Building Research Institute, Japanese Ministry of Construction, initiated a 5-year research and development project of 'Smart Materials and Structural Systems' in 1998 as a part of U.S.-Japan cooperative research efforts. The U.S. Counterpart is the National Science Foundation. Smart Structural Systems (also called as Autoadaptive Media) are defined as systems that can automatically adjust structural characteristics, in response to the change in external disturbance and environments, toward structural safety and serviceability as well as the extension of structural service life. The research and development of (1) concept and performance evaluation of smart structure system, (2) sensing of structure performance, and (3) development and evaluation of structural elements using smart materials will be conducted.

The UCSD led I-5/Gilman Advanced Technology Bridge Project will design and construct a fully functional traffic bridge of advanced composite materials across Interstate 5 in La Jolla, California. Its objective is to demonstrate the use of advanced composite technologies developed by the aerospace industry in commercial applications to increase the life expectancy of new structures and for the rehabilitation of aging infrastructure components. The structure will be a 450 ft long, 60 ft wide cable-stayed bridge supported by a 150 ft A-frame pylon with two vehicular lanes, two bicycle lanes, pedestrian walkways and utility tunnels. The longitudinal girders and pylon will be carbon fiber shells filled with concrete. The transverse deck system will consist of hollow glass/carbon hybrid tubes and a polypropylene fiber reinforced concrete deck with an arch action. Selected cables will be composite. The bridge's structural behavior will be monitored to determine how advanced composite materials perform in civil infrastructure applications. The bridge will be instrumented to obtain performance and structural health data in real time and, where possible, in a remote fashion. The sensors applied to the bridge will include electrical resistance strain gages, fiberoptic Bragg gratings and accelerometers.

The seismic response of a single-story steel building frame with a smart base isolation system is evaluated. The isolation system consists of sliding bearings combined with an adaptive fluid damper. The damping capacity of the fluid damper can be modulated in real-time based on feedback from the measured ground motion and superstructure response. The adaptive capabilities of the fluid damper enable the isolation system displacement to be controlled while simultaneously limiting the interstory drift response of the superstructure. This paper concentrates on the development of analytical models and control algorithms for the isolation system components and the superstructure. In general, the results from numerical simulations demonstrate that, for disparate earthquake ground motions, the smart isolation system is capable of simultaneously limiting both the response of the bearings and the superstructure.

Corrosion initiation and propagation of reinforcement can be monitored by means of different sensors embedded in concrete. Different sensor types for monitoring of time to corrosion initiation, usable in existing structures, were developed and tested in several materials and at different environmental conditions. Key parameters were concrete composition, chloride content, humidity, temperature. Readings of sensors to be installed in existing structures were compared to (1) the response of sensors embedded in concrete during casting, a type, well known and already proved by practical use and (2) other methods for characterization of concrete properties, such as water and chloride content and the corrosion state of the metal by visual inspection and weight loss measurements. First results show a good correlation of the longtime behavior of corrosion potential, current and resistance obtained from sensors installed in existing specimens and pre-embedded sensors. Ingress of chloride concentration and change of humidity inside the concrete could be detected and enabled an estimation of the possible corrosion behavior. These results combined with other results obtained during an EU research project will contribute to the improved evaluation procedures for deterioration of concrete structures. End-users become able to optimize their maintenance management systems and therefore costs and traffic impairments will be reduced.

Three major causes of corrosion of steel in concrete are chloride ions (Cl^-), temperature (T) and acidity (pH). Under normal operating temperatures and with pH above 13, steel does not undergo pitting corrosion. In presence of Cl^-, if the pH decreases below 12, the probability of pitting increases. Acid rain and atmospheric carbon dioxide cause the pH to drop in concrete, often leading to corrosion of the structure with the concomitant cost of repair or replacement. Currently, the pH level in concrete is estimated through destructive testing of the structures. Glass ISFET, and other pH sensors that need maintenance and calibration cannot be embedded in concrete. In this paper, we describe an inexpensive solid state pH sensor that can be embedded in concrete, to detect pH changes at the early stages. It employs a chemical reagent, trinitrobenzenesulfonic acid (TNBS) that exhibits changes in optical properties in the 12 - 14 pH range, and is held in a film of a sol-gel/TNBS composite on an optically transparent surface. A simple LED/filter/photodiode transducer monitors pH-induced changes in TNBS. Such a device needs no periodic calibration or maintenance. The optical window, the light-source and sensor can be easily housed and encapsulated in a chemically inert structure, and embedded in concrete.

Piezoelectric materials are stressed when exposed to electric field and subjected to a restraint in their motion due to the electromechanical coupling effect. Use can be made of this property to control the motion of civil engineering structures. This paper is focused on the conceptual design of a piezoelectric friction damper and the analytical study on its behavior under harmonic loads. The friction damper takes advantage of the slip mode at the friction surface to endure the large deformation in structures and uses the piezoelectric actuators to regulate the clamped force on the damper. A new algorithm is introduced to determine the friction force for increased energy dissipation capacity. It combines the hysteretic and viscous damping mechanisms. Analytical results have shown, the superiority of the proposed algorithm over others in terms of energy dissipation. The damper is then used to mitigate the dynamic responses of a single-story frame structure subjected to harmonic loads. The structural responses controlled with a friction damper are determined numerically. However, it is found that the structure with the damper can be approximately analyzed with an equivalent linear system. This approximation greatly simplifies the design of friction dampers for practical applications.

This work presents a study on the parameters that govern the performance of a new Friction Damper Device (FDD) The device was designed to dissipate seismic input energy and protect buildings from structural and nonstructural damage during moderate and severe earthquakes. The device consists of 3 steel plates that rotate against each other in different directions, and in between these plates, friction pad material discs are inserted. The damper is attached to structures by using inverted Chevron bracing system and in this work pre- stress bars were used as bracing members. The clamping force in the pretensioned bolt controls the frictional moment at the onset of sliding. The device has been tested intensively in order to verify its performance. The experimental program included two phases: (1) Testing the damper alone with Instron machine, examining three different friction-pad materials. (2) Testing a scaled steel frame model with inserted damper device. In both phases the following parameters were tested: forcing frequencies, normal forces, displacement amplitudes, pre-stressing forces and degradation under long-term cyclic excitation. The tests proved that the damper performance is: (1) Independent of forcing frequency within the range of 2 - 7 Hz; (2) Linearly dependent on displacement amplitudes; (3) Linearly dependent on normal forces; (4) Very stable over many cycles. The new device is characterized by the use of special friction pad material, which has been tested for up to 400 and 500 cycles without showing degradation of friction forces more than 5%. Besides, the steel plates were not damaged or scratched so that they can be used for many times. The comparison of results obtained from the experimental and numerical models showed a good agreement. The parameters influencing the frame with FDD were identified in advance by studying the frame's response to static and dynamic loading. The numerical studies demonstrated that the overall frame response was mainly affected by the geometry of the damper, frictional sliding moment and stiffness of the added brace. The device is very easy to manufacture and implement in structures. It is a very economic device due to material availability. It can be easily replaced if it is damaged, which is extremely unlikely, or can be readjusted after use.

Semi-active systems are becoming increasingly attractive for structural control applications because they offer some of the best features of both the passive and active systems. This paper examines one such system in which a passive tuned liquid column damper is converted into a variable damping semi-active system. Different semi-active algorithms which are based on the clipped-optimal strategy and fuzzy control theory are used to simulate such a system. The main objective of this paper is to show the applicability of such a system and to discuss the semi-active algorithms needed to achieve performance that is comparable to active systems.

This paper presents a theoretical study of heat transfer from magneto-rheological fluid (MRF) dampers. A lumped system model is developed which is capable of predicting the temperature rise for any size MRF damper. As a case study example, finned and unfinned dampers are compared for automotive-size MRF dampers. The results demonstrate that heat transfer from these devices can be enhanced considerably with the use of fins.

This paper discusses the results of expanded study of series simulations conducted to compare the effectiveness of various control systems for earthquake hazard mitigation. A systematic comparison of the performance of different control systems will be useful for the designer in selecting the most effective control system for a structure. Ideal passive, active and semi-active control systems are employed in this study. For determining the control action, an H₂/LQG control algorithm was selected for the active system and a clipped optimal control algorithm was selected for the semi- active system. In both cases the control algorithm was based on acceleration measurements for determination of the control action. To evaluate and compare the controllers, the structural responses of various 3, 6, and 10-story buildings are examined. An El Centro earthquake and pulse excitation are used as the ground excitations. The mass is held constant while the stiffness of the structure is varied to examine structures with a range of natural frequencies.

Because of the intrinsically nonlinear nature of semiactive control devices, development of control strategies that are practically implementable and can fully utilize the capabilities of these promising devices is an important and challenging task. In this study, we propose the use of an adaptive fuzzy strategy for the control of a structure installed with a magnetorheological (MR) damper. The proposed adaptive fuzzy control strategy involves the design of a fuzzy controller and an adaptation law for the combined structure-MR damper system. The objective control is to minimize the difference between a desirable response and the response of the combined system by intelligently adjusting its active component, the MR damper. The use of the adaptation law requires on-line monitoring of system response but eliminates the needs of acquiring any characteristics of the combined system in advance. The combination of the fuzzy controller and the adaptation law provides a robust control strategy that can be used on a nonlinear or uncertain system under random loads. A numerical example which involves controlling a single- degree-of-freedom structure under earthquake excitation using a MR damper is studied and presented. The simulated results indicate that the proposed adaptive fuzzy control strategy is quite effective and appropriate for the use of semiactive devices such as the MR damper.

Jacketing technology using fiber reinforced polymer (FRP) composites is being applied for seismic retrofit of reinforced concrete (RC) columns designed and constructed under older specifications. In this study, the authors develop an electromagnetic (EM) imaging technology for detecting voids and debonding between the jacket and the column, which may significantly weaken the structural performance of the column otherwise attainable by jacketing. This technology is based on the reflection analysis of a continuous EM wave sent toward and reflected from layered FRP-adhesive-concrete medium: Poor bonding conditions including voids and debonding will generate air gaps which produce additional reflections of the EM wave. In this study, dielectric properties of various materials involved in the FRP-jacketed RC column were first measured. Second, the measured properties were used for a computer simulation of the proposed EM imaging technology. The simulation demonstrated the difficulty in detecting imperfect bonding conditions by using plane waves, as the scattering contribution from the voids and debonding is very small compared to that from the jacketed column. Third, in order to alleviate this difficulty, a special dielectric lens was designed and fabricated to focus the EM wave on the bonding interface. Furthermore, the time gating technique is used in order to reduce the noise resulting from various uncertainties associated with the jacketed columns. Finally, three concrete columns were constructed and wrapped with glass-FRP jackets with various voids and debonding condition artificially introduced in the bonding interface. Using the proposed EM imaging technology with the lens especially designed and installed, these voids and debonding condition were successfully detected.

The vibratory behavior of a one dimensional spring mass system can be pictured by the superposition of traveling waves propagating along the structural network. Wave dynamics generated at natural boundaries and subsequently reflected at geometric boundaries can lead to pole-zero characteristics of a conventional Reverberated Transfer Function (RTF). By applying a wave model based virtual controller at these boundaries, a Dereverberated Transfer Function (DTF) can be obtained from the RTF. Since the DTF reveals the direct path of energy transmission across a one-dimensional structure, it is potentially useful for damage detection. In this paper, symmetric and asymmetric spring mass elements are used as the elementary cells for any arbitrary one-dimensional spring mass structure. This paper illustrates how to obtain the DTF from the RTF for discrete non-uniform structural elements. A three- degree-of-freedom (DOF) analytical building model is used for simulating several damage cases. Analytical results confirm that the DTF response can be used as a method for locating and quantifying damage in structures.

The objective of this work is to improve the probability of detecting damage and reduce the probability of false positives by combining damage detection methods. Most vibration-based NDD methods are derived from expressions relating the modal properties (i.e., mode shapes and frequencies) and/or the physical properties (i.e., stiffness or flexibility) of an undamaged structure to the modal properties of a damaged structure. These methods utilize some form of a damage indicator to identify the existence and location of damage in a structure. The basic assumption is that the modal and physical properties of the undamaged and damaged structure will differ. Thus, by measuring and comparing the modal properties of the damaged and undamaged structure one can infer whether or not damage exists and in some cases the location of the damage. In this work, we present a methodology to combine the results of the different NDD methods using the techniques of pattern recognition. To accomplish this task, we begin with a review of pattern recognition. Next, we develop a methodology to combine the results of the different NDD methods. To investigate the applicability of the combined approach we perform damage detection on a beam using two damage detection methods (Damage Index Method and a method that utilizes the parameters of an ARMA model as damage indicators) separately and then combined using the developed methodology. Finally, a comparison of the probability of detection and the probability of a false positive is made between the combined approach and the NDD methods applied separately.

This paper reviews a method of localized structural health monitoring based on relative changes in localized flexibility properties. The localized flexibility matrices are obtained either by applying a decomposition procedure to an experimentally determined global flexibility matrix or by processing the output signals of a vibration test in a substructure-by-substructure manner. The theory is based on the partitioning of the energy functional of a discrete dynamic system, for which Lagrange multipliers are utilized to enforce compatibility constraints between neighboring substructural regions. The resultant dynamics are then stated in terms of generalized variables that are unique to each substructure and the Lagrange multipliers that can be considered as interface forces which transfer energy between substructures. This theory is demonstrated with an experimental damage detection test of a bridge column model.

The damage index method is an intuitively attractive method for detecting localized stiffness perturbations through their influence on mode shapes. In spite of its attractiveness, and a large literature on the formulation of the damage index method for different types of structures and its application to specific test problems, the practical consequences which can result from its limitations, as well as its overall effectiveness, have not been demonstrated or discussed. This is an important problem since, at minimum, the qualitative characteristics and performance of a proposed diagnostic algorithm should be understood. In this paper, the authors review the damage index formulation and examine the traditional assumption step by step. Then this method has been used for numerous cases at different locations and degrees of stiffness perturbation for a large pre-stressed segmental concrete bridge. The finite element models have been used as test structures. The object is to evaluate the feasibility of the damage index method.

Synthetic Aperture Radar (SAR), capable of all-time and all- weather operation, shows promising applications in monitoring urban areas for earthquake damage detection. The objective of this study is to use a computer code for SAR simulation and to demonstrate the usefulness of SAR applications for identification of seismically induced structural damage. For this purpose, CAD models of several buildings are constructed consisting of a combination of triangular facets, arranged in a way to represent their outside shells. SAR simulation is made in the time-domain using XPATCHT computer code package. Simulated SAR images with highest resolution of 15 cm to the lowest resolution of 2 m are considered. In this simulation, the SAR antenna shoots a bundle of rays with respective angles to the object. After ray tracing, physical optics evaluate the electric field in the far field and the final SAR image is obtained by compressing the simulated data in range and cross- range directions. After obtaining the complex SAR image, magnitude and phase (for interferometry studies) information provide measures in order to identify geometrical changes. The result of the simulation indicates that edges and corners are usually very well detectable and that geometrical changes such as tilting, overturning or pancaking can be observed and measured.

An electromagnetic immune fiber-optic Extrinsic Fabry-Perot microinterferometer vibration sensor system (EFPI-V) with cantilever type sensing elements is described. Several sensors with low resonance frequency (first bending mode f₁ < 100 Hz) are installed along the edge of a taxiway of Braunschweig airport with separation distances between 15 and 60 m for investigation of ground traffic monitoring via vibrational and noise induced broadband excitation of the resonances. Modified sensors with f₁ >= 100 Hz are developed for quantitative low frequency (f < 100 Hz) acceleration measurements. Initial characterization of a 100 Hz-sensor, using a capacitive accelerometer as a reference exhibits the expected f²-dependence of the amplitude for f < 50 Hz and acceleration amplitudes down to some mg. For the first time to our knowledge field tests with an EFPI- acceleration sensor have been performed for monitoring the traffic induced vibrations of a motorway bridge (EC-project 'Smart Structures'). The measured frequency spectra show reasonable agreement with the response of the capacitive accelerometer for f < 50 Hz.

This paper presents a strategy for active damping of cable structures, using active tendons. The first part of the paper summarizes the theoretical background: the control law is briefly presented together with the main results of an approximate linear theory which allows to predict the closed- loop poles with a root locus technique. The second part of the paper reports on experimental results obtained with two test structures: the first one is a small size mock-up representative of a cable-stayed bridge during the construction phase. The control of the parametric vibration of passive cables due to deck vibration is demonstrated. The second one is a 30 m long mock-up built on the reaction wall of the ELSA test facility at the JRC Ispra (Italy); this test structure is used to demonstrate the practical implementation of the control strategy with hydraulic actuators.

Magnetorheological (MR) dampers are a promising class of devices for the control of civil structures for earthquake hazard mitigation. MR dampers exhibit both viscous damping and friction damping, where the friction damping level is controlled by an applied magnetic field. This unique characteristic, as well as low power requirements, high force capacity, and mechanical simplicity, lends them to be very suitable devices for the semi-active control of such seismically loaded structures. This study investigates semi- active control methods and their application to MR dampers. Skyhook control and a 'clipped' Continuous Sliding Mode (CSM) control are simulated both numerically and experimentally. The results show that control of civil structures with semi- actively controlled MR braces is very effective.

Stay cables, such as are used in cable-stayed bridges, are prone to vibration due to their low inherent damping characteristics. Transversely-attached passive viscous dampers have been implemented in many bridges to dampen such vibration. Several studies have investigated optimal passive linear viscous dampers, however even the optimal passive device can only add minimal damping to the cable when attached a reasonable distance from the cable deck anchor. This paper investigates the potential for improved damping using semiactive devices. The equations of motion of the cable/damper system are derived using an assumed modes approach and a control-oriented model is developed. The control-oriented model is shown to be more accurate that other models and facilitates low-order control designs. The effectiveness of passive linear viscous dampers are reviewed. The response of a cable with passive, active and semiactive dampers is studied. The response with a semiactive damper is found to be dramatically reduced compared to the optimal passive linear viscous damper for typical damper configurations, thus demonstrating the efficacy of a semiactive damper for absorbing cable vibratory energy.

This paper presents a semi-active control of a scaled two-span bridge structure. Magneto-rheological fluid (MRF) dampers are utilized as the semi-active devices and a bridge vibration control system is developed. Both open and closed-loop control systems are used to suppress the bridge deck motion under simple harmonic and simulated earthquake excitation. Effectiveness of each system is discussed. It is demonstrated that the closed-loop control systems can reduce the relative deck displacement of the bridge, while simultaneously limiting the peak damper forces.

Soil-structure interaction (SSI) has gained significant recognition of importance in the control of seismically excited structures in the past ten years. In this paper, recent developments of the SSI effect on the performance of passive, semi-active and active control strategy are summarized in general. It is followed by a short presentation on the seismic effectiveness of tuned mass dampers, variable stiffness devices and active control systems in reducing the maximum response of structures with the intent of comparing the SSI effect on various devices and control systems. Numerical studies on a 3- and a 12-story frame structure resting on a viscoelastic half space indicated that SSI tends to defeat the effectiveness of control systems. This defeat is primarily because the damping of a soil-structure system increases and the structure vibrates more like a rigid body as the soil material softens. Since nearly all devices made of smart materials either passively or actively respond to the structural deformation, their performance is likely to degrade for flexible-base structures.

A guaranteed behavior, or at least a predictable behavior, establishing the expected evolution of the shape memory properties (transformation temperatures and hysteretic behavior) is of the primary importance for most of the applications. In particular, the SMA applications in Civil Engineering require guaranteed long time devices. Mesoscopic and microscopic results will be described to increase the reliability of the materials. In particular, the effects related to the two-phase coexistence, the climate and seasonal effects on the martensitic transformation temperature and, also, the effects of fatigue related to the dislocation creation and to the subsequent modifications induced on the dynamics of the processes.

It is possible to estimate reliability of the materials during their use by recording the changes in defect density of polycrystalline structure, which can be estimated on residual stresses at a crystal micro-level. In this paper the experimental measurement results of the residual stress field changes in actuator manufactured using shape memory alloy (SMA) are presented. The experimental data are based on the investigation of the changes in the root-mean-square (RMS) micro-strains and size of coherent block in the SMA caused by thermal and mechanical loading. The study is performed on the samples of approximately equiatomic TiNi alloy. To induce the reversible martensite transformations in the material the external loading is used with subsequent data recording using the X-ray method. The results of experimental measurements of the RMS microstrain and coherent block size in austenite are presented. Based on the experimental data a novel mathematical model is proposed, which is used in the computer simulations that include the martensite transformations, twining, elastic and irreversible deformations. The experimental and computer modeling results of stress and strain field generated by the defects in polycrystalline materials are discussed.

Damage to highway systems from recent earthquakes has emphasized the need for pre-event damage assessment of the existing highway systems so that the effective measures can be taken to reduce the loss from the future earthquake. In this paper, a Monte Carlo technique is presented which can be effectively used to simulate the states of bridge as well as highway network damage. With the aid of damage data, collected after the 1994 Northridge earthquake, the fragility curves are developed for each bridge on a limited access expressway network in Los Angeles County and Orange County in California, and classified in accordance with such attributes as whether it is a single span or multiple span, how much it is skewed and the condition of soil on which it is constructed. Monte Carlo simulations of states of bridge damage are performed based on these facility curves. A set of criteria and indices are then introduced, upon calibration with Northridge experience, for simulation of the damage state of each link and then the state of network damage when subjected to scenario earthquakes. The calibration is achieved by adjusting the criteria and indices by comparing the simulated states with the actual states of network damage under the Northridge earthquake. Computational time for one realization (simulation) of states of network damage is of the order of a few seconds. Therefore, the Monte Carlo simulation-based method of network damage assessment presented here can provide a post-earthquake response decision support system for highway networks; Since the purpose of the present study is to demonstrate the efficacy of the Monte Carlo simulation method, numerical examples are performed under the conditions that only bridges are seismically vulnerable, bridge fragility curves are available, and knowledge of the state of network damage suffices for government agencies and emergency response profession to make decisions as to how search/rescue/medical teams and emergency repair crews can be dispatched and how food, potable water and other emergency supplies can be transported by an optimal use of the remaining network capacity. In this study, the spatial distribution of ground motion intensity is estimated deterministically in terms of peak ground acceleration (PGA). The spatial variation of PGA due to modeling and other sources of uncertainty is expected to have some effect on the final result. This issue is currently under study.

Crack detection technique for concrete structures is developed in this paper. This method utilized Optical Time Domain Reflectormetry (OTDR) method that broadly used in the field of optical science. Currently several crack detection techniques, such as visual inspection, crack gage, ultrasonic detection test, are used. But these methods are not economical and are time-consuming issue. Therefore, easy and economical method of detecting cracks on the surface of concrete structure or welded part of steel structure have been developed in this research, this technique utilizes optical fiber and OTDR equipment. Concrete beam model tests are performed to verify the usefulness of this technique. Results of these tests show that developed technique can detect the location of the cracks easily and correctly. Further task is to testify the method of detecting cracks on welded part of steel structure with a performance of model test and apply it to a real structure.

Recently, the method of Hilbert transform has been used successfully by the authors to identify parameters of linear structures with real eigenvalues and eigenvectors, e.g., structures with proportional damping. Frequently, linear structures may not have proportional damping so that normal modes do not exist. In this case, all the eigenvalues, eigenvectors and modeshapes are complex. In this paper, the Hilbert transform and the method of Empirical Mode Decomposition are used to identify the parameters of structures with nonproportional damping using the impulse response data. Measured impulse response signals are first decomposed into Intrinsic Mode Functions using the method of Empirical Mode Decomposition with intermittency criteria. An Intrinsic Mode Function (IMF) contains only one characteristic time scale (frequency), which may involve the contribution of a complex conjugate pair of modes with a unique frequency and a damping ratio, referred to as the modal response. It is shown that all the modal responses can be obtained from IMFs. Then, each modal response is decomposed in the frequency-time domain to yield instantaneous phase angle and amplitude as functions of time using the Hilbert transform. Based on only a single measurement of the impulse response time history at one location, the complex eigenvalues of the linear structure can be identified using a simple analysis procedure. When the response time histories are measured at all locations, the proposed methodology is capable of identifying the complex modeshapes as well as the mass, damping and stiffness matrices of the structure. The effectiveness and accuracy of the methodology presented are demonstrated through numerical simulations. It is shown that complete dynamic characteristics of linear structures with nonproportional damping can be identified effectively using the Hilbert transform and the Empirical Mode Decomposition method.

The damage detection system of a real steel truss bridge was developed to identify the location and severity of the damaged members. At first, the loading test was performed to characterize the real bridge. The real steel truss bridge was measured by electrical strain gages and accelerometers when the train passed. The measured strains and acceleration were used to refine the stiffness and the mass of the finite element model. The damage scenario, that can be happened in the real situation, was simulated by the refined finite element model. The damage localization was implemented to classify the damaged part in the bridge by the neural networks. The neural network was constructed as two steps: at 1st step, the half-span, which had some damages occurred, was found, and at 2nd step, the severest abnormal part in the total 8 parts of the real bridge was detected. The learned neural network was verified by the used data.

This study proposes a method to utilize the satellite, aerial and other remotely sensed pre- and post-disaster imagery data to perform geometric modeling and correlational analysis on the reconstructed models in order to detect the change associated, for example, with major regional and/or individual structural damage. Correlational analysis often fails to detect structural damage when only input images are utilized, especially if images are acquired under different illumination conditions. In fact, automatic detection in such cases becomes extremely challenging since making distinction of change due to structural damage from that associated with the difference in the illumination condition is extremely difficult. Many researchers have tackled this difficulty and proposed some methods of solutions including recursive hypothesis testing procedure. Although these methods provide a very useful basis for change detection, their applications are not universally successful for a variety of reasons. In order to achieve the required level of accuracy for the proposed application and locate the site of detected damage, it is proposed to use available GIS maps to register remotely sensed images. It is further necessary that a user-assisted three-dimensional model be reconstructed and correlational analysis performed. The algorithm performs successfully for change detection. However, issue of occlusion remains as a challenge that requires further investigation.

Promising results have been shown in recent studies using commercial coaxial ETDR sensing cables for health monitoring application of concrete beam structures subject to bending load. Although distributed strain monitoring and crack damage detection capabilities of the sensors were demonstrated, the low signal-to-noise ratio of the sensors smears the details of the strain measurement that the ETDR signal waveform can convey. A high-sensitivity coaxial sensor prototype specifically designed for distributed strain sensing application has been recently developed in-house. It has been shown that the prototype sensor has a much superior sensitivity in terms of ETDR signal response to applied loads than commercial coaxial cable counterpart. In this paper, the effectiveness of using an embedded high-sensitivity coaxial sensor prototype to monitor transverse shear response of a concrete cylinder is investigated. Both single and double plane transverse shear tests were conducted. The test results show that the embedded high-sensitivity ETDR prototype sensor is capable of detecting the on-set as well as monitoring the growth of shear-induced crack damages in concrete cylinder specimens.

A system has been developed and installed to continuously monitor the integrity of a railway track. In this system elastic waves are transmitted, along the rails, between transmit and receive stations spaced at 2.5 km intervals along the length of the track. The development of piezoelectric transducers, which transmit and receive the elastic waves is described. The requirements and conceptual design of the transducer are described. Results of measurements conducted in the laboratory and in the field are presented. The transducer achieved transmission over the required 2.5 km with a signal to noise ratio of approximately 30 dB at the receiver. Finite element modeling was used to obtain a better understanding of the transducer operation. Improved modeling of the wave propagation and energy loss mechanisms in the effectively infinite rail is required before the model can be used to predict optimal frequencies and methods of excitation. The present system was designed to detect complete breaks in the rail. A 'smarter' system with communication between the transmit and receive stations, more sophisticated signal processing, and wave propagation confined to the critical regions of the rail cross-section could indicate the growth of cracks before the rail breaks thus adding substantial value to the system.

In this study, the method to estimate the bridge deflection is developed using the fiber optic Bragg-grating strain sensors. Most of the evaluation of structural integrity, it is very important to measure the geometric profile, which is the major factor standing for the global behavior of civil structures, especially bridges. In the past, for the lack of the appropriate method to measure the deflection curve of bridge on site, the measurement was restricted to just a few of discrete points along the span length, which were also limited to the locations installed with the displacement transducer in advance. Hereby, with an application of classical beam theory, a formula is established estimating the continuously deflected profile from the measurement of strains at several points. In addition, strains could be measured by the use of fiber optic strain sensors, which are electro-magnetic noisy-free, and into which several points of sensing could be installed. With the strain data acquired, the proper strain curve is fitted, and finally, deflection curve would be estimated. The experimental test was carried out to verify the developed algorithm.

Distribution of axial strain in model piles was measured by Fiber Bragg Grating (FBG) sensor to investigate a possibility of measuring and analyzing the load transfer mechanism of pile foundation by Fiber Optic Sensor (FOS) system. Since FBG of different wavelengths can be multiplexed in an optical fiber, the installation of sensor system and the measurement of strains are relatively simple compared with the system consisted of strain gages. In this study, FBG sensors and electric strain gages were embedded in the piles and the distributions of load transfer measured by two sensor systems were compared. It was observed from the test results that the magnitudes of axial load measured by both systems showed insignificant difference and that the distributions of axial load by FBG were smoother than those by strain gage. Under the environments of laboratory testing, survival rate of embedded FBG system was higher than that of strain gage. Therefore, it was concluded that the use of FBG sensor has a great potential for the measurement of pile load transfer with accuracy.

In this paper, we present an improved fiber Bragg grating (FBG) sensor system using a wavelength-swept fiber laser (WSFL). The WSFL provides unique and functional output characteristics useful for sensor interrogations. Proper monitoring of measurands in FBG sensor systems requires accurate measurement of the Bragg center wavelength, and the ability to track rapid shifts of the wavelength. For the purpose, we constructed a signal processing board with an electrical circuit and real-time signal-processing program using Labview software for storage and visualizing of the data. To improve its ability to acquire massive sensor signals, multi-channel sensor arrays were also constructed. The constructed FBG sensor system using WSFL and the real-time signal-processing program could successfully measure the strains of a composite laminated beam at nine sensing points. As a practical application of infrastructure, we demonstrate four FBG sensors in an optical fiber were used to monitor strains of the smart bridge model. When the smart bridge shows the response of near certain level of strain, the bridge tells early warning sound. This early warning system could give you time to undertake remedial works on bridges before the catastrophic disaster.

There are over 578,000 bridges on public roads in the United States and more than 112,000 of them are rated as substandard either through deterioration or obsolescence. Recently, fiber reinforced polymer (FRP) composites have been investigated for building bridges due to advantages such as: reduced weight, decreased effects from environment, and speed of installation. Luna Innovations has been working closely with researchers at Atlantic Research Corporation (ARC) to develop and implement an embeddable fiber optic health monitoring system to monitor strain in composite bridge decks over time. During this research, Luna Innovations successfully embedded fiber optic strain sensors in three composite bridge decks fabricated by ARC. Strain data was recorded during 3-point bend testing of two of the bridge decks. The third bridge deck was placed at a Beta test site in November of 1999 where the strain sensors have been monitored periodically.

In this paper we consider the problem of stability of suspension bridges in the presence of random wind forces acting on the deck and the suspension cables. Total mechanical energy given by the sum of all kinetic and elastic potential energies of the structure, is used as a Lyapunov functional. Assuming negligible mechanical friction and viscous damping, it is seen that the system is conservative and that random wind forces can destabilize the system. In the presence of structural damping, provided by piezo ceramic layers or other smart materials, it is seen that the system is asymptotically stable. This is clearly illustrated by numerical results presented in the final section of the paper.

The need to monitor and undertake remedial works on large structures has greatly increased in recent years due to the appearance of widespread faults in large structures such as bridges and buildings, etc, of 20 or more years of age. The health condition of structures must be monitored continuously to maintenance the structures. In order to do in-situ monitoring, the sensor is necessary to be embedded in the structures. Fiber optic sensors can be embedded in the structures to get the health information in the structures. The fiber sensor was constructed with 3 X 3 fiber couplers to sense the multi-point strains and failure instants. The 4 RC (reinforced concrete) beams were made to 2 of A type, 2 of B type beams. These beams were reinforced by the reinforcing bars, and were tested under the flexural loading. The behavior of the beams was simultaneously measured by the fiber optic sensors, electrical strain gages, and LVDT. The states of the beams were interpreted by these all signals. By these experiments, there were verified that the fiber optic sensors could measure the structural strains and failure instants of the RC beams. The fiber sensors were well operated until the failure of the beams. It was shown that the strains of the reinforcing steel bar can be used to monitor the health condition of the beams through the flexural test of RC beams. On the other words, the results were arrived that the two strains in the reinforcing bar measured at the same point can give the information of the structural health status. Also, the failure instants of beams were well detected from the fiber optic filtered signals.

Research continues in exploring active control techniques to calm resonant floor vibrations. In this research, an electro- magnetic proof-mass actuator is used to deliver the control force in a single-input/multi-output control strategy. With the intent of improving the stability characteristics and the effectiveness of the SISO controller, the relative actuator mass displacement and the actuator mass velocity are added to the floor velocity output used in prior research by the author. Three separate performance indices are developed and implemented to illustrate their particular usefulness in designing an output feedback scheme for controlling pedestrian induced floor motion. The multi-output scheme has been shown analytically to further reduce steady-state acceleration amplitudes by a factor of 7 over the single-output scheme.

The main objective of the research in progress is to evaluate the applicability of an innovative earthquake-protective system called pneumatic foundation to building construction and industrial equipment. The system represents kind of seismic soil isolation. The research is analytical and accompanied with limited testing on a shake table. The concept of partial suppression of seismic energy flow inside a structure is known as a seismic or base isolation. Normally, this technique needs some pads to be inserted into all major load-carrying elements in a base of the building. It also requires creating additional rigidity diaphragms in the basement and a moat around the building, as well as making additional provisions against overturning and/or P-_(Delta ) effect. Besides, potential benefits of base isolation techniques should not be taken for granted: they depend on many internal and external factors. The author developed a new earthquake protective technique called pneumatic foundation. Its main components are: a horizontal protective layer located under the footing at a certain depth, and a vertical one installed along the horizontal protective layer perimeter. The first experiments proved a sizable screening effect of pneumatic foundation: two identical models of a steel frame building, put simultaneously on the same vibrating support simulating an earthquake, performed in a strikingly different manner: while the regular building model shook vigorously, the model on a pneumatic foundation just slightly trembled.

Genetic algorithms will be used for the optimization of feedback gains and controller placement for discrete building structures. The optimal design and placement of controllers at discrete locations is an important problem that will have impact on the control of civil engineering structures. Though algorithms exist for the placement of sensor/actuator systems on continuous structures, the placement of controllers on discrete civil structures is a very difficult problem. Because of the nature of civil structures, it is not possible to place sensors and actuators at any location in the structure. This usually creates a nonlinear constrained mixed integer problem that can be very difficult to solve. Using genetic algorithms in conjunction with gradient based optimization techniques will allow for the simultaneous placement and design of an effective structural control system. The introduction of genetic-based algorithms should increase the rate of convergence and thus reduce the computational time for solving the difficult control problem.

An optical strain gage, employing a hollow polyimide-coated glass capillary tube, is currently under development. The capillary tube serves as a waveguide, in which an optical signal is attenuated in an amount proportional to applied bending strain. The capillary is incorporated into an optical fiber link which acts as both the source of signal and as the return path to a photodiode detector. The inherent compatibility of this optical strain sensor with fiber optic telecommunication systems makes it amenable for incorporation into intelligent systems for the continuous monitoring and damage assessment of bridges, highways, piers, airframes, and buildings. By applying various thin films to the interior and/or exterior surfaces of the waveguide, the strain gage can be optimized for specific strain ranges. This optical strain sensor exhibits advantages in comparison to commercially available metal foil (resistance) strain gages, including gage factors 100 times larger and temperature insensitivity for operating temperatures ranging from -25 degrees Celsius to +51 degrees Celsius.

Fiber composites made of carbon fibers and organic polymers are being used to strengthen plain, reinforced, and prestressed concrete structures. The composites are becoming more popular as compared to traditional strengthening with steel plates and jackets because they do not corrode and also have a very high strength to weight ratio. Organic polymers have been used as protective coatings for more than thirty years. The impermeable membrane of the polymer seals the concrete surface of the structures preventing the ingress of salts. Their main drawback is their inability to release vapor pressure buildup that causes damage in the concrete and delamination of the bonded fiber reinforced plastic. As a result of this and other weaknesses in the organic polymers, a new generation of breathable coating materials is being developed. These compositions range from epoxy modified portland cement coatings to completely inorganic silicate systems. The durability of five of the most promising compositions was evaluated under freeze-thaw, wet-dry, and scaling conditions. The silicate matrix was also used to bond carbon tows and fabrics to unreinforced concrete members. These beams were tested after exposure to wet-dry and scaling conditions. The results indicate that the inorganic matrix can be effectively used for repairs. The carbon tows can be used to replace the existing corroded reinforcing bars. The possibility of embedding optical fibers with the carbon fibers to monitor the field performance is being studied.

This study presents a theoretical analysis of heat generation and dissipation of field-controllable magneto-rheological fluid (MRF) shock absorbers. Since MRF dampers are energy- dissipating devices, the issues of heat generation and dissipation are important in predicting their performance. A theoretical model is developed based on Bingham plastic model to estimate temperature history of the MRF dampers. The governing equation includes the MRF viscosity as a function of the temperature. The numerical solutions are compared with experimental results in order to validate the accuracy of the model, and excellent agreements are obtained.

The near-field earthquake ground motion is characterized by high peak accelerations and velocity pulses with long period components as well as large ground displacements. Such characteristics are responsible for severe damages to flexible structures. The peak ground acceleration occurs in the form of a shock, rather than a gradual build-up. As a result, passive dampers may not dissipate energies quick enough to prevent a serious damage to structures. Recently, a resetting or switching semi-active stiffness damper (RSASD or SSASD) and a semi-active electromagnetic friction damper (SAEMFD) have been shown to be effective in reducing the structural response due to dynamic loads. In this paper, the performance and effectiveness of these two semi-active hybrid isolation systems are studied extensively for base-isolated buildings subject to near-field earthquakes. Numerical results clearly demonstrate that these two semi-active dampers are effective in protecting the integrity of base-isolated structures during near-field earthquakes.