Real-Time structural health monitoring for concrete beams: a cost-effective 'Industry 4.0' Solution using Piezo Sensors

Purpose: This research paper adopts the fundamental tenets of advanced technologies in industry 4.0 to monitor the structural health of concrete beam members using cost effective non-destructive technologies. In so doing, the work illustrates how a coalescence of low-cost digital technologies can seamlessly integrate to solve practical construction problems. Methodology: A mixed philosophies epistemological design is adopted to implement the empirical quantitative analysis of ‘real-time’ data collected via sensor-based technologies streamed through a Raspberry Pi and uploaded onto a cloud-based system. Data was analysed using a hybrid approach that combined both vibration characteristic based method and linear variable differential transducers (LVDT). Findings: The research utilises a novel digital research approach for accurately detecting and recording the localisation of structural cracks in concrete beams. This nondestructive low-cost approach was shown to perform with a high degree of accuracy and precision, as verified by the LVDT measurements. This research is testament to the fact that as technological advancements progress at an exponential rate, the cost of implementation continues to reduce to produce higher accuracy ‘mass-market’ solutions for industry practitioners. Originality: Accurate structural health monitoring of concrete structures necessitates expensive equipment, complex signal processing and skilled operator. The concrete industry is in dire need of a simple but reliable technique that can reduce the testing time, cost and complexity of maintenance of structures. This was the first experiment of its kind that seeks to develop an unconventional approach to solve the maintenance problem associated with concrete structures. This study merges industry 4.0 digital technologies with a novel low-cost and automated hybrid analysis for real-time structural health monitoring of concrete beams by fusing several multidisciplinary approaches in one integral technological configuration

Quality Assessment of Composite Materials using Ultrasonic Non-Destructive Testing Methods

Non-destructive ultrasonic evaluation (NDE) is commonly used for assessment of civil infrastructure and characterization of construction materials. It is an efficient technique that could save millions of dollars with respect to traditional intrusive tests. However, limitations regarding the use of NDE techniques are still present. The conventional non-destructive testing (NDT) methods (impact echo, ultrasonic pulse velocity [UPV]) are focused on velocity; therefore, neither the frequency content of the response nor the frequency characteristics of the transmitter signal to a tested material is usually utilized. However, it has been shown that this can lead to misinterpretation of ultrasonic data. Even for the fairly simple method like UPV (where the method is based on the concept of measuring the time of flight for the first arriving ultrasonic wave from one side of the specimen to another), it has been shown that the UPV results may be affected by many factors, such as water-cement ratio, aggregate size, or distribution of moisture. Additionally, traditional wave velocity-based methods are not sufficient for early damage detection (which is an active research field in the non-destructive testing of civil infrastructure) as they use only one data point of information, neglecting the frequency content of ultrasonic signals. Finally, the long-term durability of glass-FRP (GFRP) in concrete remains an unresolved issue. The necessity of reliable NDE techniques for GFRP bars is even more important for in-situ testing of concrete members with GFRP reinforcement because the bars embedded in concrete show no visual deterioration and cannot be cut out of a structure to test in a traditional way. The main objective of this research is to enhance the understanding of the frequency effects on ultrasonic measurements and establish a comprehensive methodology for early damage detection of composite materials (based on wave velocity, attenuation, and dispersion). This research consists of four studies. First, a characterization procedure is developed, using a state-of-the-art laser Doppler vibrometer, to understand the frequency content transmitted by ultrasonic transducers typically used in civil engineering applications. Second, a group of concrete specimens of different diameter and length is tested with a traditional ultrasonic pulse velocity method (using ultrasonic transducers with different resonant frequencies and the laser vibrometer) to evaluate how the frequency content of the recorded ultrasonic measurements changes with different resonant frequency transducers and how it depends on specimen dimensions.vi Third, a new methodology, based on wavelet synchrosqueezed transform (WSST) and both velocity and attenuation approaches, is developed to address an issue of early damage detection in cementitious materials (i.e. concrete elements and cemented sand specimen). The proposed framework is verified with synthetic signals and two real, lab-scale applications. Finally, the functionality of the newly developed ultrasonic procedure (i.e. based on characterized ultrasonic transducers, the WSST, and velocity and attenuation approach) is investigated on progressive damage of glass fibre reinforced polymer specimens. The ultrasonic evaluation is verified with the traditional destructive test (i.e. shear test) and numerical simulations. The characterization procedure, developed for ultrasonic transducers typically used in civil engineering applications, reveals that frequency content, transmitted by the transducers to the tested medium, consists of more than just transducer resonant frequency. The importance of using well-characterized ultrasonic transducers (i.e. including the full frequency content in the NDT evaluation) is demonstrated on the ultrasonic evaluation of concrete elements, cemented sand specimen, and GFRP reinforcing bars. The study of frequency effects is continued with concrete cylinders of different dimensions. Therefore, practical recommendations regarding the minimum specimen length, effects of increasing length and diameter, and limitations regarding the use of high frequencies in the ultrasonic evaluation of concrete elements are given. Next, a framework based on wave velocity and attenuation (including a demonstration of the advantages of applying the wavelet synchrosqueezed transform [WSST]) is proposed for the evaluation of distributed damage (i.e. early damage induced by freeze and thaw cycles in concrete elements) and localized damage (i.e. cemented sand specimen with a subsurface void). The results indicate that the WSST technique has the potential to improve both the detection of distributed damage by up to 52% and localized damage detection by up to 36%. Finally, a progressive deterioration of GFRP reinforcing bars is studied using the developed ultrasonic procedure. The comparison of ultrasonic evaluation based on wave amplitude, destructive shear test, and numerical simulations shows that ultrasonic techniques can successfully predict the degradation of shear strength (and ultimately tensile strength) of GFRP bars (with the maximum error of 7%). The findings presented in this thesis provide practical recommendations and frameworks that can successfully increase the reliability of non-destructive ultrasonic evaluation of composite materials used in civil engineering ap

Development of lightweight structural health monitoring systems for aerospace applications

This thesis investigates the development of structural health monitoring systems (SHM) for aerospace applications. The work focuses on each aspect of a SHM system covering novel transducer technologies and damage detection techniques to detect and locate damage in metallic and composite structures. Secondly the potential of energy harvesting and power arranagement methodologies to provide a stable power source is assessed. Finally culminating in the realisation of smart SHM structures. 1. Transducer Technology A thorough experimental study of low profile, low weight novel transducers not normally used for acoustic emission (AE) and acousto-ultrasonics (AU) damage detection was conducted. This included assessment of their performance when exposed to aircraft environments and feasibility of embedding these transducers in composites specimens in order to realise smart structures. 2. Damage Detection An extensive experimental programme into damage detection utilising AE and AU were conducted in both composites and metallic structures. These techniques were used to assess different damage mechanism within these materials. The same transducers were used for novel AE location techniques coupled with AU similarity assessment to successfully detect and locate damage in a variety of structures. 3. Energy Harvesting and Power Management Experimental investigations and numerical simulations were undertaken to assess the power generation levels of piezoelectric and thermoelectric generators for typical vibration and temperature differentials which exist in the aerospace environment. Furthermore a power management system was assessed to demonstrate the ability of the system to take the varying nature of the input power and condition it to a stable power source for a system. 4. Smart Structures The research conducted is brought together into a smart carbon fibre wing showcasing the novel embedded transducers for AE and AU damage detection and location, as well as vibration energy harvesting. A study into impact damage detection using the techniques showed the successful detection and location of damage. Also the feasibility of the embedded transducers for power generation was assessed

Interfacial Bond Behaviour between FRP Sheet and Concrete under Static and Dynamic Loads

In this thesis, the effects of FRP (Fibre reinforced polymer) configurations, concrete characteristics and strain rate on the bond behaviours between FRP and concrete are investigated by intensive static and dynamic tests, analytical derivations and numerical simulations. Reliable models are proposed to predict the bonding performance. A new epoxy anchor system is proposed to enhance interfacial bond and a wave based sensing approach is used to detect the debonding process with surface mounted piezoceramic transducers

The development of fibre-optic acoustic emission sensors for structural health monitoring

Acoustic emission (AE) is widely used for condition monitoring of critical components and structures. Conventional AE monitoring techniques use piezo-electric AE sensors to detect elastic stress waves emitted from a source, such as a propagating crack. These sensors are often surface mounted and secured in place using magnetic hold-downs or adhesive tape to monitor structural components. Coupling sensor and structural components is achieved with the use of an appropriate ultrasonic couplant due to the high frequency signals emanating from an AE event (up to 1 MHz). The couplant is crucial to permit an efficient transfer of elastic waves between damage source and sensor. Piezo-electric sensors tend to be relatively bulky, so cannot be embedded into composite materials. The embedding process protects sensors against environmental stresses, prolonging operational lifetime and enhancing device sensitivity. In addition, piezo-electric AE sensors are affected by electromagnetic interference meaning that when required in challenging conditions such as in flammable or explosive environments, AE sensors need to be manufactured as intrinsically safe. Fibre-optic acoustic emission sensors (FOAES) offer several advantages over conventional piezoelectric AE sensors. FOAES can be both surface-mounted to various materials or embedded into composites owing to their small size and acrylate coating relieving the stress concentration around the sensor. The immunity of FOAES to electromagnetic interference makes these sensors attractive for condition monitoring across a wide range of operational environments. This is because the FOAES employs light at the sensing region to interrogate elastic stress waves instead of electrical components used in piezo-electric AE sensors. This study discusses the approach employed for manufacturing sensitive and reproducible FOAES in addition to methods used to characterise them. Towards the end of the investigation, a comparison between AE signals captured using both conventional piezo-electric sensors and FOAES is also provided

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

Novel Approaches for Structural Health Monitoring

The thirty-plus years of progress in the field of structural health monitoring (SHM) have left a paramount impact on our everyday lives. Be it for the monitoring of fixed- and rotary-wing aircrafts, for the preservation of the cultural and architectural heritage, or for the predictive maintenance of long-span bridges or wind farms, SHM has shaped the framework of many engineering fields. Given the current state of quantitative and principled methodologies, it is nowadays possible to rapidly and consistently evaluate the structural safety of industrial machines, modern concrete buildings, historical masonry complexes, etc., to test their capability and to serve their intended purpose. However, old unsolved problematics as well as new challenges exist. Furthermore, unprecedented conditions, such as stricter safety requirements and ageing civil infrastructure, pose new challenges for confrontation. Therefore, this Special Issue gathers the main contributions of academics and practitioners in civil, aerospace, and mechanical engineering to provide a common ground for structural health monitoring in dealing with old and new aspects of this ever-growing research field

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