Annibale Luigi Materazzi

Dynamic Characterization of a Soft Elastomeric Capacitor for Structural Health Monitoring

AbstractStructural health monitoring of civil infrastructures is a difficult task, often impeded by the geometrical size of the monitored systems. Recent advances in conducting polymers enabled the fabrication of flexible sensors capable of covering large areas, a possible solution to the monitoring challenge of mesoscale systems. The authors have previously proposed a novel sensor consisting of a soft elastomeric capacitor (SEC) acting as a strain gauge. Arranged in a network configuration, the SECs have the potential to cover very large surfaces. In this paper, understanding of the proposed sensor is furthered by evaluating its performance at vibration-based monitoring of large-scale structures. The dynamic behavior of the SEC is characterized by subjecting the sensor to a frequency sweep, and detecting vibration modes of a full-scale steel beam. Results show that the sensor can be used to detect fundamental modes and dynamic input. Also, a network of SECs is used for output-only modal identification of...

Novel nanocomposite technologies for dynamic monitoring of structures: a comparison between cement-based embeddable and soft elastomeric surface?sensors

The authors have recently developed two novel solutions for strain sensing using nanocomposite materials. While they both aim at providing cost-effective solutions for the monitoring of local information on large-scale structures, the technologies are different in their applications and physical principles. One sensor is made of a cementitious material, which could make it suitable for embedding within the core of concrete structures prior to casting, and is a resistor, consisting of a carbon nanotube cement-based transducer. The other sensor can be used to create an external sensing skin and is a capacitor, consisting of a flexible conducting elastomer fabricated from a nanocomposite mix, and deployable in a network setup to cover large structural surfaces. In this paper, we advance the understanding of nanocomposite sensing technologies by investigating the potential of both novel sensors for the dynamic monitoring of civil structures. First, an in-depth dynamic characterization of the sensors using a uniaxial test machine is conducted. Second, their performance at dynamic monitoring of a full-scale concrete beam is assessed, and compared against off-the-shelf accelerometers. Experimental results show that both novel technologies compare well against mature sensors at vibration-based structural health monitoring, showing the promise of nanocomposite technologies for the monitoring of large-scale structural systems.

Electromechanical modelling of a new class of nanocomposite cement-based sensors for structural health monitoring

This work focuses on the analysis of a new nanocomposite cement-based sensor (carbon nanotube cement-based sensor), for applications in vibration-based structural health monitoring of civil engineering structures. The sensor is constituted of a cement paste doped with multi-walled carbon nanotubes, so that mechanical deformations produce a measurable change of the electrical resistance. Prior work of some of the authors has addressed the fabrication process, dynamic behaviour and implementation to full-scale structural components. Here, we investigate the effectiveness of a linear lumped-circuit electromechanical model, in which dynamic sensing is associated with a strain-dependent modulation of the internal resistance. Salient circuit parameters are identified from a series of experiments where the distance between the electrodes is parametrically varied. Experimental results indicate that the lumped-circuit model is capable of accurately predicting the step response to a voltage input and its steady-state response to a harmonic uniaxial deformation. Importantly, the model is successful in anticipating the presence of a superharmonic component in sensor’s output.

Non-Gaussian along-wind response analysis in time and frequency domains

With special reference to the role of the non-Gaussian nature of the response, the procedures for along-wind frequency-domain analysis of MDOF structures are discussed. Assuming turbulence as a homogeneous Gaussian field, the dynamic response of structural systems is evaluated by using the power spectral density of the wind force in the case of the standard Gaussian analysis and by using both the power spectral density and bi-spectrum in the case of non-Gaussian analysis. The statistics of the response is used to estimate the peak value distribution. A parametric analysis, carried out on a steel lattice broadcasting antenna, and the comparison with suited time domain analyses of the response allowed to evaluate the reliability of the spectral methods.

Towards smart concrete for smart cities: Recent results and future application of strain-sensing nanocomposites

The use of smart technologies combined with city planning have given rise to smart cities, which empower modern urban systems with the efficient tools to cope with growing needs from increasing population sizes. For example, smart sensors are commonly used to improve city operations and management by tracking traffic, monitoring crowds at events, and performance of utility systems and public transportation. Recent advances in nanotechnologies have enabled a new family of sensors, termed self-sensing materials, which would provide smart cities with means to also monitor structural health of civil infrastructures. This includes smart concrete, which has the potential to provide any concrete structure with self-sensing capabilities. Such functional property is obtained by correlating the variation of internal strain with the variation of appropriate material properties, such as electrical resistance. Unlike conventional off-the-shelf structural health monitoring sensors, these innovative transducers combine enhanced durability and distributed measurements, thus providing greater scalability in terms of sensing size and cost. This paper presents recent advances on sensors fabricated using a cementitious matrix with nanoinclusions of Carbon Nanotubes (CNTs). The fabrication procedures providing homogeneous piezoresistive properties are presented, and the electromechanical behavior of the sensors is investigated under static and dynamic loads. Results show that the proposed sensors compare well against existing technologies of stress/strain monitoring, like strain gauges and accelerometers. Example of possible field applications for the developed nanocomposite cement-based sensors include traffic monitoring, parking management and condition assessment of masonry and concrete structures.

Static and Dynamic Strain Monitoring of Reinforced Concrete Components through Embedded Carbon Nanotube Cement-Based Sensors

The paper presents a study on the use of cement-based sensors doped with carbon nanotubes as embedded smart sensors for static and dynamic strain monitoring of reinforced concrete (RC) elements. Such novel sensors can be used for the monitoring of civil infrastructures. Because they are fabricated from a structural material and are easy to utilize, these sensors can be integrated into structural elements for monitoring of different types of constructions during their service life. Despite the scientific attention that such sensors have received in recent years, further research is needed to understand (i) the repeatability and accuracy of sensors’ behavior over a meaningful number of sensors, (ii) testing configurations and calibration methods, and (iii) the sensors’ ability to provide static and dynamic strain measurements when actually embedded in RC elements. To address these research needs, this paper presents a preliminary characterization of the self-sensing capabilities and the dynamic properties of a meaningful number of cement-based sensors and studies their application as embedded sensors in a full-scale RC beam. Results from electrical and electromechanical tests conducted on small and full-scale specimens using different electrical measurement methods confirm that smart cement-based sensors show promise for both static and vibration-based structural health monitoring applications of concrete elements but that calibration of each sensor seems to be necessary.

Self-sensing and thermal energy experimental characterization of multifunctional cement-matrix composites with carbon nano-inclusions

The recent progress of Nanotechnology allowed the development of new smart materials in several fields of engineering. In particular, innovative construction materials with multifunctional enhanced properties can be produced. The paper presents an experimental characterization on cement-matrix pastes doped with Carbon Nanotubes, Carbon Nano-fibers, Carbon Black and Graphene Nano-platelets. Both electro-mechanical and thermo-physical investigations have been carried out. The conductive nano-inclusions provide the cementitious matrix with piezo-resistive properties allowing the detection of external strain and stress changes. Thereby, traditional building materials, such as concrete and cementitious materials in general, would be capable of self-monitoring the state of deformation they are subject to, giving rise to diffuse sensing systems of structural integrity. Besides supplying self-sensing abilities, carbon nano-fillers may change mechanical, physical and thermal properties of cementitious composites. The experimental tests of the research have been mainly concentrated on the thermal conductivity and the optical properties of the different nano-modified materials, in order to make a critical comparison between them. The aim of the work is the characterization of an innovative multifunctional composite capable of combining self-monitoring properties with proper mechanical and thermal-energy efficiency characteristics. The potential applications of these nano-modified materials cover a wide range of possibilities, such as structural elements, floors, geothermal piles, radiant systems and more.

Nonlinear model of wind-induced vibrations of slender structures with circular cross-sections

Abstract In the present paper a numerical model well suited to predict the response of cylindrical slender structures subjected to the wind action is presented. The total longitudinal and lateral forces acting on this kind of structures are treated as a s sum of correlated random forces in the along-wind direction and in the across-wind direction and of deterministic aerodynamic forces arising from the transversal structural motion. The proposed model can handle all the velocity components of the structure, and the related aerodynamic forces are computed even when the structural behaviour is strongly nonlinear due to large displacement effects. With reference to some structural typologies relevant to engineering applications (chimneys and cable-stayed chimneys), some numerical examples are presented in order to show the model functionality.

Strain sensitivity of carbon nanotube cement-based composites for structural health monitoring

Cement-based smart sensors appear particularly suitable for monitoring applications, due to their self-sensing abilities, their ease of use, and their numerous possible field applications. The addition of conductive carbon nanofillers into a cementitious matrix provides the material with piezoresistive characteristics and enhanced sensitivity to mechanical alterations. The strain-sensing ability is achieved by correlating the variation of external loads or deformations with the variation of specific electrical parameters, such as the electrical resistance. Among conductive nanofillers, carbon nanotubes (CNTs) have shown promise for the fabrication of self-monitoring composites. However, some issues related to the filler dispersion and the mix design of cementitious nanoadded materials need to be further investigated. For instance, a small difference in the added quantity of a specific nanofiller in a cement-matrix composite can substantially change the quality of the dispersion and the strain sensitivity of the resulting material. The present research focuses on the strain sensitivity of concrete, mortar and cement paste sensors fabricated with different amounts of carbon nanotube inclusions. The aim of the work is to investigate the quality of dispersion of the CNTs in the aqueous solutions, the physical properties of the fresh mixtures, the electromechanical properties of the hardened materials, and the sensing properties of the obtained transducers. Results show that cement-based sensors with CNT inclusions, if properly implemented, can be favorably applied to structural health monitoring.

STRAIN-SENSING CARBON NANOTUBE CEMENT-BASED COMPOSITES FOR APPLICATIONS IN STRUCTURAL HEALTH MONITORING: PREPARATION AND MODELLING ISSUES

The authors have recently explored the use of electrically conductive cement-based composites doped with carbon nanotubes for dynamic monitoring of strain in concrete structures. While the technology appears to be very promising for cost-effective structural health monitoring, some challenges still limit its applicability to full-scale constructions. The dispersion of the nanoparticles, typically based on sonic treatment and on other special procedures, is not compatible with distributed full-scale deployments and essentially limits the applications of the technology to the fabrication of embeddable sensors. Also, the electromechanical behaviour of the composites is complex and a proper analytical model linking electrical output to accurate strain measurements is yet to be established. This work discusses these open issues in fabrication and modelling of carbon nanotube composite concrete. A fabrication procedure with potential applicability to large casting volumes is presented and experimental results highlighting its effectiveness are discussed. Results cover analysis of nanoparticles dispersion, electrical percolation, strain sensitivity and polarization.