Showing papers on "Structural health monitoring published in 2001"

Electro-Mechanical Impedance Method for Crack Detection in Thin Plates

Abstract: This paper describes the utilization of Electro-Mechanical (E/M) impedance method for structural health monitoring of thin plates. The method allows the direct identification of structural dynamics by obtaining its E/M impedance or admittance signatures. The analytical model for two-dimensions structure was developed and verified with experiments. Good matching of experimental results and calculated spectra was obtained for axial and flexural components. The ability of the method to identify the presence of damage was investigated by performing an experiment where the damage in the form of crack was simulated with An EDM slit placed at various distances from the sensor. It was found that the crack presence dramatically modifies the E/M impedance spectrum and this modification decreases as the distance between the sensor and the crack increases. Several overall-statistics damage metrics, which may be used for on-line structural heath monitoring, were investigated. Among these candidate damage metrics, the α-th power of the correlation coefficient deviation, CCD α , 3 < α < 7, used in the high frequency band 300-450 kHz, was found to be most successful. Careful selection of the high frequency band and proper choice of the appropriate damage metric were found to be essential for successful damage detection and structural health monitoring.

Structural health monitoring of innovative bridges in Canada with fiber optic sensors

Abstract: This paper describes the development and application of fiber optic sensors for monitoring bridge structures. Fiber Bragg gratings (FBGs) have been used to measure static and dynamic loads on bridge decks and columns, including composite repairs for rehabilitation purposes. A new long gage concept that permits overall average strains to be measured has also been developed with gage lengths varying from 1-20 m. These gages can be bonded to the concrete structure or imbedded in the composite repair patch. Six projects undertaken by ISIS Canada to incorporate fiber optic sensing to monitor the structural health of bridges in Canada are described. Data will be presented for several bridges that indicate a measure of system reliability over several years in a hostile environment. The benefits of fiber optic sensors will be highlighted.

Structural health monitoring system based on diffracted Lamb wave analysis by multiresolution processing

Abstract: A health monitoring system is presented composed of integrated disc-shaped, 100 µm thick and 5 mm diameter piezoelectric transducers (PZTs) working sequentially as Lamb wave emitters and receivers. The diagnostic is based on the analysis of Lamb wave signals recorded before and after damage. In the composite, delaminations are discontinuities producing mode conversion processes generating various outgoing modes. The multiresolution processing allows the isolation of various propagation modes and their extraction in order to measure, for various propagation paths, the time delay between the arrivals of the main burst and of a specific outgoing mode. This process permits, with good accuracy, the localization of damage and the estimation of its extent. The robustness and portability of this technique is demonstrated by the fact that, after validation in our laboratory, it was successfully applied to data coming from an experiment conducted in another laboratory using its own acousto-ultrasonic health monitoring hardware system.

Structural Monitoring with Fibre Optic Technology

Abstract: This is an ambitious book aimed at introducing the relatively new concepts and possibilities of optical fibre sensors for structural monitoring to the uninitiated who have an engineering or general physics background. Measures draws the reader into the volume with a description of smart structures - the structural monitoring equivalent of artificial nervous systems - before a series of back-to-basics tutorials on optical theory and photonic technology. The emphasis on smart structures early in the book is a worthy attention-grabber since it elevates the subject of structural health monitoring above just another set of techniques for making engineering measurements. The promise is to `revolutionize engineering design philosophy' by creating `intelligence within otherwise inanimate structures'. In the latter two thirds of the book, the author steps through the main issues of structural monitoring using fibre optic sensors. Intensity-based, interferometric, polarimetric and spectral sensors (including the ubiquitous Bragg grating) are compared and contrasted. The hot topic of strain versus temperature discrimination in fibre sensors earns a whole chapter and several useful techniques for overcoming this cross-sensitivity are portrayed. Installation of sensors is also discussed with reference to retro-fit and co-manufacturing (embedding) approaches. Examples of concrete constructions such as bridges (a frequent theme in the book) and fibre-reinforced plastics such as glass-fibre and carbon composite materials are considered. A chapter on `short-gauge' sensors and applications deals in some depth with the Bragg grating as a strain sensor. The methods of multiplexing and interrogating these devices are explored with many examples from both Measures' own research and the work of other groups worldwide. The Beddington Trail bridge trial in Calgary, one of the first such installations of Bragg gratings, followed by the more ambitious Confederation Bridge, also in Canada, provide concrete examples of the technology's application. The material is marred somewhat by the inferior reproduction of some of the photographs, especially those showing field installations of the optical sensors. Other applications are not neglected. A description of trials aboard a Norwegian Naval vessel with composite hull monitored by Bragg gratings is also given. Interferometric sensors in similar applications trials are also covered in chapters on short and long gauge length devices. Distributed strain and temperature sensing techniques using Fourier transform, low coherence and stimulated backscattering are covered in the penultimate chapter, which draws together distributed measurement at a small physical scale in the form of intra-Bragg grating strain profile measurements (on the scale of millimetres) and measurements over kilometres using stimulated Brillouin scattering. In this reviewer's opinion the book dwells on strain monitoring in civil engineering structures at the expense of a broader scope, which could have included, for example, the detection of impacts or the acoustic emissions from crack propagation and other forms of structural damage. Nevertheless, this volume is an impressive collection of background and examples of real applications in heavyweight engineering. It adds significantly to the claim that fibre optic sensors have at last arrived. Peter Foote

SMART Layer and SMART Suitcase for structural health monitoring applications

Abstract: Knowledge of integrity of in-service structures can greatly enhance their safety and reliability and lower structural maintenance cost. Current practices limit the extent of real-time knowledge that can be obtained from structures during inspection, are labor-intensive and thereby increase life-cycle costs. Utilization of distributed sensors integrated with the structure is a viable and cost-effective means of monitoring the structure and reducing inspection costs. Acellent Technologies is developing a novel system for actively and passively interrogating the health of a structure through an integrated network of sensors and actuators. Acellent's system comprises of SMART Layers, SMART Suitcase and diagnostic software. The patented SMART Layer is a thin dielectric film with an embedded network of distributed piezoelectric actuators/sensors that can be surface-mounted on metallic structures or embedded inside composite structures. The SMART Suitcase is a portable diagnostic unit designed with multiple sensor/actuator channels to interface with the SMART Layer, generate diagnostic signals from actuators and record measurements from the embedded sensors. With appropriate diagnostic software, Acellent's system can be used for monitoring structural condition and for detecting damage while the structures are in service. This paper enumerates on the SMART Layer and SMART Suitcase and their applicability to composite and metal structures.

Monitoring structural health using a probabilistic measure

Abstract: A Bayesian probabilistic methodology for structural health monitoring is presented. The method uses a sequence of identified modal parameter data sets to continually compute the probability of damage. In this approach, a high likelihood of a reduction in model stiffness at a location is taken as a proxy for damage at the corresponding structural location. The concept extends the idea of using as indicators of damage the changes in model parameters identified using a linear finite-element model and modal parameter data sets from the structure in undamaged and possibly damaged states. This extension is needed because of uncertainties in the updated model parameters that in practice obscure health assessment. These uncertainties arise due to effects such as variation in the identified modal parameters in the absence of damage, as well as unavoidable model error. The method is illustrated by simulating on-line monitoring, wherein specified modal parameters are identified on a regular basis and the probability of damage for each substructure is continually updated. Examples are given for abrupt onset of damage and progressive deterioration.

Structural health monitoring from fiber-reinforced composites to steel-reinforced concrete

Abstract: Accurate interpretation of sensor measurements in terms of physical changes in structures is a major challenge for the development of robust structural health monitoring systems. An active diagnostic system was proposed to detect embedded damage in fiber-reinforced composites and steel-reinforced concrete. Due to the inherent difference in material characteristics, changes in sensor measurements resulting from damage for the two material systems were found considerably different. For a given excitation, it was found that local delamination in fiber-reinforced composites reduced the measured signal strength of a nearby sensor, while rebar debond in concrete increased signal strength. Techniques based on the characteristics of these material responses to damage are being developed for adequate active sensing diagnostic systems for each material.

Fibre optic sensor network for spacecraft health monitoring

Abstract: Close meshed instrumentation or sensor networks applying conventional sensors for temperature and strain monitoring may result in excessive penalties in terms of weight constraints, reliability and sensitivity to environmental conditions, and complex interfaces. The fibre-optic sensor network described in this paper is a multiplexed system of fibre Bragg grating (FBG) strain and temperature sensors and was designed and developed for a demanding space environment, but it can also be emphasized as a promising sensor technology with high potential for non-space applications. The FBG sensor network measures both strain and temperature at the measuring conditions of the structural core of the X-38 spacecraft, by means of wavelength shifts due to tensile stress on a Bragg grating. Dependent on the fixation of the fibre, either isolated from or mechanically coupled to the structure, local thermal or mechanical loads can be determined in the temperature range from -40 to +190 °C, and in the strain range from -0.1% to +0.3%. Short-term resolution and repeatability of the strain measurement amount to 5 µe and 25 µe, respectively. The FBG sensor network is very suitable for structural health monitoring of large structures, i.e. to determine thermal and mechanical load profiles during operation, to assess residual strength of structural elements or to detect irregular working conditions. In comparison to conventional sensors like thermocouples and strain gauges, an FBG sensor network significantly reduces the amount of required front end electronics (FEE) and harness.

The Design of a Wireless Sensing Unit for Structural Health Monitoring

Abstract: Structural monitoring systems used in practice employ conventional cables to communicate sensor measurements to a centralized data acquisition unit. Cabled based systems have high installation costs and leave wires vulnerable to ambient signal noise corruption. In addressing these inherent drawbacks, a modular wireless monitoring system is proposed. Such a system promises lower capital and installation costs simultaneously ensuring reliable communication between sensing units. A proof-of-concept sensing unit has been designed and fabricated using standard integrated circuit components and wireless modem technology. Employing an enhanced RISC microcontroller, the sensing unit has powerful computational capabilities for data aggregation and processing. The sensing unit is flexible in its design by allowing any analog sensor to be used. Two MEMS based accelerometers are considered for this study.

Modal damping measurement for damage detection

Abstract: This paper describes the application of arrays of surface-bonded piezoelements to determine modal damping characteristics of a tested structure. This information may be used for structural damage detection or structural dynamics evaluation. Any array element can be used as a sender, to generate a mechanical signal sweeping the frequency range of interest. Thus induced mechanical vibrations can be picked up either by the sender, or by another transducer. Modal characteristics, and in particular damping levels, are obtained using standard modal analysis methods from the resulting frequency transfer function. Since structural or material damage is frequently associated with changes in damping, the method described in this paper can be applied for structural health monitoring. It is expected that the approach presented will be particularly useful for testing light-weight and micro-structures.

A Fuzzy Logic System for Ground Based Structural Health Monitoring of a Helicopter Rotor Using Modal Data

Abstract: A fuzzy logic system (FLS) is developed for ground based health monitoring of a helicopter rotor blade. Structural damage is modeled as a loss of stiffness at the damaged location that can result from delamination. Composite materials, which are widely used for fabricating rotor blades, are susceptible to such delaminations from barely visible impact damage. The rotor blade is modeled as an elastic beam undergoing transverse (flap) and inplane (lag) bending, axial and torsion deformations. A finite element model of the rotor blade is used to calculate the change in blade frequencies (both rotating and nonrotating) because of structural damage. The measurements used for health monitoring are the first four flap (transverse bending) frequencies of the rotor blade. The measurement deviations due to damage are then fuzzified and mapped to a set of faults using a fuzzy logic system. The output faults of the fuzzy logic system are four levels of damage (undamaged, slight, moderate and severe) at five locations along the blade (root, inboard, center, outboard, tip). Numerical results with noisy data show that the FLS detects damage with an accuracy of 100% for noise levels below 15% when nonrotating frequencies are used. The FLS also correctly classifies the ‘‘undamaged’’ condition up to noise levels of 30% thereby reducing the possibility of false alarms, a key problem for diagnostics systems. The fuzzy logic approach is thus able to extract maximum information from very limited and uncertain data. Using rotating frequencies lowers the success rate for small damage because the centrifugal stiffening caused by rotation counters the stiffness reduction caused by structural damage. The fuzzy logic system in this study is proposed as an information-processing tool to help the maintenance engineer by locating the damage area roughly but accurately for further nondestructive inspections.

Method and apparatus for short term inspection or long term structural health monitoring

Abstract: A method and apparatus is shown for implementing magnetostrictive sensor techniques for the nondestructive short term inspection or long term monitoring of a structure. A plurality of magnetostrictive sensors are arranged in parallel on the structure and includes (a) a thin ferromagnetic strip that has residual magnetization, (b) that is coupled to the structure with a couplant, and (c) a coil located adjacent the thin ferromagnetic strip. By a transmitting coil, guided waves are generated in a transmitting strip and coupled to the structure and propagate along the length of the structure. For detection, the reflected guided waves in the structure are coupled to a receiving strip and are detected by a receiving magnetostrictive coil. Reflected guided waves may represent defects in the structure.

Integrated structural health monitoring

Abstract: Structural health monitoring is the implementation of a damage detection strategy for aerospace, civil and mechanical engineering infrastructure. Typical damage experienced by this infrastructure might be the development of fatigue cracks, degradation of structural connections, or bearing wear in rotating machinery. The goal of the research effort reported herein is to develop a robust and cost-effective structural health monitoring solution by integrating and extending technologies from various engineering and information technology disciplines. It is the authors opinion that all structural health monitoring systems must be application specific. Therefore, a specific application, monitoring welded moment resisting steel frame connections in structures subjected to seismic excitation, is described along with the motivation for choosing this application. The structural health monitoring solution for this application will integrate structural dynamics, wireless data acquisition, local actuation, micro-electromechanical systems (MEMS) technology, and statistical pattern recognition algorithms. The proposed system is based on an assessment of the deficiencies associated with many current structural health monitoring technologies including past efforts by the authors. This paper provides an example of the integrated approach to structural health monitoring being undertaken at Los Alamos National Laboratory and summarizes progress to date on various aspects of the technology development.

Validation of the Eurofighter Typhoon structural health and usage monitoring system

Abstract: The structural health monitoring (SHM) system being developed for the Eurofighter Typhoon is resident on each aircraft and is integrated within existing aircraft and ground-based systems. The system will enable the operators to accurately monitor fatigue life consumption, usage information and significant structural events, thereby safeguarding the structural integrity of the aircraft. The information obtained can be used to plan maintenance actions effectively, and to manage the fleet fatigue life proactively (Hunt S R and Hebden I G, Eurofighter 2000 structural health and usage monitoring: an integrated approach 2nd Joint NASA/FAA/DoD Conf. on Aging Aircraft (Williamsburg, VA, August 31-September 3 1998)). This paper gives an overview of the philosophy and techniques involved in the validation of the Eurofighter SHM system, together with some preliminary results.

Deployment of a fiber Bragg grating-based measurement system in a structural health monitoring application

Abstract: The development and maturation of fiber optic sensor technology has been an increasingly important component of the structural health monitoring field. A strain sensor system has been developed to provide high-resolution, low-noise sets of useful data which can be analyzed and processed with a number of existing damage detection techniques. Recent research at the Naval Research Laboratory has also begun in combining vibration-based damage detection with statistical methods, and some preliminary results are included.

An Inverse Interpolation Method Utilizing In-Flight Strain Measurements for Determining Loads and Structural Response of Aerospace Vehicles

Abstract: An important and challenging technology aimed at the next generation of aerospace vehicles is that of structural health monitoring. The key problem is to determine accurately, reliably, and in real time the applied loads, stresses, and displacements experienced in flight, with such data establishing an information database for structural health monitoring. The present effort is aimed at developing a finite element-based methodology involving an inverse formulation that employs measured surface strains to recover the applied loads, stresses, and displacements in an aerospace vehicle in real time. The computational procedure uses a standard finite element model (i.e., direct analysis ) of a given airframe, with the subsequent application of the inverse interpolation approach. The inverse interpolation formulation is based on a parametric approximation of the loading and is further constructed through a least-squares minimization of calculated and measured strains. This procedure results in the governing system of linear algebraic equations, providing the unknown coefficients that accurately define the load approximation. Numerical simulations are carried out for problems involving various levels of structural approximation. These include plate-loading examples and an aircraft wing box. Accuracy and computational efficiency of the proposed method are discussed in detail. The experimental validation of the methodology by way of structural testing of an aircraft wing is also discussed.

Using GPS in structural health monitoring

Abstract: Global Positioning System technology can provide position information with accuracy to a few millimetres in near real-time. Thanks to this level of precision, the movement of structures can be monitored. The falling tendency of GPS receiver pricing and their miniaturisation, along with their modest power requirements spurred a research and development project at SUPSI which resulted in a prototype system, deemed interesting for a number of applications. It is shown that using carrier phase differential GPS, a network of receiver modules can be installed in order to perform monitoring and surveillance operations for small movements. Typical applications for this type of sensor network include monitoring of structures such as buildings, dams, bridges, as well as measuring the movement of landslides and rock formations. The system consists of a number of small receivers installed on the object to be monitored. A radio-linked base station provides for data collection, post-processing, and monitoring for correct operation of the network. Ancillary sensors may be added to the single receiver units and their measurements synchronized to the positional measurements. The base station may be programmed to initiate a warning or alarm action when absolute position differences or the velocity of movement exceed a pre-set limit.

Structural Health Monitoring With Piezoelectric Active Sensors

Abstract: A technology for non-intrusive real-time structural health monitoring using piezoelectric active sensors is presented. The approach is based on monitoring variations of the coupled electromechanical impedance of piezoelectric patches bonded to metallic structures in high-frequency bands. In each of these applications, a single piezoelectric element is used as both an actuator and a sensor. The resulting electromechanical coupling makes the frequency-dependent electric impedance spectrum of the PZT sensor a good mapping of the underlying structure's acoustic signature. Moreover, incipient structural damage can be indicated by deviations of this signature from its original baseline pattern. Unique features of this technology include its high sensitivity to structural damage, non-intrusiveness to the host structure, and low cost of implementation. These features have potential for enabling on-board damage monitoring of critical or inaccessible aerospace structures and components, such as aircraft wing joints, and both internal and external jet engine components. Several exploratory applications will be discussed.

An experimental benchmark problem in structural health monitoring

Abstract: This paper focuses on the goals of the second phase of the activities of the IASC-ASCE Structural Health Monitoring Task Group, involving the application of structural health monitoring techniques to data obtained from a four story steel frame structure tested July 19–21, 2000 at the University of British Columbia. Damage was simulated by removing bracing within the structure. An electromagnetic shaker and mass on the top floor of the structure were used to excite the structure. Accelerometers were placed throughout the structure to provide measurements of the structural responses. Three excitation cases were considered, including one ambient vibration level in which the shaker was turned off.

Structural health monitoring in composite materials using frequency response methods

Abstract: Cost effective and reliable damage detection is critical for the utilization of composite materials in structural applications. Non-destructive evaluation techniques (e.g. ultrasound, radiography, infra-red imaging) are available for use during standard repair and maintenance cycles, however by comparison to the techniques used for metals these are relatively expensive and time consuming. This paper presents part of an experimental and analytical survey of candidate methods for the detection of damage in composite materials. The experimental results are presented for the application of modal analysis techniques applied to rectangular laminated graphite/epoxy specimens containing representative damage modes, including delamination, transverse ply cracks and through-holes. Changes in natural frequencies and modes were then found using a scanning laser vibrometer, and 2-D finite element models were created for comparison with the experimental results. The models accurately predicted the response of the specimems at low frequencies, but the local excitation and coalescence of higher frequency modes make mode-dependent damage detection difficult and most likely impractical for structural applications. The frequency response method was found to be reliable for detecting even small amounts of damage in a simple composite structure, however the potentially important information about damage type, size, location and orientation were lost using this method since several combinations of these variables can yield identical response signatures.

Structural health monitoring using a fiber optic polarimetric sensor and a fiber optic curvature sensor - static and dynamic test

Abstract: In this paper, a fiber optic polarimetric sensor (FOPS) and a fiber optic curvature sensor (FOCS), for global health\damage monitoring of an aluminum specimen with different cracks, are theoretically and experimentally analyzed. The relation between the sensor sensitivity and the specimen stiffness is given and a static damage factor (SDF) is introduced to describe the stiffness reduction of the specimen. Based on this parameter, the experimental results show that the two sensors can be used as quantitative damage indicators for the global health monitoring of structures. The dynamic damage factor (DDF) is also introduced to describe the damage level of cracked beams. The relation between DDF and the frequency of nth mode is deduced. The experimental results from FOPS show that the DDF is an alternate measure of the damage and is shown to be similar to the SDF.

Methods of distributed sensing for health monitoring of composite material structures

Abstract: The use of composites in the transportation industry is hindered by their susceptibility to damage. Defects that occur during manufacturing or an impact during normal operation can significantly reduce the strength of the composite. Consequently, methods of structural health monitoring (SHM) are needed to verify and continuously monitor the integrity of composite structures. The use of integrated and distributed sensors to develop intelligent composites is a promising approach because large composite structures can be monitored with minimal human intervention. This paper discusses the use of a scanning laser vibrometer (SLV) and piezoceramic materials for distributed sensing. Results of different experiments are summarized.

Structural health monitoring using wavelet transforms

Abstract: A new method of damage detection using wavelet transforms and curvature mode shapes is proposed in this paper. A damage in the structure results in changing its dynamic characteristics such as natural frequencies, damping, and mode shapes. A number of researchers have investigated structural health monitoring techniques for identifying, locating, and quantifying the damage using the changes in the dynamic response of a damaged structure. Curvature mode shape and wavelet maps are two such methods that have already been used to locate damages. These methods have some limitations in determining the exact location of the damages. We have developed a technique by combining these two methods for enhancing the sensitivity and accuracy in damage location. The mode shapes are double differentiated using the central difference approximation to obtain the curvature mode shape. Then a wavelet map is constructed for the curvature mode shape. It is shown that this method can be used to determine the location of the damages. The proposed method is applied to detect damage in an experimental lattice structure and a cantilever beam with multiple damages. The mode shapes are obtained analytically using finite element analysis and also experimentally using laser vibrometer. The experimental results obtained are satisfactory.

A benchmark problem for structural health monitoring and damage detection

Abstract: Structural health monitoring (SHM) is a promising field with widespread application in civil engineering. However, many SHM studies apply different methods to different structures, often making side-by-side comparison of the methods difficult. This paper details the first phase in a benchmark SHM problem organized under the auspices of the IASC-ASCE Structural Health Monitoring Task Group. The scale-model structure adopted for use in this benchmark problem is described. Then, two analytical models based on the structure — one a 12DOF shear-building model, the other a 120DOF model, both finite-element based — are given. The damage patterns to be identified are listed as well as the types and number of sensors, magnitude of sensor information, and so forth. More details are available on the Task Group web site at wusceel.cive.wustl.edu/asce.shm/ .

The Development of a Wireless Modular Health Monitoring System for Civil Structures

Abstract: Current structural monitoring systems employ conventional cables to allow sensors to communicate their measurements to a central processing unit. Cabled based sensing systems for structures have high installation costs and leave wires vulnerable to ambient signal noise corruption. To address these disadvantages, a research effort has been initiated towards the development of a wireless modular monitoring system. The developed wireless modular monitoring system (WiMMS) would have lower capital and installation costs as well as ensure more reliability in the communication of sensor measurements. Some key areas of innovations emphasized are the use of a wireless communication system for inter-sensor communication, the utilization of micro-electro mechanical sensing elements, and the use of a microprocessor for advanced damage detection methods. Introduction There exists a need for a rational and economical method of monitoring the performance of civil structures over their lifespans. Monitoring systems are currently playing a dominant role in applications such as nonlinear model validation, structural health monitoring and structural control. Current design practice analytically determines a structure’s nonlinear response based upon nonlinear models of the key load carrying elements. A monitoring system can provide invaluable insight into the accuracy of these nonlinear models and can assist engineers in refining them. For example, short and long span bridges in California are being instrumented by the California Department of Transportation (Caltran) to monitor the nonlinear response of the bridges during extreme seismic events [1]. Just as important is the need of a rapid assessment of the performance and safety of civil structures. Using a monitoring system to measure structural responses, a damage detection strategy is then employed to diagnose possible short and long-term damage in a structure. Last but not least, in the structural control field, one key component of a control system is an integrated monitoring system that can provide feedback of real time measurements of structural response. With the rapid advancement of sensing, microprocessor, wireless and other technologies, one of the research challenges is to assess the benefits gained from the application of such technologies in the structural engineering field. Our research efforts have identified wireless communication technology, micro-electro mechanical (MEM) devices, microprocessors and digital signal processors, as key areas of innovation that can be used to develop a novel wireless monitoring system for civil structures. Traditional Structural Monitoring Systems The origin of commercially available structural measurement systems is from those regularly used in enclosed, laboratory settings. As a result, the systems are characterized as being of the hub-spoke architecture with accelerometers remotely placed throughout the structure but wired back to a single centralized data acquisition unit. Among the key problems inherent in these systems are the installation time and cost. From experience, the installation time of a complete measurement system for bridges and buildings, can potentially consume over 75% of the total testing time. Installation labor costs can approach well over 25% of the total system cost. Caltran reported that it costs over $300,000 per toll bridge to install a measurement system comprised of 60 to 90 accelerometers. To isolate the wires from the bridge’s harsh environment, a wire conduit is installed at a cost of $10 per linear foot [1]. Within buildings, wires are susceptible to tearing, rodent nibbling and measurement corruption through signal noise. Wireless Structural Monitoring System Our primary goal is to change the practice of using extensive cabling and high cost labor as is typical of the traditional monitoring systems to a system of inexpensive wireless embedded systems that can be installed, maintained and operated with ease (see Figure 1). Centralized Data Acquisition Sensors Cabling Sensors Cables Data Acq. Unix Box Bus Sensors Sensors M icroProcessor W ireless M odem Sensors A-to-D Batteries W ireless M odem PC Centralized Data Storage SU

Multisensor integration and fusion model that uses a fuzzy inference system

Abstract: An intelligent multisensor integration and fusion model that uses fuzzy logic is developed. Measurement data from different types of sensors with different resolutions are integrated and fused based on the confidence in them derived from information not usually used in data fusion, such as operating temperature, frequency range, fatigue cycles, etc. These are fed as additional inputs to a fuzzy inference system (FIS) that has predefined membership functions for each of these variables. The output of the FIS are weights that are assigned to the different sensor measurement data that reflect the confidence in the sensor's behavior and performance. A modular approach is adopted. It allows adding or deleting a sensor, along with its fuzzy logic controller (FLC), anytime without affecting the entire data fusion system. This paper presents a preliminary model that fuses the data from three different types of sensors that monitor the strain at a single location in a cantilever beam. This will be later extended to sensors that will be fixed at different locations on the same beam. The results from the proposed work are a stepping stone toward the development of generic autonomous sensor models that are capable of data interpretation, self-calibration, data fusion from other sources, and even learning so as to improve their performance with time. This work is aimed at the development of smart structural health monitoring systems, but has applications in diverse fields such as robotics, controls, target tracking, and biomedical imaging.

Neural system for structural health monitoring

Abstract: This is an overview paper that discusses the concept of an embeddable structural health monitoring system for use in composite and heterogeneous material systems. The sensor system is formed by integrating groups of autonomous unit cells into a structure, much like neurons in biological systems. Each unit cell consists of an embedded processor and a group of distributed sensors that gives the structure the ability to sense damage. In addition, each unit cell periodically updates a central processor on the status of health in its neighborhood. This micro-architectured synthetic nervous system has an advanced sensing capability based on new continuous sensor technology. This technology uses a plurality of serially connected piezoceramic nodes to form a distributed sensor capable of measuring waves generated in structures by damage events, including impact and crack propagation. Simulations show that the neural system can detect faint acoustic waves in large plates. An experiment demonstrates the use of a simple neural system that was able to measure simulated acoustic emissions that were not clearly recognizable by a single conventional piezoceramic sensor.