Showing papers in "Structural Control & Health Monitoring in 2005"
TL;DR: In this article, a new mathematical model was proposed to describe the dynamic behavior of a magnetorheological damper, based on a modification to the well-known LuGre friction model; it is simpler than other models already suggested in the literature and offers a similar level of accuracy.
Abstract: This paper presents a new mathematical model to describe the dynamic behavior of a magnetorheological damper. The proposed model is based on a modification to the well-known LuGre friction model; it is simpler than other models already suggested in the literature and offers a similar level of accuracy. To validate the proposed model, experimental tests applying controlled and random displacements and currents on a commercial damper were performed. Parameter identification algorithms were then used to fit the parameters that better describe the dynamic behavior of the damper. The identification scheme includes a closed-loop observer to estimate the internal state of the friction model. Results demonstrate very good model performance and indicate that the proposed model can be readily used in the design of semi-active control algorithms, state observers and on-line parameter identification schemes. Copyright © 2004 John Wiley & Sons, Ltd.
113 citations
TL;DR: In this article, the performance of the MICA and MICA2 Mote is investigated through shaking table tests employing a two-storey steel structure, and its performance for wireless measurement and specific risk monitoring applications, such as damage detection in the structure, is presented.
Abstract: Buildings are subjected to natural hazards, such as earthquakes and winds, and artificial hazards, such as fires and crimes, during their long-term use. Risk monitoring using a network of wireless sensors is one of the most promising emerging technologies for mitigation of these hazards. Recently, a smart sensor based on the Berkeley Mote platform was introduced, and an application to the next generation of structural health monitoring and control was proposed. The Mote has on-board microprocessor and ready-made wireless communication capabilities. In this paper, the performance of the MICA and MICA2 Mote is investigated through shaking table tests employing a two-storey steel structure. The acceleration sensor is tested, and its performance for wireless measurement and specific risk monitoring applications, such as damage detection in the structure, is presented. The MICA2 Mote is shown to have sufficient performance for the intended purpose. Copyright © 2005 John Wiley & Sons, Ltd.
99 citations
TL;DR: In this article, an aluminum plate monitored by piezoelectric active sensors is used to validate the performance of the prototype unit in structural health monitoring applications, and a novel damage detection methodology is proposed that uses the characteristic equation roots obtained from an autoregressive with exogenous input time-series model.
Abstract: SUMMARY The recent years have witnessed an increasing interest in using wireless structural monitoring as a low-cost alternative to tethered monitoring systems. Previous work considered wireless sensors strictly as passive elements in the monitoring system, responsible only for collection of response measurements. This paper explores expansion of the wireless structural monitoring paradigm by including actuation capabilities in the design of a wireless active sensing unit. To validate the performance of the prototype unit in structural health monitoring applications, an aluminum plate monitored by piezoelectric active sensors is used. Piezoelectric actuators mounted to the surface of the plate are commanded by the wireless active sensing unit to excite and record the element. System identification models are then used to model the linear relationship between the input excitation and the corresponding plate response. A novel damage detection methodology is proposed that uses the characteristic equation roots obtained from an autoregressive with exogenous input time-series model. Complex roots (poles) of the model’s characteristic equation are sensitive to structural damage causing a change in their location on the complex plane. Using the mean value of pole clusters, the migration of model poles are shown to be well correlated to the severity of crack damage intentionally introduced in the plate. Copyright # 2005 John Wiley & Sons, Ltd.
90 citations
TL;DR: In this paper, a comparison of the response of structures isolated by sliding systems with conventional and hysteretic models of the frictional force of the sliding system is carried out to investigate the comparative performance and computational efficiency of the two models.
Abstract: The problem of sliding structures is discontinuous one as different sets of equations of motion with varying forcing functions are required for the sliding and non-sliding phases. This is inconvenient for the numerical integration of the governing equations for the response of sliding structures. To overcome such difficulties continuous hysteretic models of the sliding systems have been presented in the past. In the present study, a comparison of the response of structures (i.e. multi-storey buildings and bridges) isolated by sliding systems with conventional and hysteretic models of the frictional force of the sliding system is carried out to investigate the comparative performance and computational efficiency of the two models. The seismic response of isolated structures is obtained by solving the governing equations of motion using a step-by-step method under single and two horizontal components of real earthquake motions. For comparative study, the seismic response of a multi-storey building obtained by the conventional model is compared with the corresponding response by the hysteretic model under different sliding isolation systems, numbers of storeys and values of the fundamental time period of the superstructure. It is found that the conventional and hysteretic models of sliding systems predict a similar seismic response for isolated structures. However, the difference in the response between the two models is relatively more for the pure friction system as compared with the sliding systems with restoring force. Further, the conventional model is relatively more computationally efficient as compared with the hysteretic model. Copyright © 2004 John Wiley & Sons, Ltd.
64 citations
TL;DR: In this article, the authors describe the application of spread spectrum fault location and wire health monitoring methods whose unique low-interference potential and high-noise immunity enable them to locate faults while networks are active.
Abstract: Aging wiring networks have been identified as an area of critical national and international concern. One of the particularly challenging problems is the location of intermittent faults that cannot be replicated on the ground. This paper describes the application of spread spectrum fault location and wire health monitoring methods whose unique low-interference potential and high-noise immunity enable them to locate faults while networks are active. The analysis and feasibility of this method has been described in previous work, and this paper focuses on evaluation of the accuracy of the method and effects of branched wire networks on the sensor response. Copyright © 2005 John Wiley & Sons, Ltd.
61 citations
TL;DR: In this paper, a fiber Bragg grating (FBG) sensor is used to measure the wavelength of the reflected light from each FBG sensor, which can be used for river surveillance monitoring, civil structural monitoring, aerospace health monitoring, and so on.
Abstract: We are developing several kinds of fiber Bragg grating (FBG) sensors for application in river surveillance monitoring, civil structural monitoring, aerospace health monitoring, and so on. In this paper we describe highly precise FBG sensing systems, specifically water-level sensors, as a practical example. We have achieved sensor accuracy of ± 0.1% F.S., i.e. ± 1 cm for a full measurement range of 10 m in water level. For other applications, FBG interrogation techniques are described for high-frequency vibration monitoring or acoustic emission detection. In this FBG interrogation system, optical filters based on planar lightwave circuit (PLC) technology are used to measure the wavelength of the reflected light from each FBG sensor. We discuss two types of the optical filter, a Mach–Zehnder interferometer (MZI) and an arrayed waveguide grating (AWG). The wavelength shift of the FBG sensor due to strain or temperature change is determined through direct detection of the light intensity ratio from the output ports of the optical filter. We have made a FBG interrogation unit which allows four-channel FBGs to be connected in series to measure strain in the x, y, and z directions as well as temperature. Copyright © 2005 John Wiley & Sons, Ltd.
60 citations
TL;DR: In this article, a sliding-mode switching controller is proposed for realizing zero-error force command tracking, which is shown that parameter uncertainty is a critical issue for force commands which require the network to operate near its optimum transmissive efficiency.
Abstract: A Regenerative Force Actuation (RFA) Network consists of multiple electromechanical forcing devices distributed throughout a structural system and actuated in such a way as to reduce the response of the structure when subject to an excitation. The associated electronics of the devices are connected together such that they are capable of sharing electrical power with each other. This makes it possible for some devices to extract mechanical energy from the structure, while others re-inject a portion of that energy back into the structure at other locations. The forcing capability of an RFA network is constrained only by the requirement that in the aggregate the total network must always dissipate energy.
The electromechanical currents generated by RFA networks must be controlled to create the desired structural forces. This control is facilitated by the alternation of a multitude of power-electronic transistor switches in the electrical network. In this study, a sliding-mode switching controller is proposed for realizing zero-error force command tracking. It is shown that parameter uncertainty is a critical issue for force commands which require the network to operate near its optimum transmissive efficiency.
RFA networks can be used to create velocity-proportional damping forces in structures. However, unlike traditional structural damping, RFA networks have the ability to create non-local and asymmetric damping forces. It is shown that this more generalized damping capability can lead to significant improvements in the forced response of a structure, as compared with traditional linear damping.
RFA networks may also be used for feedback control. In this context, the forcing capability of the RFA network is constrained by its physical limitations. In this study, a systematic method of nonlinear control design called "Damping-Reference" control is proposed, which guarantees a certain level of quadratic performance for the structural response. Variants of the control law synthesis are proposed for quadratic regulation, stochastic control, and H[infinity] control contexts.
These ideas are illustrated in the context of earthquake engineering through a simulation example, involving a three-story structure with a two-actuator RFA network installed. In this example, it is shown that the "power sharing" nature of the RFA network has a significant influence on the response.
59 citations
TL;DR: In this article, a PVDF wireless smart sensor has been developed for monitoring structures on a large scale, which is selected as the sensor element because of its flexibility, slim size, low cost and the ability of being integrated into wireless system.
Abstract: A PVDF wireless smart sensor has been developed for monitoring structures on a large scale. PVDF is selected as the sensor element because of its flexibility, slim size, low cost and the ability of being integrated into wireless system. The introducing of the wireless technology eradicates the large amount of cable needed for installation, lowers cost and the overall energy consumption, and makes real-time monitoring possible as well. Four PVDF wireless sensor units have been built and tested in this study. The application of PVDF sensor at low frequencies has been explored. The approach of using PVDF sensor as a dynamic strain gauge has been demonstrated. The method of compensating the temperature effect of PVDF sensor due to the pyroelectric effect of PVDF film has also been investigated. Copyright © 2005 John Wiley & Sons, Ltd.
54 citations
TL;DR: In this paper, the authors present experience obtained by collaboration in a form intended to educate, by example, bridge operators about potential and limitations of SHM systems, and draw out lessons relevant to the future development of structural health monitoring systems.
Abstract: Monitoring programs on four very different highway bridges originating from a range of requirements related to calibration of numerical models, assessment of load capacity and long-term tracking of performance are summarized in order to draw out lessons relevant to the future development of structural health monitoring ‘systems’. These lessons concern validation of structural models, appropriate methods for instrumentation, communication, data management and system identification. The paper presents experience obtained by collaboration in a form intended to educate, by example, bridge operators about potential and limitations of SHM systems. Copyright © 2005 John Wiley & Sons, Ltd.
53 citations
TL;DR: In this article, the seismic vulnerability of a representative Mamluk-style minaret, namely Manjaq Al-Yusufi (1349 A.D.), is investigated and some seismic protection techniques are proposed and evaluated.
Abstract: During the Egypt/Dahshur 1992 earthquake, a large number of historical Islamic minarets, especially those built during the Mamluk era, were significantly damaged. The level of damage in Mamluk-style minarets was assigned to their massive size, and their irregular distribution of mass and stiffness along their heights. In this paper, the seismic vulnerability of a representative Mamluk-style minaret, namely Manjaq Al-Yusufi (1349 A.D.) is investigated and some seismic protection techniques are proposed and evaluated. Geometrical, material, and geotechnical data were determined at the site. A realistic three-dimensional finite element model of the minaret that reflects those properties was constructed. Ambient vibration tests were then performed on the minaret, and its modal parameters such as fundamental periods and mode shapes were obtained. The ambient vibration test results were then used to update the finite element model. The seismic hazard at the minaret location was evaluated, and a seismic risk study of the minaret was performed with the conclusion that the minarets will be highly vulnerable during moderate earthquakes. A seismic protection technique that includes the use of high damping rubber bearings HDRB and vertical steel anchoring bars is proposed and evaluated. The proposed technique was found to efficiently reduce the seismic risk of the minaret under investigation. Copyright © 2004 John Wiley & Sons, Ltd.
36 citations
TL;DR: State-space identification methods are used for modal identification from earthquake records with further investigation into the effectiveness of the methods from the viewpoint of sensor layout configuration with computational costs and limits of applicability examined.
Abstract: Arrays of large numbers of sensors and accompanying complex system identification (SI) methods have been recently used in engineering applications on structures ranging from complex real space trusses to simple experimental beams. However, practical application to strong motion data recorded on large civil engineering systems is limited. In this study, state-space identification methods are used for modal identification from earthquake records with further investigation into the effectiveness of the methods from the viewpoint of sensor layout configuration. The study presented in this paper adopts a deterministic approach, which is complemented with statistical evaluation in another paper. The used SI methods include eigen realization, system realization with information matrix and subspace methods. The application of the methods on instrumented bridge systems in California is included and the performance of these methods is compared in terms of success and feasibility. Subsequently, viability of the methods on arrays of different numbers of sensors on the bridge systems is investigated. This is motivated by the fact that sensor arrays with wireless communication may be conveniently installed on civil engineering structures in the future. Computational costs and limits of applicability are examined using simulated ground motion analysis with detailed finite element models for a bridge system after validation using recorded data from real ground shaking. Moreover, the effect of the configuration of the sensor arrays is considered, accounting for different noise levels in the data to reflect more realistic situations. Copyright © 2005 John Wiley & Sons, Ltd.
TL;DR: In this paper, the authors compared the performance of load cell, stress meter, strain gauge and EM (elastomagnetic) sensory technology in a continuous structural health monitoring system (SHMS) on the structural deformational properties.
Abstract: Structural health monitoring based maintenance (SHMBM) is a basic engineering effort to collect maintenance information, forming a database system to open to the public or citizens for making decision on a suitable solution strategy to extend a structure's life. Sustainability of the infrastructure structural performance can be assessed by performing continuous structural health monitoring system (SHMS) on the structural deformational properties. The essence of SHMS can be considered to involve measurement, inspection, and assessment of in-service structures on a continuous basis with minimum labor requirement. However, human memory limitation, job changes, imperfections and inability to provide a reliable monitoring system can lead to overly optimistic reports on structural health. Therefore, a sustainable SHMS which fulfill ‘AtoE’ characteristics, i.e. accuracy, benefit, comprehensiveness, durability and ease of operation, is necessary to be consider in designing a reliable long-term SHMS. Generally, those characteristics are difficult to compare quantitatively. Specifically, some qualitatively compared sensory technologies will be reviewed in this paper by comparing the application of load cell, stress meter, strain gauge and EM (elastomagnetic) sensory technology. Furthermore, some innovative sensory technologies such as GPS-based MMS (movement monitoring systems), PDMD (peak displacement memory devices) and FOS (fiber optic sensors), are introduced to monitor global structural movement, partial structural movement and local structural deformational properties at different scales of monitored objects. Copyright © 2005 John Wiley & Sons, Ltd.
TL;DR: In this article, a case study of the one-and-a-half-century-old palace of Ksar Said, located near the Capital of Tunisia, is presented.
Abstract: This paper summarizes work conducted within the framework of a European Commission funded project on the use of appropriate modern seismic protective systems in the conservation of Mediterranean historical buildings in earthquake-prone areas. The case study is the one-and-a-half-century-old Palace of Ksar Said, located near the Capital of Tunisia. At the center of the palace, a collection of portraits and furniture are preserved in a room of great architectural and historical value which is the most precious part of the building to be protected. Ambient vibration tests were conducted to measure the acceleration at selected locations of the building. Output-only modal identification techniques were applied to extract the modal signature of the structure. A finite element model of the palace was elaborated based on the measured characteristics of stone and mortar and updated according to its measured vibratory response. Seismic vulnerability assessment of the building was carried out via three-dimensional time-history dynamic analyses of the structure. Results indicate a high vulnerability that confirms the need for intervention. A retrofit scheme is proposed that consists of a steel frame directly, attached to the portrait room structure with added fluid viscous dampers. Vulnerability assessment of the retrofitted building reveals a substantial improvement especially in the vicinity of the portrait room. Copyright © 2004 John Wiley & Sons, Ltd.
TL;DR: In this paper, the optimal attenuation of oscillations of multi-storey buildings under seismic excitations via active control is investigated, and synthesis of robust controllers is conducted by H∞-control methods utilizing linear matrix inequalities technique and an optimization algorithm.
Abstract: Optimal attenuation of oscillations of multi-storey buildings under seismic excitations via active control is investigated. Synthesis of robust controllers is conducted by H∞-control methods utilizing linear matrix inequalities technique and an optimization algorithm suggested in this paper. Copyright © 2004 John Wiley & Sons, Ltd.
TL;DR: In this paper, the authors proposed a structural health monitoring technique that uses vibrational characteristics to detect, identify and quantify damage on a cable-stayed bridge, which can be automated using a procedure based on the finite element method.
Abstract: The complex behavior of flexible structures such as cable-stayed bridges poses a challenge to the field of structural health monitoring. Modes are often closelyspaced and coupled translational and rotational motions hinder modal identification. This study proposes a structural health monitoring technique that uses vibrational characteristics to detect, identify and quantify damage. The technique can be automated using a procedure based on the finite element method. The technique is validated on an experimental model designed for this study representing a cable-stayed bridge. Accelerometers are employed to measure vertical responses of the bridge, and an impulse hammer provides the excitation to the structure. Damage is successfully detected in the experimental bridge model. Copyright © 2005 John Wiley & Sons, Ltd.
TL;DR: In this article, the authors show the results of two damage detection tests using steel frames, one of which is a five-storey steel frame with simulated damage, and the other one is a three-stagey large-scale steel Frame with cementitious devices.
Abstract: In this paper, we show the results of two damage detection tests using steel frames. The first test structure is a five-storey steel frame with simulated damage, and the other one is a three-storey large-scale steel frame with cementitious devices. Two method identifying damage, one using changes in flexibility and one using shifts in natural frequency, are applied to the frame with simulated damage. Both methods can pinpoint the storey that has damage. To the frame with cementitious devices, earthquake excitations, white noise shaking and microtremor observations are carried out. Identification method by the ARX (auto regressive exogenous) model is applied to all three cases. Natural frequency decreases, damping ratio increases and storey stiffness decreases as the experienced amplitude or input amplitude increases. A model using stick–slip elements is proposed. Natural frequency, damping ratio and storey stiffness, described by this model, are consistent with experimental results. Copyright © 2005 John Wiley & Sons, Ltd.
TL;DR: In this article, an impact damage identification approach is proposed based on this approach, which consists of hardware and software consisting of a carbon-fiber-reinforced plastic (CFRP) plate with four surface-mounted piezoelectric sensors, a digital oscilloscope, a local network, a wireless LAN card and a notebook computer.
Abstract: In this paper, an impact damage identification approach is proposed. Based on this approach, a remote impact damage identification system has been developed. The remote identification system consists of hardware and software. The hardware consists of a carbon-fiber-reinforced plastic (CFRP) plate with four surface-mounted piezoelectric sensors, a digital oscilloscope, a local network, a wireless LAN card, and a notebook computer. The software includes a source location algorithm based on fast wavelet transform and an impact load identification algorithm based on impact response inverse analysis. The piezoelectric sensors can detect Lamb wave signals generated by impact load without any amplification. The source location algorithm can reduce the influence of noise in the Lamb wave signals. When the CFRP plate is impacted, the oscilloscope promptly records the impact response signals detected by the mounted piezoelectric sensors, and the computer simultaneously receives the signals via the local network and wireless LAN card from the oscilloscope. The system can remotely identify the impact position and the impact load history with good precision in real time. Copyright © 2005 John Wiley & Sons, Ltd.
TL;DR: The Intel Mote is a new sensor node platform motivated by several design goals: increased CPU performance, improved radio bandwidth and reliability, as well as the usage of commercial off‐the‐shelf components in order to maintain cost‐effectiveness.
Abstract: The Intel Mote is a new sensor node platform motivated by several design goals: increased CPU performance, improved radio bandwidth and reliability, as well as the usage of commercial off-the-shelf components in order to maintain cost-effectiveness. This paper details the new platform architecture as well as practical experiences with the new mote regarding CPU and radio performance, networking algorithms, and battery life.
The new platform is built around an integrated wireless microcontroller consisting of an ARM7 core, a Bluetooth radio, RAM and FLASH memory, as well as various I/O options. Due to the connection-oriented nature of Bluetooth, new network formation and maintenance algorithms that are optimized for this protocol have been created. In particular, the ‘scatternet’ mode of Bluetooth has been successfully adapted to form networks comprised of multiple piconets.
The Intel Mote software architecture is based on an ARM port of TinyOS. Networking and routing layers have been created on top of the TinyOS base to provide the underlying multi-hop functionality. The network is self-organizing on startup and has mechanisms to repair failed links and circumvent failed nodes. Lower level functionality has been abstracted in the higher-level interface to allow the application programmer to utilize a virtual mesh network view without having to manage details of the Bluetooth operation. A reliable high bandwidth streaming transport layer has also been created.
The Intel Mote was deployed in a pilot equipment monitoring application using industrial vibration sensors. This application was chosen since it benefits from the increased platform capabilities and network bandwidth of the Intel Mote platform. It also represents a potentially large market in the industrial monitoring and controls sector. The paper presents a detailed analysis of the observed network operation, packet transfer rates and power consumption. More importantly, a number of the technical features of this application can be extended to other areas such as building and structural monitoring. Copyright © 2005 John Wiley & Sons, Ltd.
TL;DR: In this paper, the authors proposed a non-centralized IFF control strategy to increase the implementation efficiency of a plate-based control system, not only in terms of induced damping and signal magnitudes, but also in the sense that the best designed system can be coupled with a noncentralized approach.
Abstract: Collocated IFF control strategy is commonly used thanks to its strong quality of robustness, which is due to its intrinsic damping property. Up to now, the extensive studies available in the literature have focused only on the obtained mechanical efficiency in terms of modal damping ratios. We propose here to exhibit some mechanical design parameters allowing one to really optimize this dissipation strategy, not only in terms of induced damping, but also in terms of control signal magnitudes. We apply our criterion to two different plate systems to emphasize the effects of such design variables on the control implementation. At the end, we demonstrate how the best designed system can be coupled with a non-centralized approach to increase the implementation efficiency. Copyright © 2004 John Wiley & Sons, Ltd.
TL;DR: In this article, a framework for probabilistic estimation of structural damage, which includes identifying its existence, location, and severity, through the system identification of a building, utilizing its observed vibration data in undamaged and damaged states, is presented.
Abstract: A framework for probabilistic estimation of structural damage, which includes identifying its existence, location, and severity, through the system identification of a building, utilizing its observed vibration data in undamaged and damaged states, is presented in this paper. The method is applied to the vibration data obtained by the shaking table tests of a five-storey steel frame experimental model, to which many kinds of damaged states are given. The results from the damage detection analysis show the following: The method estimates the storey stiffness of the frame model very accurately. Even the damaged storeys corresponding to the stiffness reduction ratio of 1 or 2% are identified. The reliability of the estimated values are evaluated quantitatively and are reflected in the damage probability. This is very effective for the application to the health monitoring which requires the appropriate judgment on the damage states. Copyright © 2005 John Wiley & Sons, Ltd.
TL;DR: In this paper, the structural behavior of large, monolithic, ancient monuments consisting of heavy stone blocks connected one to the other by the gravity load alone, without the use of mortar, is investigated.
Abstract: The structural behaviour of large, monolithic, ancient monuments consisting of heavy stone blocks connected one to the other by the gravity load alone, without the use of mortar, is investigated. The Memnon Colossi, which were built fourteen centuries before Christ at Luxor in Egypt, are the case study for this construction technique. This paper summarizes the results of studies carried out on this structure within the CHIME (Conservation of Historical Monuments in the Mediterranean Area) project, funded by the European Commission.
The modal frequencies of the two statues were identified experimentally from ambient vibration measurements. Analytical models using the finite element method were also elaborated to compare the numerical results with the experimental ones, and to perform dynamic analyses. The results indicated that the distributed cracks characterizing the current state of the structure, play a significant role in the static and dynamic response of the monument. In view of the monuments' rehabilitation, an innovative technology, based on fastening the cracked blocks by pre-tensioned wires of shape memory alloy, is proposed and numerically simulated. Copyright © 2004 John Wiley & Sons, Ltd.
TL;DR: In this article, the authors presented a summary of test results obtained in the damage detection and suppression composite fuselage demonstrator program where novel developed monitoring techniques such as small-diameter optical fiber sensors were implemented in the composite structure.
Abstract: The Japanese Smart Material/Structure System Project started in 1998 with four research groups: (1) structural health monitoring; (2) smart manufacturing; (3) active/adaptive structures; and (4) actuator material/device development Based on the above research accomplishment, two demonstrators were fabricated and tested in late 2002 This paper presents a summary of test results obtained in the damage detection and suppression composite fuselage demonstrator program where novel developed monitoring techniques such as small-diameter optical fiber sensors were implemented in the composite structure This damage detection and suppression composite fuselage demonstrator provided a solid foundation for more practical applications of structural health monitoring technology in advanced large-size composite structures Copyright © 2005 John Wiley & Sons, Ltd
TL;DR: In this article, the authors presented a computational model developed for the church of Agios Ioannis Prodromos in the village of Askas, Cyprus, which contains a vast cycle of important and rare Byzantine wall paintings dating from the 15th and 16th centuries.
Abstract: The church of Agios Ioannis Prodromos in the village of Askas, Cyprus, contains a vast cycle of important and rare Byzantine wall paintings dating from the 15th and 16th centuries. Because of its importance to the cultural heritage of Cyprus, the church has been selected as one of the monuments to be studied in an INCO-MED project for the Conservation of Historical Mediterranean sites by innovative seismic protection techniques (CHIME). The computational model developed for the church is presented, as well as the measurements obtained by hammer-impact excitation. The fine-tuning of the selected computational model to match the dynamic characteristics obtained from the site measurements is also discussed. The model was used to test analytically the cost-effectiveness of damping devices in providing the best earthquake protection to the church without spoiling its monumental value. Copyright © 2004 John Wiley & Sons, Ltd.
TL;DR: In this paper, the authors proposed a load cell that uses an optical fiber Bragg grating to meet the demands for multipoint force measurements, which is based on the shift in the center wavelength of the fiber grating that occurs due to longitudinal strain.
Abstract: This study proposes a load cell that uses an optical fiber Bragg grating to meet the demands for multipoint force measurements. The load cell is based on the shift in the center wavelength of the fiber grating that occurs due to longitudinal strain. The present load cell consists of an octagonal metal frame, two resin arms fixed to the frame and an optical fiber Bragg grating bonded on the arms. Compressive vertical load applied to the frame is transformed to horizontal tensile stress that acts on the fiber grating. The frame and arms have different thermal coefficients in order to compensate for the temperature sensitivity of the fiber grating. This paper first describes the control of the sensitivity and the compensation of the temperature dependence. Second, the undesirable responses to shear and torsional forces are discussed on the basis of applying the finite element method. The performance of a prototype load cell is experimentally demonstrated and the operation principles were confirmed. Copyright © 2005 John Wiley & Sons, Ltd.
TL;DR: In this paper, a robust gain scheduled controller design applied for active vibration suppression of flexible structures is presented, and the experimental results show that the proposed robust gain scheduling control approach offers higher performance levels and can handle effectively extreme control conditions such as reconnection of the control system after power failure.
Abstract: The paper deals with robust gain scheduled controller design applied for active vibration suppression of flexible structures. The experimental set-up is a three-storey flexible structure with an active mass driver placed on the last storey.
First, system identification experiments are performed and the plant's uncertainty is deduced. Next, robust controller design with constraint on the control signal is presented. For a better trade-off between control performance and control constraint a gain scheduling approach is investigated. Finally, the control system is tested experimentally, when the input disturbance is a scaled historical earthquake record (1940 El Centro).
The experimental results show that the proposed robust gain scheduling control approach offers higher performance levels and can handle effectively extreme control conditions, such as reconnection of the control system after power failure. All results presented in the paper are experimental results. Copyright © 2004 John Wiley & Sons, Ltd.
TL;DR: In this article, a modified optimal linear control algorithm is proposed to demonstrate the effectiveness of the control system in reducing inelastic structural dynamic responses, and the proposed algorithm is then demonstrated by studying the control energy of the controlled structure.
Abstract: A modified optimal linear control algorithm is proposed to demonstrate the effectiveness of the control system in reducing inelastic structural dynamic responses. This algorithm recognizes that permanent deformation in the structure due to structural yielding produces unnecessary additional feedback control forces in the control system, and thus this deformation should not be considered in the feedback control equation. Hence the unique feature of the currently proposed algorithm is that it is based on the elastic states only. Effectiveness of the proposed algorithm is then demonstrated by studying the control energy of the controlled structure. Numerical simulations using single-degree-of-freedom system responses show that there always exists a point where the control energy consumption is maximal, and this optimal point is dependent on the structural characteristics as well as the earthquake excitation. Hence a preliminary guideline is developed to estimate this optimal point. Finally, application of the proposed algorithm on a six-storey moment-resisting frame is presented to show the effectiveness of using optimal linear control on a multi-degree-of-freedom system from the control energy perspectives. Copyright © 2004 John Wiley & Sons, Ltd.