release or any form of on-site calibration involving tension change was allowed. The solution found was a combination of built-on-site electromagnetic and fiber-optic elongation gauges, these appropriately distributed on both the cables and the anchorages. We discuss how the set of gauges allows tension and elongation measurement with the appropriate precision, and compare the initial monitoring results with the tension estimates made using a non-destructive vibration test.

This paper presents a theoretical modeling of power and energy transduction of structurally-bonded piezoelectric wafer active sensors (PWAS) for structural health monitoring (SHM). After a literature review of the state of the art, we developed a model of power and energy transduction between the PWAS and a structure containing multimodal ultrasonic guided waves. The use of exact Lamb waves modes for power modeling is an extension of our previously presented simplified model that considered axial and flexural waves with low frequency approximation. The model assumptions include: (a) straight-crested multimodal ultrasonic guided wave propagation; (b) ideal bonding (pin-force) connection between PWAS and structure; (c) ideal excitation source at the transmitter PWAS and fully-resistive external load at the receiver PWAS. Frequency response functions are developed for voltage, current, complex power, active power, etc. Multimodal ultrasonic guided wave, normal mode expansion, electromechanical energy transformation of PWAS and structure were considered. The parametric study of PWAS size and impedance match gives the PWAS design guideline for PWAS sensing and power harvesting applications

The paper presents experimental results of applying an ultrasonic monitoring system to a real-world operating hot-water supply system. The purpose of these experiments is to investigate the feasibility of continuous ultrasonic damage detection on pipes with permanently mounted piezoelectric transducers under environmental and operational variations. Ultrasonic guided wave is shown to be an efficient damage detector in laboratory experiments. However, environmental and operational variations produce dramatic changes in those signals, and therefore a useful signal processing approach must distinguish change caused by a scatterer from change caused by ongoing variations. We study pressurized pipe segments (10-in diameter) in a working hot-water supply system that experiences ongoing variations in pressure, temperature, and flow rate; the system is located in an environment that is mechanically and electrically noisy. We conduct pitch-catch tests, with a duration of 10 ms, between transducers located roughly 12 diameters apart. We applied different signal processing techniques to the collected data in order to investigate the ongoing environmental and operational variations and the stationarity of the signal. We present our analysis of these signals and preliminary detection results.

Thermoelastic guided waves, induced by a laser pulse on a material surface, demonstrate advantages for nondestructive evaluation of structures due to the non-contact feature and effectiveness to generate broadband signals. Both symmetric and asymmetric Lamb waves can be generated by the local thermal expansion from the laser energy absorption. We consider the thermomechanical equation and solve the problems using the finite element method. The capability of the finite element method for the modeling of guided wave propagation induced by laser pulses is demonstrated, and the computational efficiency is improved significantly by partitioning the plate into thermomechanical and mechanical subregions. Numerical results are compared with experimental observations of Lamb waves generated by unfocused and line-focused laser sources. Using the wavelet transform, the group velocity of A₀ mode is obtained from the detected signal and compared to the solution of Rayleigh-Lamb equations. Lamb waves in a plate with defects of different lengths are examined.

In this paper, we propose the use of highly nonlinear solitary waves (HNSWs) for the nondestructive evaluation of aluminum lap-joints bonded by high-strength two ton epoxy. A HNSW transducer was used to generate and detect the propagation of incident and reflected HNSWs. The time of flight and amplitude ratio of the reflected HNSW were adopted to interpret the bonding condition of aluminum lap-joints. Two experiments are reported. In the first experiment we monitor the curing process of a two-ton epoxy at aluminum lap-joints. In the second experiment we detect different bonding condition of aluminum lap-joints such as good bonding, fair bonding (with undesired resin to hardener ratios), slide bonding, and no bonding, after the epoxy was fully cured. The results of experiments show the proposed method is able to detect different bonding conditions of aluminum lap-joints.

For application in structural health monitoring, a folded patch antenna has been previously designed as a wireless sensor that monitors strain and crack in metallic structures. Resonance frequency of the RFID patch antenna is closely related with its dimension. To measure stress concentration in a base structure, the sensor is bonded to the structure like a traditional strain gage. When the antenna sensor is under strain/deformation together with the base structure, the antenna resonance frequency varies accordingly. The strain-related resonance frequency variation is wirelessly interrogated and recorded by a reader, and can be used to derive strain/deformation. Material properties of the antenna components can have significant effects on sensor performance. This paper investigates thermal effects through both numerical simulation and temperature chamber testing. When temperature fluctuates, previous sensor design (with a glass microfiber-reinforced PTFE substrate) shows relatively large variation in resonance frequency. To improve sensor performance, a new ceramic-filled PTFE substrate material is chosen for re-designing the antenna sensor. Temperature chamber experiments are also conducted to the sensor with new substrate material, and compared with previous design.

Wireless sensor network (WSN) is recently emerged as a powerful tool in the structural health monitoring (SHM). Due to the limitations of wireless channel capacity and the heavy data traffic, the control on the network is usually not real time. On the other hand, many SHM applications require quick response when unexpected events, such as earthquake, happen. Realizing the need to have an agile monitoring system, an approach, called sandwich node, was proposed. Sandwich is a design of complex sensor node where two Imote2 nodes are connected with each other to enhance the capabilities of the sensing units. The extra channel and processing power, added into the nodes, enable agile responses of the sensing network, particularly in interrupting the network and altering the undergoing tasks for burst events. This paper presents the design of a testbed for examination of the performance of wireless sandwich nodes in a network. The designed elements of the network are the software architecture of remote and local nodes, and the triggering strategies for coordinating the sensing units. The performance of the designed network is evaluated through its implementation in a monitoring test in the laboratory. For both original Imote2 and the sandwich node, the response time is estimated. The results show that the sandwich node is an efficient solution to the collision issue in existing interrupt approaches and the latency in dense wireless sensor networks.

The development of effective structural health monitoring (SHM) strategies is critical as aging infrastructure remains a national concern with widespread impact on the quality of our daily lives. Wireless smart sensor networks (WSSNs) are an attractive alternative to traditional SHM systems for their lower deployment cost and their ability to enable new methods of distributed data processing. While acceleration has been the primary measurement utilized in most WSSN SHM applications, practically and accurately capturing structural deflections has been proven much more challenging. Displacement sensors produce reliable low-frequency measurements but are often difficult to implement in long-term field deployments. Conventional technologies for measuring deflection, both dynamic and static, are either too bulky or expensive to be integrated into WSSNs or lack sufficient accuracy. This paper presents the validation and characterization of a network of low-cost, wireless radar-based sensors for the enhancement of low-frequency vibrationbased bridge monitoring and the measurement of static bridge deflections. Experimental results utilizing a laboratoryscale truss bridge are presented and the performance of the wireless radar sensors is compared to conventional vibration and displacement transducers. In addition, challenges associated with detection distance, interference rejection and signal processing are discussed.

Increasingly, NASA exploration mission objectives include sample acquisition tasks for in-situ analysis or for potential sample return to Earth. To address the requirements for samplers that could be operated at the conditions of the various bodies in the solar system, a piezoelectric actuated percussive sampling device was developed that requires low preload (as low as 10N) which is important for operation at low gravity. This device can be made as light as 400g, can be operated using low average power, and can drill rocks as hard as basalt. Significant improvement of the penetration rate was achieved by augmenting the hammering action by rotation and use of a fluted bit to provide effective cuttings removal. Generally, hammering is effective in fracturing drilled media while rotation of fluted bits is effective in cuttings removal. To benefit from these two actions, a novel configuration of a percussive mechanism was developed to produce an augmenter of rotary drills. The device was called Percussive Augmenter of Rotary Drills (PARoD). A breadboard PARoD was developed with a 6.4 mm (0.25 in) diameter bit and was demonstrated to increase the drilling rate of rotation alone by 1.5 to over 10 times. Further, a large PARoD breadboard with 50.8 mm diameter bit was developed and its tests are currently underway. This paper presents the design, analysis and preliminary test results of the percussive augmenter.

Real time global subsurface geo-sensing and monitoring can be achieved using a new concept of wireless sensor networks. The new concept uses the signal strength variation of wireless sensor nodes in the host medium as the main indicator of a subsurface event or change in physical properties of the soil such as water content, density, and formation of discontinuities. The feasibility of implementing the wireless signal networks for subsurface monitoring has been investigated through laboratory simulation experiments which demonstrated that the wireless signal networks is a viable approach for a reliable geo-sensing and monitoring of subsurface hazards. The challenges facing the wireless signal networks for implementation in geo-sensing and subsurface monitoring are discussed in this paper. These challenges are divided into network and geo-media categories and potential solutions to these challenges are offered for most cases.

In recent years, wireless sensor network (WSN), as a powerful tool, has been widely applied to structural health monitoring (SHM) due to its low cost of deployment. Several commercial hardware platforms of wireless sensor networks (WSN) have been developed and used for structural monitoring applications [1,2]. A typical design of a node includes a sensor board and a mote connected to it. Sensing units, analog filters and analog-to-digital converters (ADCs) are integrated on the sensor board and the mote consists of a microcontroller and a wireless transceiver. Generally, there are a set of sensor boards compatible with the same model of mote and the selection of the sensor board depends on the specific applications. A WSN system based on this node lacks the capability of interrupting its scheduled task to start a higher priority task. This shortcoming is rooted in the hardware architecture of the node. The proposed sandwich-node architecture is designed to remedy the shortcomings of the existing one for task preemption. A sandwich node is composed of a sensor board and two motes. The first mote is dedicated to managing the sensor board and processing acquired data. The second mote controls the first mote via commands. A prototype has been implemented using Imote2 and verified by an emulation in which one mote is triggered by a remote base station and then preempts the running task at the other mote for handling an emergency event.

DuraMote is a MEMS-based remote sensing system, which is developed for the NIST TIP project, Next Generation SCADA for Prevention and Mitigation of Water System Infrastructure Disaster. It is designed for supervisory control and data acquisition (SCADA) of pipe ruptures in water distribution systems. In this project, a method is developed to detect the pipe ruptures by analyzing the acceleration data gathered by DuraMote which consists of two primary components; the first, "Gopher" contains the accelerometers and are attached to the water pipe surface noninvasively, and the second, "Roocas" is placed above ground supplying the power to, and retrieving the data from the multiple Gophers, and then transmit the data through Wi-Fi to a base station. The relays support the Wi-Fi network to facilitate the transmission. A large scale bridge provides an ideal test-bet to validate the performance of such a complex monitoring system as DuraMote for its accuracy, reliability, robustness, and user friendliness. This is because a large bridge is most of the time subjected to susceptible level of ambient vibration due to passing loads, wind, etc. DuraMote can record the acceleration time history arising from the vibration making it possible to estimate the frequency values of various bridge vibration modes. These estimated frequency values are then compared with the values computed from analytical model of the bridge for the verification of the accuracy of DuraMote. It is noted that such a verification method cannot be used practically by deploying DuraMote on a water distribution network since the dynamic behavior of a pipe network, either above or underground, is too complex to model analytically for this purpose, and in addition, the network generally lacks conveniently recordable ambient vibration. In this experiment, the performance of DuraMote system was tested being installed on the Hwamyung Bridge, a 500 m long RC cable stayed bridge in Korea for long term monitoring. In total, the system consisted of 24 accelerometers, 13 Gophers, 10 Roocas, 5 relays, and 1 base station. As it happened, the bridge was subjected to heavy rain, winds, and a typhoon during the experiment allowing the DuraMote to demonstrate extra ordinary robustness and durability. Indeed, in spite of the rough weather, acceleration data was continuously recorded from which natural frequencies, mode shapes, and other structural parameters were calculated. This opportunity would not have happened if the experiment was planned for a shorter duration.

Embedded computation in wireless sensor networks (WSN) can extract useful information from sensor data in a fast and efficient manner. Embedded computing has the benefit of saving both bandwidth and power. However, computational capability often comes at the expense of power consumption on the wireless sensor node. This is an especially critical issue for battery powered wireless sensor nodes. By developing a hybrid network consisting of wireless units optimized for sensing interspersed with more powerful computationally focused units, it is now possible to build a network that is more efficient and flexible than a homogeneous WSN. For this project, such a network was developed using Narada units as low-power sensing units and iMote2 units as ultra-efficient computational engines. In order to demonstrate the capabilities of such a configuration a network was created to extract structural modal parameters based on Markov parameters. This paper validates the performance of the heterogeneous WSN using a laboratory structure tested under impulse loading.

Wireless Smart Sensor Networks (WSSNs) facilitates a new paradigm to structural identification and monitoring for civil infrastructure. Conventional monitoring systems based on wired sensors and centralized data acquisition and processing have been considered to be challenging and costly due to cabling and expensive equipment and maintenance costs. WSSNs have emerged as a technology that can overcome such difficulties, 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 is common practice, WSSNs require decentralized computing algorithms to reduce data transmission due to the limitation associated with wireless communication. Thus, several system identification methods have been implemented to process sensor data and extract essential information, including Natural Excitation Technique with Eigensystem Realization Algorithm, Frequency Domain Decomposition (FDD), and Random Decrement Technique (RDT); however, Stochastic Subspace Identification (SSI) has not been fully utilized in WSSNs, while SSI has the strong potential to enhance the system identification. This study presents a decentralized system identification using SSI in WSSNs. The approach is implemented on MEMSIC's Imote2 sensor platform and experimentally verified using a 5-story shear building model.

During or after an earthquake event, building system often experiences large strains due to shaking effects as observed during recent earthquakes, causing permanent inelastic deformation. In addition to the inelastic deformation induced by the earthquake effect, the post-earthquake fires associated with short fuse of electrical systems and leakage of gas devices can further strain the already damaged structures during the earthquakes, potentially leading to a progressive collapse of buildings. Under these harsh environments, measurements on the involved building by various sensors could only provide limited structural health information. Finite element model analysis, on the other hand, if validated by predesigned experiments, can provide detail structural behavior information of the entire structures. In this paper, a temperature dependent nonlinear 3-D finite element model (FEM) of a one-story steel frame is set up by ABAQUS based on the cited material property of steel from EN 1993-1.2 and AISC manuals. The FEM is validated by testing the modeled steel frame in simulated post-earthquake environments. Comparisons between the FEM analysis and the experimental results show that the FEM predicts the structural behavior of the steel frame in post-earthquake fire conditions reasonably. With experimental validations, the FEM analysis of critical structures could be continuously predicted for structures in these harsh environments for a better assistant to fire fighters in their rescue efforts and save fire victims.

This paper will discuss a new distributed fiber optics sensing technology that uses an array of low reflectivity fiber gratings having the same center wavelength. Furthermore this array would be embedded in a military grade reinforced outdoor cable. Three of these gratings cables are to be stitched onto a meter high geo textile and used as a solution for landslides warning. The special cable is made with a material that prevents moisture penetration and provides extra pulling strength of up to 500 Newtons. The geo-textile provides the added restraining force of up to 1100 Newtons. The solution is therefore capable of not only measuring small earth movements but also provides added time delay in a pending crisis so that people can evacuate from danger.

The SmartBrick network is an autonomous and wireless solution for structural health monitoring of civil infrastructures. The base station is currently in its third generation and has been laboratory- and field-tested in the United States and Italy. The second generation of the sensor nodes has been laboratory-tested as of publication. In this paper, we present recent enhancements made to hardware and software of the SmartBrick platform. Salient improvements described include the development of a new base station with fully-integrated long-range GSM (cellular) and short-range ZigBee communication. The major software improvement described in this paper is migration to the ZigBee PRO stack, which was carried out in the interest of interoperability. To broaden the application of the platform to critical environments that require survivability and fault tolerance, we have striven to achieve compliance with military standards in the areas of hardware, software, and communication. We describe these efforts and present a survey of the military standards investigated. Also described is instrumentation of a three-span experimental bridge in Washington County, Missouri; with the SmartBrick platform. The sensors, whose output is conditioned and multiplexed; include strain gauges, thermocouples, push potentiometers, and three-axis inclinometers. Data collected is stored on site and reported over the cellular network. Real-time alerts are generated if any monitored parameter falls outside its acceptable range. Redundant sensing and communication provide reliability and facilitate corroboration of the data collected. A web interface is used to issue remote configuration commands and to facilitate access to and visualization of the data collected.

In this study, wireless structural health monitoring (SHM) system of cable-stayed bridge is developed using Imote2- platformed smart sensors. In order to achieve the objective, the following approaches are proposed. Firstly, vibrationand impedance-based SHM methods suitable for the pylon-cable-deck system in cable-stayed bridge are briefly described. Secondly, the multi-scale vibration-impedance sensor node on Imote2-platform is presented on the design of hardware components and embedded software for vibration- and impedance-based SHM. In this approach, a solarpowered energy harvesting is implemented for autonomous operation of the smart sensor node. Finally, the feasibility and practicality of the multi-scale sensor system is experimentally evaluated on a real cable-stayed bridge, Hwamyung Bridge in Korea. Successful level of wireless communication and solar-power supply for smart sensor nodes are verified. Also, vibration and impedance responses measured from the target bridge which experiences various weather conditions are examined for the robust long-term monitoring capability of the smart sensor system.

Wireless Smart Sensor Networks (WSSNs) have attracted great attention in recent years for Structural Health Monitoring (SHM), enabling better understanding of the dynamic behavior of large scale civil infrastructures through dense deployment of sensors. With a fraction of the deployment time and cost compared with wired SHM systems, WSSNs can serve as ideal systems for campaign-type monitoring for (i) short-term, in-service performance evaluation, (ii) postdisaster condition assessment, (iii) design optimization of long-term SHM system before permanent deployment, etc. Efficient data collection is generally needed in campaign monitoring due to limited operation time. A number of improvements have been made to the Illinois SHM Project (ISHMP) Services Toolsuite to facilitate efficient data collection for campaign monitoring. A post-sensing time synchronization scheme is proposed to reduce the latency of data collection while maintaining high accuracy of synchronization of collected data. A multi-hop bulk data transfer approach using multiple RF channels is also implemented to achieve high data throughput.

Fatigue cracks often initiate at the weld toes of welded steel connections. Usually, these cracks cannot be identified by the naked eyes. Existing identification methods like dye-penetration test and alternating current potential drop (ACPD) may be useful for detecting fatigue cracks at the weld toes. To apply these non-destructive evaluation (NDE) techniques, the potential sites have to be accessible during inspection. Therefore, there is a need to explore other detection and monitoring techniques for fatigue cracks especially when their locations are inaccessible or cost of access is uneconomical. Electro-mechanical Impedance (EMI) and Lamb wave techniques are two fast growing techniques in the Structural Health Monitoring (SHM) community. These techniques use piezoelectric ceramics (PZT) for actuation and sensing. Since the monitoring site is only needed to be accessed once for the instrumentation of the transducers, remote monitoring is made possible. The permanent locations of these transducers also translate to having consistent measurement for monitoring. The main focus of this study is to conduct a comparative investigation on the effectiveness and efficiency of the EMI technique and the Lamb wave technique for successful fatigue crack identification and monitoring of welded steel connections using piezoelectric transducers. A laboratory-sized non-load carrying fillet weld specimen is used in this study. The specimen is subjected to cyclic tensile load and data for both techniques are acquired at stipulated intervals. It can be concluded that the EMI technique is sensitive to the crack initiation phase while the Lamb wave technique correlates well with the crack propagation phase.

A beamforming array technique with 4 sensors is applied to a cylindrical plate for detecting point of impact. Linear array of acoustic sensors attached to the plate record the waveforms of Lamb waves generated at the impact point with individual time delay. An optimization technique with an objective function is incorporated into the beamforming technique in order to deal with the direction dependent Lamb wave speeds in a cylindrical geometry. The optimization is carried out using the experimentally obtained wave speed as a function of propagation direction. The maximum point in beamforming plot with minimized objective function corresponds to the localized point of impact. The proposed technique is experimentally verified by comparing the predicted points with the exact points of impact on a cylindrical aluminum plate. For randomly chosen points of impact the beamforming technique successfully predicts location of the exact acoustic source.

This paper studies the development of a PWAS-based wireless AE sensor that consumes around 2 mW. Low power charge amplifiers were designed and implemented to match the high impedance of the PWAS transducer to the low impedance of the passive wireless transponder. Two different designs of the charge amplifier were evaluated using an ultrasound pitch-catch system and pencil lead break experiments. Wireless acquisition of the AE signal was demonstrated. The low-power consumptions of the amplifiers indicate that a battery-less wireless AE sensor can be achieved using energy harvesting devices.

This research investigates the field performance of a mobile sensor network designed for structural health monitoring. Each mobile sensing node (MSN) is a small magnet-wheeled tetherless robot that carries sensors and autonomously navigates on a steel structure. A four-node mobile sensor network is deployed for navigating on the top plane of a space frame bridge. With little human effort, the MSNs navigate to different sections of the steel bridge, attach accelerometers, and measure structural vibrations at high spatial resolution. Using high-resolution data collected by a small number of MSNs, detailed modal characteristics of the bridge are identified. A finite element model for the bridge is constructed according to structural drawings, and updated using modal characteristics extracted from mobile sensing data.

Structural health monitoring (SHM) is crucial for detecting sudden and progressive damage and for preventing catastrophic structural failure. Piezoelectric materials have been widely adopted for their use as sensors and as actuators. Piezoceramics (such as lead zirconate titanate) offer high piezoelectricity but are mechanically brittle. Poly(vinylidene fluoride) (PVDF) piezopolymers are conformable to complex structural surfaces but exhibit lower piezoelectricity. So as to achieve a combination of these desirable properties, piezoelectric zinc oxide (ZnO) nanomaterials are proposed for embedment in flexible polymer matrices during fabrication to yield high-performance piezoelectric nanocomposites. The main objective of this research is to characterize the piezoelectricity of nanocomposites formed by embedding ZnO nanoparticles in a PVDF-trifluoroethylene (TrFE) matrix. Film fabrication is performed by dispersing ZnO into a PVDFTrFE solution and then by spin coating the solution onto a rigid substrate. A high electric field is applied to each of the films for poling, and the films' remnant polarization is quantified by measuring their ferroelectric response using a Sawyer-Tower circuit. Graphs of electric field compared to electric displacement can be obtained for determining the films' piezoelectricity. Finally, validation of their sensing performance is achieved by hammer impact testing.

Due to their cost-effectiveness and ease of installation, smart wireless sensors have received considerable recent attention for structural health monitoring of civil infrastructure. Though various wireless smart sensor networks (WSSN) have been successfully implemented for full-scale structural health monitoring (SHM) applications, monitoring of low-level ambient strain still remains a challenging problem for wireless smart sensors (WSS) due to A/D converter resolution, inherent circuit noise, and the need for automatic operation. In this paper, the design and validation of high-precision strain sensor board for Imote2 WSS platform and its application to SHM of a cable-stayed bridge are presented. By accurate and automated balancing the Wheatstone bridge, signal amplification of up to 2507-times can be obtained. Temperature compensation and shunt calibration are implemented. In addition to traditional foil-type strain gages, the sensor board has been designed to accommodate a friction-type magnet strain sensor, facilitating fast and easy deployment. The sensor board has been calibrated using lab-scale tests, and then deployed on a full-scale cable-stayed bridge to verify its performance.

For the safety of cable-stayed bridges, it is very important to ensure the tensile forces of cables. The loss of cable force could significantly reduce load carrying capacity of the structure and even results in structural collapse. This study presents a smart PZT-interface associated with wireless sensing device for tendon force-loss monitoring in cable-stayed bridge. The following approaches are carried out to achieve the objective. Firstly, a smart PZT-interface is designed to monitor the cable force-loss by using electromechanical impedance-based method. Secondly, wireless impedance sensor node is designed for impedance monitoring. The sensor node is mounted on the high-performance Imote2 sensor platform to fulfill high operating speed, low power requirement and large storage memory. Finally, a system of smart PZT-interface and wireless sensor node is evaluated for its performance on a lab-scale cable-anchorage model.

Growing public concern regarding the health of the aging civil infrastructure has spurred research in structural health monitoring (SHM). Recent advances in wireless smart sensor (WSS) technology has significantly lowered the cost of SHM systems and resulted in WSS being successfully implemented at full-scale. However, assuring accurate timesynchronized WSS nodes in a network is still a challenging problem. Generally, WSS synchronization is realized by communicating a sensors' CPU clock information over the network. However, such a synchronization approach becomes more challenging as the network size increases. Reliable communication is not easily achieved due to longer communication distance, larger numbers of sensors, and complexity of a distributed sensor network. Moreover, CPU clocks may not be sufficiently reliable for accurate time-synchronization due to substantial tolerance errors in crystal and/or temperature effects. In this study, the use of low-cost GPS receivers for time synchronizing WSSs is explored to resolve these issues. GPS sensors offer the potential to provide high-accuracy synchronization --- nano-second level even with low-cost GPS receivers. The GPS-assisted time synchronization approach overcomes network communication limitations to realize time-synchronization in large-scale networks of WSS.

A passive, wireless sensor has been developed at the University of Texas at Austin to monitor the insitu conductivity of concrete within civil infrastructure systems. Electrical conductivity is one possible indicator of corrosion of embedded reinforcement and thereby provides information on structural performance. The sensors would be attached to the reinforcement cages before placement of the concrete and interrogated as part of a routine inspection over the service life. A new sensor design, a non-contact conductivity sensor, is being developed to minimize the likelihood of damage to the sensor during placement of the concrete; a metal element is positioned above the sensor body but is not connected to the resonant circuit within the sensor. In order to verify the response of the non-contact conductivity sensors, they were submerged in liquids of increasing conductivity. Analysis of the measured data demonstrated that the noncontact conductivity sensors successfully detected conductivity variations in liquids.

In the field of structural health monitoring using wireless sensors, considerable research attention has been recently given to vibration-based energy harvesting devices for exploring their feasibility as a power source of a wireless sensor node. Most of the previous studies have focused on lab-scale tests for performance validation. For real application, however, field tests on developed energy harvesting devices should be conducted, because their performance may be considerably affected by change in the testing environment. In this study, a new electromagnetic energy harvester is proposed, which is more suitable for civil engineering application, and the preliminary field test on a real cable-stayed bridge are conducted to validate its effectiveness.

A foot ulcer is the initiating factor in 85% of all diabetic amputations. Ulcer formation is believed to be contributed by both pressure and shear forces. There are commercially available instruments that can measure plantar pressure. However, instruments for plantar shear measurement are limited. In this paper, we investigate the application of antenna sensors for shear and pressure measurement. The principle of operation of both antenna sensors will be discussed first, followed by detailed descriptions on the antenna designs, sensor fabrication, experimental setup, procedure and results. Because the antenna sensors are small in size, can be wirelessly interrogated, and are frequency multiplexable, we plan to embed them in shoes for simultaneous mapping of plantar shear and pressure distributions in the future.

This paper shows an evaluating method of synchronization between a structure and Central Pattern Generators (CPGs), which are embedded in a controller designed for an active mass damper. A neural oscillator composing the CPGs has nonlinear and entrainment properties. Therefore, the proposed controller has possibility to exhibit the characteristic of robustness, when the structural parameters, i.e. stiffness or damping, are changed by earthquakes and the like. Our earlier studies have proposed the new controller and ascertained the efficacy of vibration suppression. However, there has been no study to evaluate the controller's above-mentioned properties. For tuning into practical application, the reliability and robustness along with the controller's vibration mitigation performance must be analyzed. In this paper, phase reduction theory is tried to appraise the synchronization between a structure and the CPGs. In this case, the synchronization between the target structure and a single neural oscillator constituting the CPGs is required to be investigated. Therefore, the single neural oscillator's the harmonization characteristic with sinusoidal input is firstly examined, and the synchronization region is expressed using phase response curves. In addition, the mutual synchronization between the structure and the single neural oscillator is studied under sinusoidal input using the result of the harmonization characteristic.

In the simultaneous localization and mapping (SLAM) problem, it is required for a robotic system to acquire the map of its environment while simultaneously localizing itself relative to this evolving map. In order to solve the SLAM problem, given observations of the environment and control inputs, the joint posterior probability of the robot pose and the map are estimated by using recursive filters such as the extended Kalman filter (EKF) and the particle filter. The implementation of these filters requires a motion model to describe the evolution of the robot pose with control inputs, and additionally, an observation model to describe the relations between the robot pose and measurements of the environment. In general, the motion model is derived from the kinematics of the robotic system, without taking the system dynamics into account. In this article, the authors investigate the performance and efficacy of standard SLAM algorithms when the dynamics of the robotic system is taken into account in the motion model and provide experimental results to complement the simulation findings.

Silicon has piezoresistive property that allows designing strain sensor with higher gauge factor compared to conventional metal foil gauges. The sensing element can be micro-scale using MEMS, which minimizes the effect of strain gradient on measurement at stress concentration regions such as crack tips. The challenge of MEMS based strain sensor design is to decouple the sensing element from substrate for true strain measurement and to compensate the temperature effect on the piezoresistive coefficients of silicon. In this paper, a family of MEMS strain sensors with different geometric designs is introduced. Each strain sensor is made of single crystal silicon and manufactured using deposition/ etching/oxidation steps on a n- doped silicon wafer in (100) plane. The geometries include sensing element connected to the free heads of U shape substrate, a set of two or more sensing elements in an array in order to capture strain gradients and two directional sensors. The response function and the gauge factor of the strain sensors are identified using multi-physics models that combine structural and electrical behaviors of sensors mounted on a strained structure. The relationship between surface strain and strain at microstructure is identified numerically in order to include the relationship in the response function calculation.

In this research, longitudinal strain and peel stress in adhesive-bonded single-lap joint of carbon fiber reinforced plastics (CFRP) were measured and estimated by embedded fiber Bragg grating (FBG) sensor. Two unidirectional CFRP substrates were bonded by epoxy to form a single-lap configuration. The distributed strain measurement system is used. It is based on optical frequency domain reflectometry (OFDR), which can provide measurement at an arbitrary position along FBG sensors with the high spatial resolution. The longitudinal strain was measured based on Bragg grating effect and the peel stress was estimated based on birefringence effect. Special manufacturing procedure was developed to ensure the embedded location of FBG sensor. A portion of the FBG sensor was embedded into one of CFRP adherends along fiber direction and another portion was kept free for temperature compensation. Photomicrograph of cross-section of specimen was taken to verify the sensor was embedded into proper location after adherend curing. The residual strain was monitored during specimen curing and adhesive joint bonding process. Tensile tests were carried out and longitudinal strain and peel stress of the bondline are measured and estimated by the embedded FBG sensor. A two-dimensional geometrically nonlinear finite element analysis was performed by ANSYS to evaluate the measurement precision.

This paper presents a wireless interrogation system using impedance switching and amplitude modulation to detect the resonant frequency shift of antenna sensors under external load. The wireless antenna sensor, constructed by a few microwave components, is able to detect small strain changes without requiring any local power source. First, the principle of operation of the unpowered wireless interrogation system is discussed, followed by the characterization of the effect of applied strains on the resonant frequency of the antenna sensor. The shifts of the resonant frequency under different loads were correlated to the strains experienced by the antenna sensor. The experimental results agreed well with the analytical prediction.

Previous research demonstrated that a thin self-healing layer is effective in recovering partial sandwich composite performance after an impact event. Many studies have been conducted that show the possibility of using Fiber Bragg Grating (FBG) sensors to monitor the cure of a resin through strain and temperature monitoring. For this experiment, FBG sensors were used to monitor the curing process of a self-healing layer within a twelve-layer fiberglass laminate after impact. First, five self-healing sandwich composite specimens were manufactured. FBG sensors were embedded between the fiberglass and foam core. Then the fiberglass laminate was impacted with the use of a drop tower and the curing process was monitored. The collected data was used to compare the cure of the resin and fiberglass alone to the cure of the resin from a self-healing specimen. For the low viscosity resin system tested, these changes were not sufficiently large to identify different polymerization states in the resin as it cured. These results indicate that applying different resin systems might increase the efficiency of the self-healing in the sandwich composites.

Wind energy is an increasingly important component of this nation's renewable energy portfolio, however safe and economical wind turbine operation is a critical need to ensure continued adoption. Safe operation of wind turbine structures requires not only information regarding their condition, but their operational environment. Given the difficulty inherent in SHM processes for wind turbines (damage detection, location, and characterization), some uncertainty in conditional assessment is expected. Furthermore, given the stochastic nature of the loading on turbine structures, a probabilistic framework is appropriate to characterize their risk of failure at a given time. Such information will be invaluable to turbine controllers, allowing them to operate the structures within acceptable risk profiles. This study explores the characterization of the turbine loading and response envelopes for critical failure modes of the turbine blade structures. A framework is presented to develop an analytical estimation of the loading environment (including loading effects) based on the dynamic behavior of the blades. This is influenced by behaviors including along and across-wind aero-elastic effects, wind shear gradient, tower shadow effects, and centrifugal stiffening effects. The proposed solution includes methods that are based on modal decomposition of the blades and require frequent updates to the estimated modal properties to account for the time-varying nature of the turbine and its environment. The estimated demand statistics are compared to a code-based resistance curve to determine a probabilistic estimate of the risk of blade failure given the loading environment.

Localization of defects and determination of the depth and size using Infrared Thermography is a critical problem in wind turbine blades. Infrared Thermography offers significant advantages over other Nondestructive Testing modalities due to fast, wide-area inspection capabilities. Lock-in Thermography is an ideal method for defect detection due to the presence of deep-lying defects in wind turbine blades, which otherwise go undetected. Multivariate Outlier Analysis is used in conjunction with Lock-in technique to enhance the detectability of the defect. Results are presented on defects present in a 9m CX-100 wind turbine blade that was designed by the Sandia National Laboratory. A defect depth estimation technique based on Pulsed Thermography is also presented. A 3D depth estimation model is presented which aims to address the shortcomings of the classical depth estimation methods that are primarily based on the 1D heat conduction equation. Results are presented on a stainless steel sample with flat-bottom defects at known depths. The results are in excellent agreement with the proposed theory.

The wind energy industry is rapidly growing in order to meet the increasing world energy demands as well as the need for clean and renewable energy sources. With the goal to explore new technologies and innovations which could help potentially improve the efficiency and effectiveness of wind energy, the NDE/SHM laboratory at UCSD acquired a unique wind turbine blade that will be used for performing several research projects related to wind turbine blade technology and non-destructive inspection techniques. The blade was built using the CX-100 design developed by TPI Composites, Inc. and Sandia National Laboratory (SNL). The 9-m blade was constructed with several embedded defects that represent the most common manufacturing defects typically found, such as out-of-plane waviness, composite delamination, and adhesive disbond. The defects were embedded during the manufacturing process by using similar methods developed by both TPI and SNL for simulating actual defect characteristics. Though the blade is small in comparison to the average utility sized blade of around 40 meters, the blade features similar materials and manufacturing methods, allowing for several inspections techniques to be studied on a representative platform. The inspection techniques include advanced infrared thermography and other guided wave techniques.

We will present a simple and low cost method to visualize local strain distribution in deformed aluminum plates. In this study, aluminum plates were coated with opal photonic crystal film with tunable structural color. The photonic crystal films consist of a silicone elastomer that contains an array of submicron polystyrene colloidal particles. When the aluminum sheets were stretched, the change in the spacing of the colloidal particles in the opal film alters the color of the film. This approach could be useful as a new strain gauge having a visual indicator to detect mechanical deformation.

There is a growing interest in making sensors, optoelectronic and electronic devices with nanomaterials. Carbon nanotubes (CNTs) are unique materials due to their excellent electrical, mechanical and thermal properties, and also have good chemical stability. Single-walled carbon nanotubes (SWNTs) are formed by one atomic layer and have an extended π-bonding configuration. The conductivity of SWNTs is sensitive to trace amount of molecules or ions attached onto their surfaces. CNTs have exceptionally high sensitivity and fast response and were utilized in numerous chemical and biological sensing applications for environmental monitoring. One of the present problems with SWNT sensors is their nonselective response to many analytes. SWNTs networks were assembled onto the microelectrodes by a low temperature, low cost Dielectrophoretic (DEP) assembly process. SsDNA of different sequences were used to functionalize the nanotubes and improved their response to the gas vapors dramatically. To reduce the undesirable response of SWNTs to interfering analytes, a wireless nanosensor array with six channels each functionalized with different molecules were developed to measure the resistances of six SWNT sensors simultaneously during exposure to gases. The responses of different DNA decorated SWNTs and bare SWNTs to toxic organics were measured simultaneously and displayed by a GUI interface. Development of this wireless sensor array enabled real-time gas monitoring with various DNA functionalized SWNTs from a distance.

The steel cables in long span bridges such as cable-stayed bridges and suspension bridges are critical members which suspend the load of main girders and bridge floor slabs. Damage of cable members can occur in the form of crosssectional loss caused by fatigue, wear, and fracture, which can lead to structural failure due to concentrated stress in the cable. Therefore, nondestructive examination of steel cables is necessary so that the cross-sectional loss can be detected. Thus, an automated cable monitoring system using a suitable NDE technique and a cable climbing robot is proposed. In this study, an MFL (Magnetic Flux Leakage- based inspection system was applied to monitor the condition of cables. This inspection system measures magnetic flux to detect the local faults (LF) of steel cable. To verify the feasibility of the proposed damage detection technique, an 8-channel MFL sensor head prototype was designed and fabricated. A steel cable bunch specimen with several types of damage was fabricated and scanned by the MFL sensor head to measure the magnetic flux density of the specimen. To interpret the condition of the steel cable, magnetic flux signals were used to determine the locations of the flaws and the level of damage. Measured signals from the damaged specimen were compared with thresholds set for objective decision making. In addition, the measured magnetic flux signal was visualized into a 3D MFL map for convenient cable monitoring. Finally, the results were compared with information on actual inflicted damages to confirm the accuracy and effectiveness of the proposed cable monitoring method.

For the structural monitoring of railway bridges, electromagnetic interference (EMI) is a significant problem as modern railway lines are powered by high-voltage electric power feeding systems. Fiber optic sensing systems are free from EMI and have been successfully applied in civil engineering fields. This study presents the application of fiber Bragg grating (FBG)-based sensing systems to precast concrete box railway bridges. A 20 m long full-scale precast concrete box railway girder was fabricated and tested in order to identify its static performance. The experimental program involved the measurement of the nonlinear static behavior until failure. Multiplexed FBG strain sensors were embedded along the length of steel rebar and a strain-induced wavelength shift was measured in order to monitor internal strains. The measured values from the FBG-based sensors are compared with the results using electric signal-based sensors. The results show that the FBG sensing system is promising and can improve the efficiency of structural monitoring for modern railway bridges.

With the rapid development of electrical circuits, Micro electromechanical system (MEMS) and network technology, wireless smart sensor networks (WSSN) have shown significant potential for replacing existing wired Structural health monitoring (SHM) systems due to their cost effectiveness and versatility. A few structural systems have been monitored using WSSN measuring acceleration, temperature, wind speed, humidity; however, a multi-scale sensing device which has the capability to measure the displacement has not been yet developed. In this project, a new highaccuracy displacement sensing system has been developed combining a high resolution analog displacement sensor and MEMS-based wireless microprocessor platform. The wireless sensor is calibrated in the laboratory to get the high precision displacement data from analog sensor. The developed multi-scale sensing system is evaluated in a laboratory bridge structure to check its performance. Finally, the developed hybrid multi-scale displacement sensing system was deployed on in-service highway bridge for SHM.

Cost-effective and reliable damage detection models are crucial for successful monitoring of any ancient or modern age engineering structure. Lead Zirconate Titanate (PZT) based electromechanical impedance (EMI) method is emerging as a promising alternate for conventional structural health monitoring (SHM) of various engineering structures. The PZT patches are usually surface bonded and then excited in the presence of electric field to a desired frequency spectrum. The excitations result in prediction of unique frequency dependent electromechanical (EM) admittance signature. Any change in the signature during the monitoring period indicates dis-integrity/ damage in the host structure. However, apart from locating damages, the increase in severity of damages has to be predicted on time to avoid collapse of the entire structure. This paper presents such a model which had effectively predicted the severity of damages along a principle direction of the structure. This was achieved by experimental damage study on plates and subsequent verification by semi numerical 3D model. Statistical root mean square deviation (RMSD) index was used for evaluating the damages made on plates. Additionally, a new frequency proximity index (FPI) was introduced to measure the effectiveness of the model. RMSD measures the changes in height of peaks of signature and FPI scales the frequency spectrum of signature. Thus results of RMSD index and FPI are used as complementary to each other to study damage propagation in a structure.

In this study, an inexpensive depth sensor is used to identify defects in pavements. This depth sensor consists of an infrared projector and camera. An innovative approach is proposed to interpret the data acquired by this sensor. The proposed system in this study is a breakthrough achievement for autonomous cost-effective condition assessment of roads and transportation systems. Various road conditions including patching, cracks, and potholes can be robustly and autonomously assessed using the proposed approach. Several field experiments have been carried out to evaluate the capabilities of this system. The field tests clearly demonstrate the superior features of the developed system in this study compared to conventional approaches for pavement evaluation.

Recent progress in radar techniques and systems has led to the development of a microwave interferometer, potentially suitable for non-contact displacement monitoring of civil engineering structures. This paper describes a new interferometric radar system, named IBIS-S, which is possible to measure the static or dynamic displacement at multiple points of structures simultaneously with high accuracy. In this paper, the technical characteristics and specification of the radar system is described. Subsequently, the actual displacement sensitivity of the equipment is illustrated using the laboratory tests with random motion upon a shake table. Finally the applications of the radar system to the measurement on a cable-stayed bridge and a prestressed concrete bridge are presented and discussed. Results show that the new system is an accurate and effective method to measure displacements of multiple targets of structures. It should be noted that the current system can only measure the vibration of the target position along the sensor's line of sight. Hence, proper caution should be taken when designing the sensor posture and prior knowledge of the direction of motion is necessary.

Sensing systems play a lead role in the structural health monitoring (SHM) paradigm by performing actuation, data acquisition, and communication in order to enable the implementation of a health monitoring strategy. In many applications power provision is limited by the use of a battery as their power capacity often fails to exceed the intended long-term sensing requirements of the host structure. Energy harvesting has emerged as a potential powering solution to provide autonomous functionality to sensing systems. Galvanic corrosion as a form of energy harvesting has proved to be a viable source for operating simple low-power sensing and computing platforms for marine structures. The power characteristics of the energy harvester define a unique design problem for the sensor node power electronics, as the output voltage and current are extremely limited. This initiative considers the design of a sensor node that makes use of high-efficiency switching converters and low-power microprocessors to reduce the power demands on the energy harvester. In addition, the power electronics features a low duty-cycle control circuit to isolate the energy harvester from the sensing electronics for more efficient operation. A sensing proof-of-concept is conducted by means of temperature measurement.

This paper presented an experimental study on piezoelectric impedance based cubic and axial compressive strength gain monitoring in concrete during curing process. The piezoceramic (PZT) patch was attached on the concrete specimen to collect the monitoring signal. The electro-mechanical impedance (EMI) spectra of surface bonded PZT patch were collected using an impedance analyzer by sweeping the frequency. A regression analysis is conducted to establish the empirical relationship between the relative strength gain of concrete and the monitored relative resonant frequency change of the EMI spectra. The established empirical formula is used for concrete strength monitoring via EMI spectra. The results tell that the EMI technique is a practical and reliable nondestructive test method for concrete strength gain monitoring.

Singular value decomposition (SVD) is a powerful linear algebra tool. It is widely used in many different signal processing methods, such principal component analysis (PCA), singular spectrum analysis (SSA), frequency domain decomposition (FDD), subspace identification and stochastic subspace identification method ( SI and SSI ). In each case, the data is arranged appropriately in matrix form and SVD is used to extract the feature of the data set. In this study three different algorithms on signal processing and system identification are proposed: SSA, SSI-COV and SSI-DATA. Based on the extracted subspace and null-space from SVD of data matrix, damage detection algorithms can be developed. The proposed algorithm is used to process the shaking table test data of the 6-story steel frame. Features contained in the vibration data are extracted by the proposed method. Damage detection can then be investigated from the test data of the frame structure through subspace-based and nullspace-based damage indices.

The estimation of translational and rotational displacement of large structures is usually considered as major indicators for structural safety. Recently, several vision-based measurement methods have been developed. Most vision-based systems, however, estimate displacements in 1-D or 2-D space. There are six degree of freedom (6-DOF) measurement methods using combination of lasers and cameras. But, the system is complex to install and not easy to maintain. To mitigate this problem, this paper proposes a simple 6-DOF displacement measurement system using only one camera and a planar marker. Using the square shaped planar marker, whose world geometry is known a priori, the 6-DOF relation between the marker and the camera can be calculated. The camera with a built-in lens captures a marker image and detects corners of the marker. Using homography transformation, 6-DOF relative pose information to the structure is estimated. In order to verify the feasibility of the proposed system, experimental tests are performed. The system for experiments consists of a chargecoupled device (CCD) camera with a built-in 37× zoom lens for maker image processing. The square marker is installed about 20 meters distance away from the camera, and the displacement is estimated. The results show the applicability of the proposed 6-D measurement system to real structures.

Ultrasonic guided waves have been utilized for accurate diagnosis of structural integrities for thin structural components. In this paper, wave propagation excited by surface-mounted instruments such as PZT and MFC transducer rings in an infinite isotropic hollow cylinder is investigated. A mathematical model of the wave propagation system is studied both analytically and numerically. A detailed derivation of the characteristic equation of the system is conducted, and the development of waves is simulated using the Finite Element (FE) method. Compared with the analytical results, the accuracy of the numerical modeling is verified and Lamb wave propagation in pipes with defects is studied as well.

To inspect structural conditions, structural displacement is needed to be monitored at any time. Therefore, our previous study proposed a ViSP (Visually Servoed Paired structured light system) which is composed of two sides facing with each other, each with a camera, a screen, and one or two lasers controlled by a 2-DOF manipulator. In this system, the relative translational and rotational displacement between two sides can be estimated by calculating positions of the projected laser beams on the screens and the rotation angles of the manipulators. To validate the performance of the system, the various experimental tests with a two-story structural model were performed. The estimated results were compared with the results from a laser displacement sensor which can be considered as a reference. The results show that the presented system has potential of estimating the response of the structures with high accuracy in real time.

The ability to penetrate subsurfaces and perform sample acquisition at depths of meters is critical for future NASA in-situ exploration missions to bodies in the solar system, including Mars, Europa, and Enceladus. A corer/sampler was developed with the goal of acquiring pristine samples by reaching depths on Mars beyond the oxidized and sterilized zone. The developed rotary-hammering coring drill, called Auto-Gopher, employs a piezoelectric actuated percussive mechanism for breaking formations and an electric motor rotates the bit to remove the powdered cuttings. This sampler is a wireline drill that is incorporated with an inchworm mechanism allowing thru cyclic coring and core removal to reach great depths. The penetration rate is optimized by simultaneously activating the percussive and rotary motions of the Auto-Gopher. The percussive mechanism is based on the Ultrasonic/Sonic Drill/Corer (USDC) mechanism, which is driven by a piezoelectric stack, demonstrated to require low axial preload. The Auto-Gopher has been produced taking into account the lessons learned from the development of the Ultrasonic/Sonic Gopher that was designed as a percussive ice drill and was demonstrated in Antarctica in 2005 to reach about 2 meters deep. A field demonstration of the Auto-Gopher is currently being planned with the objective of reaching as deep as 3 to 5 meters in tufa formation.

The search for present or past life in the Universe is one of the most important objectives of NASA's exploration missions. Drills for subsurface sampling of rocks, ice and permafrost are an essential tool for astrobiology studies on other planets. Increasingly, it is recognized that drilling via a combination of rotation and hammering offers an efficient and effective rapid penetration mechanism. The rotation provides an intrinsic method for removal of cuttings from the borehole while the impact and shear forces aid in the fracturing of the penetrated medium. Conventional drills that use a single actuator are based on a complex mechanism with many parts and their use in future mission involves greater risk of failure and/or may require lubrication that can introduce contamination. In this paper, a compact drill is reported that uses a single piezoelectric actuator to produce hammering and rotation of the bit. A horn with asymmetric grooves was designed to impart a longitudinal (hammering) and transverse force (rotation) to a keyed free mass. The drill requires low axial pre-load since the hammering-impacts fracture the rock under the bit kerf and rotate the bit to remove the powdered cuttings while augmenting the rock fracture via shear forces. The vibrations 'fluidize' the powdered cuttings inside the flutes reducing the friction with the auger surface. This action reduces the consumed power and heating of the drilled medium helping to preserve the pristine content of the acquired samples. The drill consists of an actuator that simultaneously impacts and rotates the bit by applying force and torque via a single piezoelectric stack actuator without the need for a gearbox or lever mechanism. This can reduce the development/fabrication cost and complexity. In this paper, the drill mechanism will be described and the test results will be reported and discussed.

There is a great need for compact, efficient motors for driving various mechanisms including robots or mobility platforms. A study is currently underway to develop a new type of piezoelectric actuators with significantly more strength, low mass, small footprint, and efficiency. The actuators/motors utilize piezoelectric actuated horns which have a very high power density and high electromechanical conversion efficiency. The horns are fabricated using our recently developed novel pre-stress flexures that make them thermally stable and increases their coupling efficiency. The monolithic design and integrated flexures that pre-stresses the piezoelectric stack eliminates the use of a stress bolt. This design allows embedding solid-state motors and actuators in any structure so that the only macroscopically moving parts are the rotor or the linear translator. The developed actuator uses a stack/horn actuation and has a Barth motor configuration, which potentially generates very large torque and speeds that do not require gearing. Finite element modeling and design tools were investigated to determine the requirements and operation parameters and the results were used to design and fabricate a motor. This new design offers a highly promising actuation mechanism that can potentially be miniaturized and integrated into systems and structures. It can be configured in many shapes to operate as multi-degrees of freedom and multi-dimensional motors/actuators including unidirectional, bidirectional, 2D and 3D. In this manuscript, we are reporting the experimental measurements from a bench top design and the results from the efforts to miniaturize the design using 2×2×2 mm piezoelectric stacks integrated into thin plates that are of the order of 3 × 3 × 0.2 cm.

Venus is one of the planets in the solar systems that are considered for potential future exploration missions. It has extreme environment where the average temperature is 460°C and its ambient pressure is about 90 atm. Since the existing actuation technology cannot maintain functionality under the harsh conditions of Venus, it is a challenge to perform sampling and other tasks that require the use of moving parts. Specifically, the currently available electromagnetic actuators are limited in their ability to produce sufficiently high stroke, torque, or force. In contrast, advances in developing electro-mechanical materials (such as piezoelectric and electrostrictive) have enabled potential actuation capabilities that can be used to support such missions. Taking advantage of these materials, we developed a piezoelectric actuated drill that operates at the temperature range up to 500°C and the mechanism is based on the Ultrasonic/Sonic Drill/Corer (USDC) configuration. The detailed results of our study are presented in this paper.

There are emerging sensor technologies that will be deployed in future rotorcraft or retrofitted to existing rotorcraft and aircraft for structural diagnostics and prognostics. The vehicle health management system is likely to contain heterogeneous sensor arrays. Thus the structural state awareness may require information data fusion from dissimilar sensor (heterogeneous) system. This paper reviews the state of the art commercial of the shelf (COTS) and emerging sensor technologies for structural damage monitoring of rotorcraft and aircraft health.

NASA Glenn Research Center (GRC), in collaboration with GE Aviation, has begun the development of a smart adaptive structure system with piezoelectric transducers to improve composite fan blade damping at resonances. Traditional resonant damping approaches may not be realistic for rotating frame applications such as engine blades. The limited space in which the blades reside in the engine makes it impossible to accommodate the circuit size required to implement passive resonant damping. Thus, we have developed a novel digital shunt scheme to replace the conventional electric passive shunt circuits. The digital shunt dissipates strain energy through the load capacitor on a power amplifier. GE designed and fabricated a variety of polymer matrix fiber composite (PMFC) test specimens. We investigated the optimal topology of PE sensors and actuators for each test specimen to discover the best PE transducer location for each target mode. Also a variety of flexible patches, which can conform to the blade surface, have been tested to identify the best performing piezoelectric patch. The active damping control achieved significant performance at target modes. This work has been highlighted by successful spin testing up to 5,000 rpm of subscale GEnx composite blades in GRC's Dynamic Spin Rig.

It is well known that the gas turbine blade vibrations can give rise to catastrophic failures and a reduction of the blades life because of fatigue related phenomena^[1]-[3] . In last two decades, the adoption of piezoelectric elements, has received considerable attention by many researcher for its potential applicability to different areas of mechanical, aerospace, aeronautical and civil engineering. Recently, a number of studies of blades vibration control via piezoelectric plates and patches have been reported^[4]-[6] . It was reported that the use of piezoelectric elements can be very effective in actively controlling vibrations. In one of their previous contributions^[7] , the authors of the present manuscript studied a model to control the blade vibrations by piezoelectric elements and validated their results using a multi-physics finite elements package (COMSOL) and results from the literature. An optimal placement method of piezoelectric plate has been developed and applied to different loading scenarios for realistic configurations encountered in gas turbine blades. It has been demonstrated that the optimal placement depends on the spectrum of the load, so that segmented piezoelectric patches have been considered and, for different loads, an optimal combination of sequential and/or parallel actuation and control of the segments has been studied. In this paper, an experimental investigation carried out by the authors using a simplified beam configuration is reported and discussed. The test results obtained by the investigators are then compared with the numerical predictions ^[7] .

Bridge managers often make decisions based on experience or common sense, somehow regardless of the action suggested by instrumental monitoring systems. Managers weigh differently the monitoring results based on their prior perception of the state of the structure and make decisions keeping in mind the possible effects of the action they can undertake. We propose a rational framework to include the impact of these issues on decision making, based on the concept of Value of Information. The methodology is demonstrated by the case study of the Streicker Bridge, a newly built pedestrian bridge on Princeton University campus.

Experimental works are done to assess the seismic behavior of concrete beams reinforced with superelastic alloy (SEA) bars. Applicability of newly developed Cu-Al-Mn SEA bars, characterized by large recovery strain, low material cost, and high machinability, have been proposed as partial replacements for conventional steel bars in order to reduce residual deformations in structures during and after intense earthquakes. Four-point reverse-cyclic bending tests were done on 1/3 scale concrete beams comprising three different types of specimens - conventional steel reinforced concrete (ST-RC), SEA reinforced concrete (SEA-RC), and SEA reinforced concrete with pre-tensioning (SEA-PC). The results showed that SEA reinforced concrete beams demonstrated significant enhancement in crack recovery capacity in comparison to steel reinforced beam. Average recovery of cracks for each of the specimens was 21% for ST-RC, 84% for SEA-RC, and 86% for SEA-PC. In addition, SEA-RC and SEA-PC beams demonstrated strong capability of recentering with comparable normalized strength and ductility relative to conventional ST-RC beam specimen. ST-RC beam, on the other hand, showed large residual cracks due to progressive reduction in its re-centering capability with each cycle. Both the SEA-RC and SEA-PC specimens demonstrated superiority of Cu-Al-Mn SEA bars to conventional steel reinforcing bars as reinforcement elements.

Tuned liquid column damper (TLCD) is used to reduce wind induced building acceleration by tuning its natural frequency to that of a building. After building construction, its natural frequency may differ from the original one. Thus, TLCD installed at a building should have the shifted natural frequency without its serious structural modification. Conventional TLCD changes its natural frequency by only regulating liquid height, which destroys U shape of TLCD. This study proposes new concept of TLCD which yields wide range of natural frequency with very simple modification maintaining original shape. Vertical columns of TLCD are divided into several individual cell type small columns. The liquid in individual cell type columns cannot move by air pressure if their tops are sealed. By taking appropriate number of cell type columns in sealed condition, sectional area ratio of vertical and horizontal columns is changed, which can provide new natural frequency same to shifted natural frequency of a building. TLCD's with multi cells are analytically evaluated and experimentally verified using shaking table test according to the number of sealed cell type small columns.

Continued advancements in steel and concrete materials as well as improved computer-optimized designs are resulting in more efficient floor structures, which have longer spans and are more lightweight. In addition, there is a tendency for offices to be more open-plan with fewer internal partitions. These structures possess low and closely spaced natural frequencies, sometimes falling within the range of frequencies produced by human activities, as well as low damping levels. Vibration serviceability problems are thus arising more frequently than before. The tendency for developers to require floor structures suitable for a variety of types of occupation so as to increase their economic viability also has clear ramifications for their vibration serviceability. Active vibration control (AVC) is emerging as a viable technology for mitigation of human-induced vibrations in problem floors. Past AVC research work, as demonstrated in analytical studies and successfully implemented in field trials, have focused predominantly on collocated sensor and actuator pairs in SISO or multi-SISO direct-output feedback schemes, for example, direct velocity feedback (DVF). This paper demonstrates the potential benefits that may be derived from using model-based control approaches, for example, in isolating and controlling specific problematic frequencies only. The approaches investigated here comprise of independent modal space control (IMSC) and pole-placement controllers that are implemented in SISO, SIMO, and MIMO control structures. Both the analytical and experimental studies presented are based on a laboratory structure. Attenuations in target modes of vibration ranged between 15.0-27.0 dB in the analytical studies and experimental implementation for all the controllers studied. Further, both analytical studies and experimental implementation yielded a 70-89 % reduction in acceleration responses from two different walking frequencies.

Many variable stiffness and damping devices have been proposed to mitigate the unwanted effects of vibrations. Although the stiffness or damping of these devices may be varied in real-time, many are limited in range and speed. The objective of this study is to propose a new variable stiffness/damping device to improve upon these limitations. The continuously variable amplification device (CVAD) is comprised of a spherical continuously variable transmission (SCVT) augmented with rack-and-pinions and connected in series with a simple stiffness or damping element. The CVAD amplifies linear motion to the stiffness or damping element, and then amplifies the element force back through the system. The resulting CVAD force is increased by a factor equal to the amplification factor squared, relative to the stiffness or damping element alone. The amplification factor is determined by a single controllable parameter that can be adjusted rapidly in real-time. The resulting system is capable of producing a large, continuous, and instantaneous range of stiffness or damping. In the present work, the concept for the CVAD is proposed and equations are presented for the effective stiffness and damping of the CVAD connected in series with both linear and rotational elements. Then, corresponding mathematical models are developed based on the system's dynamics considering the motion of each component. Numerical simulations are performed for the CVAD connected to a linear and rotational stiffness element and subject to a harmonic input. The results indicate that the same wide range of effective stiffness can be achieved using both elements.

The vibration serviceability of civil engineering structures under human dynamic excitation is becoming ever more critical with the design and redevelopment of structures with reduced mass, stiffness and damping. A large number of problems have been reported in floors, footbridges, sports stadia, staircases and other structures. Unfortunately, the range of options available to fix such problems are very limited and are primarily limited to structural modification or the implementation of passive vibration control measures, such as tuned mass dampers. This paper presents the initial development of a new framework for advanced methods of control of humaninduced vibrations in civil engineering structures. This framework includes both existing passive methods of vibration control and more advanced active, semi-active and hybrid control techniques, which may be further developed as practical solutions for these problems. Through the use of this framework, rational decisions as to the most appropriate technologies for particular human vibration problems may be made and pursued further. This framework is also intended to be used in the design of new civil engineering structures, where advanced control technologies may be used both to increase the achievable slenderness and to reduce the amount of construction materials used and hence their embodied energy. This will be an ever more important consideration with the current drive for structures with reduced environmental impact.

An innovative three-story timber building, using self-centering, post-tensioned timber shear walls as the main horizontal load resisting system and lightweight non-composite timber-concrete floors, has recently been completed in Nelson, New Zealand. It is expected to be the trailblazer for similar but taller structures to be more widely adopted. Performance based standards require an advanced understanding of building responses and in order to meet the need for in-situ performance data the building has been subjected to forced vibration testing and instrumented for continuous monitoring using a total of approximately 90 data channels to capture its dynamic and long-term responses. The first part of the paper presents a brief discussion of the existing research on the seismic performance of timber frame buildings and footfall induced floor vibrations. An outline of the building structural system, focusing on the novel design solutions, is then discussed. This is followed by the description of the monitoring system. The analysis of monitoring results starts with a discussion of the monitoring of long-term deformations. Next, the assessment of the floor vibration serviceability performance is outlined. Then, the forced vibration tests conducted on the whole building at different construction stages are reviewed. The system identification results from seismic shaking records are also discussed. Finally, updating of a finite element model of the building is conducted.

SHM systems are becoming feasible with the growth of computer and sensor technologies during the last decade. However, high cost prevents SHM to become common in general homes. The reason of this high cost is partially due to many accelerometers. In this research, we propose a moving sensor agent robot with accelerometers and a laser range finder (LRF). If this robot can properly measure accurate acceleration data, the cost of SHM would be cut down and resulting in the spread of SHM systems. Our goal is to develop a platform for SHM using the sensor agent robot. We designed the prototype robot to correctly detect the floor vibrations and acquire the micro tremor information. When the sensor agent robot is set in the mode of acquiring the data, the dynamics of the robot should be tuned not to be affected by its flexibility. To achieve this purpose the robot frame was modified to move down to the ground and to provide enough rigidity to obtain good data. In addition to this mechanism, we tested an algorithm to correctly know the location of the robot and the map of the floor to be used in the SHM system using the LRF and Simultaneously Localization and Mapping (SLAM).

Evacuation systems for buildings are designed based on event scenarios, so they are not prepared for unexpected events that are not included in the scenarios. In this paper, we propose a new active evacuation guidance system using sensor agent robots. We first introduce a Structural Health Monitoring (SHM) system to be used in conjunction with sensor agent robots for active evacuation guidance. Then the role of sensor agent robots is explained. An algorithm to immediately access the safety of the building after a large earthquake is also proposed using only the information taken by a sensor agent robot.

Aging society and development of technology has led to people's stronger demand for a safe and energy-saving life. Along with this background, a research called "Biofication of Living Spaces" has been in progress to create safe and comfortable spaces for each person, by taking in the abilities of living things. Physiological adaption is one important feature of living things. Living things are able to regulate their internal environment and maintain a stable condition. This is called homeostasis. We proposed a way to make human as a controller and a sensor in the homeostasis control of architectural spaces. Instead of a hormone, an uncomfortable feeling is captured as a control signal in the system, and for this research, we chose the sleepiness of a person in the situation of meetings as the signal. In order to generate a person become a sensor or a controller, the space itself needs to automatically capture the person's unconscious movements. In this research, we focused on acquiring unconscious behavior of a person using Kinect and electroencephalograph as calibration. The objective of this research is to recognize a person's sleepiness as an uncomfortable feeling during meetings and to propose the method using Kinect.

This paper evaluates the conductive properties and sensing capabilities of various smart materials being considered for enhancing parachute performance. In a previous review of sensing technologies, several materials showed potential for parachute implementation - specifically, electrically conductive textiles and dielectric electro-active polymers (DEAPs). Past efforts have been focused on mechanically testing and evaluating the sensing performance of conductive fabrics (coated with carbon nanotubes, polypyrrole and polyaniline) and DEAPs. While some of the conductive fabrics demonstrated sufficient sensing capability, they were not conductive enough to implement into an intelligent parachute sensor network for transmitting power or data. Also, attaching or stitching DEAPs to the parachute fabric has proven to be a challenge. The primary goal of this paper is to investigate the use of highly-conductive textiles in an intelligent textile sensor network for sensing and as a means to transmit power or electrical signals. The applications of the materials investigated in this paper may also extend beyond parachutes to any large-scale textile structure.

Many embedded structural monitoring applications require extremely low-power sensors and signal processing capabilities. In particular, the continuous monitoring of vibrations, impacts, and acoustic noise within a structure typically requires significant power for not only the transducers themselves, but also the signal conditioning, analog to digital conversion, and digital signal processing necessary to extract useful information from the captured waveforms [1,2,3,4]. This paper presents a sensor methodology that performs spectral decomposition of acoustic and vibration waveforms using arrays of micromechanical resonant structures, mechanical filters, and embedded active films, with signal processing being performed in the mechanical domain. The use of embedded active films in these devices results in sensors that can be, in some instances, self-powered by the vibrations being detected. A MEMS-based acoustic emission spectral sensor employing an embedded electret film has been fabricated and tested in an impact environment. Sensor fabrication was performed using in situ polarization of the active film after completing the entire fabrication flow. This sensor consisted of an array of tuned micromechanical resonant elements with natural frequencies varying across the spectrum of interest. The sensor was incorporated into a ball drop apparatus in which controlled acoustic pulses could be delivered to the structure under test. Spectral output from the sensor was collected and could be used to distinguish between impacts involving different material sets and impact energies without the use of digital signal processing and its associated power consumption.

The purpose of this paper is to analyse the possibility to manufacture and verify the self-sensing capability of composite materials plates with an embedded network of NiTi shape memory alloys (SMA) used as transducers for structural integrity. Firstly, the thermo-electrical material properties of SMAs were investigated to assess their capability to sense strain within. The results showed that the electrical resistance variation provided by the shape memory alloys network enables a built in and fast assessment of the stress distribution over the entire structure. Then, by transmitting a low amperage current, results in an electric and thermal flow through the entire SMA network. Using an IR Camera it is possible to capture the emitted thermal waves from the sample and create an image of the thermal field within the material. Consequently, analysing the behaviour of the heating curves on different points of the sample, it is possible to identify potential variation in the apparent temperature of the composite, leading to the identification of damages within the composite structure.

MEMS gyroscopes are used in many applications including harsh environments such as high-power, high-frequency acoustic noise. If the latter is at the natural frequency of the gyroscope, the proof mass will be overexcited giving rise to a corrupted gyroscope output. To mitigate the effect of the high-power, high-frequency acoustic noise, it is proposed to use nickel microfibrous sheets as an acoustic damper. For this purpose, the characterization of vibration damping in Nickel microfibrous sheets was examined in the present research effort. The sheets were made from nickel fibers with cellulose as a binding agent using a wet-lay papermaking technique. Sintering was done at 1000 °C to remove all the cellulose giving rise to a porous material. Square sheets of 20 cm were made from three diameters of nickel fibers namely 4, 8, and 12 microns. The sheets were cut into smaller pieces to fit the requirements of a fixture specially designed for this study. The fixture was attached to a LDS V408 shaker with a mass resting on a stack of the microfibrous sheets to simulate transmitted vibration by base motion with the sheet stack acting as a damper. A series of experiments was conducted using these 3 fiber diameters, different number of layers of microfibrous sheets and varying the vibration amplitude. From the collected vibration data, the stiffness and damping ratio of the microfibrous material was characterized.

The connection technology between silica Fiber Bragg Grating sensors (FBGs) and ultra-high temperature ceramic composites (UHTCs) is solved to measure the temperature and strain at the same time when the structural temperature higher than 500°C in this paper. A series experiments were carried out to compare the connection properties, and then the best adhesive was selected. A lot of attempts have been made to choose the best curing process. The experiments were carried out at 500°C, and results shown that the response wavelength and the heated temperature have positive linear relationship. The wavelength will increase 0.0096nm with the temperature rise 1°C, and 1με changes will induce the response wavelength increase 0.002nm. A feasible method for high temperature measuring based fiber Bragg grating was given in this study, and the results of this study can be used as an important reference data for hot structure the thermal protection systems designing.

Recent advances in materials science have resulted in a proliferation of flexible structures for high-performance civil, mechanical, and aerospace applications. Large aspect-ratio aircraft wings, composite wind turbine blades, and suspension bridges are all designed to meet critical performance targets while adapting to dynamic loading conditions. By monitoring the distributed shape of a flexible component, fiber optic shape sensing technology has the potential to provide valuable data during design, testing, and operation of these smart structures. This work presents a demonstration of such an extended-range fiber optic shape sensing technology. Three-dimensional distributed shape and position sensing is demonstrated over a 30m length using a monolithic silica fiber with multiple optical cores. A novel, helicallywound geometry endows the fiber with the capability to convert distributed strain measurements, made using Optical Frequency-Domain Reflectometry (OFDR), to a measurement of curvature, twist, and 3D shape along its entire length. Laboratory testing of the extended-range shape sensing technology shows

In this paper, a new coaxial cable Bragg grating (CCBG) is developed as a strain sensor and the sensor's capacity for large range strain measurement in structural health monitoring (SHM) is demonstrated for the first time. The sensor device is comprised of regularly spaced periodic discontinuities along a coaxial cable. The discontinuities are fabricated using a computer numerical controlled (CNC) machine to drill holes in the cable. Each discontinuity generates a weak reflection to the electromagnetic wave propagating inside the cable. Superposition of these weak reflections produces a strong reflection at discrete frequencies that can be explained by Bragg grating theory. By monitoring the resonant frequency shift of the sensor's reflection or transmission spectra, strain measurement sensitivity of 20με and a dynamic range of 50000με (5%) were demonstrated for axial strain measurements. The experimental results show that the CCBG sensors perform well for large strain measurement needed in structural health monitoring (SHM).

Fiber optic strain sensors, such as Fiber Bragg Gratings (FBG), have a great potential in the use in smart structures thanks to their small transversal size and the possibility to make an array of many sensors. They can be embedded in carbon fiber structures and their effect on the structure is nearly negligible. On the other hand, some critical aspects should be evaluated, such as higher cost and lower SNR respect to traditional technologies. In this work a simple carbon fiber structure has been developed, composed of a thin cantilever with 14 longitudinal FBG sensors and 3 piezoelectric actuators (PZT). A dynamic 1 kHz swept-laser interrogator was used to gather the FBG data: the output is a digital signal and the time delay introduced has been measured. This is a critical point that restricts the highest controllable frequency: our results show that the limit is at about 50 Hz. A control system has been developed and many control strategies have been evaluated to suppress vibration, from the simplest single-sensor to single-actuator strategy, up to modal control. The SNR of the input data has been found to be critical. The use of FBG sensors allows improving the performance of the control because they give a large number of measurements regarding the state of deformation of the whole structure. Modal control was found to have the best results thanks to its best use of all the sensors data.

This paper proposes structural health monitoring technology based on the strain mapping of composite airframe structures through their life cycles by FBG sensors. We carried out operational load tests of small-sized mockup specimens of CFRP pressure bulkhead and measured the strain by FBG sensors. In addition, we confirmed strain change due to stiffener debondings. Moreover, debonding detectability of FBG sensors were investigated through the strain monitoring test of CFRP skin-stiffener panel specimens. As a result, the strain distribution varied with damage configurations. Moreover, the change in strain distribution measured by FBG sensors agrees well with numerical simulation. These results demonstrate that FBG sensors can detect stiffener debondings with the dimension of 5mm in composite airframe structures.

In this paper, a preliminary study on the development of a wireless image-based sensor for two-dimensional (2D) crack propagation monitoring is reported. This sensor contains an optical navigation sensor board (ADNS-9500) which is incorporated into the Imote2 IPR2400 platform. To monitor crack propagation, the Imote2 sends a signal to the ADNS-9500 to switch on the built-in laser and camera collecting images reflected from the concrete surface. The captured images are processed by an optical flow method to obtain the relative displacement between images. A series of tests have been conducted to calibrate the accuracy of the proposed crack sensor. Results show that the crack sensor exhibits a strong linearity under 2D movement and can track the movement quiet well.

The bridges over navigation waterways are exposed to ship collision and ship-bridge collision accidents have been widely reported worldwide. The measurement of ship impact force during a collision accident is of great importance for condition assessment of ship-collided bridges and subsequent strategic actions made by the bridge authority. The impact force of ship-bridge collision is usually evaluated by use of the measured structural responses during ship collision and an identification algorithm, but the accuracy is limited. In this paper, a method for direct impact force identification of ship-bridge collision using smart piezoelectric sensors is proposed. The feasibility and effectiveness of the proposed method is demonstrated by experimental study on a scale pier model of a cable-stayed bridge. The piezoelectric sensors are embedded into the scale pier model and the impact force is generated by a hammer. Various impact sceneries are taken into account to investigate the capacity of the piezoelectric sensors for impact force identification. Through acquiring the voltage signals from the piezoelectric sensors at different locations, the impact force is identified with the aid of the calibrated relationship between the impact force and the voltage output.

Wind energy utilization as a reliable energy source has become a large industry in the last 20 years. Nowadays, wind turbines can generate megawatts of power and have rotor diameters that are on the order of 100 meters in diameter. One of the key components in a wind turbine is the blade which could be damaged by moisture absorption, fatigue, wind gusts or lighting strikes. The wind turbine blades should be routinely monitored to improve safety, minimize downtime, lower the risk of sudden breakdowns and associated huge maintenance and logistics costs, and provide reliable power generation. In this paper, a real-time wind turbine blade monitoring system using fiber Bragg grating (FBG) sensors with the fiber optic rotary joint (FORJ) is proposed, and applied to monitor the structural responses of a 600 W small scale wind turbine. The feasibility and effectiveness of the FORJ is validated by continuously transmitting the optical signals between the FBG interrogator at the stationary side and the FBG sensors on the rotating part. A comparison study between the measured data from the proposed system and those from an IMote2-based wireless strain measurement system is conducted.

Scour due to floods and rapid river flow is one of the major causes of bridge failures, which erodes the foundation materials below bridge piers and abutments. Sensors and monitoring provide vital information on the stability of bridges that are subjected to scour. In this study, an ultrasonic technology-based monitoring system is set up. Ultrasonic sensor is placed on a vertically-fixed trail and can move upward and downward. The ultrasonic sensor sends, and the ultrasonic wave signal will be reflected from the river bed. The exact location of the river bed can be calculated through the wave signal travel time from sending to receiving and wave velocity. Due to the sensor moving in a range in the vertical direction, the river bed map can be portrayed through the monitoring data. The feasibility and accuracy of the monitoring system has been validated through a test in laboratory. The test results indicate that the ultrasonic technology-based monitoring system can measure the scour in real time with reasonable accuracy and reliability.

Fundamental functionalities of wireless smart sensors to measure full-scale bridge vibration, such as time synchronization, loss-less multihop communication, and capability to capture small ambient vibrations, are maturing; dense vibration measurement of large structures using wireless smart sensors is expected to reveal the detailed condition of existing structures. An arch bridge is chosen as a target bridge and densely instrumented by 48 wireless smart sensors. Traffic induced vibration of the bridge has been measured before and after its seismic retrofit. The differences between the measured dynamic characteristics are considered to represent the effects of seismic retrofit. The dense measurement allows comparison of spatial characteristics such as detailed mode shapes, in addition to comparison of natural frequencies. Comparison of densely measured mode shapes reveals their changes, which are then used to update the finite element model of the bridge. The measurement, data analysis, and model updating indicate a potential use of dense instrumentation of wireless smart sensor network for structural condition assessment.

Civil engineering structures, such as reinforced concrete frames, exhibit nonlinear hysteretic behavior when subject to dynamic loads, such as earthquakes. The ability to detect damages in structures after a major earthquake will ensure their reliability and safety. Innovative analysis techniques for damage detection of structures have been extensively studied recently. However, practical and effective damage identification techniques remain to be developed for nonlinear structures, in particular hysteretic reinforced concrete (RC) structures. In this paper, a smooth hysteretic model with stiffness and strength degradations and with the pinching effect is used to represent the dynamic characteristics of reinforced concrete (RC) frames. A system identification method capable of detecting damages in nonlinear structures, referred to as the adaptive quadratic sum-square error with unknown inputs (AQSSE-UI), is used to detect damages in hysteretic RC frames. The performance of the AQSSE-UI technique is demonstrated by the experimental data. A 1/3 scale 2-story RC frame has been tested experimentally on the shake table at NCREE, Taiwan. This 2-story RC frame was subject to different levels of ground excitations back to back. The RC frame is firstly considered as a linear model with rotational springs and the tracking of the degradation of the stiffness parameters is carried out using the AQSSE-UI technique. Then the same RC frame is considered as a nonlinear structure with plastic hinges following a smooth hysteretic model. Experimental results show that the AQSSE-UI technique is quite effective for tracking of : (i) the stiffness degradation of linear structures, and (ii) the non-linear hysteretic parameters with stiffness and strength degradations.

Structural health monitoring of civil infrastructure systems like concrete bridges and dams has become critical because of the aging and overloading of these CIS. Most of the available SHM methods are not in-situ and can be very expensive. The triboluminescence multifunctional cementitious composites (TMCC) have in-built crack detection mechanism that can enable bridge engineers to monitor and detect abnormal crack formation in concrete structures so that timely corrective action can be taken to prevent costly or catastrophic failures. This article reports the fabrication process and test result of the flexural characterization of the TMCC. Accelerated durability test indicated that the 0.5 ZnS:Mn/Epoxy weight fraction ITOF sensor configuration to be more desirable in terms of durability. The alkaline environment at the highest temperature investigated (45 °C) resulted in significant reduction in the mean glass transition and storage moduli of the tested ITOF thin films. Further work is ongoing to correlate the TL response of the TMCC with damage, particularly crack opening.

We developed a damage assessment package to assess buildings with various isolation systems. The package provides seven items to be used for damage assessment based on ARX method, MOESP method and double integration of acceleration data. The necessary condition for the package is to have a monitoring system with accelerometers at least at three levels i.e. on foundation, isolation layer and on top floor or roof of the building. Using this package, the performance of the isolation systems as well as superstructure during the earthquake can be quantitatively estimated. The package was tested for a 7-story base-isolated building in Yokohama, Japan. The building experienced the 2011 Tohoku Earthquake of the moment magnitude 9.0.

Scour is a very severe problem for bridge. In this paper, a bridge scour monitoring system based on active thermometry is proposed. The monitoring system fulfills scour monitoring based on the different patterns of temperature change between in liquid and in solid after heating due to their distinctive heat transfer behaviors. It utilizes a thermal cable to generate heat with a heating belt and concurrently measure temperature with DS18B20s. Several experimental tests were conducted using the system. Results confirm the methodology and substantiate the scour monitoring system.

In this paper we present preliminary experimental results relative to the application of open loop monolithic folded pendulum sensors to the control of large band multi-stage suspensions (seismic attenuators) and inertial platforms in the band 0.01 ± 100Hz. In fact, beyond the obvious compactness and robustness of monolithic implementations of folded pendulum, high sensitivity, large measurement band (10^-7 ÷ 100Hz), tunability of the resonance frequency (necessary to adapt the sensors to the mechanics), high sensitive integrated laser optical readout (e.g. optical lever, laser interferometer), and very good immunity to environmental noises are some of the main advantages of this class of sensors. The results are presented and discussed in this paper together with the planned further developments and improvements.

In this paper we present the scientific data recorded by tunable mechanical monolithic horizontal seismometers located in the Gran Sasso National Laboratory of the INFN, within thermally insulating enclosures onto concrete slabs connected to the bedrock. The main goals of this long term test are a preliminary seismic characterization of the site in the frequency band 10^-5÷1Hz and the acquisition of all the relevant information for the optimization of the sensors.

The paper describes a tilt meter sensor for geophysical applications, based on Folded Pendulum (FP) mechanical sensor. Both the theoretical model and the experimental results of a tunable mechanical monolithic FP tilt meter prototype are presented and discussed. Some of the most important characteristics, like the measured resolution of ≈ 0.1 nrad at 100mHz, are detailed. Among the scientific results, earth tilt tides have been already observed with this monolithic FP tilt meter prototype.

This paper describes a new mechanical implementation of a folded pendulum based inertial sensor, configurable as seismometer and as accelerometer.1 The sensor is compact, light, scalable, tunable (< 100mHz), with large band (10^-6 Hz÷10Hz), high quality factor (Q > 1500 in air) instrument and good immunity to environmental noises, guaranteed by an integrated laser optical readout. The measured sensitivity curve is in very good agreement with the theoretical one (10^-12 m/√Hz in the band (0.1 ÷ 10Hz). Typical applications are in the field of earthquake engineering, geophysics, and in all applications requiring large band-low frequency performances coupled with high sensitivities.

Damage to infrastructure is a real concern at present, caused primarily by worldwide climate anomalies, global warming, and natural disasters. Korea has begun research to develop a high precision patch/implant system using new IT as a basis, as critical element in building/large structure safety management, to adjust to this situation. Technologies which must be developed for this research are those which measure and evaluate the soundness and safety of structures based on the measurements of an attached sensor. During the research period, optical fiber sensor patches and wireless sensor capsule implants along with various sensor technologies, stress sensing and structure condition evaluation technologies, high durability sensors and low-power compact smart structure sensors will be developed effectively for network hardware technologies. Similarly high precision image processing for automatic crack extraction will be developed along with radiation sensor application technologies, combined management/control technologies for development systems, and practical technologies for building/large structure development systems. Through the results, we hope to acquire higher sensor system performance with a measurement scope (for precision, etc.) goal at least 200% better than conventional sensor systems. The goal is to attain safety management planning and commercialization for automatic and high technology buildings/large structures. If such research is successfully developed, groundbreaking developments for maintenance related facilities is expected.

After a large earthquake, the evaluation of damage of structures is an important task for structural health assessment. Therefore, the structural health monitoring (SHM) has become major researches which focus in the area of structural dynamics. As we known, the presence of damage or deterioration in a structure can be detected by the changes in the natural frequencies of the structure. Furthermore mode shape changes can be categorized as damage localization¹. Besides, many damage detection algorithms based on the modal properties of structure such as modal frequencies, mode shapes, curvature mode shapes and modal flexibilities have been studied for several decades. However, in most algorithms, identifying the precise location and magnitude of the damage is difficult. If not completely impossible, the accuracy and reliability is not sufficient². Using only modal frequencies and their mode shapes changes to qualify damage seems very difficult to get the real damage in many previous studies. This research desires to test the applicability of mode-based damage assessment method to the real-size building, in order to give correlation between simulation models and real building with the changes in frequencies and mode shapes. The data of the simulations and E-defense Tests on the full-scale four-story steel building will be used to test this exiting method.

Due to the general overloading of vehicles, premature failure of bridges and roads are more and more obvious. Structural behaviors of engineering structures need real-time monitoring and diagnosis, timely detection of structural damage, evaluation of their safety, and necessary precautions, in order to prevent major accident such as the collapse of bridges and roads. But the existing monitoring system, which is very expensive, does not apply to the low budget structures. Therefore, a potable, low-cost, low-power structural monitoring system, which consists of electric resistance strain gauge, collection and execution unit, graph collection system and analysis software, is designed in this paper. The system can collect the critical data about the force of pavement to take the certain judge algorithm. The alarm will be given and the overburden data will be transmitted to IDC to make the further analysis when the pavement is overburden. At the same time, the plates of overweight vehicles can be collected and sent to the relevant departments. The system has the features of simple structure, easy realization, and low cost, which fills the application gaps in structural health monitoring of low-budget project.

A human centered system for building is demanded to meet variety of needs due to the diversification and maturation of society. Smart buildings and smart houses have been studied to satisfy this demand. However, it is difficult for such systems to respond flexibly to unexpected events and needs that are caused by aging and complicate emotion changes. With this regards, we suggest "Biofied Buildings". The goal for this research is to realize buildings that are safer, more comfortable and more energy-efficient by embedding adaptive functions of life into buildings. In this paper, we propose a new control system for building environments, focused on physiological adaptation, particularly homeostasis, endocrine system and immune system. Residents are used as living sensors and controllers in the control loop. A sensor agent robot is used to acquire resident's discomfort feeling, and to output hormone-like signals to activate devices to control the environments. The proposed system could control many devices without establishing complicated scenarios. Results obtained from some simulations and the demonstration experiments using an LED lighting system showed that the proposed system were able to achieve robust and stable control of environments without complicated scenarios.

In this paper the concept and design of the Hybrid Sensor Bus (HSB) system for telecommunication satellites is presented. The HSB development in the frame of an ESA-ARTES project has been started in 2011 and the system will be tested as flight demonstrator onboard the German Heinrich Hertz communication satellite (H2Sat) in 2016. In state-of-the-art telecommunication platforms hundreds of sensors are necessary for satellite control and monitoring. The sensors are wired point-to-point (p2p) to the satellite management unit (SMU) which results in a high mass impact but preliminary increases AIT effort and thereby the overall satellite costs. Sensor bus architectures reduce AIT cost by reduction of wiring effort, reduction in required test time and by providing a flexible sensor network topology. The HSB system is based on a modular concept including a controller module, a fiber-optic interrogator module and an I²C electric interrogator module The HSB system provides advanced performance which includes programmable and sensor specific alarm functions, averaging of dedicated sensor values and thereby a reduction of SMU processor load. The combination of electrical I²C sensors for punctual resolved measurements and fiber-optic sensors for e.g. thermal mapping of panels by embedding sensor fibers in the satellite structures results in a versatile system. In this paper we present the design of the HSB system taking into account the requirements from European platform manufacturers. The HSB design yields a product which can be implemented as replacement of standard p2p systems to build up a more cost efficient sensor system for geostationary satellites.

This research presents a music recommendation system based on multiple users' communication excitement and productivity. Evaluation is conducted on following two points. 1, Does songA recommended by the system improve the situation of dropped down communication excitement? 2, Does songB recommended by the system improve the situation of dropped down and productivity of collaborative work? The objective of this system is to recommend songs which shall improve the situation of dropped down communication excitement and productivity. Songs are characterized according to three aspects; familiarity, relaxing and BPM(Beat Per Minutes). Communication excitement is calculated from speech data obtained by an audio sensor. Productivity of collaborative brainstorming is manually calculated by the number of time-series key words during mind mapping. First experiment was music impression experiment to 118 students. Based on 1, average points of familiarity, relaxing and BPM 2, cronbach alpha factor, songA(high familiarity, high relaxing and high BPM song) and songB(high familiarity, high relaxing and low BPM) are selected. Exploratory experiment defined dropped down communication excitement and dropped down and productivity of collaborative work. Final experiment was conducted to 32 first meeting students divided into 8 groups. First 4 groups had mind mapping 1 while listening to songA, then had mind mapping 2 while listening songB. Following 4 groups had mind mapping 1 while listening to songB, then had mind mapping 2 while listening songA. Fianl experiment shows two results. Firstly, ratio of communication excitement between music listening section and whole brain storming is 1.27. Secondly, this system increases 69% of average productivity.

Advanced fiber reinforced composite materials are becoming the main structural materials of next generation of aircraft because of their high strength and stiffness to weight ratios, and strong designability. In order to take full advantages of composite materials, there is a need to develop an embeddable multifunctional sensing system to allow a structure to "feel" and "think" its structural state. In this paper, the concept of multifunctional sensor network integrated with a structure, similar to the human nervous system, has been developed. Different types of network sensors are permanently integrated within a composite structure to sense structural strain, temperature, moisture, aerodynamic pressure; monitor external impact on the structure; and detect structural damages. Utilizing this revolutionary concept, future composite structures can be designed and manufactured to provide multiple modes of information, so that the structures have the capabilities for intelligent sensing, environmental adaptation and multi-functionality. The challenges for building such a structural state sensing system and some solutions to address the challenges are also discussed in the paper.

This work focuses on an unsupervised, data driven statistical approach to detect and monitor fatigue crack growth in lug joint samples using surface mounted piezoelectric sensors. Early and faithful detection of fatigue cracks in a lug joint can guide in taking preventive measures, thus avoiding any possible fatal structural failure. The on-line damage state at any given fatigue cycle is estimated using a damage index approach as the dynamical properties of a structure change with the initiation of a new crack or the growth of an existing crack. Using the measurements performed on an intact lug joint as baseline, damage indices are evaluated from the frequency response of the lug joint with an unknown damage state. As the damage indices are evaluated, a Bayesian analysis is committed and a statistical metric is evaluated to identify damage state(say crack length).

Due to an increase in an elderly-people household, and global warming, the design of building spaces requires delicate consideration of the needs of elderly-people. Studies of intelligent spaces that can control suitable devices for residents may provide some of functions needed. However, these intelligent spaces are based on predefined scenarios so that it is difficult to handle unexpected circumstances and adapt to the needs of people. This study aims to suggest a Genetic adaption algorithm for building spaces. The feasibility of the algorithm is tested by simulation. The algorithm extend the existing design methodology by reflecting ongoing living information quickly in the variety of patterns.

This paper analyzes effects of harmonically varying damping on a multi-degree-of freedom system. Our recent research applied the method of the harmonically varying damping to vibration mitigation of a single-degree-of-freedom structure with sinusoidal base excitation having two frequencies. In the study, an ideal variable damper is used in conjunction with the secondary sinusoidal base excitation to reduce response due to the primary base excitation. If the primary sinusoidal base excitation contains the natural frequency of the system, resonance is induced. However, another resonance can be generated by the modulated component caused by the variable damping device and the secondary base excitation. The additional resonance is adjusted to be out of phase with the primary response, resulting in effective control of the structure. However, no such study considering the multi-degree-of-freedom system has been conducted. This paper presents the effect of the harmonically varying damping on the multi-degree-of-freedom system, especially; the influence on two structures in parallel with a variable damper between there is discussed.

Optimal sensor placement is key issues of structures health monitoring (SHM). In study of sensor placement, the main achievement focus on optimal criterions of sensor locations based on modal test, while optimal criterions of sensor locations based on damage identification, optimal method of sensor locations and optimal sensor number should be investigated further. In this study, a novel optimal sensor placement strategy based on sensitivity is proposed. Optimal sensor placement based on sensitivity analysis is an alternation method to consider damage identification. The basic idea of the proposed methodology is that influence range of different damage parameters is different. First, damage sensitivities in every element based on modal parameters are calculated. Then the elements that are sensitive to damage are selected. According to the detection of damage sensitivity in these elements, minimums number can be found by sensitivity. At last, the elements that are not selected are considered as not sensitive to modal parameters and would be placed the strain sensors. Numerical simulation of a three-dimensional truss structure is implemented to evaluate the minimum sensor number of different damage parameters according to the above methods. Moreover, damage location can be detected under singledamage situation and the element with most severe damage can be identified in multi-damage case using the proposed sensor placement.

This paper presents the basic concept of a damage assessment methodology for ceiling elements with the aid of smart sensor board and inspection robot. In this proposed system, the distributed smart sensor boards firstly detect the fact of damage occurrence. Next, the robot inspects the damage location and captures the photographic image of damage condition. The smart sensor board for the proposed system mainly consists of microcontroller, strain gage and LAN module. The inspection robot integrated into the proposed system has a wireless camera and wireless LAN device for receiving signal to manipulate itself. At first, the effectiveness of the smart sensor board and inspection robot is tested by experiments of a full-scale suspended ceiling utilizing shaking table facilities. The model ceiling is subjected to several levels of excitations and thus various levels of damages are caused. Next, this robot inspection scheme is applied to the ceiling of a real structure damaged by the 2011 off the pacific coast of Tohoku Earthquake. The obtained results indicate that the proposed system can detect the location and condition of the damage.

Substructure Isolation Method (SIM) is used for large substructure identification. It utilizes the responses of global structure to construct the responses of the isolated substructure, which is a virtual and independent structure with the same system parameters as the real substructure. Then, the substructure identification is carried out equivalently via the isolated substructure and flexibly by some of the existing identification methods which aim originally at the large structure. Therefore, the performance of the SIM offers the possibility that the large substructure can be identified. A numerical bridge model is used to verify the proposed method, which preforms efficiently and accurately.

This paper presents a Substructure Virtual Distortion Method (SVDM) for damage identification based on Virtual Distortion Method (VDM). VDM is a fast structural reanalysis method by introducing virtual distortions to simulate structural damages. SVDM extends the virtual distortions regard to the damaged elements to the related substructures. Such that the required number of virtual distortions depends on the substructure other than the elements, which reduces the computational work a lot. In addition, for a structure under a certain external force, the dynamic responses may be reflected by a few of main eigenvectors, and thus it only needs to compute the virtual distortions which are relative with these main eigenvectors. This further reduces the computational work. In this paper, first the relation among the virtual distortions of the substructure, actual distortions, and the substructure damage extents are derived; then the main distortions of the substructure are chosen by the contribution analysis of the distortions to the structural responses. In this way, the damages are optimized and identified by minimizing the least square distance between the measured response and the estimated response. A numerical frame model is used to verify the proposed method.

The development of techniques capable of evaluating deterioration of reinforced concrete (RC) is instrumental to the advancement of the structural health monitoring (SHM) and service life estimate for constructed facilities. One of the main causes leading to degradation of RC is the corrosion of the steel reinforcement. This process can be modeled phenomenologically, while laboratory tests aimed at studying durability responses are typically accelerated in order to provide useful results within a realistic period of time. Among nondestructive methods, acoustic emission (AE) is emerging as a tool to detect the onset and progression of deterioration mechanisms. In this paper, the development of accelerated corrosion and continuous AE monitoring test set-up for RC specimens are presented. Relevant information are provided with regard to the characteristics of the corrosion circuit, continuous measurement and acquisition of corrosion potential, selection of AE sensors and AE parameter setting. Results from small-scale pre-notched RC specimens aim to isolate the frequency spectrum where the corrosion first takes place. Waveform analysis critical in the definition of a prognosis model will extend the AE dataset for the onset of corrosion.

Recently, many studies have been exerted on developing ultrasonic transducers that can feature high frequencies for better resolutions and compact sizes for the limit space nondestructive testing applications. Conventional ultrasonic transducers, which are made by piezoelectric materials, suffer from issues such as low frequencies and bulky sizes due to the difficulty of dicing piezoelectric materials into smaller pieces. On the other hand, generating ultrasonic signals by photoacoustic principle is a promising way to generate a high frequency ultrasonic pulse. Optical fiber is a very compact material that can carry the light energy. By combining the photoacoustic principle and the optical fiber together, a novel ultrasonic transducer that features a high frequency and a compact size could be achieved. In this paper, an ultrasonic transducer using gold nanoparticles as the photoacoustic generation material is described. Gold nanoparticles are deposited on the end surface of an optical fiber acting as the ultrasonic generator. A cavity and a diaphragm are fabricated in the center of the fiber using as the ultrasonic receiver. A phase array technique is applied to the transducer to steer the direction of the acoustic beam. Simulation results demonstrated that the photoacoustic ultrasonic transducer is feasible.

New federal regulations now mandate North American railroad bridge owners to closely assess the structural capacity of their bridges. Consequently, railroad companies are currently looking into developing and exploring monitoring systems for specific bridges, to help them improve and develop bridge safety in order to help comply with this new rule. The first part of this paper explains the significance of the new federal law. The new rule comes from the Federal Railroad Administration (FRA), Department of Transportation (DOT), and it falls under the 49 Code of Federal Regulations (CFR), Parts 213 and 237¹. It requires railroad track owners to know the safe capacity of their bridges and to additionally conduct special inspections if either weather or other exceptional conditions make them necessary to ensure safe railroad bridge operations. The second part of this paper will cover past and current studies about the viability of bridge health monitoring, and actual structural monitoring experiences for railroad bridges. Finally, lessons learned from these monitoring examples, as well as recommendations for future applications, are suggested, including wireless monitoring strategies for railroad bridges such as: campaign sensing inspections (periodic monitoring); bridge replacement observations (short term monitoring); and permanent bridge instrumentation (long term monitoring).

Piezoelectric actuators are a popular choice in micro- and nano-positioning devices. Traditional sensorless position control approaches use a hysteresis mapping between voltage and position in a voltage feedforward control scheme. However, this mapping is affected by frequency, temperature, aging etc. Recently, charge control for positioning is also attracting interest among researchers due to the linear relationship between position and charge. Conversely, a sophisticated hardware design is required to minimize charge drift. This limits charge based controllers for practical applications. In this study, a new self-sensing control technique is proposed which requires neither an accurate inverse mapping nor a sophisticated charge controller. This technique uses a position estimate that is obtained by fusing a traditional charge based position measurement with a novel capacitance based position measurement. Upon achieving a reliable position estimate, it is shown that a traditional PI control scheme is sufficient for tracking applications. Different wave forms having multiple lifts and rates were tested. Error is reduced upto 75% using a self-sensing feedback control when compared to open loop actuation. These results compare well with traditional self-sensing control techniques found in literature.

Cracks on a bridge deck should be ideally detected at an early stage in order to prevent further damage. To ensure safety, it is necessary to inspect the quality of concrete decks at regular intervals. Conventional methods usually include manual inspection of concrete surfaces to determine defects. Though very effective, these methods are time-inefficient. This paper presents the use of computer-vision techniques in detection and analysis of cracks on a bridge deck. High quality images of concrete surfaces are captured and subsequently analyzed to build an automated crack classification system. After feature extraction using the training set images, statistical inference algorithms are employed to identify cracks. The results demonstrate the feasibility of the proposed crack observation and classification system.

The corrosion of reinforced concrete structures is a major issue from both a structural safety and maintenance management point of view. Early detection of the internal degradation process provides the owner with sufficient options to develop a plan of action. An accelerated corrosion test was conducted in a small scale concrete specimen reinforced with a 0.5 inch (13 mm) diameter prestressing strand to investigate the correlation between corrosion rate and acoustic emission (AE). Corrosion was accelerated in the laboratory by supplying anodic current via a rectifier while continuously monitoring acoustic emission activity. Results were correlated with traditional electrochemical techniques such as half-cell potential and linear polarization. The location of the active corrosion activity was found through a location algorithm based on time of flight of the stress waves. Intensity analysis was used to plot the relative significance of the damage states present in the specimen and a preliminary grading chart is presented. Results indicate that AE may be a useful non-intrusive technique for the detection and quantification of corrosion damage.

SnO₂ gas sensors were fabricated on polyurethane (PU) polymer surfaces with nanospike structures. These nanospikes are replicated with a low-cost soft nanolithography method from silicon nanospike surfaces formed by femtosecond pulsed laser irradiation. The hydrophobicity of the sensing surface was enhanced by a monolayer coating of silane (1H,1H,2H,2H-perfluorooctyltrichlorosilane, PFOTS). The resulting self-cleaning behavior enabled sensing in environments with high moisture and heavy particulate content, while performing cleaning-in-place operations to prolong the lifetime of the sensors. Failure studies were performed to quantify the effects on the sensitivity of water washing. Contact angle measurements showed that the hydrophobicity was weakened after many cycles of droplet washing due to wear of the PFOTS film and/or damage of the nanoscale spike structure. It was also found that the baseline signal increased with droplet washing, while the sensitivity changed randomly within about 7.5%, so that the sensitivity of the gas sensor remained at a constant level after several thousand cycles of water washing.

Real-time structural health monitoring (SHM) systems are applied many fields. Recently, the interest about wind energy was increased by the demand of clean energy in the world and many researches were actively performed for applying SHM technology to wind turbine systems. Piezoelectric sensor is one kind of sensor which is widely used for SHM system to assess damage creation. In this paper, the small scale wind turbine blade was fabricated and health monitoring of the blade was performed using the piezoelectric sensor. The quasi-static bending test of the blade was carried out and the PVDF (Polyvinylidene fluoride) sensors, which are polymer type piezoelectric materials, were used for health monitoring. Two-cycle test was performed; the load was applied during 350 sec and removed at the first cycle, and load was applied again until the blade was broken completely at the second cycle. The voltage of PVDF sensors were measured during the quasi-static bending test in order to find out the moment when the damage occurrence started. The voltage of the sensor critically changed at the moment of damage occurred.

Finite element model updating based on a multi-scale data is demonstrated on a skewed in-service highway bridge. The multi-scale data approach provides an evidence-based method to create a bound of model class to ensure that the optimum model retains physical connectivity to the real structure. The need for this hybrid approach to model selection comes from the challenges of applying model updating to online structural health monitoring (SHM) strategy based on output-only measurements of in-service highway bridges, which should consider various uncertainties. In vibration-based FE model updating methods, the optimum model is selected by minimizing the error between modal parameters of the model and the real structure. A major drawback of model selection is the probability that the optimum model has no physical connectivity with the real structure. This is because a large set of updating parameters is required to increase accuracy. In this paper, an evidence-based approach to model selection using temperature-induced tilts is implemented in which the cyclical static behavior of a bridge is used to create a bound of possible models. This approach has a strong potential to be applicable to large civil structures with sparse array of sensors.

Since the National Bridge Inventory (NBI) was first conducted, structural health monitoring (SHM) of U.S. bridge infrastructure has consisted largely of time and labor-intensive surveys with subjective results. In-situ and embedded sensors, while more reliable and accurate, can be costly and in many cases infeasible for SHM because they require installation in hard-to-reach places or during construction. Remote sensing (RS) technologies such as radar, electrooptical imaging and laser scanning may offer an innovative, cost-effective method of monitoring the dynamic conditions of U.S. bridges in real-time. While some RS techniques may be costly for state agencies to deploy on their own, RS imagery is available through government agencies or commercial vendors for moderate or no cost. How can disparate RS datasets be integrated with one another and with inventory data in a way that is meaningful to bridge asset management decision makers? This paper discusses the development and functionality of the Bridge Condition Decision Support System (DSS), a web-based asset management tool for bridge managers and inspectors. The DSS seamlessly merges bridge metrics from RS data with NBI inventory data allowing decision makers to compare up-to-date bridge condition metrics from multiple inputs as a time series. It enables analysis of RS and inventory data available through user-friendly web services which can also expose virtually unlimited server-side data processing. Using open-source software, the authors developed a scalable, spatially-aware bridge condition database with a fast and flexible server application programming interface (API) and a cross-browser compatible web mapping application written in Javascript.

The innovative coaxial cable Bragg grating (CCBG) sensor not only achieves the attractive attributes of high resolution, remote operation and multiplexing capability, but also has the advantages of large strain capability and robustness to survive harsh conditions, suitable for structural health monitoring (SHM). The Q-factor of the resonances in CCBG is studied in this paper by coupled mode theory (CMT), to obtain a better understanding of the device physics. The relationships between geometrical parameters and the Q-factor are investigated quantitatively and closed-from expressions are obtained. Design guidelines are developed to improve the Q-factor and consequently improve the senor sensitivity and accuracy.

Active vibration control (AVC) is a relatively new technology for the mitigation of annoying human-induced vibrations in floors. However, recent technological developments have demonstrated its great potential application in this field. Despite this, when a floor is found to have problematic floor vibrations after construction the unfamiliar technology of AVC is usually avoided in favour of more common techniques, such as Tuned Mass Dampers (TMDs) which have a proven track record of successful application, particularly for footbridges and staircases. This study aims to investigate the advantages and disadvantages that AVC has, when compared with TMDs, for the application of mitigation of pedestrian-induced floor vibrations in offices. Simulations are performed using the results from a finite element model of a typical office layout that has a high vibration response level. The vibration problems on this floor are then alleviated through the use of both AVC and TMDs and the results of each mitigation configuration compared. The results of this study will enable a more informed decision to be made by building owners and structural engineers regarding suitable technologies for reducing floor vibrations.

The Vibrofiber sensor is a Fabry-Perot cavity formed between two broad band fiber gratings creating interference fringes. It was introduced three years ago to monitor the vibration and temperature rise of the stator end winding in a power generator.(1) This paper will discuss the use of Vibrofiber to monitor the deflection of the bridge under adverse conditions: wide temperature swings, excess load, strong winds, earth quake, etc. The fringes in these cavity sensors have features like peaks and valleys which are sensitive to temperature and strain. When the bridge becomes overloaded, we are interested in knowing the extent of the deflection. In addition, we might want to locate the cause of the overload. A simple Sagnac FBG interferometer has been invented to provide such diagnostics. A pair of long fibers with such cavity sensors can be installed on the underside of the target bridge segment between two supporting columns. The objective is to monitor the deflection together with any distortion of the bridge deck. Each of the 2 long fiber segments has a pair of cavity sensors, one measures the deflection as a result of the excess strain, and the other measures temperature and provides compensation for the deflection data. An array of cavity sensors with different center wavelengths will be used to support the typical multi-segment bridge structure. The interrogation unit is based on a tunable laser that can hop to different ITU grids. A separate DFB laser will run a grating based Sagnac interferometer, measuring weight in motion, identifying the speed and the make of vehicle in traffic and provide deflection diagnostics. Overloaded trucks and speeding vehicles can be captured and tagged for corrective actions. The interrogation unit is equipped with wireless Ethernet communication enabling the monitoring of many bridges from a central location and similarly warning can be initiated to alert the central traffic control ahead of any problems.

In this study, we introduce a real-time vision-based modal parameters estimation system, in which a high-speed vision system operates in real time at 10000 fps for noncontact structural dynamics estimation. The high-speed vision system can extract the displacements of 100 points on a vibrating cantilever beam in 96 × 512 images at 10000 fps by implementing a column-moment calculation circuit logic on a field-programmable logic array. Based on these vibration displacements, the modal parameters of the cantilever beam are simultaneously determined by using an improved output-only modal parameters estimation algorithm. To demonstrate the performance of our 10000-fps vision-based modal parameters estimation system, the resonant frequencies and mode shapes of vibrating steel cantilever beams with artificial damage were estimated in real time.

Shear wall system is widely adopted in high rise buildings because of its high lateral stiffness in resisting earthquakes. According to the concept of ductility seismic design, coupling beams in shear wall structure are required to yield prior to the damage of wall limb. However, damage in coupling beams results in repair cost post earthquake and even in some cases it is difficult to repair the coupling beams if the damage is severe. In order to solve this problem, a novel passive SMA damper was proposed in this study. The coupling beams connecting wall limbs are split in the middle, and the dampers are installed between the ends of the two cantilevers. Then the relative flexural deformation of the wall limbs is transferred to the ends of coupling beams and then to the SMA dampers. After earthquakes the deformation of the dampers can recover automatically because of the pseudoelasticity of austenite SMA material. In order to verify the validity of the proposed dampers, seismic responses of a 12-story coupled shear wall with such passive SMA dampers in coupling beams was investigated. The additional stiffness and yielding deformation of the dampers and their ratios to the lateral stiffness and yielding displacements of the wall limbs are key design parameters and were addressed. Analytical results indicate that the displacement responses of the shear wall structure with such dampers are reduced remarkably. The deformation of the structure is concentrated in the dampers and the damage of coupling beams is reduced.

Object grasping by robotic hands in unstructured environments demands a sensor that is durable, compliant, and responsive to static and dynamic force conditions. In order for a tactile sensor to be useful for grasp control in these, it should have the following properties: tri-axial force sensing (two shear plus normal component), dynamic event sensing across slip frequencies, compliant surface for grip, wide dynamic range (depending on application), insensitivity to environmental conditions, ability to withstand abuse and good sensing behavior (e.g. low hysteresis, high repeatability). These features can be combined in a novel multimodal tactile sensor. This sensor combines commercial-off-the-shelf MEMS technology with two proprietary force sensors: a high bandwidth device based on PZT technology and low bandwidth device based on elastomers and optics. In this study, we focus on the latter transduction mechanism and the proposed architecture of the completed device. In this study, an embedded LED was utilized to produce a constant light source throughout a layer of silicon rubber which covered a plastic mandrel containing a set of sensitive phototransistors. Features about the contacted object such as center of pressure and force vectors can be extracted from the information in the changing patterns of light. The voltage versus force relationship obtained with this molded humanlike finger had a wide dynamic range that coincided with forces relevant for most human grip tasks.

Cable force is one of the most important parameters of cable-stayed bridge. Since cable system carries most of selfweight of the bridge, the loss of cable force could significantly reduce load carrying capacity of the bridge. This study presents a hybrid structural health monitoring (SHM) method for cable-anchorage system of cable-stayed bridge using smart sensor and interface. The following approaches are carried out to achieve the objective. Firstly, a hybrid SHM method is newly designed for tension force monitoring in cable-anchorage system. In the method, vibration response of cable is utilized for tension force monitoring of global cable, and impedance response of anchorage is utilized to detect tension force change of local tendon. A smart PZT-interface is also designed for sensitively monitoring of electromechanical impedance changes in tendon-anchorage subsystem. Secondly, wireless vibration and impedance sensor network working on Imote2 platform are outlined with regarding to hardware design and embedded software. Finally, an experiment on lab-scale cable-anchorage system is performed to evaluate the feasibility of the proposed SHM method.

This paper presents a vibration-based structural health monitoring (SHM) technique using a high sensitive wireless sensor node for caisson-type breakwater. To achieve the objective, the following approaches are implemented. Firstly, vibration-based SHM method is selected for caisson-type breakwater. The feasibility of the vibration-based SHM method is examined for the caisson structure by FE analysis. Foundation loss damage is considered as the damage of caisson-type breakwater. Secondly, a wireless SHM system with a high sensitive wireless sensor node is designed. The sensor node is built on an imote2 platform. The vibration-based SHM method is embedded on the sensor node. Finally, the performance of the wireless SHM technique is estimated from experimental tests on a lab-scaled caisson. The vibration responses and damage monitoring results are compared with the proposed wireless system and conventional wired system.

This paper illustrates an experimental campaign conducted under laboratory conditions on a full-scale reinforced concrete three-dimensional frame instrumented with wireless sensors developed within the Memscon project. In particular it describes the assumptions which the experimental campaign was based on, the design of the structure, the laboratory setup and the results of the tests. The aim of the campaign was to validate the performance of Memscon sensing systems, consisting of wireless accelerometers and strain sensors, on a real concrete structure during construction and under an actual earthquake. Another aspect of interest was to assess the effectiveness of the full damage recognition procedure based on the data recorded by the sensors and the reliability of the Decision Support System (DSS) developed in order to provide the stakeholders recommendations for building rehabilitation and the costs of this. With these ends, a Eurocode 8 spectrum-compatible accelerogram with increasing amplitude was applied at the top of an instrumented concrete frame built in the laboratory. MEMSCON sensors were directly compared with wired instruments, based on devices available on the market and taken as references, during both construction and seismic simulation.

In recent years, there is an increasing interest in utilizing small, efficient, plug-and-play (PnP) designs for components of satellite systems. This contribution describes a mechanical design of a sensor package to be placed aboard an AAC Microtec QuadSat PnP Satellite. A sensor package includes a Langmuir Plasma Probe (LPP) for the in-orbit measurement of plasma properties. By measuring the potential between the electrode in the plasma and the electrode outside the plasma, a function can be developed between the voltage potential and the current flowing back out of the plasma. The paper details mechanical design, fabrication, and system integration of a low cost, low mass LPP on aboard of a QuadSat PnP Satellite. The mission life of the satellite, governing the sensor package design, is anticipated to be one month. Details of the sensor package mechanical design are provided and sensor validation procedures are discussed.

For a nuclear containment structure, the structural health monitoring is essential because of its high potential risk and grave social impact. In particular, the tendon and anchorage zone are to be monitored because they are under high tensile or compressive stress. In this paper, a method to monitor the tendon force and the condition of the anchorage zone is presented by using the impedance-based health diagnosis system. First, numerical simulations were conducted for cases with various loose tensile forces on the tendon as well as damages on the bearing plate and concrete structure. Then, experimental studies were carried out on a scaled model of the anchorage system. The relationship between the loose tensile force and the impedance-based damage index was analyzed by a regression analysis. When a structure gets damaged, the damage index increases so that the status of damage can be identified. The results of the numerical and experimental studies indicate a big potential of the proposed impedance-based method for monitoring the tendon and anchorage system.

Corrosion is a major problem for civil infrastructure and is one of the leading factors in infrastructure deterioration. Techniques such as half-cell potential can be used to periodically monitor corrosion, but can be difficult to reliably interpret. Wired systems have large installation cost and long-term reliability issues due to wire corrosion. In this paper an embedded inductively coupled coil sensor able to monitor the corrosion potential of reinforcement steel in concrete is presented. The sensor is based on a coil resonator whose resonant frequency changes due to the corrosion potential being applied across a parallel varactor diode. The corrosion potential can be monitored externally using an inductively coupled coil. An accelerated corrosion test shows that it can measure corrosion potentials with a resolution of less than 10 mV. This sensor will detect corrosion at the initiation stage before observable corrosion has taken place. The wireless sensor is passive and simple in design, making it an inexpensive, battery less option for long-term monitoring of the corrosion potential of reinforcing steel.

The remarkable mechanical and electrical properties exhibited by carbon nanotubes (CNTs) have encouraged efforts to develop mass production techniques. As a result, CNTs are becoming increasingly available, and more attention from both the academic world and industry has focused on the applications of CNTs in bulk quantities. These opportunities include the use of CNTs as conductive filler in insulating polymer matrices and as reinforcement in structural materials. The use of composites made from an insulating matrix and highly conductive fillers is becoming more and more important due to their ability to electromagnetically shield and prevent electrostatic charging of electronic devices. In recent years, different models have been proposed to explain the formation of the conductive filler network. Moreover, intrinsic difficulties and unresolved issues related to the incorporation of carbon nanotubes as conductive fillers in an epoxy matrix and the interpretation of the processing behavior have not yet been resolved. In this sense, a further challenge is becoming more and more important in composite processing: cure monitoring and optimization. This paper considers the potential for real-time control of cure cycle and dispersion of a modified epoxy resin system commonly utilized in aerospace composite parts. It shows how cure cycle and dispersion control may become possible through realtime in-situ acquisition of dielectric signal from the curing resin, analysis of its main components and identification of the significant features.

Current procedures in post-earthquake safety and structural assessment are performed by a skilled triage team of structural engineers/certified inspectors. These procedures, in particular the physical measurement of the damage properties, are time-consuming and qualitative in nature. Spalling has been accepted as an important indicator of significant damage to structural elements during an earthquake, and thus provides a sound springboard for a model in machine vision automated assessment procedures as is proposed in this research. Thus, a novel method that automatically detects regions of spalling on reinforced concrete columns and measures their properties in image data is the specific focus of this work. According to this method, the region of spalling is first isolated by way of a local entropy-based thresholding algorithm. Following this, the properties of the spalled region are depicted by way of classification of the extent of spalling on the column. The region of spalling is sorted into one of three categories by way of a novel global entropy-based adaptive thresholding algorithm in conjunction with well-established image processing methods in template matching and morphological operations. These three categories are specified as the following: (1) No spalling; (2) Spalling of cover concrete; and (3) Spalling of the core concrete (exposing reinforcement). In addition, the extent of the spalling along the length of the column is quantified. The method was tested on a database of damaged RC column images collected after the 2010 Haiti Earthquake, and comparison of the results with manual measurements indicate the validity of the method.

SnO₂ thin film room-temperature gas sensors have been fabricated on silicon nanospike surfaces prepared by femtosecond pulsed laser irradiation. The surface morphologies of the as-fabricated silicon nanospikes and SnO₂ thin film gas sensors indicate that the surface roughness increased significantly after the SnO₂ layer was deposited. The surface morphology and electric field distribution of the silicon nanospikes were studied with atomic force microscopy (AFM) and the electric force microscopy (EFM), respectively. The comparison between AFM morphology and EFM images shows that the aspect ratio of the nanostructures in the EFM image was larger than that in the AFM image, which indicates that the nanospikes on the silicon surface can induce an enhanced electric field around their sharp features. The electric field around the tips is further enhanced when there is electric current flowing through the SnO2 layer. The enhanced electric field and increased surface area on the nanospike structures are the main contributors to the high sensitivity of these room temperature gas sensors.

This paper presents a novel ultrasonic guided wave based inspection methodology for detecting and evaluating gas accumulation in nuclear cooling pipe system. The sensing is in-situ by means of low-profile permanently installed piezoelectric wafer sensors to excite interrogating guided waves and to receive the propagating waves in the pipe structure. Detection and evaluation is established through advanced cross time-frequency analysis to extract the phase change in the sensed signal when the gas is accumulating. A correlation between the phase change and the gas amount has been established to provide regulatory prediction capability based on measured sensory data.

This paper presents a miniature fiber optic temperature sensor and its application in concrete structural health monitoring. The temperature sensor is based on Fabry-Perot (FP) principle. The endface of the fiber was wet etched. A piece of borosilicate glass was thermally deposited into the cavity on the etched endface to form an FP cavity. Temperature calibration experiments were performed. A sensor with 30 μm microcavity length was demonstrated to have a sensitivity of 0.006 nm/°C and linearity coefficient of 0.99. During the early-age of concreting, the sensor was embedded in the concrete structure to monitor the temperature change caused by the exothermic chemical reaction between the cement and water. The dramatically increased temperature inside the structure was directly related to its future structural health. During the concrete hydration experiment, the measured peak temperature of concrete specimens was 59.7 °C 12.5 hour after concrete casting.

Ionic Polymer Transducers (IPTs) have both actuation and sensing capabilities. However, the electromechanical response of an IPT as a sensor is quite different from the response as an actuator. IPT sensors are not limited to bending, i.e., they also produce current for compressive, extensional, and shear deformations. A robust physical model must be able to predict the existence of a sensing signal in all modes of deformation. Such a model could subsequently be adapted to form a roadmap toward enhancing sensitivity. In this study, the objective is to experimentally define IPT sensing characteristics in shear deformation (non-bending) and compare the empirical results with predictions derived from a model based on the streaming potential hypothesis. An in-house displacement control rig is employed to establish empirical results in shear sensing. A finite element approach is employed in the companion model development. The IPTs considered employ Nafion as the ionic polymer layer, while the electrode includes high surface area ruthenium oxide, RuO2, metallic powder and deposited per the Direct Assembly Process.

A micro-corrosion sensor technology utilizing PDMS (polydimethylsiloxane) and micro/nano -metal particles, as the sensing element, was proposed and currently under-development. One of the key challenges encountered is the removal of the native oxides inherently existing on the metal particles. Numerous techniques were experimented to counter this problem, with swell-based protocols being identified as the most promising solution. Swelling of the composite enhances the diffusion of oxide etchants into and etched oxides out of the material matrix. Two different swelling characterizations, utilizing liquid-based solvents and supercritical CO2 emersions, will be presented here. In terms of compatibility, common microfabrication solvents were used to evaluate the former, while supercritical CO2 is often used in the release of stiction sensitive microstructures. Both methods are classified as low temperature techniques (less than 100 degrees Celcius). Commonly, the composite exhibits a swelling ratio of 10-20%, exhibiting more sensitive to the percentage content of the metal particles albeit well below those reported in literature for pure cross -linked PDMS. The swelling time-constant is found to be on the order of minutes (CO2) to tens of minutes (liquid solvent) while oxide removal for cubed coupons with 6.35mm on each side is on the order of hours. Also in both cases, the oxide etching performance is dependent on the amount of dilation of the material and the mixing compatibility between the swelling agent and the etchant (such as acetic acid and hexafluoroacetylacetone, respectively for copper oxides). The etch