TOMONORI NAGAYAMA | The University of Tokyo (original) (raw)

Papers by TOMONORI NAGAYAMA

IABSE Symposium, Weimar 2007: Improving Infrastructure Worldwide, 2007

This paper describes possible applications of sensing technology for railroad bridges maintenance... more This paper describes possible applications of sensing technology for railroad bridges maintenance, repair and replacement, and identifies potential areas of development of sensing technology towards applications which could be used today by railroad bridge engineers. The novel experience carried out on the field under railroad traffic brings to the table areas of improvement and development. Ideas and suggestions are included on how to develope this potential ready-to-be tool for bridge maintenance and replacement.

IABSE Congress, Stockholm 2016: Challenges in Design and Construction of an Innovative and Sustainable Built Environment, 2016

Corrosion at girder-ends is a major deterioration pattern of steel bridges. The severity needs to... more Corrosion at girder-ends is a major deterioration pattern of steel bridges. The severity needs to be quantified though the evaluation is not trivial. As an alternative, this paper proposes to use Local Vibration Modes (LVM). The existence of LVMs and the sensitivity of their frequencies to damage are examined. The damage severity is then quantified using a superposition method. This method calculates LVM frequencies under various damage severities and shapes using database of LVM of a limited number of fundamental damage patterns, which is prepared in advance by finite element analysis (FEA). The result is then used to evaluate damage severity from the measured LVM frequencies. Furthermore, relationship between LVM and load carrying capacity, prepared by FEA on various corrosion patterns, is used to evaluate the load carrying capacity from measured LVM frequencies. The developed methods are examined on a FE model of a steel bridge girder end.

Engineering Structures, 2017

Passing vehicles cause bridge deformation and vibration. Overloaded vehicles can result in fatigu... more Passing vehicles cause bridge deformation and vibration. Overloaded vehicles can result in fatigue damage to, or even failure of, the bridge. The bridge response is related to the properties of the passing vehicles, particularly the vehicle weight. Therefore, a bridge weigh-in-motion system for estimating vehicle parameters is important for evaluating the bridge condition under repeated load. However, traditional weigh-in-motion methods, which involve the installation of strain gauges on bridge members and calibration with known weight truck, are often costly and time-consuming. In this paper, a method for the identification of moving vehicle parameters using bridge acceleration responses is investigated. A time-domain method based on the Bayesian theory application of a particle filter is adopted. The bridge pavement roughness is estimated in advance using vehicle responses from a sensor-equipped car with consideration of vehicle-bridge interaction, and it is utilized in the parameter estimation. The method does not require the calibration. Numerical simulations demonstrate that the vehicle parameters, including the vehicle weight, are estimated with high accuracy and robustness against observation noise and modeling error. Finally, this method is validated through field measurement. The resulting estimate of vehicle mass agrees with the measured value, demonstrating the practicality of the proposed method.

Smart Structures and Systems, 2009

Smart sensors densely distributed over structures can use their computational and wireless commun... more Smart sensors densely distributed over structures can use their computational and wireless communication capabilities to provide rich information for structural health monitoring (SHM). Though smart sensor technology has seen substantial advances during recent years, implementation of smart sensors on full-scale structures has been limited. While users often postulate that wired sensing systems can be simply replaced by wireless systems, off-the-shelf wireless systems are unlikely to provide the data users expect. Sensor component characteristics limit the quality of data collected; data from smart sensors may be inadequate due to packet loss during communication, time synchronization errors, and slow communication speeds. This paper addresses these issues common to smart sensor applications for structural health monitoring by developing corresponding middleware services, i.e., reliable communication, synchronized sensing, and model-based data aggregation. These middleware services are implemented on the Imote2 smart sensor platform, and their efficacy demonstrated experimentally. or the frequency of operation (Nagayama et al. 2007a). The lack of these functionalities has prevented SHM application users from analyzing structures in detail based on smart sensor measurement data. This paper addresses these issues by developing corresponding middleware services that are common to many SHM applications. Among the middleware services are reliable communication, synchronized sensing, and data aggregation. These middleware services are developed employing a smart sensor platform, the Imote2, which is designed for data-intensive applications such as SHM applications. The middleware services are then implemented on the Imote2 running TinyOS. The idea behind these services are generally applicable to other smart sensor platforms, and the middleware service can be ported to platforms which have similar hardware characteristics, e.g. RAM size, as the Imote2. The implemented middleware services are evaluated and validated experimentally. 2. BACKGROUND 2.1 Reliable data transfer RF communication is not as reliable as wired communication, due to packet loss. The most common cause for packet loss results from the fact that as distance between nodes increases, the signal-to-noise ratio drops, causing bit errors in the transmitted packet. When the receiver detects a bit error, it drops the entire packet. Interference between multiple simultaneously transmitting nodes, called a collision, can likewise result in the loss of one or both packets. These communication failures may take place for both packets carrying commands to sensor nodes and packets carrying measured data. If packets carrying commands are lost, destination nodes fail to perform certain tasks. When smart sensors are designed to perform complex sets of tasks, collaborating with other sensors nodes, command packet loss may cause sensor nodes to behave unexpectedly, possibly leading to network failure. If packets carrying measurement data are lost, destination nodes cannot fully reconstruct the sender's data. SHM applications employing smart sensors must address this packet loss problem. Retransmission-and acknowledgment-based approaches are candidates to reduce the packet loss rate during wireless communication.These two approaches are first explained briefly. retransmission without acknowledgment can statistically improve the reliability of communication. If the packet loss rate is expected to be approximately constant over time, retransmission can virtually eliminate data loss; the number of repetitions can be dynamically adjusted based on measured packet loss rates. When the packet loss rate is high, the number of repetitions is increased. Such protocols, however, cannot guarantee communication success rate deterministically. In smart sensor networks, burst packet loss may take place, which undermines the effectiveness of this approach. Interference from other nearby RF transmission devices operating in the same frequency range, for example, may cause a large number of packets to be dropped. If the packet loss rate is high during all the successive retransmissions, the loss of many packets is unavoidable. designed communication protocol involving acknowledgment messages can be notably inefficient. Many acknowledgment messages may be required, waiting times may be long, and the same packets may need to be sent many times. Furthermore, RF components on many smart sensor platforms including the Imote2 are in either a listening mode or transmission mode, making the need for frequent switch between the two modes unwelcome. During transmission, the Imote2 cannot receive packets. Nonetheless, transmission and reception are deeply interwoven in many acknowledgement-based approaches. Interwoven transmission and reception of acknowledgement-based approaches may result in slow data transfer. Instead of acknowledging each packet, the reliable communication protocol developed by Mechitov et al. (2004) sends a set of packets and then waits for acknowledgment. If the receiver does not receive acknowledgment, the same set of packets is sent again. Upon reception of acknowledgment, the sender moves on to the next set of packets. The size of a set of packets needs to be optimized. A small size of packet set necessitates a larger number of acknowledgement packets; a large size of packet set, on the other hand, results in retransmitting large numbers of packets even when only one packet is lost. Therefore, the number of acknowledgement packets cannot be drastically reduced.

SPIE Proceedings, 2012

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

Smart Structures and Systems, 2015

Belt conveyors, widely used in various industries worldwide, are often exposed to corrosive envir... more Belt conveyors, widely used in various industries worldwide, are often exposed to corrosive environment. Decades after construction, many of the support structures of belt conveyors have severe degradation, which may cause structural failure and functional stop of associated industries. To ensure the safety and reliability, effective and efficient damage identification of belt conveyor support structures is essential. However, application of existing global vibration-based damage identification techniques to these structures is difficult due to unavailability of baseline condition, the possible presence of multiple corroded members in a single structure, and the effect of nonstructural components that are occasionally updated. In this paper, a damage identification method of the main members of a belt conveyor support structure is proposed and validated through numerical and experimental studies. Cross-sectional modes (CSMs), shown to exist on the main member numerically and experimentally, are utilized. Eigenvalue analysis of an FE model of the support structure reveals the characteristics of CSMs and localized CSMs (LCSMs). A damage identification method based on these modes is developed; the existence and location of the damage is evaluated from current state of the structure without the need for before-after comparison. By identifying the distinct LCSMs, multiple damages are also independently identified.

Smart Structures and Systems, 2010

Wireless smart sensor networks (WSSNs) have been proposed by a number of researchers to evaluate ... more Wireless smart sensor networks (WSSNs) have been proposed by a number of researchers to evaluate the current condition of civil infrastructure, offering improved understanding of dynamic response through dense instrumentation. As focus moves from laboratory testing to full-scale implementation, the need for multi-hop communication to address issues associated with the large size of civil infrastructure and their limited radio power has become apparent. Multi-hop communication protocols allow sensors to cooperate to reliably deliver data between nodes outside of direct communication range. However, application specific requirements, such as high sampling rates, vast amounts of data to be collected, precise internodal synchronization, and reliable communication, are quite challenging to achieve with generic multi-hop communication protocols. This paper proposes two complementary reliable multi-hop communication solutions for monitoring of civil infrastructure. In the first approach, termed herein General Purpose Multi-hop (GPMH), the wide variety of communication patterns involved in structural health monitoring, particularly in decentralized implementations, are acknowledged to develop a flexible and adaptable any-to-any communication protocol. In the second approach, termed herein Single-Sink Multi-hop (SSMH), an efficient many-to-one protocol utilizing all available RF channels is designed to minimize the time required to collect the large amounts of data generated by dense arrays of sensor nodes. Both protocols adopt the Ad-hoc On-demand Distance Vector (AODV) routing protocol, which provides any-to-any routing and multi-cast capability, and supports a broad range of communication patterns. The proposed implementations refine the routing metric by considering the stability of links, exclude functionality unnecessary in mostly-static WSSNs, and integrate a reliable communication layer with the AODV protocol. These customizations have resulted in robust realizations of multi-hop reliable communication that meet the demands of structural health monitoring.

Journal of Japan Society of Civil Engineers, Ser. A1 (Structural Engineering & Earthquake Engineering (SE/EE)), 2016

Doboku Gakkai Ronbunshu, 2003

IABSE Conference, Guangzhou 2016: Bridges and Structures Sustainability - Seeking Intelligent Solutions, 2016

Damage detection is essential for ensuing safety of bridges, and many damage detection methods ha... more Damage detection is essential for ensuing safety of bridges, and many damage detection methods have been developed in the past few years, which utilizes static or dynamic responses. In this paper, a curvature-based method is proposed for damage detection. In order to verify its reliability and efficacy, laboratory experiment is conducted on a beam specimen, and the measured displacement is used to identify damage with the proposed method. Damage location and severity were both identified. Taking into account measurement noise, two techniques are proposed to reduce effect of measurement noise. The first one uses averaged multiple measurement, and the other one chooses reasonable interval for curvature calculation. They are both verified with the measurements from the laboratory test.

JOURNAL OF JAPAN SOCIETY OF HYDROLOGY AND WATER RESOURCES, 2013

SPIE Proceedings, 2008

Industrialized nations have a huge investment in the pervasive civil infrastructure on which our ... more Industrialized nations have a huge investment in the pervasive civil infrastructure on which our lives rely. To properly manage this infrastructure, its condition or serviceability should be reliably assessed. For condition or serviceability assessment, Structural Health Monitoring (SHM) has been considered to provide information on the current state of structures by measuring structural vibration responses and other physical phenomena and conditions. Civil infrastructure is typically large-scale, exhibiting a wide variety of complex behavior; estimation of a structure's state is a challenging task. While SHM has been and still is intensively researched, further efforts are required to provide efficient and effective management of civil infrastructure. Smart sensors, with their on-board computational and communication capabilities, offer new opportunities for SHM. Without the need for power or communication cables, installation cost can be brought down drastically. Smart sensors will help to make monitoring of structures with a dense array of sensors economically practical. Densely installed smart sensors are expected to be rich information sources for SHM. Efforts toward realization of SHM systems using smart sensors, however, have not resulted in full-fledged applications. All efforts to date have encountered difficulties originating from limited resources on smart sensors (e.g., small memory size, small communication throughput, limited speed of the CPU, etc.). To realize an SHM system employing smart sensors, this system needs to be designed considering both the characteristics of the smart sensor and the structures to be monitored. This research addresses issues in smart sensor usages in SHM applications and realizes, for the first time, a scalable and extensible SHM system using smart sensors. The ix CONTENTS LIST OF FIGURES .

Structures Congress 2008, 2008

This presentation discusses the possibilities associated between the existing available applied r... more This presentation discusses the possibilities associated between the existing available applied research in wireless sensors and the always increasing need to identify/address existing railroad bridges performance under actual traffic. In one hand, universities and research centers today are developing the advance theory and framework for the use of wireless sensors in structures health monitoring .To implement wireless sensors in the areas where quantitative / objective data is required. Timber trestle bridges are carrying most of the main line traffic in the US, especially in the South Regions, and a significant number of those are in need of maintenance and or replacement. The maintenance and/or replacement of timber bridges is based on visual/direct and individual inspections, which can not assess objective/quantitative data of the bridge performance under loading. Different bridge inspectors will not be able to determine objective parameters for different bridges, and even more, different loading conditions. The dynamic response of the timber trestle bridge continues to be an isolated parameter that can not be compared with the existing maintenance/inspection program. The authors gathered data obtained by connecting wireless sensors to existing timber trestle bridges which were identified to show excessive longitudinal and transversal displacement under regular traffic loading. The paper includes the description on the implementation process of wireless sensors under real on-site conditions, critique to the results and their validity, and proposed improvements in the entire data acquisition, comprised in concrete proposals. It finally summarizes recommendations for future/potential use in the railroad timber trestle railroad bridge maintenance, inspection and assessment.

Doboku Gakkai Ronbunshuu A, 2009

Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2010, 2010

ABSTRACT Wireless smart sensors equipped with computational and wireless communication capabiliti... more ABSTRACT Wireless smart sensors equipped with computational and wireless communication capabilities are expected to provide rich information for structural health monitoring (SHM); inexpensive nature of sensors nodes and wireless communication allow dense sensor instrumentation over structures. While dense measurement is advantageous with regard to spatially characterizing structural dynamic behaviors, limited sensing accuracy of inexpensive wireless sensor nodes possibly bounds applications. For example, small ambient vibration may not be captured by smart sensor nodes. This paper proposes a combined use of low-cost smart sensors and high accuracy sensors for dynamic measurement of bridges to alleviate the influence of this limitation.

Doboku Gakkai Ronbunshuu F, 2010

Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2010, 2010

This paper presents a structural health monitoring (SHM) system using a dense array of scalable s... more This paper presents a structural health monitoring (SHM) system using a dense array of scalable smart wireless sensor network on a cable-stayed bridge (Jindo Bridge) in Korea. The hardware and software for the SHM system and its components are developed for low-cost, efficient, and autonomous monitoring of the bridge. 70 sensors and two base station computers have been deployed to monitor the bridge using an autonomous SHM application with consideration of harsh outdoor surroundings. The performance of the system has been evaluated in terms of hardware durability, software reliability, and power consumption. 3-D modal properties were extracted from the measured 3-axis vibration data using output-only modal identification methods. Tension forces of 4 different lengths of stay-cables were derived from the ambient vibration data on the cables. For the integrity assessment of the structure, multi-scale subspace system identification method is now under development using a neural network technique based on the local mode shapes and the cable tensions.

Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2010, 2010

In recent years, Structural Health Monitoring (SHM) has emerged as an important research area in ... more In recent years, Structural Health Monitoring (SHM) has emerged as an important research area in civil engineering. To investigate both local and global damage criteria, a dense array of sensors is anticipated to be required for large civil engineering structures. Traditional centralized data acquisition systems do not provide a scalable approach, since the shear number of accompanying wires, fiber optic cables, or other physical transmission medium may be prohibitive. Wireless communications have the potential to significantly impact monitoring systems. To assist in dealing with the large amount of data that will be generated, on-board processing at the sensor allows a portion of the computation to be done locally on the sensor's embedded microprocessor. The Mica Mote platform, along with Tiny Operating System (TinyOS) developed at the University of California at Berkeley offers for the first time, an open hardware/software environment for broad smart sensing research. However, because the accelerometers on the existing sensor boards have both poor low frequency sensitivity and high noise density, their suitability for civil engineering applications is unclear. This paper presents results for a new sensor board employing an SD-1221 accelerometer, which overcomes many of the deficiencies of the existing sensor. Finally, a number of the challenges still remaining are identified.

IABSE Congress, Chicago 2008: Creating and Renewing Urban Structures – Tall Buildings, Bridges and Infrastructure, 2008

Monitoring of structures is expected to offer rich information on structural performance evaluati... more Monitoring of structures is expected to offer rich information on structural performance evaluation. While the performance of existing structures may differ from their designs, monitoring of dynamic behaviors potentially provides indications of how close or far the performance is to the designs and unexpected differences that might be important to the safety. In this paper, monitoring of two bridges in Japan as well as dynamic and structural analyses of the monitoring data is presented. Ambient vibration and seismic response records are utilized in performance evaluation of these bridges. The dense sensor instrumentation on the bridges and long-term monitoring provides exceptional opportunities to obtain insight into the behaviors of the bridges and performance of their components.

Structure and Infrastructure Engineering, 2009

and-conditions-of-access.pdf This article may be used for research, teaching and private study pu... more and-conditions-of-access.pdf This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, redistribution , reselling , loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.

IABSE Symposium, Weimar 2007: Improving Infrastructure Worldwide, 2007

This paper describes possible applications of sensing technology for railroad bridges maintenance... more This paper describes possible applications of sensing technology for railroad bridges maintenance, repair and replacement, and identifies potential areas of development of sensing technology towards applications which could be used today by railroad bridge engineers. The novel experience carried out on the field under railroad traffic brings to the table areas of improvement and development. Ideas and suggestions are included on how to develope this potential ready-to-be tool for bridge maintenance and replacement.

IABSE Congress, Stockholm 2016: Challenges in Design and Construction of an Innovative and Sustainable Built Environment, 2016

Corrosion at girder-ends is a major deterioration pattern of steel bridges. The severity needs to... more Corrosion at girder-ends is a major deterioration pattern of steel bridges. The severity needs to be quantified though the evaluation is not trivial. As an alternative, this paper proposes to use Local Vibration Modes (LVM). The existence of LVMs and the sensitivity of their frequencies to damage are examined. The damage severity is then quantified using a superposition method. This method calculates LVM frequencies under various damage severities and shapes using database of LVM of a limited number of fundamental damage patterns, which is prepared in advance by finite element analysis (FEA). The result is then used to evaluate damage severity from the measured LVM frequencies. Furthermore, relationship between LVM and load carrying capacity, prepared by FEA on various corrosion patterns, is used to evaluate the load carrying capacity from measured LVM frequencies. The developed methods are examined on a FE model of a steel bridge girder end.

Engineering Structures, 2017

Passing vehicles cause bridge deformation and vibration. Overloaded vehicles can result in fatigu... more Passing vehicles cause bridge deformation and vibration. Overloaded vehicles can result in fatigue damage to, or even failure of, the bridge. The bridge response is related to the properties of the passing vehicles, particularly the vehicle weight. Therefore, a bridge weigh-in-motion system for estimating vehicle parameters is important for evaluating the bridge condition under repeated load. However, traditional weigh-in-motion methods, which involve the installation of strain gauges on bridge members and calibration with known weight truck, are often costly and time-consuming. In this paper, a method for the identification of moving vehicle parameters using bridge acceleration responses is investigated. A time-domain method based on the Bayesian theory application of a particle filter is adopted. The bridge pavement roughness is estimated in advance using vehicle responses from a sensor-equipped car with consideration of vehicle-bridge interaction, and it is utilized in the parameter estimation. The method does not require the calibration. Numerical simulations demonstrate that the vehicle parameters, including the vehicle weight, are estimated with high accuracy and robustness against observation noise and modeling error. Finally, this method is validated through field measurement. The resulting estimate of vehicle mass agrees with the measured value, demonstrating the practicality of the proposed method.

Smart Structures and Systems, 2009

Smart sensors densely distributed over structures can use their computational and wireless commun... more Smart sensors densely distributed over structures can use their computational and wireless communication capabilities to provide rich information for structural health monitoring (SHM). Though smart sensor technology has seen substantial advances during recent years, implementation of smart sensors on full-scale structures has been limited. While users often postulate that wired sensing systems can be simply replaced by wireless systems, off-the-shelf wireless systems are unlikely to provide the data users expect. Sensor component characteristics limit the quality of data collected; data from smart sensors may be inadequate due to packet loss during communication, time synchronization errors, and slow communication speeds. This paper addresses these issues common to smart sensor applications for structural health monitoring by developing corresponding middleware services, i.e., reliable communication, synchronized sensing, and model-based data aggregation. These middleware services are implemented on the Imote2 smart sensor platform, and their efficacy demonstrated experimentally. or the frequency of operation (Nagayama et al. 2007a). The lack of these functionalities has prevented SHM application users from analyzing structures in detail based on smart sensor measurement data. This paper addresses these issues by developing corresponding middleware services that are common to many SHM applications. Among the middleware services are reliable communication, synchronized sensing, and data aggregation. These middleware services are developed employing a smart sensor platform, the Imote2, which is designed for data-intensive applications such as SHM applications. The middleware services are then implemented on the Imote2 running TinyOS. The idea behind these services are generally applicable to other smart sensor platforms, and the middleware service can be ported to platforms which have similar hardware characteristics, e.g. RAM size, as the Imote2. The implemented middleware services are evaluated and validated experimentally. 2. BACKGROUND 2.1 Reliable data transfer RF communication is not as reliable as wired communication, due to packet loss. The most common cause for packet loss results from the fact that as distance between nodes increases, the signal-to-noise ratio drops, causing bit errors in the transmitted packet. When the receiver detects a bit error, it drops the entire packet. Interference between multiple simultaneously transmitting nodes, called a collision, can likewise result in the loss of one or both packets. These communication failures may take place for both packets carrying commands to sensor nodes and packets carrying measured data. If packets carrying commands are lost, destination nodes fail to perform certain tasks. When smart sensors are designed to perform complex sets of tasks, collaborating with other sensors nodes, command packet loss may cause sensor nodes to behave unexpectedly, possibly leading to network failure. If packets carrying measurement data are lost, destination nodes cannot fully reconstruct the sender's data. SHM applications employing smart sensors must address this packet loss problem. Retransmission-and acknowledgment-based approaches are candidates to reduce the packet loss rate during wireless communication.These two approaches are first explained briefly. retransmission without acknowledgment can statistically improve the reliability of communication. If the packet loss rate is expected to be approximately constant over time, retransmission can virtually eliminate data loss; the number of repetitions can be dynamically adjusted based on measured packet loss rates. When the packet loss rate is high, the number of repetitions is increased. Such protocols, however, cannot guarantee communication success rate deterministically. In smart sensor networks, burst packet loss may take place, which undermines the effectiveness of this approach. Interference from other nearby RF transmission devices operating in the same frequency range, for example, may cause a large number of packets to be dropped. If the packet loss rate is high during all the successive retransmissions, the loss of many packets is unavoidable. designed communication protocol involving acknowledgment messages can be notably inefficient. Many acknowledgment messages may be required, waiting times may be long, and the same packets may need to be sent many times. Furthermore, RF components on many smart sensor platforms including the Imote2 are in either a listening mode or transmission mode, making the need for frequent switch between the two modes unwelcome. During transmission, the Imote2 cannot receive packets. Nonetheless, transmission and reception are deeply interwoven in many acknowledgement-based approaches. Interwoven transmission and reception of acknowledgement-based approaches may result in slow data transfer. Instead of acknowledging each packet, the reliable communication protocol developed by Mechitov et al. (2004) sends a set of packets and then waits for acknowledgment. If the receiver does not receive acknowledgment, the same set of packets is sent again. Upon reception of acknowledgment, the sender moves on to the next set of packets. The size of a set of packets needs to be optimized. A small size of packet set necessitates a larger number of acknowledgement packets; a large size of packet set, on the other hand, results in retransmitting large numbers of packets even when only one packet is lost. Therefore, the number of acknowledgement packets cannot be drastically reduced.

SPIE Proceedings, 2012

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

Smart Structures and Systems, 2015

Belt conveyors, widely used in various industries worldwide, are often exposed to corrosive envir... more Belt conveyors, widely used in various industries worldwide, are often exposed to corrosive environment. Decades after construction, many of the support structures of belt conveyors have severe degradation, which may cause structural failure and functional stop of associated industries. To ensure the safety and reliability, effective and efficient damage identification of belt conveyor support structures is essential. However, application of existing global vibration-based damage identification techniques to these structures is difficult due to unavailability of baseline condition, the possible presence of multiple corroded members in a single structure, and the effect of nonstructural components that are occasionally updated. In this paper, a damage identification method of the main members of a belt conveyor support structure is proposed and validated through numerical and experimental studies. Cross-sectional modes (CSMs), shown to exist on the main member numerically and experimentally, are utilized. Eigenvalue analysis of an FE model of the support structure reveals the characteristics of CSMs and localized CSMs (LCSMs). A damage identification method based on these modes is developed; the existence and location of the damage is evaluated from current state of the structure without the need for before-after comparison. By identifying the distinct LCSMs, multiple damages are also independently identified.

Smart Structures and Systems, 2010

Wireless smart sensor networks (WSSNs) have been proposed by a number of researchers to evaluate ... more Wireless smart sensor networks (WSSNs) have been proposed by a number of researchers to evaluate the current condition of civil infrastructure, offering improved understanding of dynamic response through dense instrumentation. As focus moves from laboratory testing to full-scale implementation, the need for multi-hop communication to address issues associated with the large size of civil infrastructure and their limited radio power has become apparent. Multi-hop communication protocols allow sensors to cooperate to reliably deliver data between nodes outside of direct communication range. However, application specific requirements, such as high sampling rates, vast amounts of data to be collected, precise internodal synchronization, and reliable communication, are quite challenging to achieve with generic multi-hop communication protocols. This paper proposes two complementary reliable multi-hop communication solutions for monitoring of civil infrastructure. In the first approach, termed herein General Purpose Multi-hop (GPMH), the wide variety of communication patterns involved in structural health monitoring, particularly in decentralized implementations, are acknowledged to develop a flexible and adaptable any-to-any communication protocol. In the second approach, termed herein Single-Sink Multi-hop (SSMH), an efficient many-to-one protocol utilizing all available RF channels is designed to minimize the time required to collect the large amounts of data generated by dense arrays of sensor nodes. Both protocols adopt the Ad-hoc On-demand Distance Vector (AODV) routing protocol, which provides any-to-any routing and multi-cast capability, and supports a broad range of communication patterns. The proposed implementations refine the routing metric by considering the stability of links, exclude functionality unnecessary in mostly-static WSSNs, and integrate a reliable communication layer with the AODV protocol. These customizations have resulted in robust realizations of multi-hop reliable communication that meet the demands of structural health monitoring.

Journal of Japan Society of Civil Engineers, Ser. A1 (Structural Engineering & Earthquake Engineering (SE/EE)), 2016

Doboku Gakkai Ronbunshu, 2003

IABSE Conference, Guangzhou 2016: Bridges and Structures Sustainability - Seeking Intelligent Solutions, 2016

Damage detection is essential for ensuing safety of bridges, and many damage detection methods ha... more Damage detection is essential for ensuing safety of bridges, and many damage detection methods have been developed in the past few years, which utilizes static or dynamic responses. In this paper, a curvature-based method is proposed for damage detection. In order to verify its reliability and efficacy, laboratory experiment is conducted on a beam specimen, and the measured displacement is used to identify damage with the proposed method. Damage location and severity were both identified. Taking into account measurement noise, two techniques are proposed to reduce effect of measurement noise. The first one uses averaged multiple measurement, and the other one chooses reasonable interval for curvature calculation. They are both verified with the measurements from the laboratory test.

JOURNAL OF JAPAN SOCIETY OF HYDROLOGY AND WATER RESOURCES, 2013

SPIE Proceedings, 2008

Industrialized nations have a huge investment in the pervasive civil infrastructure on which our ... more Industrialized nations have a huge investment in the pervasive civil infrastructure on which our lives rely. To properly manage this infrastructure, its condition or serviceability should be reliably assessed. For condition or serviceability assessment, Structural Health Monitoring (SHM) has been considered to provide information on the current state of structures by measuring structural vibration responses and other physical phenomena and conditions. Civil infrastructure is typically large-scale, exhibiting a wide variety of complex behavior; estimation of a structure's state is a challenging task. While SHM has been and still is intensively researched, further efforts are required to provide efficient and effective management of civil infrastructure. Smart sensors, with their on-board computational and communication capabilities, offer new opportunities for SHM. Without the need for power or communication cables, installation cost can be brought down drastically. Smart sensors will help to make monitoring of structures with a dense array of sensors economically practical. Densely installed smart sensors are expected to be rich information sources for SHM. Efforts toward realization of SHM systems using smart sensors, however, have not resulted in full-fledged applications. All efforts to date have encountered difficulties originating from limited resources on smart sensors (e.g., small memory size, small communication throughput, limited speed of the CPU, etc.). To realize an SHM system employing smart sensors, this system needs to be designed considering both the characteristics of the smart sensor and the structures to be monitored. This research addresses issues in smart sensor usages in SHM applications and realizes, for the first time, a scalable and extensible SHM system using smart sensors. The ix CONTENTS LIST OF FIGURES .

Structures Congress 2008, 2008

This presentation discusses the possibilities associated between the existing available applied r... more This presentation discusses the possibilities associated between the existing available applied research in wireless sensors and the always increasing need to identify/address existing railroad bridges performance under actual traffic. In one hand, universities and research centers today are developing the advance theory and framework for the use of wireless sensors in structures health monitoring .To implement wireless sensors in the areas where quantitative / objective data is required. Timber trestle bridges are carrying most of the main line traffic in the US, especially in the South Regions, and a significant number of those are in need of maintenance and or replacement. The maintenance and/or replacement of timber bridges is based on visual/direct and individual inspections, which can not assess objective/quantitative data of the bridge performance under loading. Different bridge inspectors will not be able to determine objective parameters for different bridges, and even more, different loading conditions. The dynamic response of the timber trestle bridge continues to be an isolated parameter that can not be compared with the existing maintenance/inspection program. The authors gathered data obtained by connecting wireless sensors to existing timber trestle bridges which were identified to show excessive longitudinal and transversal displacement under regular traffic loading. The paper includes the description on the implementation process of wireless sensors under real on-site conditions, critique to the results and their validity, and proposed improvements in the entire data acquisition, comprised in concrete proposals. It finally summarizes recommendations for future/potential use in the railroad timber trestle railroad bridge maintenance, inspection and assessment.

Doboku Gakkai Ronbunshuu A, 2009

Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2010, 2010

ABSTRACT Wireless smart sensors equipped with computational and wireless communication capabiliti... more ABSTRACT Wireless smart sensors equipped with computational and wireless communication capabilities are expected to provide rich information for structural health monitoring (SHM); inexpensive nature of sensors nodes and wireless communication allow dense sensor instrumentation over structures. While dense measurement is advantageous with regard to spatially characterizing structural dynamic behaviors, limited sensing accuracy of inexpensive wireless sensor nodes possibly bounds applications. For example, small ambient vibration may not be captured by smart sensor nodes. This paper proposes a combined use of low-cost smart sensors and high accuracy sensors for dynamic measurement of bridges to alleviate the influence of this limitation.

Doboku Gakkai Ronbunshuu F, 2010

Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2010, 2010

This paper presents a structural health monitoring (SHM) system using a dense array of scalable s... more This paper presents a structural health monitoring (SHM) system using a dense array of scalable smart wireless sensor network on a cable-stayed bridge (Jindo Bridge) in Korea. The hardware and software for the SHM system and its components are developed for low-cost, efficient, and autonomous monitoring of the bridge. 70 sensors and two base station computers have been deployed to monitor the bridge using an autonomous SHM application with consideration of harsh outdoor surroundings. The performance of the system has been evaluated in terms of hardware durability, software reliability, and power consumption. 3-D modal properties were extracted from the measured 3-axis vibration data using output-only modal identification methods. Tension forces of 4 different lengths of stay-cables were derived from the ambient vibration data on the cables. For the integrity assessment of the structure, multi-scale subspace system identification method is now under development using a neural network technique based on the local mode shapes and the cable tensions.

Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2010, 2010

In recent years, Structural Health Monitoring (SHM) has emerged as an important research area in ... more In recent years, Structural Health Monitoring (SHM) has emerged as an important research area in civil engineering. To investigate both local and global damage criteria, a dense array of sensors is anticipated to be required for large civil engineering structures. Traditional centralized data acquisition systems do not provide a scalable approach, since the shear number of accompanying wires, fiber optic cables, or other physical transmission medium may be prohibitive. Wireless communications have the potential to significantly impact monitoring systems. To assist in dealing with the large amount of data that will be generated, on-board processing at the sensor allows a portion of the computation to be done locally on the sensor's embedded microprocessor. The Mica Mote platform, along with Tiny Operating System (TinyOS) developed at the University of California at Berkeley offers for the first time, an open hardware/software environment for broad smart sensing research. However, because the accelerometers on the existing sensor boards have both poor low frequency sensitivity and high noise density, their suitability for civil engineering applications is unclear. This paper presents results for a new sensor board employing an SD-1221 accelerometer, which overcomes many of the deficiencies of the existing sensor. Finally, a number of the challenges still remaining are identified.

IABSE Congress, Chicago 2008: Creating and Renewing Urban Structures – Tall Buildings, Bridges and Infrastructure, 2008

Monitoring of structures is expected to offer rich information on structural performance evaluati... more Monitoring of structures is expected to offer rich information on structural performance evaluation. While the performance of existing structures may differ from their designs, monitoring of dynamic behaviors potentially provides indications of how close or far the performance is to the designs and unexpected differences that might be important to the safety. In this paper, monitoring of two bridges in Japan as well as dynamic and structural analyses of the monitoring data is presented. Ambient vibration and seismic response records are utilized in performance evaluation of these bridges. The dense sensor instrumentation on the bridges and long-term monitoring provides exceptional opportunities to obtain insight into the behaviors of the bridges and performance of their components.

Structure and Infrastructure Engineering, 2009

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