Development of Wireless Self-powered (WiSe) Sensors for Structural Health Monitoring of Highway Bridges
June 16, 2015 to June 15, 2016
1.Collaborators and Affiliations
Washington State University - Pullman (WSU) (led by Prof. Pizhong Qiao) is joined byThe University of Alaska - Fairbanks (UAF) (led by Prof. J. Leroy Hulsey) to form a strong multidisciplinary research team in response to the PacTrans’call for collaborative multi-institutional proposals (see PI’s resumes in Appendices). Profs. Qiao and Hulsey have been in collaboration for three sponsored research projects since 2007, and their collaborations have fostered several new civil/transportation engineering technologies (e.g., smart FRP sandwich highway bridge decks, I-Lam panels for highway bridge girder collision protection and monitoring, durable concrete materials and their life prediction methodologies).
Dr. Pizhong Qiao, P.E. is a Professorat the WSU Department of Civil & Environmental Engineering. He will be responsible for developing and implementing the proposed wireless self-powered (WiSe) sensor technology. He received his Ph.D. in Civil Engineering (Advanced Materials, Solid Mechanics and Structures) from West Virginia University in 1997. Dr. Qiao has been extensively working in development, research and application of advanced and high performance materials (smart materials, polymer composites, and sustainable concrete) in civil and aerospace engineering. He was honored with the 2007 Outstanding Technical Contribution Award from the ASCE Aerospace Division for his contribution in the area of “fracture mechanics of layered structures”. He is the recipient of the 2011 and 2012 Outstanding Faculty Researcher award at the WSU Department of Civil and Environmental Engineering as well as the 2012 Anjan Bose Outstanding Researcher Award from WSU College of Engineering and Architecture. Dr. Qiao’s expertise in smart materials and structural health monitoring will contribute to developing and implementing the proposed WiSe technologies for safety monitoring of transportation infrastructure.
Dr. Leroy Hulsey, P.E., S.E. is a Structural Engineering Professor at UAF. He has over 40 years of research experience on bridge performance and safety related to the complex interaction between traffic loads and climatic conditions. Dr. Hulsey has extensive experience developing sensors, instrumenting and evaluating long-term performance of bridge components. Dr. Hulsey has a strong publication record as it relates to bridge and material response in cold climates. Dr. Hulsey has also conducted studies to examine liquefaction of partially frozen sands and silts. His contributions at the University of Alaska Fairbanks are recognized by serving as an Assistant Director of the Alaska University Transportation Center. He serves on committees at ACI and TRB. During the summer of 2014, Dr. Hulsey was an invited speaker at the 10th International Conference on Earthquake Engineering. His research relates to the effects of cold temperatures on the accuracy and stability of WiSe sensors and their application for safety monitoring of highway bridges.
2.Project Goal
The objective of the proposed research is to develop a Wireless Self-powered Structural Health Monitoring (WiSe-SHM) system for bridge safety assessment and monitoring in Northern region, particularly the extreme cold environment (such as Alaska) where the transportation infrastructure cannot be easily accessed and their safety cannot be monitored due to their remoteness and weather condition. The identification algorithm of proposed WiSe-SHM system is based on dynamic response, and the sensor system is developed based on combination of MEMS and CMOS micro power technology and RFID technique. The innovation in the proposed sensor systems will reduce the operational cost while maintaining the reliability and robustness of structural assessment system. Surface application or attachment system of the sensor will be developed for potential rapid application. Environmental and loading effects (e.g., temperature changed, loading condition) to the sensor system, attachment/bonding condition and measurement quality will be investigated as well. The smart WiSe-SHM system will be implemented and tested in laboratory model for validation of the concept and for correlation with the numerical model. The field implementation will be conducted in the actual highway or pedestrian bridges in the end of this project. The proposed smart WiSe-SHM system will fit the PacTrans’ theme on “Technological Impacts on Safety”, and it will greatly promote strategic development and application of advanced technologies on safety. More important, the safety of transportation infrastructure in cold regions is real time and continuously monitored with the proposed technology.
3.Relevancy of Institutional Partnerships
The WSU-UAF team brings together decades of collective experience in smart materials, structural health monitoring, seismic/tsunami hazards, and highway bridge performance under extreme weathers. Profs. Hulsey and Qiao have collaborated a few sponsored research projects since 2007, and their collaborations have resulted in several critical technologies with particular signification for cold region transportation safety. The research team is assembled to address the research needs in the proposed scope, with the unique expertise of each of the two partnering institutions playing a significant and meaningful role and added value to address the crosscutting issue with an interdisciplinary approach. Prof. Qiao brings his expertise in smart materials (with a focus on structural dynamics and sensors), and he will develop and test the proposed smart wireless self-powered (WiSe) system for highway bridge safety in cold region. Dr. Hulsey at UAF will implement the developed WiSe system and assist in the task of identifying critical highway bridges for safety monitoring while contributing his expertise in the fields of bridge engineering, effects of temperature extremes on transportation structures, and related modeling and data collection.
4.Research Background and Problem Statement
Need for Rapid Monitoring of Highway Bridge Safety
The report of the Secretary of Transportation to Congress [1] indicates that 29.6% of the nation’s 583,000 bridges are deficient and in need of repair or replacement. This number will grow, as many bridges will age and approach the end of their design life. Highway bridges are classified according to their function, structural type, and structural material, and to retain them in continuous readiness, a reliable maintenance program need to be established. Accordingly, reliable maintenance and monitoring system of bridge condition are significant factor in maintaining the safety and function of the bridge structures. Inspection is a significant element of the bridge maintenance program [2]. One of its activities is onsite load testing, for which the objectives of the testing are to determine and quantify the safe load carrying capacity and the behavior of the bridge structures. Thus, effective bridge monitoring systems should be able to probe structural health condition and suggest proper recommendations for repair or disuse, thus preventing rapid catastrophic failures.
Conducting accurate monitoring of structural condition and evaluation on the structural safety will also reduce the cost of bridge maintenance, which is an important interest to the government and private agencies responsible for maintaining the bridge. Further reduction can be achieved by developing a system that minimizes labor involvement during the process of monitoring procedure (e.g., testing preparation, wiring management, data acquisition, etc.). Current methods for bridge monitoring systems rely on strain gages, strain transducers, accelerometer or Linear Variable Displacement Transducers (LVDT), which the wiring system of these sensors can generate challenging problems. While it is difficult to assess cost associated with management of these wires, it is evident that wire management is a major source for labor intensity and the long installation time [3]. Moreover, sensors connected with wires are more vulnerable to loss and damage. In the cold region, it is difficult to install the conventional sensor systems, and most of transportation infrastructure are not easy to be accessed. A wireless sensors systems based on optical fiber is a promising alternative for bridge monitoring system [4]. However, the cost of the optical fiber sensors is still quite expensive for field applications.
Motivated by the need to improve transportation infrastructure and meet demand of rapid assessment of bridge structural capability at minimum cost, while increasing reliability and improving safety, a Wireless Self-powered Structural Health Monitoring (WiSe-SHM) system that has capability of monitoring and assessinghighway bridge conditions rapidly is proposed.
Structural Health Monitoring for Transportation Infrastructure Safety
Problem of maintenance and repair of existing civil infrastructures involves detection of damage at early stage. Obviously, repairing the damage at early stage will save a lot of cost as compared to replacement or reconstruction of the whole structure. Common method for bridge assessment is by visual inspection, especially for bridge deck. However, visual inspection technique has limited capability to detect subsurface or internal damages [5]. Dynamics-based method for structural assessment as monitoring and diagnostic technique offers an alternative to the conventional or visual techniques, and has been developed for several years and used in other fields such as automotive, aeronautical and mechanical engineering. The primary objective of dynamic testing in this structural assessment method is to determine the modal characteristics of the structures, which lead to determination of the mechanical characteristics for structural integrity monitoring or evaluation.
Application of dynamic response based structural health monitoring for civil infrastructure, especially for bridges, attracts interest of many researchers in recent years. Application on the concrete type of bridges shows promising results in the area of damage identification [6-9]. Applications for composite bridge structures have also been reported [10,11]; these works mainly dealt with the vibration characteristics of the composite bridge decks and the changes on these characters due to the presence of damage. These studies showed that the technique has capability to identify the mechanical characteristics of the structure and has great potential for development of highway bridge safety or health monitoring.
The important key of efficient structural monitoring is to develop an integrated monitoring algorithm for identification of dynamic parameters and the mechanical characteristics, then correlate the measured information with the standard criteria, which compile diagnostic and recommendation information. However, several aspects of structural health/safety monitoring are needed to investigate and develop prior to actual field implementation, which will be the address to accomplish the proposed system. In order to establish a reliable structural safety evaluation, it is necessary to produce a consistent dynamic response at each relevant mode. Selection of excitation source is an essential problem in generating reliable response. Impulse and harmonic excitations are the common method of excitation in dynamic testing and ambient excitation is particularly interesting, since it involve the structural behavior in operating conditions. Transducers and sensors mounting technique is also deserved detail attention in order to measure the vibration with precision, since bad mounting affects the measured data and alters the identification of dynamic parameters. Many environmental conditions of the bridge can also affect both the mounting condition and the measured data, due to changes in the material properties of the structure. Hence, it is important to consider the influence of environmental effects in the development of structural assessment technique. Among many environmental variations, temperature has the most significant effects. This is especially important for the place with large diurnal variation and for the structural parts sensitive to the temperature (e.g., support, expansion joints).
Wireless Self-powered Structural Health/SafetyMonitoring (WiSe-SHM) System
The ultimate goal of structural health monitoring (SHM) technology is to develop autonomous systems for continuous monitoring, inspection and structural condition/safety assessment with minimum labor involvement [12]. To achieve the goal, a self-powered sensor technology for structural safety assessment of bridges is proposed to eliminate the dependency of the system to a power source, which required periodic replacement for battery or wiring management for AC power source. A wireless technology commonly known as radio frequency identification (RFID) is incorporated to eliminate completely the dependency to the wiring problem, which will reduce the total cost of structural maintenance program. Integration of these two technologies (self-powered and RFID), which results in a small size wireless sensor system, allows for rapid attachment to the surface structures of interest where the monitoring system regularly acquires, processes, and stores data, preferably while the structure is in service, and indicate the structure integrity condition, as graphically illustrated in Figure 1. The combination of Micro-Electro-Mechanical Systems (MEMS) and CMOS micro power technology holds the key to a low cost, highly reliable, and robust solution to the structural assessment system. The system with adhesive tags containing sensors recently developed by New Jersey Microsystems, Inc. (NJM)(in which Prof. Qiao has been collaborating in the past) is advancement beyond the battery-operated system.
The wireless system consists of RFID flexible tags, an interrogator/reader, and a host computer with a structural assessment data acquisition program (PC). The RF field is used to send the data to the reader. The reader/interrogator transmits energy to the tag, transmits command to the tag, and detects backscatter data modulation. The innovation we are proposing, as shown in Figure 1, uses the small tags (shown in red), which are remotely powered by magnetic induction fields and interrogated by a printed circuit card in a personal computer. The same radio frequency band is used to provide power and data to the tag and to reflect a data-modulated signal back to the interrogator.
We believe that the successful implementation of this sensor suite will be a breakthrough technology achievement providing tag-type sensors for structural safety monitoring application. The combination of improved energy-harvesting methods, smart energy-management strategies and accepted standards for wireless sensors will greatly expand the market potential of wireless sensing. While a variety of wireless data systems have been available worldwide for a number of years, their current popularity has increasing dramatically.
Figure 1Illustration of use of the proposed wireless system for structural health and safety monitoring
Attributes and Benefit of the Proposed WiSe-SHM System (Potential Impact and Benefit)
Conventional structural heath monitoring (SHM) methods (e.g., standard NDEs) usually provide limited local information or are difficult to implement as an on-board and automatic system, particularly in cold region like Alaska. More reliable and effective SHM systems are needed to improve the structural integrity monitoring and safety. Smart materials as sensors and actuators (e.g., piezoelectric materials) provide a great potential in SHM applications, and they are small in size and can be easily integrated with structures to form smart structures and remotely accessible in cold region. The proposed technique of identification process is based on dynamic response of the structures. The natural frequencies and mode shapes are directly related to the stiffness of the structures. Decrease in frequencies or changes in mode shapes will indicate changing or decrease in the stiffness of the structures. By developing relationships between the changes of dynamic parameters and the changes of stiffness, damage in the structures can be identified. Recent advances in wireless communication and MEMS technologies provide a unique opportunity to integrate with smart SHM algorithm and develop an on-line and self-powered wireless sensing system.
To meet the strategic theme “technological impacts on safety” of PacTrans, our effort in collaboration with New Jersey Microsystems, Inc. (NJM) and state/county transportation agencies will aim at development of an innovative and effective Wireless Self-powered structural health monitoring (WiSe-SHM) system using smart materials and RFID technology. This effort will be initially targeted to the development of a potential Structural Dynamics Based-Smart SHM System, followed by integrating with piezo-based self-powered sensors and wireless technology. Piezoelectric materials will be primarily used in this study as smart sensors and actuators in the self-powered system; they are miniature in size and can be easily integrated/attached to structures. The signal data obtained from surface-bonded piezo-patches or films represent curvature deformations, which are more accurate and advantageous compared to displacements measured from the LVDTs or accelerometers. Corresponding analytical and experimental programs will be developed. The smart SHM systems with a limited number of piezoelectric sensors can be easily implemented in the bridge systems, provide health monitoring over the entire structures, and are retrofit-capable. With aid of microelectromechanical system (MEMS) and wireless technologies, the proposed smart WiSe-SHM system will make remote self-powering and self-sensing a reality.
The six major benefits of the proposed concept are summarized as follows:
(1)Effectiveness and Efficiency: The self-powered sensor system eliminatesnecessity of power supply and battery, and thus it forms a self-sustained and harvesting system with minimum energy and labor involved. While combining with wireless communication technologies, the proposed WiSe-SHM system reduces the burden of wiring management and makes the remote sensing and monitoring a reality, particularly useful in cold region. Integrating the self-powered wireless sensor system with the structural dynamics-based SHM algorithm, the smart WiSe-SHM system is effective to identify the health conditions (e.g., the presence, location and size of the damage/defect and the performance levels)oftransportation structures.
(2)Integration: The MEMS-based WiSe-SHM sensor system is miniature in size and can be easily integrated with the hostingtransportation structures so that monitoring and damage detection mechanism becomes part of the structure by sensing and actuating directly from the structures.
(3)Reliability and Sensitivity: The dynamics-based SHM algorithm employs the surface-bonded piezoelectric sensors to measure the dynamic response (i.e., frequency, strain, curvature shapes, and anti-resonance) of the structures. The curvature mode shapes measured from the piezoelectric sensors are more sensitive and accurate to quantify the damage, compared to the conventional displacement mode shape-based approaches using accelerators. The arrangement of the smart sensors is designed to be sensitive to location and size of the damage. Further, the effects of temperature and attachment schemes will be investigated, which provides the reliability information of the proposed sensors.