Monitoring Civil Engineering Research Articles

Editorial for Special Issue “Radar Imaging in Challenging Scenarios from Smart and Flexible Platforms”

Microwave radar imaging plays a key role in several civilian and defense applications, such as security, surveillance, diagnostics and monitoring in civil engineering and cultural heritage, environment observation, with particular emphasis on disasters and crisis management, where it is required to remotely sense the area of interest in a timely, safe and effective way. To address these constraints, a technological opportunity is offered by radar systems mounted onboard smart and flexible platforms, such as ground-based ones, airplanes, helicopters, drones, unmanned aerial and ground vehicles (UAV and UGV). For this reason, radar imaging based on data collected by such platforms is gaining interest in the remote sensing community. However, a full exploitation of smart and flexible radar systems requires the development and use of image formation techniques and reconstruction approaches able to exploit and properly deal with non-conventional data acquisition configurations. The other main issue is related to the need to operate in challenging environments, and still deliver high target detection, localization and tracking. These environments include through the wall imaging, rugged terrain and rough surface/subsurface. In these cases, one seeks mitigation of the adverse effects of clutter and multipath via the implementation of effective signal processing strategies and electromagnetic modeling.

Seismometers Within Cities: A Tool to Connect Earth Sciences and Society

The high degree of human activities in urban environments produces large background vibrations that makes it difficult to use data acquired in these areas for classical seismology. Seismometers installed within cities have been typically been used for the study of seismic hazard or for monitoring civil engineering problems. However, with the development of monitoring techniques based on the interpretation of the so-called seismic ambient noise, these data have gained scientific interest. Our objective is to discuss an additional utility of seismometers deployed within a city; its use as a tool to connect society with Earth sciences. Many citizen activities, from traffic to music concerts, produce vibrations that can be recorded seismically, and our experience shows that these records attract the attention of the media and social networks. With the emergence of low-cost and easy-to-use instruments in recent years, more citizens can now record ground motion and become interested in the interpretation of the recorded seismograms. The installation of permanent seismic networks in educational centers has proven to be a good approach to introduce students to Earth sciences at the national level and can also be developed at the urban scale using this new instrumentation. In this contribution we will first review the previous results related to the identification of the sources of vibration in urban areas and then present a new ongoing project based on the deployment of a seismic network in educational centers located in the city of Barcelona.

Application of Artificial Intelligence Method in Civil Engineering Monitoring

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Smart RFID Sensors Embedded in Building Structures for Early Damage Detection and Long-Term Monitoring.

In civil engineering, many structures are made of reinforced concrete. Most degradation processes relevant to this material, e.g., corrosion, are related to an increased level of material moisture. Therefore, moisture monitoring in reinforced concrete is regarded as a crucial method for structural health monitoring. In this study, passive radio frequency identification (RFID)-based sensors are embedded into the concrete. They are well suited for long-term operation over decades and are well protected against harsh environmental conditions. The energy supply and the data transfer of the humidity sensors are provided by RFID. The sensor casing materials are optimised to withstand the high alkaline environment in concrete, having pH values of more than 12. Membrane materials are also investigated to identify materials capable of enabling water vapour transport from the porous cement matrix to the embedded humidity sensor. By measuring the corresponding relative humidity with embedded passive RFID-based sensors, the cement hydration is monitored for 170 days. Moreover, long-term moisture monitoring is performed for more than 1000 days. The experiments show that embedded passive RFID-based sensors are highly suitable for long-term structural health monitoring in civil engineering.

Research on new FBG soil pressure sensor and its application in engineering

Since the existing soil pressure box sensor has low accuracy for monitoring the main lateral soil pressure outside the foundation pit wall, and inability to achieve three-dimensional soil pressure monitoring, a three-dimensional soil pressure sensor is designed based on the fiber Bragg grating (FBG) sensing device, containing six pressure surfaces and pressure diaphragms. This sensor has the capability to monitor the space's three-dimensional stress distribution with high sensitivity to monitor data, less liability to damage and long service life. Performance tests implemented on the produced prototype transducer and sensitivity is tested as 382.30769pm/MPa, 362.83692pm/MPa, 341.56308pm/MPa, 318.46154pm/MPa, 415.04615pm/MPa and 428.92308pm/MPa in the range of 0–3 MPa with lowest fitting error 0.99902. Moreover, the deviation of drift values for the measured wavelength to theoretically calculated value in the full range is nearly 2.3%, 1.6%, 0.49%, 1.6%, 0.4% and 1.3%. Consequently, this transducer meets the accuracy requirements of stress and deformation measurement for the structural health monitoring in civil engineering. To monitor the real-time deep soil pressure of the foundation pit wirelessly, four displacement sensors, which have been tested and calibrated, are installed in the foundation pit of the east square in the special-class station on Line 1 of Taiyuan rail transit. Subsequently, the reason for the change in the soil pressure on the monitored section is analyzed and compared with actual working conditions in the field verifying the effectiveness of the three-dimensional soil pressure sensing based on FBG in the soil pressure monitoring when constructing foundation pit.

An Embedded Surface Acoustic Wave Pressure Sensor for Monitoring Civil Engineering Structures

This paper proposes a novel embedded surface acoustic wave (SAW) pressure sensor for monitoring civil engineering structures. The sensor consists of a pressure cell and a sensing chip in a metal housing. The whole interior of the sensor is filled with silicone oil for pressure transfer. The sensing chip is a SAW die packaged in a seal cavity to monitor the pressure of the silicone oil. Therefore, the external pressure applied to the cell can be detected by this method. In order to optimize the structure, the strain behavior and pressure measurement of the SAW device are analyzed in detail. The positions of the inter-digital transducer and reflectors on the SAW substrate are designed deliberately. The SAW device is fabricated by a lift-off process. The sensor is characterized by a network analyzer. The pressure sensitivity tested is 0.4°/kPa and the nonlinearity is 1.02%. The maximum absolute error is 2.9° in the range of 0–500 kPa.

Structural damage identification based on autoencoder neural networks and deep learning

Artificial neural networks are computational approaches based on machine learning to learn and make predictions based on data, and have been applied successfully in diverse applications including structural health monitoring in civil engineering. It is difficult to optimize the weights in the neural networks that have multiple hidden layers due to the vanishing gradient issue. This paper proposes an autoencoder based framework for structural damage identification, which can support deep neural networks and be utilized to obtain optimal solutions for pattern recognition problems of highly non-linear nature, such as learning a mapping between the vibration characteristics and structural damage. Two main components are defined in the proposed framework, namely, dimensionality reduction and relationship learning. The first component is to reduce the dimensionality of the original input vector while preserving the required necessary information, and the second component is to perform the relationship learning between the features with the reduced dimensionality and the stiffness reduction parameters of the structure. Vibration characteristics, such as natural frequencies and mode shapes, are used as the input and the structural damage are considered as the output vector. A pre-training scheme is performed to train the hidden layers in the autoencoders layer by layer, and fine tuning is conducted to optimize the whole network. Numerical and experimental investigations on steel frame structures are conducted to demonstrate the accuracy and efficiency of the proposed framework, comparing with the traditional ANN methods.

Theoretical and experimental study on fiber-optic displacement sensor with bowknot bending modulation

Abstract A novel and simple fiber-optic sensor for measuring a large displacement range in civil engineering has been developed. The sensor incorporates an extremely simple bowknot bending modulation that increases its sensitivity in bending, light source and detector. In this paper, to better understand the working principle and improve the performance of the sensor, the transduction of displacement to light loss is described analytically by using the geometry of sensor and principle of optical fiber loss. Results of the calibration tests show a logarithmic function relationship between light loss and displacement with two calibrated parameters. The sensor has a response over a wide displacement range of 44.7 mm with an initial accuracy of 2.65 mm, while for a small displacement range of 34 mm it shows a more excellent accuracy of 0.98 mm. The direct shear tests for the six models with the same dimensions were conducted to investigate the application of the sensor for warning the shear and sliding failure in civil engineering materials or geo-materials. Results address that the sliding displacement of sliding body can be relatively accurately captured by the theory logarithmic relation between sliding distance and optical loss in a definite structure, having a large dynamic range of 22.32 mm with an accuracy of 0.99 mm, which suggests that the sensor has a promising prospect in monitoring civil engineering, especially for landslides.

Fiber Bragg grating based sensing system: Early corrosion detection for structural health monitoring

Fiber optic sensors have been widely used in chemical and biomedical applications and are now being extended to structural health monitoring (SHM) in the civil engineering field. Due to the destructive nature of tests for corrosion monitoring, a non-destructive system was developed to monitor rebar corrosion via fiber Bragg grating (FBG). In this study, two different methods are proposed and tested; FBG with Polydimethylsiloxane (PDMS) coating and bare FBG. FBG sensors were embedded on the specimen to monitor the expansion strain caused by rebar corrosion, and their performances were monitored by observing the Bragg wavelength shift. A significant wavelength shift for the FBG without coating was observed on day 17, whereas for the PDMS coating, the significant wavelength shift occurred on day 10. This proves that PDMS coated FBGs have a higher sensitivity for corrosion detection as compared to non-coated ones. The overall results of both methods after etching have shown a good linear response. Strain induced by the corrosion shows good linear response as corrosion rate increased. Corrosion rate were calculated from the conventional weight loss measurement method. These sensors can be installed for real-time and non-destructive SHM monitoring in civil engineering.

A framework for the damage evaluation of acoustic emission signals through Hilbert–Huang transform

The acoustic emission (AE) is a powerful and potential nondestructive testing method for structural monitoring in civil engineering. Here, we show how systematic investigation of crack phenomena based on AE data can be significantly improved by the use of advanced signal processing techniques. Such data are a fundamental source of information that can be used as the basis for evaluating the status of the material, thereby paving the way for a new frontier of innovation made by data-enabled analytics. In this article, we propose a framework based on the Hilbert–Huang Transform for the evaluation of material damages that (i) facilitates the systematic employment of both established and promising analysis criteria, and (ii) provides unsupervised tools to achieve an accurate classification of the fracture type, the discrimination between longitudinal (P-) and traversal (S-) waves related to an AE event. The experimental validation shows promising results for a reliable assessment of the health status through the monitoring of civil infrastructures.

Dielectric, piezoelectric and damping properties of novel 2-2 piezoelectric composites

Here, a strip-shaped 2-2 cement/polymer-based piezoelectric composite was designed and fabricated. The dielectric, piezoelectric and electromechanical coupling properties of the composite were investigated as well as the coupling effects between the thickness and lateral modes of the piezoelectric composites. The dielectric and piezoelectric properties of the composites can be greatly influenced by variations of the piezoelectric ceramic volume fraction and the structural dimensions of the composites. Excellent properties have been achieved for ultrasonic transducer applications in civil engineering monitoring fields, such as large piezoelectric voltage constants, high thickness electromechanical coupling coefficients and low acoustic impedance. The damping property of the composites was especially studied. The maximum damping loss factor of the composites is between 0.28–0.32, and the glass transition temperature is between 55°–66 °C.

Capteur Brillouin réparti à fibre optique à haute résolution et longue portée

Brillouin-based distributed optical fiber sensors have been the subject of intense research in recent years because they offer a unique solution for continuous, real-time monitoring in civil engineering and petroleum industry. These sensors provide strain or temperature measurements with meter spatial resolution over several tens of kilometers. In this work we demonstrate two new Brillouin fiber sensors with enhanced performances based on advanced modulation formats from high-speed lightwave communications systems. We first report a Brillouin distributed sensor with enhanced centimeter resolution using a digital phase-shift keying technique. The second one uses a quadrature phase-shift keying modulator as a single-sideband modulator to balance the pump depletion and the fiber loss by the Brillouin gain. Combined with a specially-designed in-line bidirectional Erbium-doped fiber amplifier, we demonstrate that this technique allows for the achievement of long-range distributed sensing over 100 km.

Investigation of Time Series Representations and Similarity Measures for Structural Damage Pattern Recognition

This paper investigates the time series representation methods and similarity measures for sensor data feature extraction and structural damage pattern recognition. Both model-based time series representation and dimensionality reduction methods are studied to compare the effectiveness of feature extraction for damage pattern recognition. The evaluation of feature extraction methods is performed by examining the separation of feature vectors among different damage patterns and the pattern recognition success rate. In addition, the impact of similarity measures on the pattern recognition success rate and the metrics for damage localization are also investigated. The test data used in this study are from the System Identification to Monitor Civil Engineering Structures (SIMCES) Z24 Bridge damage detection tests, a rigorous instrumentation campaign that recorded the dynamic performance of a concrete box-girder bridge under progressively increasing damage scenarios. A number of progressive damage test case datasets and damage test data with different damage modalities are used. The simulation results show that both time series representation methods and similarity measures have significant impact on the pattern recognition success rate.

Experimental Investigation of a Self-Sensing Hybrid GFRP-Concrete Bridge Superstructure with Embedded FBG Sensors

A self-sensing hybrid GFRP-concrete bridge superstructure, which consists of two bridge decks and each bridge deck is comprised of four GFRP box sections combined with a thin layer of concrete in the compression zone, was developed by using eight embedded FBG sensors in the top and bottom flanges of the four GFRP box sections at midspan section of one bridge deck along longitudinal direction, respectively. The proposed self-sensing hybrid bridge superstructure was tested in 4-point loading to investigate its flexural behavior and verify the operation of the embedded FBG sensors. The longitudinal strains of the hybrid bridge superstructure were recorded using the embedded FBG sensors as well as the surface-bonded electric resistance strain gauges. The experimental results indicate that the embedded FBG sensors can faithfully record the longitudinal strains of the hybrid bridge superstructure in tension at bottom flanges and in compression at top flanges of the four GFRP box sections over the entire loading range, as compared with the surface-bonded strain gauges. So, the proposed self-sensing hybrid GFRP-concrete bridge superstructure can reveal its internal strains in serviceability limit state as well as in strength limit state, and it will have wide applications for long-term monitoring in civil engineering.

Piezoelectric radiofrequency transducers as passive buried sensors

We demonstrate that single-piezoelectric substrate-based acoustic transducers act as ideal sensors for probing with various RADAR strategies. Because these sensors are intrinsically passive devices working in the radiofrequency range, they exhibit improved interrogation range and robustness with respect to silicon-based radio frequency identification tags. Both wideband (acoustic delay lines) and narrowband (acoustic resonators) transducers are shown to be compatible with pulse-mode and frequency-modulated continuous-wave RADAR strategies, respectively. We particularly focus on the ground-penetrating RADAR (GPR) application in which the lack of local energy source makes these sensors suitable candidates for buried applications in roads, building or civil engineering monitoring. A novel acoustic sensor concept – high-overtone bulk acoustic resonator – is especially suited as sensor interrogated by a wide range of antenna set, as demonstrated with GPR units working in the 100 and 200 MHz range.

AUTOMATED LOW-COST PHOTOGRAMMETRY FOR FLEXIBLE STRUCTURE MONITORING

Abstract. Structural monitoring requires instruments which can provide high precision and accuracy, reliable measurements at good temporal resolution and rapid processing speeds. Long-term campaigns and flexible structures are regarded as two of the most challenging subjects in monitoring engineering structures. Long-term monitoring in civil engineering is generally considered to be labourintensive and financially expensive and it can take significant effort to arrange the necessary human resources, transportation and equipment maintenance. When dealing with flexible structure monitoring, it is of paramount importance that any monitoring equipment used is able to carry out rapid sampling. Low cost, automated, photogrammetric techniques therefore have the potential to become routinely viable for monitoring non-rigid structures. This research aims to provide a photogrammetric solution for long-term flexible structural monitoring purposes. The automated approach was achieved using low-cost imaging devices (mobile phones) to replace traditional image acquisition stations and substantially reduce the equipment costs. A self-programmed software package was developed to deal with the hardware-software integration and system operation. In order to evaluate the performance of this low-cost monitoring system, a shaking table experiment was undertaken. Different network configurations and target sizes were used to determine the best configuration. A large quantity of image data was captured by four DSLR cameras and four mobile phone cameras respectively. These image data were processed using photogrammetric techniques to calculate the final results for the system evaluation.

Procedure to evaluate the accuracy of laser-scanning systems using a linear precision electro-mechanical actuator

Deformation monitoring is critical for the inspection of civil engineering structures. Three-dimensional laser-scanning systems can provide the ability to control unexpected deformations that cannot be monitored with traditional topographic instruments, such as total stations or levels. Technical datasheets provided by laser manufacturers typically give the accuracy of single-point measurements, but these specifications can be improved using surface-fitting of the data points. In this study, a procedure is used to detect the true accuracy that can be achieved using surface-fitting techniques. The procedure uses a precision actuator that moves an aluminium plate whose shift can be measured by the geodetic instrumentation. Accuracy is calculated as the difference between the values given by the actuator and the values from the geodetic instruments. The procedure is tested using a laser scanner, Riegl LMS Z390i and a total station, Leica TCR 1102. Similar results are obtained in both cases and accuracies are less than 1 mm. The results confirm that this Riegl system can be used to detect small deformations and can be applied to monitor civil engineering structures. The single point measurements confirm the data provided by the laser scanner manufacturer with an accuracy of approximately 6 mm.

Aligned carbon nanotube based ultrasonic microtransducers for durability monitoring incivil engineering

Structural health monitoring of porous materials such as concrete is becoming a majorcomponent in our resource-limited economy, as it conditions durable exploitation ofexisting facilities. Durability in porous materials depends on nanoscale features which needto be monitored in situ with nanometric resolution. To address this problem, we putforward an approach based on the development of a new nanosensor, namely a capacitivemicrometric ultrasonic transducer whose vibrating membrane is made of alignedsingle-walled carbon nanotubes (SWNT). Such sensors are meant to be embedded in largenumbers within a porous material in order to provide information on its durability bymonitoring in situ neighboring individual micropores. In the present paper, we report onthe feasibility of the key building block of the proposed sensor: we have fabricatedwell-aligned, ultra-thin, dense SWNT membranes that show above-nanometer amplitudesof vibration over a large range of frequencies spanning from 100 kHz to 5 MHz.

All-Solid-State Reference Electrode Based on Polymer Composites for Corrosion Monitoring of Steel in Concrete

Corrosion of steel structures has been found to be a problem Corrosion can be managed but not eliminated, so detecting corrosion will remain an issue no matter how effective corrosion prevention programs become. Electrochemical reaction is the basically process of steel corrosion in civil engineering, so electrochemical method is the best way to monitor corrosion grade. Liquid state reference is often used in lab to study steel corrosion by triple electrode system, but it is very difficultly used in steel bar corrosion monitoring in civil engineering. Firstly, liquid reference’s life is, generally speaking, very short. The steel corrosion is a very slow process, corrosion monitoring should be tens of years, so the liquid reference’s life is not long enough for corrosion monitoring; Secondly, the reference electrode’s strength have to be very high. Obviously, liquid electrode reference can not meet the requirement. In this paper, a novel all solid state reference electrode (ASSRE) has been developed. There are three layers in the electrode. Four kinds of components have been included in first and second layer. Additional AgCl powder has been used to inhibit AgCl decrease which is on the surface of Ag wire by complexing effect. There is only one kind of component in third layer. There are four steps to prepare the reference electrode: electrolyze, pre-mixed components, modelling and sintering. Finally, the potential of ASSR has been measured by SCE.

Cost-effective vision-based system for monitoring dynamic response of civil engineering structures

This study develops a cost-effective vision-based displacement measurement system for real-time monitoring of dynamic responses of large-size civil engineering structures such as bridges and buildings. The system simply consists of a low-cost digital camcorder and a notebook computer equipped with digital image-processing software developed in this study. A target panel with predesigned marks is attached to a structure, whose movement is captured by the digital camcorder placed at a fixed point away from the measurement point. The captured images are streamed to the notebook computer and processed by the software to compute displacement in real time. The efficacy of the system in measuring dynamic responses was demonstrated through laboratory tests, seismic shaking table tests on a steel building frame, and a field experiment on a bridge. In order to simultaneously measure displacements of multiple points, this study further developed a time synchronization system, in which TCP/IP protocol is employed for communications. The effectiveness of the time synchronization system was also experimentally verified. The vision-based system developed in this study is simple, cost-effective, easy to install, and capable of real-time measurement of dynamic responses, making the system ideal for monitoring civil engineering structures. Copyright © 2009 John Wiley & Sons, Ltd.