Structural Monitoring System Research Articles

Experimental investigation on structural degradation and dynamic characterization of a cycle-pedestrian bridge

In the last century in Italy and, in particular, in Padua, the cycle-pedestrian bridges represented a connective system of the city that assumed a historical and strategic importance. Indeed, the city owes a significant part of its vitality to this type of works. However, some of these constructions are affected by significant material degradation phenomena and by structural issues related to the dynamic interaction between pedestrians and structure (a.k.a. “lock-in” effect). This paper will explore the case of a historic cycle-pedestrian bridge illustrating the construction methods, the realization phases and the maintenance works carried out. The adopted identification techniques are then illustrated with reference to the operational modal analysis (OMA) and the experimental investigations carried out in the static and dynamic field. The tests were conducted with particular reference to the possibilities of improving the dynamic behaviour of the bridge in terms of frequencies on the horizontal plane. The experimental results before and after the introduction of some constraints to the horizontal displacement are then illustrated, as well as the results of a series of non-destructive tests on some significant points of the structural elements. The work closes by examining possible future structural solutions and related monitoring systems.

Structural Damage Classification in Offshore Structures Under Environmental Variations and Measured Noises Using Linear Discrimination Analysis

Changing environmental conditions and measured noises often affect the dynamic responses of structures and can obscure subtle changes in the vibration characteristics caused by damage. To address this issue, a new method for classifying damage in offshore structures under varying environmental conditions and measured noises is proposed using linear discrimination analysis (LDA). Two sets of data on dynamic characteristics, one from healthy structures and the other from unknown testing structures, are used to determine the optimal projection vector. This vector is perpendicular to the discriminant hyperplane and is used for damage classification. The damage‐sensitive features are extracted by projecting both sets of data onto this vector. These features are then used with the hypothesis test technique to determine the condition state of the testing structure. Numerical studies on offshore wind turbine structures and experimental validations of a deep‐sea mining system are being conducted to evaluate the effectiveness of the proposed approach. The study also examines the impact of mode combinations, measured noises and samples on the performance of the approach. The results indicate that the proposed approach can accurately assess the structural health state even in the presence of environmental changes and noise contamination, even with limited samples. The promising performance of the approach will facilitate the establishment of an online structural monitoring system to ensure the safety of offshore structures.

Vision-based dynamic monitoring of a post-tensioned concrete bridge under vehicular traffic

Computer vision for the purpose of structural dynamic monitoring of bridges has received much interest in recent years given the possibility of measuring displacement time-histories in absence of stationary points, using hardware that has accessible costs and is easy to operate. The review of the state-of-the-art shows that vision-based monitoring can potentially provide results equivalent to those obtained with the use of well-established contact sensors such as displacement transducers and accelerometers. Applications to real full-scale steel bridges and footbridges showed the possibilities of this technology in real-world conditions as well as difficulties and challenges posed by the surrounding environment. However, despite the many contributions published in the technical literature, very few applications involved post-tensioned concrete bridges, a very common solutions in the Italian road network and in many other countries. Characterized by a stiffer response as compared to steel bridges and footbridges, post-tensioned concrete bridges with their lower displacement magnitude and higher natural frequency might represent a more demanding testbed for vision-based monitoring. Accordingly, this study focused on the performance analysis of a vision-based structural monitoring system when applied to medium-span post-tensioned simply supported concrete bridges. The experimental outcomes show very interesting potentialities together with some critical aspects relevant to the vibrations induced in the tripod supporting the video camera that require attention to ensure the accuracy of the measurements.

Self-powered wireless structural sensors for long-term monitoring of bridges

The present work introduces the design of a self-powered wireless static and dynamic structural monitoring system developed by Wisepower Srl and deployed on some bridges along the S.S. 675 "Umbro-Laziale" (former "Civitavecchia - Orte" junction) since 2018. The most significant aspect of the developed monitoring system lies in the fact that it consists of a wireless network of MEMS accelerometers (noise spectral density in all axes: 22.5 μg/√Hz, and sensitivity: 3.9 μg/LSB) powered by energy harvesting systems, which can convert environmental energy (i.e. vibrations and light) into electrical energy collected in batteries, so extending the life and minimizing the maintenance cycles of the devices. Vibration-based energy harvesting is achieved through a non-linear resonator, which utilizes a wider spectrum of frequencies compared to traditional linear vibration energy harvesters owing to its non-linear dynamics. The efficiency of the system is further enhanced by the combination of solar panels, overcoming the limitations associated with traditional wiring or batteries, widening the lifespan of the electronics, and reducing the maintenance costs. The paper reports the analysis method and the data elaboration of some ambient acceleration records, validating the system for natural frequencies identification.

Correction of Misalignment Errors in the Integrated GNSS and Accelerometer System for Structural Displacement Monitoring

Structural health monitoring (SHM) systems are widely deployed to monitor the dynamic behaviors of large civil infrastructures such as bridges and tall buildings. Global Navigation Satellite System- (GNSS-) based technologies are often a key component in such an SHM system considering the unique capability of GNSS in determining real-time displacements. GNSS often integrates with an accelerometer to achieve complementary advantages. However, due to the various error sources in GNSS measurements and accelerometer, accuracies of GNSS and accelerometer fusion results often cannot meet the requirements of SHM. We propose to integrate a multi-antenna GNSS and an accelerometer with an unscented multi-rate Kalman filter (UMRKF-MA) to correct the system misalignment errors between the sensors, aiming to produce a much more accurate real-time displacement measurement technology for monitoring large civil infrastructures. Extensive experiments with datasets gathered using a shaking table have indicated that the proposed method was able to improve the accuracy of real-time displacement measurements by up to about 40–65% compared to some existing approaches, and that a 1 mm level of real-time monitoring of displacements could be achieved with the method. The method has also been applied to process a dataset from a real-world long-span bridge when heavy vehicles passed through the bridge in a loading test and significantly improved results were obtained.

On using the DFOS for damage identification in civil engineering structures

AbstractThe application of distributed fiber optic sensing (DFOS) technologies to the monitoring of civil engineering structures has been widely developed in recent years. In particular, fiber optic sensing (FOS) using the Rayleigh backscattering phenomenon of the laser frequency spectrum has been used to continuously measure strain along the fiber optic sensor with high spatial resolution. However, the practical implementation of fiber optic sensorsin the field is still a challenge. These include, but are not limited to, the bonding between fiber sensor cables and the surrounding medium, the practical way in which fiber optic sensors can be installed in concrete structures, and the analysis of crack width using the strain distribution along the fiber. Compared to classical discrete sensors, the DFOS has a great potential to detect, localize and quantify crack formation even in the early stages of microcracking. This paper discusses the potential and challenges of using distributed fiber optic sensors for crack detection in concrete structures. In this sense, different types of mechanical tests on concrete structures using different fiber optic sensors, and different bonding techniques are presented to explore the possibilities of crack detection in concrete structures and its potential for practical structural health monitoring (SHM) systems of civil structures.

Balanced Definition of Thresholds for Mode Tracking in a Long-Term Seismic Monitoring System

The catastrophic events of recent years have strengthened the awareness of the fragility of the built heritage and the importance of careful and targeted maintenance. This, in combination with the development of modern techniques for the analysis of large datasets, has favoured the diffusion of long-term seismic monitoring systems for the protection of structures. In the field of structural health monitoring, data-driven techniques allow crucial information to be extracted from measurements without the need to model the physical phenomena involved, circumventing potential limitations that may arise. On the other hand, however, the results of data-driven approaches are based entirely on the measured structural response; this is why a high reliability of the procedure for extracting diagnostic parameters is essential. In this perspective, a Mode Tracking procedure is proposed to obtain coherent time histories of the modal frequencies of a structure as environmental conditions vary. The procedure is applied to the Sanctuary of Vicoforte, an important monumental structure located in Piedmont, known for its imposing oval dome and characterized by a permanent structural monitoring system. This study aims to disentangle the frequency time series and obtain a rigorous database on which to set up damage identification processes.

Consistent mapping of marine structures with an autonomous surface vehicle using motion compensation and submap-based filtering

Inspection and maintenance of marine energy farms are becoming increasingly important as more farms are developed and constructed. In this study, structural monitoring system using an autonomous surface vehicle (ASV) has been proposed to enable the inspection of an offshore power plant under harsh ocean disturbances. In particular, the ASV uses guidance and control laws to minimize the deviation from the desired path in waypoint tracking. The ASV was also equipped with multi-modal sensors – sonar and light detection and ranging (LiDAR) – for mapping underwater and surface structures. By utilizing the navigation sensors, the motion of the ASV in ocean disturbances was accurately estimated and incorporated into the mapping process to produce consistent multi-modal maps. Furthermore, dedicated outlier removal methods were proposed to improve the performance over conventional approaches in real offshore data. We considered the sparsity of the sonar and LiDAR data in their respective modality during acquisition and designed novel submap-based filtering to remove the outliers. To validate the proposed system, a field test was conducted on an offshore wave farm structure. It was verified that the ASV can cope with ocean disturbances in its waypoint tracking, and the resulting multi-modal maps are consistent and outlier-free.

Study of the Reasonable Acquisition Frequency Evaluation Method of Midspan Deflection of Medium- and Small-Span Beam Bridges

The objective of this study is to further promote and apply the structural monitoring system to medium and small bridges, given the relative delays in scientific research, technical specifications, and engineering practice for the safety monitoring of small and medium-span girder bridges, as well as the relative simplicity of the structural system of these bridges, their well-defined forces, and the relatively large proportion of live load responses during operation. These concepts are proposed based on the evaluation method of live loading (As therefore, this paper suggests the notion of sensor acquisition frequency and appropriate acquisition frequency based on the live load assessment method and the fundamental reliability theory). Based on the time-history curve depicting the midspan deflection response of the vehicle-bridge coupling system, the frequency domain analysis reveals that the power spectrum at −3 dB corresponds to the response cutoff frequency. Significantly, the cutoff frequency mentioned is double the acquisition frequency considered suitable for the study. Based on the definition of a quasi-static response, it can be deduced that the velocity of a load does not exert any influence on the quasi-static response of a bridge structure. As a result, the derivation of the components related to the midspan deflection of a bridge’s quasi-static response is presented, together with a recommended set of methodological guidelines for the extraction of finite elements. This study introduces a novel approach for determining the cutoff frequency of the structural response by utilizing the characteristics of amplitude spectrum estimation and power spectrum estimation in frequency domain analysis. The cutoff frequency of the signal is determined by analyzing the amplitude-frequency curve of the power spectrum. Subsequently, the probability density function of the original time-history curve data is estimated based on the amplitude spectrum. Finally, reliability analysis is conducted by calculating the ratio of the amplitude spectrum area of the signal obtained through a reasonable acquisition frequency to the area of the amplitude spectrum function of the original signal. This analysis verifies the reliability of the proposed method for determining the midspan deflection acquisition frequency.

Spacecraft Segment Damage Identification Method Based on Fiber Optic Strain Difference Field Reconstruction and Norm Calculation

Real-time online identification of spacecraft segment damage is of great significance for realizing spacecraft structural health monitoring and life prediction. In this paper, a damage response characteristic field inversion algorithm based on the differential reconstruction of strain response is proposed to solve the problem of not being able to recognize the small damages of spacecraft structure directly by the strain response alone. Four crack damage location identification methods based on vector norm computation are proposed, which realize online identification and precise location of structural damage events without external excitation by means of spacecraft structural working loads only. A spacecraft segment structural damage monitoring system based on fiber optic grating sensors was constructed, and the average error of damage localization based on the curvature vector 2 norm calculation was 2.58 mm, and the root-mean-square error was 1.98 mm. The results show that the method has superior engineering applicability for on-orbit service environments.

An Automated Wireless System for Monitoring Concrete Structures Based on Embedded Electrical Resistivity Sensors: Data Transmission and Effects on Concrete Properties.

Modern infrastructure heavily relies on robust concrete structures, underscoring the critical need for effective monitoring to ensure their safety and durability. This paper addresses this imperative issue by introducing an innovative automated and wireless system for continuous structural monitoring. By employing embedded electrical resistivity sensors coupled with a wireless-based data transmission mechanism, real-time data collection becomes feasible. We provide a general description of the system's architecture and its application in a pilot study covering the effects of the devices on concrete properties and data transmission. The dielectric properties of concrete specimens were investigated under natural and accelerated curing/degradation and the results were used in the final design of the antenna device. Furthermore, a pilot test comprising four reinforced concrete columns was used to investigate the range of data transmission from inside to outside of the concrete, the effects of the hardware device on the compressive strength and concrete distribution in the columns, and the data transmission quality in real time under realistic exposure conditions.

Vision-Based Structural Monitoring: Application to a Medium-Span Post-Tensioned Concrete Bridge under Vehicular Traffic

Video processing for structural monitoring has attracted much attention in recent years thanks to the possibility of measuring displacement time histories in the absence of stationary points close to the structure, using hardware that is simple to operate and with accessible costs. Experimental studies show a unanimous consensus on the potentialities of vision-based monitoring to provide accurate results that can be equivalent to those obtained from accelerometers and displacement transducers. However, past studies mostly involved steel bridges and footbridges while very few applications can be found for concrete bridges, characterised by a stiffer response with lower displacement magnitudes and different frequency contents of their dynamic behaviour. Accordingly, the attention of this experimental study is focused on the application of a vision-based structural monitoring system to a medium-span, post-tensioned, simply supported concrete bridge, a very common typology in many road networks. The objective is to provide evidence on the quality of the results that could be obtained using vision-based monitoring, understanding the role and influence on the accuracy of the measurements of various parameters relevant to the hardware settings and target geometry, highlighting possible difficulties, and providing practical recommendations to achieve optimal results.

Study of the transverse strain effect on the Fiber Bragg Grating Sensor (FBGS) response with polyimide coating under experimental biaxial tests

The aim of this research work is to study the behaviour of Fiber Bragg Grating (FBG) sensors to interpret their response more accurately in a structural monitoring system. In the presence of a complex stress state, a structure is subjected to strain fields in multiple directions simultaneously and the sensors used for its structural monitoring are affected as well. However, the traditional procedure to calibrate FBG sensors consists of uniaxial tensile tests to calculate a strain sensitivity factor (K) that relates the sensor response to the strain measured during the test. In this study, a polyimide coated FBG sensor is embedded in a cruciform composite specimen to analyse its response to biaxial strain states. The experimental methodology has consisted of carrying out a campaign of biaxial tests on this specimen in which the longitudinal strain (εx) has been kept constant and the transverse strain (εy) has been varied by means of a triaxial testing machine to reproduce different plane stress states. Biaxial tests have allowed to study experimentally the influence of the εy on the longitudinal measurement of the FBG sensor and therefore on the calibration procedure. Finally, the experimental results obtained in both uniaxial and biaxial tests have been compared to the strain-optic theory.

Dynamic response of a slender structure to thunderstorm outflow excitation through numerical analysis and full-scale monitoring

Thunderstorm outflows have been causing damage and failure in slender light structures susceptible to dynamic excitation. With the goal of contributing to the design of wind-safer structures, researchers have proposed simplified models for the downburst wind field through wind tunnel tests and field wind data collection. In this research, the proposed wind field models were applied to calculate the dynamic response of a slender-light structure during two real case studies of downburst winds. The result was compared with the structure’s response recorded by the structural response monitoring system during the two case studies. When time-varying aerodynamic coefficients obtained from wind tunnel testing are used, the comparison of the mean response showed that the alongwind response of the structure is overestimated while the crosswind response is underestimated. In general, contrary to the crosswind response, the calculated alongwind response of the structure was comparable to the registered response with a percentage difference of not more than 25%. Outcomes highlighted the importance of a proper definition of wind field parameters such as turbulence intensity and space coherence of downburst wind as well as structural parameters such as aerodynamic coefficients and damping ratio of the structure to the prediction of the dynamic response.

Analysis of full-scale wind and pressure measurements on a low-rise frame-supported fabric expedient aircraft hangar

The use of lightweight fabric structures as a substitute for traditional building materials, such as wood, concrete, masonry, and steel has become more commonplace. Attractive selection criteria include speed of construction as well as being an economically affordable alternative for many owners. However, lightweight fabric structures come with unique engineering considerations such as the increased vulnerability to environmental loading from wind and snow when compared to more traditional and massive (i.e., heavier) building systems. This paper examines the wind-induced response of an in-service 818 SM (8,800 sf) frame-supported fabric Large-Area Maintenance Structure monitored using a suite of structural and environmental instrumentation. Analysis of such structures is missing in the published literature. The study evaluates structural performance relative to the structural design parameters and assumptions using a combination of an in-situ monitoring study, numerical modeling, and targeted material and component-level testing that characterized accurate fundamental material properties and the behavior of key connections. The study finds a high degree of uncertainty in the longitudinal load path for the Main Wind Force Resisting System (MWFRS) due to the flexibility of the structure. Additionally, irregularly shaped structures that deviate significantly from rectangular, gable-roofed structures, wind tunnel testing or other means should be used to demonstrate that the maximum wind effects are adequately enveloped. This study also demonstrates a framework for fully remote structural monitoring systems that can provide near-continuous monitoring of the structural response of in-service structures.

Risk assessment of a masonry arch bridge: from on‐site inspections to continuous monitoring

AbstractThe paper presents an application of a risk‐based methodology – developed as a joint research between Politecnico di Milano and Regione Lombardia – for the prioritization of interventions and the subsequent monitoring of a masonry arch bridge affected by riverbed erosion. Firstly, available data on the regional bridge inventory is evaluated to assign a structural and hydraulic class of attention. Subsequently, onsite inspections and in‐depth documentary analysis were performed, and, finally, a quasi‐static structural and hydraulic monitoring system was installed to detect scour‐induced effects. The monitoring of piers rotation is performed using tiltmeters installed at the skewback of the arches. Environmental parameters, such as temperature, water level and riverbed changes, are also measured to check possible correlation with the monitored rotations. The results from the first two years of monitoring highlight abnormal changes in the rotationtemperature correlation of some piers.

A Finite Element Analysis of the Effects of Anchorage Reaction Forces and Moments on Structural Stability of Mast Climbing Work Platforms

Mast climbing work platforms (MCWPs) have been increasingly used for construction projects, whereas their safety remains an important issue. As the mast in the Mast climbing work platform (MCWP) system is “slender” structurally, its anchorages must play an important role in maintaining its stability. Therefore, the anchorages and their attachments to a construction structure are likely among the most critical components for the MCWPs. This study developed finite element models of a representative MCWP and applied them to analyze the characteristics of the reaction forces at the anchorages when the work platform operates at different heights and under different loading conditions and to simulate the mast structure responses to the failure of one of the three anchorages. The results of this study indicate that the anchorage reaction forces are sensitive to the loading and operational conditions of the MCWP. The responses of the anchorage reaction forces may reflect the stability status or risk potential of the mast structure of the MCWP to collapse. The characteristics of the anchorage forces identified in this study can be used to help develop a structural safety monitoring system, to minimize the risk of catastrophic failures of MCWPs. The knowledge obtained in the study would help improve MCWP safety management at construction sites and help MCWP manufacturers to improve anchorage design and installation procedures to reduce the risk of the mast structure’s instability or collapse.

Photogrammetry-based bending monitoring and load identification of steel truss structures

The bending of steel truss structures is an important gauge for detecting, identifying, and evaluating potential issues with structural safety performance. The limitations and high cost of traditional monitoring methods make it challenging to carry out stable long-term monitoring. Therefore, this paper developed a displacement monitoring system for steel truss structures which fulfill the requirements of having low cost, high stability, and ease of operation. The system is based on the improved sub-pixel positioning technology, achieving precise positioning in unfavorable conditions such as long structure-camera distance, angle skew, and dim light. Then, this system was calibrated through field experiment and compared with other measurement systems. Finally, a load identification method was developed to identify discrepancies between the true load and the design load. This method uses optimization functions to identify the true load applied in the experiment, and the optimization parameter obtained by a genetic algorithm iteration is output as the optimal solution. The results suggest that the photogrammetric system performs well in practical engineering applications and can provide advantages including high precision, low cost, simple operation, etc. Results obtained by the load identification method agree well with measurements obtained from the actual structure, and can serve as a tool for evaluating the mechanical properties of similar structures. This method monitors potential risks of steel truss structures, and greatly improve the stability and safety of such structures.

Proctoring and Monitoring-Based Examination System

Abstract: Due to COVID-19, Online Examination hasgained the most popularity over the previous year across all educational sectors. However, the institutions are having a lot of trouble with the proctoring procedures. There must be a solution found if the way we live is to become the new norm.In this project, we put up a plan to create an AI-based integrated system that can aid in avoiding exam cheating, as well as various methods and technologies that would allowthe proctor to be absent from the exam at all times. Our AI- based algorithm will be able to recognize any irregularities in an exam. Our system guarantees a moral examination atmosphere free of unethical behavior. Our technology monitors the activities of students who attend school in distant locations. Our method can aid in the detection and prevention of exam-related cheating. You can conduct your entire exam without using any paper. By switching to our technology, we can significantly reduce the cost of managing and administering exams. Our solution is compatible with the conventional exam method. The emergence of the online examination system (OES) is the best example of these reforms, and the monitoring system is intended to assure the fairness and impartiality of the OES. The growth of modern educational technology has pushed changes in teaching patterns and examination patterns. The paper describes the OES and monitoring system's structure and operation, highlights the major issues with communication and security, and offers remedies. The network examination criteria have been met by the system. In this project, we've suggested a way to stop exam cheating by creating an AI-basedintegrated system. We've also provided several methods and tools that eliminate the need for the proctor to be present during the exam. Any unfairness in a test will be detectable by our AI-based approach. Here, we offer methods and resources that eliminate the requirement for the proctor to be present for the entire exam. Any unfairness in a test will be detectable by our AI-based approach. Here, we offer methods and resources that eliminate the requirement for the proctor to be present for the entire exam. Neural networks and machine learning are the foundation of this. Our AI- based technology will be able to recognize any unethical exam practices. Our tests showed that the suggestedsystem is superior to the ones already in use

Experience of operation monitoring system of the cat-bone bridge through the Petrovskaya Channel in the alignment of the Western Speed Diameter Highway in St. Petersburg

Aim: Analysis of the current monitoring system of the engineering structures of a cable-stayed bridge across the Petrovsky Canal in the alignment of the Western High-Speed ​​Diameter highway in St. Petersburg.
 Methods and Materials: Statistical data from the databases of the existing system of monitoring engineering structures is used to obtain the results. The tasks, set within the framework of the study, are accomplished by applying the theoretical methods of scientific knowledge: the analytical method, the mathematical statistics theory, induction.
 Results: Analysis of the current monitoring system of engineering structures is presented with a description of one of the main problems the impossibility of synchronizing readings from all sensors during considered period of time, which leads to the inability to correctly assess the stress-strain state of the bridge structure as a whole. Discovered problem solutions are proposed, further research prospect is determined in part of the imperfection of monitoring systems for long-span facilities.
 Conclusion: The obtained study results can be used in designing and installation of monitoring systems of the engineering structures for cable-stayed bridges, as well as for modernization and optimization of existing monitoring systems to improve the quality of assessing technical condition of structures assessment.