Bridges Structural Health Monitoring and Deterioration Detection Synthesis of Knowledge and Technology

INE/AUTC 10.0

Multi-axial strain monitoring of fibre reinforced thermosetting plastics using embedded highly birefringent optical fibre Bragg sensors

There is a growing interest in the use of fibre reinforced plastics (FRPs) as high-grade construction material for variouw applications that need to be lightweight, yet strong in sometimes harsh loading conditions. Despite the growing popularity of structural composite materials, one has to realize that their mechanical behaviour is significantly different compared to conventional isotropic construction materials. Strain monitoring of an in-service structure should greatly enhance the insight and confidence in the (long-term) behaviour of high performance composite structures. Structural health monitoring necessitates the possibility of measuring multi-axials strain fields. High birefringent optical fibres (HiBi-fibres) with Bragg grating can become a solution in this matter. Designing a multi-axial strain sensor based on optical FBGs should meet several basic requirements which are discussed in this dissertation

Use of wire extensometers for monitoring pavement performance in areas of slope instability

In 1998, the Gregory Developmental Road was diverted around the western side of the Highway-Reward Mine to allow overburden stripping operations in the open cut. In 2005, mining operations concluded, but several months later cracking was detected in the pavement of the Gregory Developmental Road (Coffey Geotechnics 2011a). This cracking is thought to be the result of slope instability in the western wall of the open cut mine. The Department of Transport and Main Roads, Queensland (TMR) were requested to provide an instrumentation and monitoring system for the site. The monitoring is required to provide data that can be used to analyse ground movements and to provide an early-warning system to notify TMR staff of any road surface deformations that may impose a risk to road users. For the basis of the monitoring system, several types of instrumentation were considered. Case studies of instrumentation installations used to monitor slope instability were examined in an attempt to identify the most suitable system. Wire extensometers were eventually selected as the best solution for the site. A system of 3 wire extensometers and a weather station, connected to satellite telemetry was installed on the remote site, as the basis of the early-warning instrumentation system. The wire extensometer system required the design and fabrication of unique hardware for the installation to be successful. A satellite telemetry system was selected to provide reliable communication of the collected data, and in order to prevent vandalism and threat from fire, the logging, power, telemetry and weather station systems were installed on a custom-designed 8-metre tall mid-hinged pole. Temperature sensors at each of the wire extensometer locations were also fitted in order to determine if the extreme temperature fluctuations have any effect on the operation of the extensometers. Data from the instruments located on site is automatically sent to a web server, where it can be viewed by key personnel. The system will also provide automatic alerts in the form of SMS messages if the devices detect movement or rainfall in excess of the predetermined thresholds. The wire extensometer system provides a unique solution to the requirement for a reliable early-warning system on the remote site. The proven success and reliability of the system has provided a cost effective alternative to traditional instrumentation systems for monitoring pavements in the vicinity of unstable slopes. In addition, the data provided by the weather station will be made available to the Bureau of Meteorology (BOM) for inclusion in its nationwide distribution network

Comparative in situ study of dynamic load generated by gravel piles measured by a fiber-optic interferometer

Currently, all the technology used for seismic monitoring is based on sensors in the electrical domain. There are, however, other physical principles that may enable and fully replace existing devices in the future. This paper introduces one of these approaches, namely the field of fiber optics, which has great potential to be fully applied in the field of vibration measurement. The proposed solution uses a Michelson fiber-optic interferometer designed without polarization fading and with an operationally passive demodulation technique using three mutually phase-shifted optical outputs. Standard instrumentation commonly used in the field of seismic monitoring in geotechnical engineering was used as a reference. Comparative measurements were carried out during the implementation of gravel piles, which represents a significant source of vibration. For the correlation of the data obtained, the linear dependence previously verified in laboratory measurements was used. The presented results show that the correlation is also highly favorable (correlation coefficient in excess of 0.9) from the values measured in situ, with an average deviation for the oscillation velocity amplitude of the optical sensor not exceeding 0.0052.Web of Science2215art. no. 557

Advanced Sensors for Real-Time Monitoring Applications

It is impossible to imagine the modern world without sensors, or without real-time information about almost everything—from local temperature to material composition and health parameters. We sense, measure, and process data and act accordingly all the time. In fact, real-time monitoring and information is key to a successful business, an assistant in life-saving decisions that healthcare professionals make, and a tool in research that could revolutionize the future. To ensure that sensors address the rapidly developing needs of various areas of our lives and activities, scientists, researchers, manufacturers, and end-users have established an efficient dialogue so that the newest technological achievements in all aspects of real-time sensing can be implemented for the benefit of the wider community. This book documents some of the results of such a dialogue and reports on advances in sensors and sensor systems for existing and emerging real-time monitoring applications

Time-Domain Fiber Loop Ringdown Sensor and Sensor Network

Optical fibers have been mostly used in fiber optic communications, imaging optics, sensing technology, etc. Fiber optic sensors have gained increasing attention for scientific and structural health monitoring (SHM) applications. In this study, fiber loop ringdown (FLRD) sensors were fabricated for scientific, SHM, and sensor networking applications. FLRD biosensors were fabricated for both bulk refractive index (RI)- and surface RI-based DNA sensing and one type of bacteria sensing. Furthermore, the effect of glucose oxidase (GOD) immobilization at the sensor head on sensor performance was evaluated for both glucose and synthetic urine solutions with glucose concentration between 0.1% and 10%. Detection sensitivities of the glucose sensors were achieved as low as 0.05%. For chemical sensing, heavy water, ranging from 97% to 10%, and several elemental solutions were monitored by using the FLRD chemical sensors. Bulk indexbased FLRD sensing showed that trace elements can be detected in deionized water. For physical sensing, water and cracking sensors were fabricated and embedded into concrete. A partially-etched single-mode fiber (SMF) was embedded into a concrete bar for water monitoring while a bare SMF without any treatment was directly embedded into another concrete bar for monitoring cracks. Furthermore, detection sensitivities of water and crack sensors were investigated as 10 ml water and 0.5 mm surface crack width, respectively Additionally fiber loop ringdowniber Bragg grating temperature sensors were developed in the laboratory; two sensor units for water, crack, and temperature sensing were deployed into a concrete cube in a US Department of Energy test bed (Miami, FL). Multi-sensor applications in a real concrete structure were accomplished by testing the six FLRD sensors. As a final stage, a sensor network was assembled by multiplexing two or three FLRD sensors in series and parallel. Additionally, two FLRD sensors were combined in series and parallel by using a 2×1 micro-electromechanical system optical switch to control sensors individually. For both configurations, contributions of each sensor to two or three coupled signals were simulated theoretically. Results show that numerous FLRD sensors can be connected in different configurations, and a sensor network can be built up for multiunction sensing applications

Development, Evaluation and Implementation of Sensor Techniques for Bridges Critical to the National Transportation System

The evolution of structural materials and sensor technology has impacted the bridge industry by improving the robustness of the highway network and providing behavior based condition assessments. During the last decades, conventional materials have been supplemented with state-of-the-art materials (e.g., carbon and fiber based, ultra-high performance concrete, etc.). The evolution of smart or intelligent structures by incorporating systems to quantify performance will continue to revolutionize the bridge industry. While laboratory and field applications have indicated that smart materials are appropriate for bridge applications, additional investigations regarding sensor installation, deployment and data reduction are still needed. The work described herein is a collection of field and laboratory tests in which sensors were applied to verify structural and material behavior and develop smart members for integration as part of a structural health monitoring system for bridge superstructures. Three projects are presented in which new materials and unique structures were evaluated using specialized sensors and monitoring techniques. Two basket-handle arch pedestrian bridges with high-strength steel hanger rods supporting a pre-cast, post-tensioned concrete panel deck system were monitored to prevent deck cracks in the vicinity of the hanger rods. Fiber optic sensors and externally mounted accelerometers were attached to the hanger rods to indirectly determine the tensile forces during incremental construction stages and in service conditions. For the second project, a three-span prestressed concrete (PC) girder, composite deck bridge was monitored and evaluated. One end span consisted of composite FRP deck panels and was compared to the opposite cast-in-place reinforced concrete deck end span. Strategically placed transducers measured strain levels on the PC girders and the FRR panels from controlled live and ambient traffic loadings to determine the degree of composite action, load distribution, and maximum in-service strains. A FRP panel temporary bypass bridge was evaluated as a replacement to typical steel temporary bridges as part of the third project. The research focused on the design, fabrication, construction and load testing of this state-of-the-art bridge. This bridge was instrumented with transducers for measuring deflections and loaded with a static truck at pertinent locations to evaluate its performance. A five year research plan was established to develop a conceptual smart timber bridge made of glued laminated (glulam) stringers and a transverse glulam deck. Both stock and custom fiber optic sensor packages were implemented to quantify the structural response. The first of multiple phases of this national five year plan includes the development of an efficient structural health monitoring system and a smart timber bridge field demonstration. To support these goals, two types of FBG sensors packages were developed, the first evaluated the structural strain response and the second isolated the sensor from mechanical strain for detecting deterioration parameters (e.g., moisture content, corrosion, wood deterioration, etc.). Techniques were developed for embedding and attaching the FBG sensor packages to glulam specimens. Small scale specimens were instrumented with the custom FBG sensor packages and tested under a range of temperature and loading conditions to determine sensor viability. A full scale glulam beam was instrumented with similar FBG sensor packages to demonstrate applicability and evaluate performance at service level proportions. From this work, the following contributions in structural bridge monitoring were added to the state-of-the-art: * Application of FBG sensors and accelerometers to monitor the structural behavior of a bridge during construction. * Applied testing of non-traditional FRP deck panels to validate composite action. * Initial development of a smart timber bridge structural health monitoring system. * Development of FBG sensor packages for implementation in glulam members as part of a smart timber bridge

Unbonded Portland Cement Concrete Overlay/Pavement Monitoring with Integrated Grating and Scattering Optical Fiber Sensors

This report summarizes the findings and results from a laboratory and field study on the strain distribution and crack development in 3 thick concrete panels cast on top of existing concrete pavements as a rapid rehabilitation strategy for roadways. Both fiber Bragg gratings (FBG) and Brillouin Optical Time Domain Reflectometry/Analysis (BOTDR/A) were applied and tested for their feasibility and effectiveness in distributed strain measurement and crack detection. For laboratory tests, six 6\u27×6 panels were cast similar to their corresponding field construction. Each was tested under both truck loads and under threepoint loads. The performance of distributed BOTDR/A strain measurements was compared with that of FBG sensors. In field study, the performance of FBG sensors was compared with that from strain gauges when the ambient temperature was measured with thermocouples. Overall, hairline to major cracks can be successfully detected with the distributed BOTDA measurements. The strain distributions measured from the FBG and BOTDR/A sensors are consistent. The FBG readings are in good agreement with those of strain gauges. Both FBG and BOTDR/A technologies are promising for pavement monitoring

Optical fibre sensors for monitoring prestressed concrete structures in nuclear power plants

This thesis was previously held under moratorium from 20th November and 20th November 2015.Lifetime extensions of nuclear fission reactors in the UK are required to satisfy growing demands for electrical power. Many of these reactors are nearing the end of their original design life, so the continued structural integrity, particularly of the reactors' prestressed concrete pressure vessels and containments is of prime concern. Currently, a lift-off inspection of a 1 % random sample of prestressing tendons is performed at 18 month to 5 year intervals to ensure adequate prestress is present in these structures, but the extended life times are making higher resolution, more frequent and in-depth monitoring techniques more desirable. In this thesis, a method of instrumenting prestressing strands with optical fibre Bragg grating strain sensors is outlined. An all-metal encapsulation and bonding technique is developed to ensure sensor reliability under the radioactive and high-stress environments of fission reactors. This 'smart strand' is complemented by a specially developed interrogation scheme capable of continuously and automatically monitoring static and dynamic nanoscale changes in Bragg grating strain. High-resolution interrogation was achieved by extending an interferrometric demodulation technique into the static measurement regime. By modulating the strain sensitivity using a fast optical switch, strain signals could be recovered independently of noise sources using various signal processing algorithms. The application of this technology could augment the continued monitoring of concrete vessel integrity, reducing both the risks and costs associated with performing lift-off measurements in the current and next generation of nuclear reactors.Lifetime extensions of nuclear fission reactors in the UK are required to satisfy growing demands for electrical power. Many of these reactors are nearing the end of their original design life, so the continued structural integrity, particularly of the reactors' prestressed concrete pressure vessels and containments is of prime concern. Currently, a lift-off inspection of a 1 % random sample of prestressing tendons is performed at 18 month to 5 year intervals to ensure adequate prestress is present in these structures, but the extended life times are making higher resolution, more frequent and in-depth monitoring techniques more desirable. In this thesis, a method of instrumenting prestressing strands with optical fibre Bragg grating strain sensors is outlined. An all-metal encapsulation and bonding technique is developed to ensure sensor reliability under the radioactive and high-stress environments of fission reactors. This 'smart strand' is complemented by a specially developed interrogation scheme capable of continuously and automatically monitoring static and dynamic nanoscale changes in Bragg grating strain. High-resolution interrogation was achieved by extending an interferrometric demodulation technique into the static measurement regime. By modulating the strain sensitivity using a fast optical switch, strain signals could be recovered independently of noise sources using various signal processing algorithms. The application of this technology could augment the continued monitoring of concrete vessel integrity, reducing both the risks and costs associated with performing lift-off measurements in the current and next generation of nuclear reactors

Testing of Materials and Elements in Civil Engineering

This book was proposed and organized as a means to present recent developments in the field of testing of materials and elements in civil engineering. For this reason, the articles highlighted in this editorial relate to different aspects of testing of different materials and elements in civil engineering, from building materials to building structures. The current trend in the development of testing of materials and elements in civil engineering is mainly concerned with the detection of flaws and defects in concrete elements and structures, and acoustic methods predominate in this field. As in medicine, the trend is towards designing test equipment that allows one to obtain a picture of the inside of the tested element and materials. Interesting results with significance for building practices were obtained