38 research outputs found
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
Damage detection of concrete piles subject to typical damages using piezoceramic based passive sensing approach
Pile foundations are typically comprised in concealed construction work. In recent years, some major categories of concrete piles subject to typical damages have caused a lot of engineering disasters and accidents. These accidents have been caused by collapse of civil structures resulting in great casualties and economic loss. Therefore, damage detection and real-time health monitoring on foundation piles is an urgent research requirement. In this research, a piezoceramic based passive sensing approach is proposed to detect typical damages types of concrete piles, including partial mud intrusion, secondary concrete pouring interface, circumferential crack, and full mud intrusion. In this passive sensing approach, induced stress waves are generated by the impact hammer on the top surface of a pile and one smart aggregate embedded on the bottom of each pile is used as a sensor to receive the propagating wave signals. These sensors are embedded before pouring concrete. Structural defects affect the natural frequency of the pile. The power spectrum of piles with different types of damage were compared by plotting the sensor signals in frequency domain. The natural frequency decreases with the increase in defect severity. The experimental results demonstrate that the proposed approach can detect all four typical damage types in concrete piles
Characterization of concrete materials using non-destructive wave-propagation testing techniques
Non-destructive testing (NDT) of concrete members has been widely used for characterisation of material and assessment of functional structures without impairing their functions and performances. This thesis focuses on addressing critical challenges related to the practical implementation of NDT techniques based on wave-propagation approaches for characterisation of concrete members used in civil infrastructures. Specially, this research aims to achieve three interdependent objectives related to developing NDT techniques with piezoceramic-based transducers: monitoring of very early-age concrete hydration process, detection, and monitoring of cracking in concrete members of different complexity under loading. The concept of piezoceramic-based Smart Aggregate (SA) transducers is central to this research. Embedded SA transducers with an active sensing method have shown great potential for characterisation of construction materials such as concrete and concrete-steel composites. Based on the developed SA based approaches, an active sensing approach with appropriate arrangement of SAs in and on concrete members, and analysis of the received signal using the power spectral density, total received power and damage indexes is developed and applied in this thesis. To confirm its applicability for characterisation of very early-age concrete, a systematic investigation is performed into concrete specimens with different values of water-to-cement ratio due to slightly different initial water amounts, and different separation distances between the embedded SAs. For the detection and monitoring of cracking in concrete members under loading the mounted SA based approach is proposed and applied. It is shown that NDT systems, based on this approach, provide detection and monitoring of cracking in a variety of concrete members under loading, including relatively simple concrete beams and reinforced concrete beams under bending, and reinforced concrete slab as a part of a complex composite member under cyclic loading. Comparisons are provided between the proposed system and conventional load cell and strain gauge systems with each tested member
Damage detection of concrete piles subject to typical damages using piezoceramic based passive sensing approach
Pile foundations are typically comprised in concealed construction work. In recent years, some major categories of concrete piles subject to typical damages have caused a lot of engineering disasters and accidents. These accidents have been caused by collapse of civil structures resulting in great casualties and economic loss. Therefore, damage detection and real-time health monitoring on foundation piles is an urgent research requirement. In this research, a piezoceramic based passive sensing approach is proposed to detect typical damages types of concrete piles, including partial mud intrusion, secondary concrete pouring interface, circumferential crack, and full mud intrusion. In this passive sensing approach, induced stress waves are generated by the impact hammer on the top surface of a pile and one smart aggregate embedded on the bottom of each pile is used as a sensor to receive the propagating wave signals. These sensors are embedded before pouring concrete. Structural defects affect the natural frequency of the pile. The power spectrum of piles with different types of damage were compared by plotting the sensor signals in frequency domain. The natural frequency decreases with the increase in defect severity. The experimental results demonstrate that the proposed approach can detect all four typical damage types in concrete piles
Damage detection of concrete piles subject to typical damages using piezoceramic based passive sensing approach
Pile foundations are typically comprised in concealed construction work. In recent years, some major categories of concrete piles subject to typical damages have caused a lot of engineering disasters and accidents. These accidents have been caused by collapse of civil structures resulting in great casualties and economic loss. Therefore, damage detection and real-time health monitoring on foundation piles is an urgent research requirement. In this research, a piezoceramic based passive sensing approach is proposed to detect typical damages types of concrete piles, including partial mud intrusion, secondary concrete pouring interface, circumferential crack, and full mud intrusion. In this passive sensing approach, induced stress waves are generated by the impact hammer on the top surface of a pile and one smart aggregate embedded on the bottom of each pile is used as a sensor to receive the propagating wave signals. These sensors are embedded before pouring concrete. Structural defects affect the natural frequency of the pile. The power spectrum of piles with different types of damage were compared by plotting the sensor signals in frequency domain. The natural frequency decreases with the increase in defect severity. The experimental results demonstrate that the proposed approach can detect all four typical damage types in concrete piles
Advanced Sensing, Fault Diagnostics, and Structural Health Management
Advanced sensing, fault diagnosis, and structural health management are important parts of the maintenance strategy of modern industries. With the advancement of science and technology, modern structural and mechanical systems are becoming more and more complex. Due to the continuous nature of operation and utilization, modern systems are heavily susceptible to faults. Hence, the operational reliability and safety of the systems can be greatly enhanced by using the multifaced strategy of designing novel sensing technologies and advanced intelligent algorithms and constructing modern data acquisition systems and structural health monitoring techniques. As a result, this research domain has been receiving a significant amount of attention from researchers in recent years. Furthermore, the research findings have been successfully applied in a wide range of fields such as aerospace, manufacturing, transportation and processes
An experimental study and a proposed theoretical solution for the prediction of the ductile/brittle failure modes of reinforced concrete beams strengthened with external steel plates
An experimental study and a proposed theoretical solution are conducted in the present study to investigate the ductile/brittle failure mode of reinforced concrete beams strengthened with an external steel plate. The present experimental study has fabricated and tested six steel plate-strengthened RC beams and one non-strengthened RC beam under 4-point bending loads. The proposed theoretical model is then developed based on the observed experimental results to analyze the crack formation, to determine the distance between vertical cracks and to quantitatively predict the ductile/brittle failure mode of plate-strengthened RC beams. The experimental study shows that the failure mode is based on the sliding of concrete along with the external plate. This slip is limited between two vertical cracks, from which the maximum stress in the external steel is determined. Based on comparisons conducted in the present study, excellent agreements of the stresses/strains in soffit steel plates, crack distances, and system failure modes between the current theoretical solution and the previous and present experimental results are observed. 
PZT Sensor Arrays for Integrated Damage Monitoring in Concrete Structures
The broad objective of the work reported here is to provide a fundamental basis for the use of Lead Zirconate Titanate (PZT) patches in damage detection of concrete structures. Damage initiation in concrete structures starts with distributed microcracks, which eventually localize to form cracks. By the time surface manifestation in the form of visible cracking appears there may be significant degradation of the capacity of the structure. Early detection of damage, before visible signs appear on the surface of the structure is essential to initiate early intervention, which can effectively increase the service life of structures. Development of monitoring methodologies involves understanding the underlying phenomena and providing a physical basis for interpreting the observed changes in the parameters which are sensed. PZT is a piezoelectric material, which has a coupled constitutive relationship. In the case of the PZT patches bonded to a concrete structure, any sensing strategy requires developing an understanding of the coupled electromechanical (EM) response of the PZT-concrete system.
The challenges associated with the use of PZT patches for damage monitoring in a concrete substrate include providing the following: a clear understanding of the fundamental response of the PZT patch when bonded to a concrete substrate; interpretation of the coupled response of the PZT patch under load induced damage; and development of an efficient, continuous monitoring methodology to sense a large area of the concrete substrate. Due to a lack of a fundamental basis, the use of PZT patches in concrete structures often involves inferring the measured response using model-based procedures. The work outlined in this thesis addresses the key issue of developing the theoretical basis and providing an experimental validation for PZT-based damage monitoring methodology for concrete structures. A fundamental
understanding of response of the PZT patch when bonded to concrete substrate is developed. The outcome of the work is an integrated local and distributed sensing methodology for concrete structures by combining the electromechanical impedance and stress wave propagation methods using an array of bonded PZT patches.
The work presented in this thesis is focused on using PZT patches bonded to a concrete substrate. A fundamental understanding of the coupled electromechanical behaviour of a PZT patch under an applied electrical excitation in an electrical impedance (EI) measurement, is developed. The influence of the substrate size and its material properties on the frequency dependent EI response of a PZT patch is investigated using concrete substrates of different sizes. The dynamic response of a PZT patch is shown to consist of resonance modes of the PZT patch with superimposed structural response. The resonance behaviour of the PZT patch is shown to be influenced by the material properties of the substrate. The size dependence in the EI response of a PZT patch bonded to a concrete substrate is produced by the dynamic behaviour of the structure. The size of the local zone of the concrete material substrate in the vicinity of the bonded PZT patch, which influences the frequency dependent EI response of the PZT patch is identified. For each resonant mode, a local zone of influence, which is free from the influence of boundary is identified. The dynamic response of the PZT resonant mode is influenced by the elastic material properties and damping within the zone of influence. The structural effects of the concrete substrate produced by the finite size of the specimen are separated from the material effects produced by the material properties and the material damping in the coupled EM response of the bonded PZT patch. The influence of size of the concrete substrate on the coupled impedance response of the PZT is identified with peaks of
structural resonance, which are superimposed on the resonant peaks of the bonded PZT patch
The EI response of the PZT patch when bonded to concrete for detecting load-induced damage from distributed microcrack to localized cracks within the zone of influence of the PZT patch is investigated. Using an approach which combines an understanding of the coupled EM constitutive behaviour of PZT with experimental validation, a methodology is developed to decouple the effects of stress and damage in the substrate on the coupled EM response of a PZT patch. The features in the EI signature of a bonded PZT patch associated with stress and damage are identified. An increasing level of distributed damage in the concrete substrate produces a decrease in the magnitude and the frequency of the resonant peak of the bonded PZT patch. The substrate stress produces a counter acting effect in the EI spectrum of the bonded PZT patch. A measurement procedure for the use of bonded PZT patches for continuous monitoring of stress-induced damage in the form of distributed microcracks in a structure under loading is developed.
An integrated methodology for damage monitoring in concrete structures is developed by combining the EI method for local sensing and the stress wave propagation-based method in a distributed sensing mode. An array of surface mounted PZT sensors are deployed on a concrete beam. The EI measurements from individual PZT sensors are used for detecting damage within the local zone of influence. PZT sensor pairs are used as actuators and sensors for distributed monitoring using stress wave propagation. A stress-induced crack is introduced in a controlled manner. It is detected very accurately from the full-field displacement measurement obtained using digital image correlation. The crack opening profile in concrete produced by the fracture is established from the surface displacement measurements. From the measurements of bonded PZTs, the localized crack is detected in the zone of influence by EI.
The change in compliance of the material medium due to a localized crack is small and it is reflected in the smaller change in the measured EI when compared to distributed damage. Stress wave based measurements sensitively detect crack openings on the order of 10m. The material discontinuity produced by a closed crack, after removal of the stress is also detected. A damage matrix is developed for stress wave based method which is independent of transmission path to assess the severity of damage produced by the crack in a concrete structure
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
Damage identification in FRP-retrofitted concrete structures using linear and nonlinear guided waves
Structural health monitoring (SHM) involves the implementation of damage identification
methods in engineering structures to ensure structural safety and integrity. The paramount
importance of SHM has been recognised in the literature. Among different damage
identification methods, guided wave approach has emerged as a revolutionary technique.
Guided wave-based damage identification has been the subject of intensive research in the past
two decades. Meanwhile, applications of fibre reinforced polymer (FRP) composites for
strengthening and retrofitting concrete structures have been growing dramatically. FRP
composites offer high specific stiffness and high specific strength, good resistance to corrosion
and tailorable mechanical properties. On the other hand, there are grave concerns about longterm
performance and durability of FRP applications in concrete structures. Therefore, reliable
damage identification techniques need to be implemented to inspect and monitor FRPretrofitted
concrete structures.
This thesis aims to explore applications of Rayleigh wave for SHM in FRP-retrofitted
concrete structures. A three-dimensional (3D) finite element (FE) model has been developed
to simulate Rayleigh wave propagation and scattering. Numerical simulation results of
Rayleigh wave propagation in the intact model (without debonding at FRP/concrete interface)
are verified with analytical solutions. Propagation of Rayleigh wave in the FRP-retrofitted
concrete structures and scattering of Rayleigh waves at debonding between FRP and concrete
are validated with experimental measurements. Very good agreement is observed between the
FE results and experimental measurements. The experimentally and analytically validated FE
model is then used in numerical case studies to investigate the scattering characteristic. The scattering directivity pattern (SDP) of Rayleigh wave is studied for different debonding size
to wavelength ratios and in both backward and forward scattering directions. The suitability
of using bonded mass to simulate debonding in the FRP-retrofitted concrete structures is also
investigated. Besides, a damage localisation method is introduced based on the time-of-flight
(ToF) of the scattered Rayleigh wave. Numerical case studies, involving different locations
and sizes of debonding, are presented to validate the proposed debonding localisation method.
Nonlinear ultrasonics is a novel and attractive concept with the potential of baseline-free
damage detection. In this thesis, nonlinear Rayleigh wave induced at debondings in FRPretrofitted
concrete structures, is studied in detail. Numerical results of nonlinear Rayleigh
wave are validated with experimental measurements. The study considers both second and
third harmonics of Rayleigh wave. A very good agreement is observed between numerical and
experimental results of nonlinear Rayleigh wave. Directivity patterns of second and third
harmonics for different debonding size to the wavelength ratios, and in both backward and
forward scattering directions, are presented. Moreover, a damage image reconstruction
algorithm is developed based on the second harmonic of Rayleigh wave. This method provides
a graphical representation for debonding detection and localisation in FRP-retrofitted concrete
structures. Experimental case studies are used to demonstrate the performance of the proposed
technique. It is shown that the proposed imaging method is capable of detecting the debonding
in the FRP-retrofitted concrete structures.
Overall, this PhD study proves that Rayleigh wave is a powerful and reliable means of
damage detection and localisation in FRP-retrofitted concrete structures.Thesis (Ph.D.) -- University of Adelaide, School of Civil, Environmental and Mining Engineering, 201